Tesi sul tema "Surface mass balance modelling"

The Antarctic grounding zone has a disproportionately large effect on glacier dynamics and ice sheet stability relative to its size but remains poorly characterised across much of the continent. Accurate ice velocity and thickness information is needed in the grounding zone to determine glacier outflow and establish to what extent changing ocean and atmospheric conditions are affecting the mass balance of individual glacier catchments. This thesis describes new satellite remote sensing techniques for measuring ice velocity and ice thickness, validated using ground measurements collected on the Beardmore, Skelton and Darwin Glaciers and applied to other Transantarctic Mountain outlet glaciers to determine ice discharge. Outlet glaciers in the Transantarctic Mountains provide an important link between the East and West Antarctic Ice Sheets but remain inadequately studied. While long-term velocities in this region are shown here to be stable, instantaneous velocities are sensitive to stresses induced by ocean tides, with fluctuations of up to 50% of the mean observed in GPS measurements. The potential error induced in averaged satellite velocity measurements due to these effects is shown to be resolvable above background noise in the grounding zone but to decrease rapidly upstream. Using a new inverse finite-element modelling approach based on regularization of the elastic-plate bending equations, tidal flexure information from differential InSAR is used to calculate ice stiffness and infer thickness in the grounding zone. This technique is shown to be successful at reproducing the thickness distribution for the Beardmore Glacier, eliminating current issues in the calculation of thickness from freeboard close to the grounding line where ice is not in hydrostatic equilibrium. Modelled thickness agrees to within 10% of ground penetrating radar measurements. Calibrated freeboard measurements and tide-free velocities in the grounding zones of glaciers in the western Ross Sea are used to calculate grounding zone basal melt rates, with values between 1.4 and 11.8 m/a⁻¹ in this region. While strongly dependent on grounding line ice thickness and velocity, melt rates show no latitudinal trend between glaciers, although detailed error analysis highlights the need for much improved estimates of firn density distribution in regions of variable accumulation such as the Transantarctic Mountains.

Le Bilan de Masse de Surface (BMS, c'est-à-dire les précipitations de neige auxquelles est retranchée l'ablation par sublimation, ruissellement ou érosion) de la calotte polaire Antarctique représente une contribution majeure et encore mal connue à l'évolution actuelle du niveau des mers. Le stockage d'eau douce par accumulation de neige sur la calotte posée est supposé s'intensifier au cours du 21eme siècle, modérant l'élévation du niveau des mers et modifiant la dynamique glaciaire. Les trois-quarts du bilan de masse de surface Antarctique sont concentrés au dessous de 2000 m d'altitude alors que cette zone ne représente que 40% de la surface de la calotte posée. Les précipitations orographiques sont une contribution majeure à l'accumulation dans cette région, il est donc crucial d'estimer précisément ce terme. La modélisation de ce processus est fortement dépendant de la résolution des modèles, car les pentes de la calotte influencent l'intensité des précipitations orographiques. La sublimation et la fonte de la neige sont eux aussi fortement dépendant de l'élévation. Bien qu'ils contribuent actuellement peu au bilan de masse de surface de l'Antarctique, ils sont susceptibles de subir des changements importants au cours des prochains siècles. Les modèles atmosphériques de climat, globaux ou régionaux, ne peuvent pas atteindre une résolution allant au delà de 40 km sur l'Antarctique pour des simulations à l'échelle du siècle du fait de coûts de calcul importants. A ces résolutions, la topographie des zones côtières Antarctique n'est pas correctement représentée. C'est pourquoi nous avons développé le modèle de régionalisation SMHiL (Surface Mass balance High-resolution downscaLing) qui permet d'estimer les composantes du bilan de masse de surface Antarctique à haute résolution (~15 km) à partir de champs atmosphériques de plus grande échelle. Nous calculons l'effet de la topographie fine sur les précipitations orographiques et sur les processus de couche limite menant à la sublimation, la fonte et le regel. SMHiL est validé pour la période actuelle à partir d'un jeu de données inédit constitué de plus de 2700 observations de qualité contrôlée. Cependant, les observations représentatives du BMS de la zone côtière Antarctique y sont sous-représentées. Dans ce contexte, nous montrons que la ligne de balise mise en place par l'observatoire GLACIOCLIM-SAMBA en bordure de calotte constitue une référence pour estimer les performances des modèles. Enfin, nous utilisons SMHiL à l'aval du modèle de circulation générale LMDZ4 pour évaluer les variations de BMS au cours du 21eme et du 22eme siècles. Le BMS à haute résolution est significativement différent de celui de LMDZ4 et est plus proche du BMS observé pour la période actuelle. Les résultats suggèrent que les précédentes estimations d'augmentation du BMS au cours du prochain siècle étaient sous-estimées de près de 30% par LMDZ4. Les changements de BMS à faible élévation résulteront d'une compétition entre l'augmentation d'accumulation de neige et de ruissellement. SMHiL est un outil destiné à être appliqué à l'aval d'autres modèles de climat, globaux ou régionaux, pour une meilleure estimation des variations futures du niveau des mers
The Antarctic Surface Mass Balance (SMB, i.e. the snow accumulation from which we subtract ablation by sublimation, run-off or erosion) is a major yet badly known contribution to changes in the present-day sea level. Water storage by snow accumulation on the Antarctic continent is expected to increase in the 21st century, which would moderate the rise in sea level and impact the ice dynamic response of the ice sheet. Three-quarters of the Antarctic SMB are concentrated below 2000 m above sea level whereas this area represents only 40% of the grounded ice sheet area. Orographic precipitation is a major contributor to snow accumulation in this region, which is why a better estimation of this term is important. The representation of this process by models depends to a great extent on the resolution of the model, since precipitation amounts depend on the ice sheet slopes. Sublimation and snowmelt also depend on elevation, and although they are presently minor contributors to the Antarctic SMB, their role is expected to become more important in the coming centuries. Global and regional atmospheric climate models are unable to achieve a 40-km resolution over Antarctica at a century time scale, due to their computing cost. At this resolution, the Antarctic coastal area is still badly represented. This is why we developed the downscaling model SMHiL (Surface mass balance high-resolution downscaling) to estimate the Antarctic SMB components at a high resolution (~15 km) from large-scale atmospheric forcings. We computed the impact of the high-resolution topography on orographic precipitation amounts and the boundary layer processes that lead to sublimation, melting and refreezing. SMHiL has been validated for the present period with a dataset composed of more than 2700 quality-controlled observations. However, very few of these observations are representative of the Antarctic coastal area. In this context, we show that the GLACIOCLIM-SAMBA stake lines located on the ice sheet coast-to-plateau area is an appropriate reference to evaluate model performance. Finally, we used SMHiL to estimate the SMB changes during the 21st and 22nd centuries, by downscaling the atmospheric global climate model LMDZ4. The high-resolution SMB is significantly different from the SMB given by LMDZ4 and is closer to the observed one for the present period. Our results suggest that previous studies using the LMDZ4 models underestimated the future increase in SMB in Antarctica by about 30%. Future changes in the Antarctic SMB at low elevations will result from the conflict between higher snow accumulation and runoff. The downscaling model is a powerful tool that can be applied to climate models for a better assessment of a future rise in sea level

Mass changes of polar ice sheets have an important societal impact, because they affect global sea level. Estimating the current mass budget of ice sheets is equivalent to determining the balance between the surface mass gain through precipitation and the outflow across the grounding line. In Antarctica, the latter is mainly governed by oceanic processes and outlet glacier dynamics.

In this thesis, we assess the mass balance of a part of eastern DronningMaud Land via an input/output method. Input is given by recent surface accumulation estimations of the whole drainage basin. The outflow at the grounding line is determined from the radar data of a recent airborne survey and satellite-based velocities using a flow model of combined plug flow and simple shear. We estimate the regional mass balance in this area to be between 1.88±8.50 and 3.78±3.32 Gt a−1 depending on the surface mass balance (SMB) dataset used. This study also reveals that the plug flow assumption is acceptable at the grounding line of ice streams.

The mass balance of drainage basins is governed by the dynamics of their outlet glaciers and more specifically the flow conditions at the grounding line. Thanks to an airborne radar survey we define the bed properties close to the grounding line of the West Ragnhild Glacier (WRG) in the Sør Rondane Mountains. Geometry and reflectivity analyses reveal that the bed of the last 65 km upstream of the grounding line is sediment covered and saturated with water. This setting promotes the dominance of basal motion leading to a change in the flow regime: in the interior flow is governed by internal deformation while its relative importance decreases to become driven by basal sliding.

Subsequently we present the results of the reconstruction of the SMB across an ice rise through radar data and inverse modelling. The analysis demonstrates that atmospheric circulation was stable during the last millennium. Ice rises induce an orographic uplift of the atmospheric flow and therefore influence the pattern of the SMB across them, resulting in an asymmetric SMB distribution. Since the geometry of the internal reflection horizons observed in radar data depends on the SMB pattern, the asymmetry observed in radar layers reveals the trajectories of air masses at the time of deposit. We present an original and robust method to quantify this SMB distribution. Combining shallow and deep radar layers, SMB across Derwael Ice Rise is reconstructed. Two methods are employed as a function of the depth of the layers: i.e. the shallow layer approximation for the surface radar layers and an optimization technique based on an ice flow model for the deeper ones. Both methods produce similar results. We identify a difference in SMB magnitude of 2.5 between the flanks and the ice rise divide, as well as a shift of ≈4 km between the SMB maximum and the crest. Across the ice rise, SMB exhibits a very large variability, ranging from 0.3 to 0.9 mw.e. a−1. This anomaly is robust in time.

Finally we draw a comprehensive description of the Sør Rondane Mountains sector. The glacial system is close to the equilibrium and seems stable but evidences suggest that it is a fragile equilibrium. The proximity of the open ocean certainly favours the interaction between warm water and the ice shelf cavity conducting to potential important melting. The thinning associated with this melting can detach the ice shelf from pinning points. This will reduce the buttressing from the ice shelf, outlet glaciers will accelerate and mass transfer toward the ocean will increase. Therefore, the future of Antarctic Ice Sheet directly depends on the changes affecting its boundaries and assessing the sensitivity of the ice sheets is essential to quantify and anticipate the future variation of mass balance.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished

L'hydrologie continentale s'intéresse à tous les aspects du cycle de l'eau des terres émergées et représente les flux de masse d'eau qui sont échangées. Que ce soit dans le sous-sol, au sein des lacs ou dans le brassage continu des torrents, l'eau et les processus hydrologiques associés entretiennent un lien direct avec la dynamique atmosphérique et la variabilité climatique. La représentation, à l'échelle globale, de ces processus hydrologiques s'appuie sur des techniques de modélisation qui, au CNRM, passent par un système couplé composé du modèle de surface ISBA et du modèle de routage en rivière CTRIP. Ces dernières années, les progrès réalisés sur les paramétrisations existantes et la représentation des nouveaux processus dans ISBA comme dans CTRIP ont abouti à une nette amélioration des performances de ce système pour des applications hydrologiques régionales ou globales couplées avec un modèle de climat. Dans la continuité de ces efforts, l'objectif principal de cette thèse est de développer une paramétrisation dynamique des lacs pour intégrer leur bilan de masse dans le modèle global CTRIP à 1/12°. Par ailleurs, le modèle développé, MLake, propose un diagnostic sur le marnage des lacs afin de permettre le suivi du niveau d'eau basé sur des mesures satellitaires. Bénéficiant d'un réseau de mesures dense et de forçages climatiques à haute résolution, le bassin versant du Rhône a été choisi pour évaluer localement MLake sur la période 1960-2016. Les résultats sur trois stations de jaugeages montrent une progression nette des performances de CTRIP dans la simulation des débits du Rhône aboutissant à un lissage des hydrographes qui se caractérise par un écrêtement des débits de crues et un soutien à l'étiage. Par ailleurs, la confrontation du diagnostic sur les niveaux d'eau du Léman avec des mesures locales révèle une capacité du modèle à suivre les cycle annuels et inter-annuels du marnage. Une deuxième évaluation s'est ensuite portée à l'échelle globale pour confirmer le comportement du modèle dans des conditions hydroclimatiques contrastées. Cette évaluation confirme la capacité du modèle à simuler des débits réalistes mais révèle la perturbation importante du cycle hydrologique naturel par l'anthropisation. Enfin les résultats préliminaires d'une simulation globale démontre l'intérêt d'utiliser MLake avec une amélioration systématique des scores dans les zones de grande densité lacustre. Ainsi, 45% des stations évaluées, principalement dans les régions arctiques, présentent une amélioration des scores statistiques. Enfin, cette étude engage une réflexion sur les perspectives d'améliorations du modèle, notamment la mise en place d'une bathymétrie de lac à l'échelle globale, en vue d'un couplage avec un modèle de climat et de l'utilisation des données de la future mission spatiale SWOT
The water cycle encompasses the main processes related to mass fluxes that influence the atmosphere and climate variability. More specifically, continental hydrology refers to the water transfer occurring at the land surface and sub-surface. Modelling is one of the main methods used for the representation of these processes at regional to global scales. The land surface model system used in this thesis is composed of the ISBA land surface model coupled to the river routing model TRIP that combines the CNRM’s latest developments for use in stand-alone hydrological applications or coupled to a climate model. This PhD is focused on the development and evaluation of lake mass-balance dynamics and water level diagnostics using a new non-calibrated model called MLake which has been incorporated into the 1/12° version of the CTRIP model. Simulated river flows forced by high resolution hydrometeorological forcings are evaluated for the Rhone river basin against in situ observations coming from three river gauges over the period 1960-2016. Results reveal the positive contribution of MLake in simulating Rhone discharge and in representing the lake buffer effects on peak discharge. Moreover, the evaluation of the simulated and observed water level variations show the ability of MLake to reproduce the natural seasonal and interannual cycles. Based on the same framework, a final evaluation was conducted in order to assess the value of the non-calibrated MLake model for global hydrological applications. The results confirmed the capability of the model to simulate realistic river discharges worldwide. At 45% of the river gauge stations, which are mostly located within regions of high lake density, the new model resulted in improved simulated river discharge. The results also highlighted the strong effect of anthropization on the alterations of river dynamics, and the need for a global representation of human-impacted flows in the model. This study has lead to several future perspectives, such as the incorporation of a parametrization of lake hypsometry for use at global scale. The implementation of such developments will improve the representation of vertical water dynamics and facilitate both the coupling of MLake within the CNRM earth system model framework and the future spatial mission SWOT for improved future global hydrological and water resource projections

Au cours du Quaternaire (depuis 2.6 Ma), les calottes glaciaires connaissent différents épisodes d'avancée-retrait correspondant aux cycles glaciaires-interglaciaires. L'étude de ces événements épisodiques permet de mieux comprendre les mécanismes à l'origine de l'évolution de la Terre et d'améliorer les prévisions dans le contexte du réchauffement climatique actuel.La simulation des interactions entre les calottes polaires et le climat sur des échelles de temps aussi longues nécessite des approches de modélisation numérique qui représentent suffisamment le système réel tout en maintenant des coûts de calcul faibles. Dans la première partie de cette thèse, j'utilise un modèle système terre système terrestre de complexité intermédiaire (iLOVECLIM) couplé au modèle 3D de calotte polaires GRISLI pour simuler l'avancée abrupte de la calotte glaciaire au début du dernier cycle glaciaire (120-115 kaBP). Les résultats indiquent que les débuts de glaciation ne peuvent pas être expliqués uniquement par la théorie astronomique (en résponse aux forçages orbitaux). Les rôles de la biosphère et de l'océan par le biais de différents mécanismes de rétroaction doivent être inclus pour expliquer la localisation et l'étendue de l'avancée de la calotte glaciaire. De plus, une simulation appropriée du processus d'accumulation de la calotte glaciaire est essentielle pour obtenir des résultats corrects.Dans la deuxième partie de la thèse, j'étudie les comportements d'un modèle de neige multicouche BESSI afin de fournir une simulation de bilan de masse de surface (SMB) davantage basée sur la physique pour iLOVECLIM-GRISLI. Le modèle de neige présente de bons résultats par rapport à un modèle climatique régional MAR de pointe pour le climat actuel dans différentes conditions de calotte glaciaire. Pour le dernier interglaciaire (130-116 kaBP), BESSI forcé par iLOVECLIM montre une plus grande sensibilité aux forçages climatiques que la paramétrisation SMB existante d'iLOVECLIM-GRISLI. En outre, l'évolution du SMB simulée par BESSI-iLOVECLIM se situe également dans une fourchette acceptable par rapport à d'autres études. Cependant, comme ce modèle de neige est davantage fondé sur la physique que la paramétrisation existante, l'influence des biais d'iLOVECLIM est plus importante pour BESSI, ce qui nuit à ses performances. Moyennant des travaux à venir sur la correction de biais et la méthode de couplage, mon étude ouvre la voie à l'utilisation de BESSI dans le cadre du couplage entre le modèle de climat iLOVECLIM et le modèle de calottes glaciaires GRISLI
During the Quaternary (since 2.6 Ma), ice sheets experience different advance-retreat episodes corresponding to glacial-interglacial cycles. Studying these episodic events provides a better understanding of the mechanisms behind the Earth's evolution, improving the future projection for the current global warming.Simulating ice sheet-climate interactions for long timescales requires numerical modeling approaches that sufficiently represent the real system while maintaining low computational costs. In the first part of this thesis, I utilize an Earth System of Intermediate Complexity (iLOVECLIM) coupled to the 3D ice sheet model GRISLI to simulate the abrupt ice sheet advance during the beginning of the last glacial cycle (120-115 kaBP). The results indicate glacial inceptions cannot be explained solely by the astronomical theory (the influence of orbital forcings). The roles of the biosphere and ocean through different feedback mechanisms must be included to explain the location and extent of ice sheet advance. Also, an appropriate simulation of the ice sheet accumulation process is essential to obtain results consistent with the paleo records.In the second part of the thesis, I investigate the behaviors of a multi-layer snow model BESSI to provide a more physics-based surface mass balance (SMB) simulation for iLOVECLIM-GRISLI. The snow model exhibits good results compared to a state-of-the-art Regional Climate Model MAR for the present-day climate under different ice sheet conditions. For the Last Interglacial (130-116 kaBP), BESSI forced by iLOVECLIM shows higher sensitivity to the climate forcings than the existing SMB parameterization of iLOVECLIM-GRISLI. Additionally, the SMB evolution simulated by BESSI-iLOVECLIM is also in an acceptable range compared to other studies. However, since this snow model is more physics-based than the existing parameterization, the influence of biases of iLOVECLIM is more significant for BESSI, hampering its performance. With further work to come on bias correction and the coupling method, my study paves the way for the use of BESSI in the coupling between the iLOVECLIM climate model and the GRISLI ice sheet model

As the world’s population is growing, so is the demand for agricultural products. However, natural nitrogen (N) fixation and phosphorus (P) availability cannot sustain the rising agricultural production, thus, the application of N and P fertilisers as additional nutrient sources is common. It is those anthropogenic activities that can contribute high amounts of organic and inorganic nutrients to both surface and groundwaters resulting in degradation of water quality and a possible reduction of aquatic life. In addition, runoff and sewage from urban and residential areas can contain high amounts of inorganic and organic nutrients which may also affect water quality. For example, blooms of the cyanobacterium Lyngbya majuscula along the coastline of southeast Queensland are an indicator of at least short term decreases of water quality. Although Australian catchments, including those with intensive forms of land use, show in general a low export of nutrients compared to North American and European catchments, certain land use practices may still have a detrimental effect on the coastal environment. Numerous studies are reported on nutrient cycling and associated processes on a catchment scale in the Northern Hemisphere. Comparable studies in Australia, in particular in subtropical regions are, however, limited and there is a paucity in the data, in particular for inorganic and organic forms of nitrogen and phosphorus; these nutrients are important limiting factors in surface waters to promote algal blooms. Therefore, the monitoring of N and P and understanding the sources and pathways of these nutrients within a catchment is important in coastal zone management. Although Australia is the driest continent, in subtropical regions such as southeast Queensland, rainfall patterns have a significant effect on runoff and thus the nutrient cycle at a catchment scale. Increasingly, these rainfall patterns are becoming variable. The monitoring of these climatic conditions and the hydrological response of agricultural catchments is therefore also important to reduce the anthropogenic effects on surface and groundwater quality. This study consists of an integrated hydrological–hydrochemical approach that assesses N and P in an environment with multiple land uses. The main aim is to determine the nutrient cycle within a representative coastal catchment in southeast Queensland, the Elimbah Creek catchment. In particular, the investigation confirms the influence associated with forestry and agriculture on N and P forms, sources, distribution and fate in the surface and groundwaters of this subtropical setting. In addition, the study determines whether N and P are subject to transport into the adjacent estuary and thus into the marine environment; also considered is the effect of local topography, soils and geology on N and P sources and distribution. The thesis is structured on four components individually reported. The first paper determines the controls of catchment settings and processes on stream water, riverbank sediment, and shallow groundwater N and P concentrations, in particular during the extended dry conditions that were encountered during the study. Temporal and spatial factors such as seasonal changes, soil character, land use and catchment morphology are considered as well as their effect on controls over distributions of N and P in surface waters and associated groundwater. A total number of 30 surface and 13 shallow groundwater sampling sites were established throughout the catchment to represent dominant soil types and the land use upstream of each sampling location. Sampling comprises five rounds and was conducted over one year between October 2008 and November 2009. Surface water and groundwater samples were analysed for all major dissolved inorganic forms of N and for total N. Phosphorus was determined in the form of dissolved reactive P (predominantly orthophosphate) and total P. In addition, extracts of stream bank sediments and soil grab samples were analysed for these N and P species. Findings show that major storm events, in particular after long periods of drought conditions, are the driving force of N cycling. This is expressed by higher inorganic N concentrations in the agricultural subcatchment compared to the forested subcatchment. Nitrate N is the dominant inorganic form of N in both the surface and groundwaters and values are significantly higher in the groundwaters. Concentrations in the surface water range from 0.03 to 0.34 mg N L..1; organic N concentrations are considerably higher (average range: 0.33 to 0.85 mg N L..1), in particular in the forested subcatchment. Average NO3-N in the groundwater has a range of 0.39 to 2.08 mg N L..1, and organic N averages between 0.07 and 0.3 mg N L..1. The stream bank sediments are dominated by organic N (range: 0.53 to 0.65 mg N L..1), and the dominant inorganic form of N is NH4-N with values ranging between 0.38 and 0.41 mg N L..1. Topography and soils, however, were not to have a significant effect on N and P concentrations in waters. Detectable phosphorus in the surface and groundwaters of the catchment is limited to several locations typically in the proximity of areas with intensive animal use; in soil and sediments, P is negligible. In the second paper, the stable isotopes of N (14N/15N) and H2O (16O/18O and 2H/H) in surface and groundwaters are used to identify sources of dissolved inorganic and organic N in these waters, and to determine their pathways within the catchment; specific emphasis is placed on the relation of forestry and agriculture. Forestry is predominantly concentrated in the northern subcatchment (Beerburrum Creek) while agriculture is mainly found in the southern subcatchment (Six Mile Creek). Results show that agriculture (horticulture, crops, grazing) is the main source of inorganic N in the surface waters of the agricultural subcatchment, and their isotopic signature shows a close link to evaporation processes that may occur during water storage in farm dams that are used for irrigation. Groundwaters are subject to denitrification processes that may result in reduced dissolved inorganic N concentrations. Soil organic matter delivers most of the inorganic N to the surface water in the forested subcatchment. Here, precipitation and subsequently runoff is the main source of the surface waters. Groundwater in this area is affected by agricultural processes. The findings also show that the catchment can attenuate the effects of anthropogenic land use on surface water quality. Riparian strips of natural remnant vegetation, commonly 50 to 100 m in width, act as buffer zones along the drainage lines in the catchment and remove inorganic N from the soil water before it enters the creek. These riparian buffer zones are common in most agricultural catchments of southeast Queensland and are indicated to reduce the impact of agriculture on stream water quality and subsequently on the estuary and marine environments. This reduction is expressed by a significant decrease in DIN concentrations from 1.6 mg N L..1 to 0.09 mg N L..1, and a decrease in the �15N signatures from upstream surface water locations downstream to the outlet of the agricultural subcatchment. Further testing is, however, necessary to confirm these processes. Most importantly, the amount of N that is transported to the adjacent estuary is shown to be negligible. The third and fourth components of the thesis use a hydrological catchment model approach to determine the water balance of the Elimbah Creek catchment. The model is then used to simulate the effects of land use on the water balance and nutrient loads of the study area. The tool that is used is the internationally widely applied Soil and Water Assessment Tool (SWAT). Knowledge about the water cycle of a catchment is imperative in nutrient studies as processes such as rainfall, surface runoff, soil infiltration and routing of water through the drainage system are the driving forces of the catchment nutrient cycle. Long-term information about discharge volumes of the creeks and rivers do, however, not exist for a number of agricultural catchments in southeast Queensland, and such information is necessary to calibrate and validate numerical models. Therefore, a two-step modelling approach was used to calibrate and validate parameters values from a near-by gauged reference catchment as starting values for the ungauged Elimbah Creek catchment. Transposing monthly calibrated and validated parameter values from the reference catchment to the ungauged catchment significantly improved model performance showing that the hydrological model of the catchment of interest is a strong predictor of the water water balance. The model efficiency coefficient EF shows that 94% of the simulated discharge matches the observed flow whereas only 54% of the observed streamflow was simulated by the SWAT model prior to using the validated values from the reference catchment. In addition, the hydrological model confirmed that total surface runoff contributes the majority of flow to the surface water in the catchment (65%). Only a small proportion of the water in the creek is contributed by total base-flow (35%). This finding supports the results of the stable isotopes 16O/18O and 2H/H, which show the main source of water in the creeks is either from local precipitation or irrigation waters delivered by surface runoff; a contribution from the groundwater (baseflow) to the creeks could not be identified using 16O/18O and 2H/H. In addition, the SWAT model calculated that around 68% of the rainfall occurring in the catchment is lost through evapotranspiration reflecting the prevailing long-term drought conditions that were observed prior and during the study. Stream discharge from the forested subcatchment was an order of magnitude lower than discharge from the agricultural Six Mile Creek subcatchment. A change in land use from forestry to agriculture did not significantly change the catchment water balance, however, nutrient loads increased considerably. Conversely, a simulated change from agriculture to forestry resulted in a significant decrease of nitrogen loads. The findings of the thesis and the approach used are shown to be of value to catchment water quality monitoring on a wider scale, in particular the implications of mixed land use on nutrient forms, distributions and concentrations. The study confirms that in the tropics and subtropics the water balance is affected by extended dry periods and seasonal rainfall with intensive storm events. In particular, the comprehensive data set of inorganic and organic N and P forms in the surface and groundwaters of this subtropical setting acquired during the one year sampling program may be used in similar catchment hydrological studies where these detailed information is missing. Also, the study concludes that riparian buffer zones along the catchment drainage system attenuate the transport of nitrogen from agricultural sources in the surface water. Concentrations of N decreased from upstream to downstream locations and were negligible at the outlet of the catchment.

This work is about finding an appropriate modelling complexity for a mass-balance model for phosphorus in Lake Vänern, Sweden. A statistical analysis of 30 years of water quality data shows that epilimnion and hypolimnion have different water quality and should be treated separately in a model. Further vertical division is not motivated. Horizontally, the lake should be divided into the two main basins Värmlandssjön and Dalbosjön. Shallow near shore ares, bays and areas close to point sources have to be considered as specific sub-basins if they are to be modelled correctly.

These results leads to the use of a model based on ordinary differential equations. The model applied is named LEEDS (Lake Eutrophication Effect Dose Sensitivity) and considers phosphorus and suspended particles. Several modifications were made for the application of the model to Lake Vänern. The two major ones are a revision of the equations governing the outflow of phosphorus and suspended particle through the outflow river, and the inclusion of chemical oxygen demand (COD) into the model, in order to model emissions from pulp and paper mills. The model has also been modified to handle several sub-basins.

The LEEDS model has been compared to three other eutrophication models applied to Lake Vänern. Two were simple models developed as parts of catchment area models and the third was a lake model with higher resolution than the LEEDS model. The models showed a good fit to calibration and validation data, and were compared in two nutrient emission scenarios and a scenario with increased temperature, corresponding to the green house effect.

A biofilter model was developed using the mass and energy balances in the gas, liquid and solid phases, which related the biofilter performance to the water content in the packing material. A key simplification of the model was that the concentration gradients in the biofilm were neglected by treating the biofilm/water layer as well mixed and in instantaneous equilibrium with the gas phase. Thus, the biofilm geometry and density parameters were lumped into the overall degradation term. The solid phase was treated as a separate well-mixed layer but solid phase dynamics were accounted for by using the Linear Driving Force (LDF) mass transfer model. The mixed form of Richard's equation together with experimentally obtained unsaturated hydraulic conductivity and water retention curves for compost were used in the continuity equation for the liquid water phase. This approach produced a model where all parameters could be potentially independently determined. The model was used to test suitable irrigation strategies for a biofilter system degrading toluene subject to different operational conditions. Under this approach both unidirectional and directionally switched biofilter configurations were tested for a 1 m long column. The unidirectional schemes incorporated both open and closed loop irrigation schemes, where the latter was based on commonly used on-line moisture measurement techniques. All schemes were evaluated based on the removal efficiency achieved and the leachate produced. Simulations under a constant irrigation rate of 5.46x 10⁻²g/m²s for a mass loading range of 13-60 g/m³h yielded removals ranging from 88%-26%. An order of magnitude drop in leachate under the high loading indicated severe drying in the system. For a high mass loading of 60 g/m³h, directional switching with a one-day frequency yielded a removal of 33% Vs 26% in an up flow scheme with similar leachate rates. Feedback control on water content provided an improved removal of 84% as compared to 73% under constant irrigation, when both schemes were subjected to load and inlet air step disturbances from 13 g/m³h to 62 g/m³h and from 298 K to 283 K respectively. A sensitivity analysis indicated that the model was most sensitive to the relationship between moisture content and degradation, which was also reflected by the high sensitivity of the model to the kinetic parameters in the degradation term. A novel batch recycle reactor was thus developed to investigate the effect of water content changes on the degradation rate in low water content systems such as biofilters. The reactor tightly controlled the water content of the unsaturated packing material by using the principle of a suction cell. Experimental runs were performed with toluene as the contaminant using unamended compost at a constant temperature of 30°C. Matric potential in the compost was maintained at values between -6 and -36 cm H₂O and the gas phase was monitored by sampling/gas chromatography. A soil water retention curve relating matric potential to gravimetric water content was generated for the compost. Periodic dry weight analyses of reactor samples together with the water retention curve verified moisture content control. Degradation results demonstrated a biologically limited region followed by a non-linear region at lower concentrations. Elimination capacities were obtained along the wetting and drying curves and changes in the water content affected the removal rates in the linear region ranging from 155 g/m³h to 24 g/m³h over the matric potential range investigated. Repeatability studies indicated that moisture content was the most likely parameter that influenced the changes in performance. Batch scale experiments were also performed using microbially inhibited compost, which provided linear sorption isotherms for toluene on compost at concentrations between 0-1000 ppmv and temperature values of 25°C and 35°C. The simulation model developed here provides a useful tool to implement and evaluate various operational schemes under different irrigation strategies. This is achieved by way of greater flexibility in incorporating the various schemes into the base model and the comparatively low simulation time to obtain the relevant results.

our simulations of the surface mass balance (SMB) of the Greenland ice sheet (GrIS) are compared over the period 1960-2008. Three use a regional climate model to downscale ECMWF reanalysis (ERA-40) and operational analysis data, while the fourth uses the same inputs but an empirical downscaling approach and melt model. These reconstructions have been used in a variety of applications but prior to this study little was known about their consistency with each other and the impact of the downscaling method on the result. The reconstructions are compared to assess the consistency in regional, seasonal and integrated 5MB components and evaluated against a suite of observational data. Three key areas of difference between the models have been identified. Firstly differences in how the ERA-40 reanalysis data are downscaled by the models. Secondly differences in how the 5MB components are calculated. And thirdly differences in the domain, the ice sheet mask used. Total 5MB estimates for the GrIS are in agreement within 34% of the four-model average when a common ice sheet mask is used. When models' native land/ice/sea masks are used this spread increases to 57%. The components of 5MB, with the exception of refreeze, show a similar level of agreement once a common mask is used. Previously noted differences in the models I estimates are partially explained by ice sheet mask differences. Agreement is higher (18% spread) in the accumulation area than the ablation area (38% spread) suggesting relatively high uncertainty in the estimation of ablation processes. Regionally there is less agreement, suggesting spatially compensating errors improve the integrated estimates. Modelled 5MB estimates are compared with in situ observations, gravimetric observations from GRACE and altimetry observations from ICESat. Through the use of a surface density and firn compaction model individual components of 5MB are, indirectly, able to be evaluated against altimetry observation.

Baltic archipelago areas have high nature values despite being polluted from various antrophogenic activities within the Baltic Sea catchment area and from long-range transport of airborne substances. The discovery of environmental problems in the Baltic Sea in the 1960s led to countermeasures that gradually gave results in reducing the toxic pollution, e.g. from PCBs. Today, much of the environmental management is focused on reducing the effects of eutrophication. There is a demand from society on science to develop strategies that can direct remedial actions so that the cost-effectiveness is maximised. This work focuses on how mass-balance models can be used to understand how coastal ecosystems are controlled by abiotic processes and to predict the response to changes in loading of different substances. Advection, sedimentation and burial are examples of general transport processes that are regulated by morphometrical characteristics, e.g. size, form, effective fetch and topographical openness. This is why different coastal areas have different sensitivity to loading of pollutants. A comparison of six phosphorus and chlorophyll models of different complexity showed that the model performance was not improved with more state variables of total phosphorus (TP) than two water and two sediment compartments. Modelling chlorophyll as a separate state variable did not improve the results for individual values compared to a simple regression against total phosphorus in surface water. Field investigations of the phosphorus content in accumulation sediments along the coast of Svealand showed a distribution pattern that probably is related to differences in the redox status. The average content of mobile phosphorus was much higher than previously found in offshore Baltic sediments indicating that sediments may play an important role for the phosphorus turnover in Baltic archipelago areas. A one-year field study to measure the levels of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in water, sediments and fish during different seasons was carried out in Kallrigafjärden Bay. The collected data set was used to test a mass-balance model for PCCD/F-turnover. It was possible to reproduce the concentrations of different PCDD/F-congeners with high accuracy using a general model approach, including one water compartment and two sediment compartments, indicating that the applied model has the necessary qualifications for successful predictions of PCDD/F-turnover in Baltic coastal areas.
Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 736

The aim of this research was to demonstrate the relationship between variations in summertime surface mass balance of the McMurdo Ice Shelf and atmospheric processes. The approach encompassed a broad range of techniques. An existing energy balance mass balance model was adapted to deal with debris-covered ice surfaces and modified to produce distributed output. Point based surface energy and mass balance for two key surfaces of the ice shelf were linked to different synoptic types that were identified using a manual synoptic classification. The distributed model was initialised with distributed parameters derived from satellite remote sensing and forced with data from a regional climate model. Patterns of summertime surface mass balance produced by the distributed model were assessed against stake measurements and with respect to atmospheric processes. During the summers of 2003-2004 and 2004-2005 an automatic weather station (AWS) was operated on bare and debris-covered ice surfaces of the McMurdo Ice shelf, Antarctica. Surface mass balance was calculated using the energy balance model driven by the data from the AWS and additional data from permanent climate stations. Net mass balance for the measurement period was reproduced reasonably well when validated against directly measured turbulent fluxes, stake measurements, and continuously measured surface height at the AWS. For the bare ice surface net radiation provided the major energy input for ablation, whereas sensible heat flux was a second heat source. Ablation was by both melt (70%) and sublimation (30%). At the debris-covered ice site investigated, it is inferred that the debris cover is sufficient to insulate the underlying ice from ablation. Synoptic weather situations were analysed based on AVHRR composite images and surface pressure charts. Three distinct synoptic situations were found to occur during the summers, these were defined as Type A, low pressure system residing in the Ross Sea Embayment; Type B, anticyclonic conditions across region; and Type C, a trough of low pressure extending into the Ross Sea Embayment. A dependence of surface energy fluxes and mass balance on synoptic situation was identified for the bare ice surface. The distributed model was found to produce spatial patterns of mass balance which compared well with stake measurements. Mass balance patterns show that the McMurdo Ice Shelf was generally ablating in the west, and accumulating in the east during summer. Areas of enhanced ablation were found which were likely to be caused by the surface conditions and topographic effects on the wind field. The mean summertime surface mass balance across the entire ice shelf for the 2003-2004 and 2004-2005 summers were –2.5 mm w.e. and –6.7 mm w.e. respectively. The differences between the two summers are inferred to be a result of more frequent type A conditions occurring during the summer of 2004-2005.

The water and heat exchange in thesoil-snow-vegetation-atmosphere system was studied in order toimprove the quantitative knowledge of land surface processes.In this study, numerical simulation models and availabledatasets representing arable land, sub-alpine snowpack, andboreal forest were evaluated at both diurnal and seasonaltimescales. Surface heat fluxes, snow depth, soil temperatures andmeteorological conditions were measured at an agriculturalfield in central Sweden during three winters and two summersfrom 1997 to 2000 within the WINTEX project. A one-dimensionalsimulation model (COUP) was used to simulate the water and heatbalance of the field. Comparison of simulated and measured heatfluxes in winter showed that parameter values governing theupper boundary condition were more important for explainingmeasured fluxes than the formulation of the internal mass andheat balance of the snow cover. The assumption of steady stateheat exchange between the surface and the reference height wasinadequate during stable atmospheric conditions. Independentestimates of the soil heat and water balance together with thecomparison of simulated and measured surface heat fluxes showedthat the eddy-correlation estimates of latent heat fluxes fromthe arable field were on average 40 % too low. The ability of a multi-layered snowpack model (SNTHERM) tosimulate the layered nature of a sub-alpine snowpack wasevaluated based on a dataset from Switzerland. The modelsimulated the seasonal development of snow depth and densitywith high accuracy. However, the models ability to reproducethe strong observed snowpack layering was limited by theneglection of the effect of snow microstructure on snowsettling, and a poor representation of water redistributionwithin the snowpack. The representation of boreal forest in the land surfacescheme used within a weather forecast (ECMWF) model was testedwith a three-year dataset from the NOPEX forest site in centralSweden. The new formulation with separate energy balances forvegetation and the soil/snow beneath the tree cover improvedthe simulation of seasonal and diurnal variations in latent andsensible heat flux. Further improvements of simulated latentheat fluxes were obtained when seasonal variation in vegetationproperties was introduced. Application of the COUP model withthe same dataset showed that simulation of evaporation fromintercepted snow contributed to a better agreement with themeasured sensible heat flux above forests, but also indicatedthat the measurements might have underestimated latent heatflux. The winter sensible heat flux above the forest wasfurther improved if an upper limit of the aerodynamicresistance of 500 s m-1 was applied for stable conditions. A comparison of the water and heat balance of arable landand forest confirmed the general knowledge of the differencesbetween these two surface types. The forest contributed withconsiderably more sensible heat flux to the atmosphere than thearable land in spring and summer due to the lower albedo andrelatively less latent heat flux. Latent heat flux from theforest was higher in winter due to the evaporation ofintercepted snow and rain. The net radiation absorbed by theforest was 60 % higher than that absorbed by the arable land,due to the lower surface albedo in winter. Key words:soil; snow; land surface heat exchange;forest; arable land; eddy-correlation.
QC 20100614

Understanding the Earth's climate system and particularly climate variability presents one of the most difficult and urgent challenges in science. The Antarctic plays a crucial role in the global climate system, since it is the principal region of radiative energy deficit and atmospheric cooling. An assessment of regional climate model HIRHAM is presented. The simulations are generated with the HIRHAM model, which is modified for Antarctic applications. With a horizontal resolution of 55km, the model has been run for the period 1958-1998 creating long-term simulations from initial and boundary conditions provided by the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA40 re-analysis. The model output is compared with observations from observation stations, upper air data, global atmospheric analyses and satellite data. In comparison with the observations, the evaluation shows that the simulations with the HIRHAM model capture both the large and regional scale circulation features with generally small bias in the modeled variables. On the annual time scale the largest errors in the model simulations are the overestimation total cloud cover and the colder near-surface temperature over the interior of the Antarctic plateau. The low-level temperature inversion as well as low-level wind jet is well captured by the model. The decadal scale processes were studied based on trend calculations. The long-term run was divided into two 20 years parts. The 2m temperature, 500 hPa temperature, MSLP, precipitation and net mass balance trends were calculated for both periods and over 1958 - 1998. During the last two decades the strong surface cooling was observed over the Eastern Antarctica, this result is in good agreement with the result of Chapman and Walsh (2005) who calculated the temperature trend based on the observational data. The MSLP trend reveals a big disparity between the first and second parts of the 40 year run. The overall trend shows the strengthening of the circumpolar vortex and continental anticyclone. The net mass balance as well as precipitation show a positive trend over the Antarctic Peninsula region, along Wilkes Land and in Dronning Maud Land. The Antarctic ice sheet grows over the Eastern part of Antarctica with small exceptions in Dronning Maud Land and Wilkes Land and sinks in the Antarctic Peninsula; this result is in good agreement with the satellite-measured altitude presented in Davis (2005) . To better understand the horizontal structure of MSLP, temperature and net mass balance trends the influence of the Southern Annual Mode (SAM) on the Antarctic climate was investigated. The main meteorological parameters during the positive and negative Antarctic Oscillation (AAO) phases were compared to each other. A positive/negative AAO index means strengthening/weakening of the circumpolar vortex, poleward/northward storm tracks and prevailing/weakening westerly winds. For detailed investigation of global teleconnection, two positive and one negative periods of AAO phase were chosen. The differences in MSLP and 2m temperature between positive and negative AAO years during the winter months partly explain the surface cooling during the last decades.
Eine der dringendsten wissenschaftlichen Herausforderungen besteht darin, das Klimasystem der Erde und die Prozesse zu verstehen, die seine Klimavariabilität bestimmen. Die Antarktis spielt eine entscheidende Rolle im globalen Klimasystem, da sie die wesentliche Energiesenke und atmosphärische Abkühlregion darstellt. In dieser Arbeit wird das regionale Klimamodell HIRHAM zur Untersuchung des Klimas der Antarktis eingesetzt, das dafür speziell angepasst wurde. Mit einer horizontalen Auflösung von 50 km und 25 vertikalen Schichten wurden Simulationen für 40 Jahre von 1958-1998 durchgeführt, wobei die Anfangs- und Randbedingungen durch die ERA40 Daten des ECMWF (European Centre for Medium-Range Weather Forecasts) geliefert wurden. Die Modellergebnisse wurden mit Daten von Beobachtungsstationen, aerologischen Vertikalsondierungen, globalen Analysedaten und Satellitendaten verglichen. Diese Validierung zeigt, dass die HIRHAM Modellsimulationen die globalen und regionalen Zirkulationsmuster mit einem vertretbaren Modellfehler generieren. Auf der jährlichen Zeitskale zeigen sich die größten Modellfehler in einer Überbestimmung der totalen Wolkenbedeckung und der kalten bodennahen Temperaturen der Atmosphäre. Die bodennahen Inversionen und katabatischen Windsysteme werden durch das Modell gut wiedergegeben. Dekadische Prozesse wurden durch Trendberechnungen analysiert. Dazu wurden die 40 Jahre umfassenden Simulationen in zwei 20 Jahre Abschnitte von 1958-1978 und 1979-1998 unterteilt. Die Trends in den 2m Temperaturen, im mittleren Bodenluftdruck, 500 hPa Geopotential, Niederschlag und der Netto Massenbilanz wurden berechnet. In den letzten zwei Dekaden wurde eine starke atmosphärische Abkühlung an der Oberfläche in der Ostantarktis simuliert, die in guter Übereinstimmung mit den Trendanalysen aus Beobachtungen von Chapman und Walsh (2005) steht. Der Trend im mittleren Bodenluftdruck weist deutliche Unterschiede zwischen den ersten Periode 1958-1978 und der zweiten Periode 1979-1998 auf. Insgesamt verstärkt sich über die untersuchten 40 Jahre der zirkumpolare Tiefdruckwirbel und die kontinentale Antizyklone. Die Nettomassenbilanz und der Niederschlag zeigen einen positiven Trend über der Antarktischen Halbinsel, Wilkes Land und Dronning Maud Land. Das antarktische Eisschild wächst im östlichen Teil der Antarktis mit geringen Ausnahmen in Dronning Maud Land und Wilkes Land an und schächt sich über der antarktischen Halbinsel ab. Dieses Resultat befindet sich in Übereinstimmung mit den Akkumulationstrends von Davis (2005) auf der Basis von Satellitendaten. Die horizontalen Strukturen der simulierten antarktischen Trends im mittleren Bodenluftdruck, in der 2m Temperatur und der Netto Massenbilanz wurden mit Trends des globalen Telekonnektionsmusters der Südhemisphäre verglichen. Dazu wurden wesentliche atmosphärische Parameter für positive und negative Phasen der Antarktischen Oszillation (AAO) analysiert. Die positiven/negativen AAO Phasen gehen einher mit einer Verstärkung/Abschwächung des zirkumpolaren Tiefdruckwirbels, verstärkten/reduzierten Stormtracks und verstärkten/abgeschwächten Westwinden. Für eine tiefergehende Untersuchung wurden zwei positive und eine negative AAO Phase miteinander verglichen. Die Unterschiede im Bodenluftdruck und der 2m Temperatur zwischen den positiven und negativen AAO Perioden können den Abkühlungstrend während der letzten Dekaden zu großen Teilen erklären.

Dissertação para obtenção do Grau de Mestre em Engenharia do Ambiente, perfil Engenharia Sanitária
This thesis was carried as a collaboration of Delft University of Technology (TU Delft) and the companies Waternet and KWR. The main project aims to study the possibility of thermal energy recovery from wastewater, reducing the carbon dioxide (CO2) emissions linked to the energy sector. The present work is based on a previous computational model that was developed to simulate heat recovery from wastewater for constant flow rate and temperature of water. The first goal is to simulate a wastewater discharge. In order to achieve this, a Gaussian function was added to the boundary conditions for water flow rate and water temperature. As a second goal, this work aims to assess the significance of the terms present in the water heat balance and air heat balance equations. Binary coefficients were added in each term of both equations and then all the combinations were computed. The unsteady situation successfully simulated a main discharge and numerical predictions for water temperature and flow rate are presented. The deviations associated with the modified cases for the two equations suggest that the heat flux pipe to water (!!") and heat flux pipe to air (!!") terms are crucial for water and air heat balance predictions,respectively. In order to smooth extra oscillations, the time step (dt) was reduced and a smaller relative size of oscillations was obtained. This work concludes with a section of future developments in order to improve the results obtained. Despite of the fact that the current state of these routines does not allow us to accurately assess heat exchanges in pipes, promising results were obtained, proving that numerical modelling of heat recovery will contribute greatly to the development of the main project.

Western Antarctica has been experiencing significant warming for at least the past fifty years. While higher Net Surface Mass Balance (SMB) over West Antarctica during this period of warming is expected, SMB reconstructions from ice cores reveal a more complex pattern during the period of warming. The mechanisms giving rise to SMB variability over the West Antarctic Ice Sheet (WAIS) are not well understood due to lack of instrumental data. The Southern Annular Mode (SAM) and El Niño Southern Oscillation (ENSO) are believed to contribute to WAIS SMB variability but the assumption has not been rigorously tested. SMB during years where SAM and ENSO are in extreme phases is compared to average SMB from the period 1979-2010. Additionally, atmospheric circulation anomalies are used to assess what circulation patterns accompany extreme modes of climate during the same period. The results suggest that significantly lower SMB occurs when SAM is in an extremely positive phase or ENSO is in an extremely negative phase. Additionally, atmospheric circulation anomalies show that certain circulation patterns accompany extreme modes of climate, which contribute to SMB variability over the WAIS. Ultimately, the location of low and high pressure cells is the best predictor for extreme accumulation events over the WAIS. These results are verified by assessing observed net SMB trends from a network of firn cores located from the central WAIS. Seven new firn cores are added to improve the spatial network of regional net SMB measurements. Reconstructed net SMB is calculated from new firn core records, and compared to the existing cores. The new suite of preliminary firn core records show the same significant decreasing trend that is observed in existing cores. This represents a negative region-wide SMB trend that is likely in part due to trends in SAM and ENSO.

In the Kebnekaise Massif, Northern Sweden, the west facing glacier, Rabots glaciär, is loosing volume at a significantly higher rate than east facing, Storglaciären. By analyzing data from automatic weather stations situated on the ablation area on the glaciers we investigated the effect of meteorological differences on ablation. There was a difference in micro-climate between Rabots glaciär and Storglaciären. Generally Storglaciären had slightly warmer and drier air, had less or a thinner cloud layer but more precipitation. On both glaciers a glacier wind is dominant but high wind velocities were common especially on Storglaciären indicating a larger influence from the synoptic system. There was a good correlation for temperature and vapor pressure between the glaciers that indicate that both glaciers are strongly affected by the synoptic system. The meteorological parameters have similar effect on the ablation on the glaciers. Temperature, vapor pressure and the turbulent heat fluxes are the only meteorological parameters that suggest a linear affect on ablation. Net shortwave radiation contribute with the greatest amount of energy for ablation but decreased in relative importance as the temperature increased. Shortwave radiation, sensible and latent heat contributed with a total 184Wm-2 on Rabots glaciär and 222Wm-2 on Storglaciären. Rabots glaciär seem to have a significantly greater relative importance of the turbulent heat fluxes than Storglaciären. Although the differences in micro-climate were not great, using the ablation for Storglaciären to estimate ablation on Rabots glaciär would over estimate the ablation with 0.5m w.e..

Water is essential for all life on earth. Global population increase and climate change are projected to increase the water stress, which already today is very high in many areas of the world. The differences between the largest and smallest global runoff estimates exceed the highest continental runoff estimates. These differences, which are caused by different modelling and measurement techniques together with large natural variabilities need to be further addressed. This thesis focuses on global water balance models that calculate global runoff, evaporation and water storage from precipitation and other climate data.

A new global water balance model, WASMOD-M was developed. Already when tuned against the volume error it reasonable produced within-year runoff patterns, but the volume error was not enough to confine the model parameter space. The parameter space and the simulated hydrograph could be better confined with, e.g., the Nash criterion. Calibration against snow-cover data confined the snow parameters better, although some equifinality still persisted. Thus, even the simple WASMOD-M showed signs of being overparameterised.

A simple regionalisation procedure that only utilised proximity contributed to calculate a global runoff estimate in line with earlier estimations. The need for better specifications of global runoff estimates was highlighted.

Global modellers depend on global data-sets that can have low quality in many areas. Major sources of uncertainty are precipitation and river regulation. A new routing method that utilises high-resolution flow network information in low-resolution calculations was developed and shown to perform well over all spatial scales, while the standard linear reservoir routing decreased in performance with decreasing resolution. This algorithm, called aggregated time-delay-histogram routing, is intended for inclusion in WASMOD-M.

Abstract In this PhD Thesis were reported the main results obtained analysing melting processes at the surface of some selected Alpine glaciers. In particular mitigation strategies to reduce snow and ice ablation at the surface of the Dosdé Glacier (Lombardy Alps) and the Presena Glacier (Trentino) were analyzed to evaluate their effectiveness and applicability. Moreover some modeling approaches were applied to distribute ice and snow melting at the surface of the Dosdè debris free Glacier and the Venerocolo debris covered Glacier (Lombardy Alps) also to evaluate glacier meltwater discharge. As regards the applied strategies to reduce ice and snow melting they were performed on two different glacier sites: the Presena Glacier, where skiing activates are performed from November to June without interruptions and only a short pause occurs during the hottest summer months, and the Dosdè Glacier, an Alpine glacier without strong human impacts where only trekking and mountaineering are performed. Then on the first site the preservation of winter snow is important to guarantee the possibility of performing skiing activities also in spring and early summer and several facilities (sly lifts and snow cats among the others) area available to perform and manage the mitigation strategies. Moreover snow cover presents peculiar features (density and strength different with respect to the natural conditions) due to the action of snow cats. Differently on the Dosdè glacier snow cover derived only by snowfalls and avalanches and it presents density and strength typical of a natural and untouched cold environment. No facilities area available to perform and manage the experiments. Then on this two different glacier sites the experiments we performed had different purposes: at the Dosdè Glacier we tested on natural snow the efficiency of artificial covers to preserve snow and ice. Then only a small glacier area was covered with a special material (Iceprotector500 ©) and some instruments were installed as well to measure albedo and energy balance at the glacier surface and at the surface of the artificial cover. Differently on the Presena Glacier the Autonomous Province of Trento asked for having an assessment of the effect of a wide artificial cover (up to 70,000 m2) on the glacier mass balance as they initiated an actual program of mitigation of snow and ice ablation to change drastically the glacier mass balance and then to preserve the possibility to use the Presena Glacier as a tourist resource. On this glacier we evaluated not only the artificial cover efficiency in reducing ablation of compact snow but also we evaluated the impact of this method on the whole glacier seasonal variation. In addition on this glacier was also possible to test different artificial covers (varying their chemical compositions, their thickness and their weight per area unit) to evaluate the most convenient for such purposes. As regards the modeling of ice and snow melting we followed different approaches. The main aim was to develop a simple method capable to describe the natural variability of glacier melt starting from simple data as air temperature and solar radiation which can be easily measured or evaluated. Other main input data are glacier melt rates measured on the field at least for short period. In particular we applied an enhanced melt index obtained by considering both positive degree days and incoming solar radiation. Different attempts were performed by applying index calibration over short period (high accuracy but difficult to be applied on different years) and by calibrate the index on larger time frame (less accuracy but higher possibility of make the models running on different time windows). To calculate the whole glacier mass balance we also described temporal and spatial variability of snow coverage. This issue is particularly difficult on the Italian Alps since poor data are available to describe snow depth and density at higher elevations. Also in this case our modeling approaches started from simple and largely available data (slope, aspect and elevation of each glacier pixel) and from some fundamental field data collected at the begging and at the end of the summer periods (snow depth and density evaluated trough snow pits). To improve our snow coverage modeling we also tested the use of a georadar to acquire a large sample of snow depth data coupling such information with snow density from snow pits. Last but not least the glacier modeling approaches are based on robust series of climatic data. In fact as preliminary work we performed during the PhD was an analysis of all the available meteo data describing the climate settings of the study sites to evaluate their reliability. We check all the series (through statistical tests) thus obtaining a good record of data which constituted the main input of our glacier models and analysis. We also evaluated local lapse rates to be applied in our models. This part of the research was reported and explained in the Annex.

With the use of a process-orientated ecosystem model andmeasurements conducted at different Swedish coniferous forestsites, abiotic and biotic interactions between tree and soilwere identified and related to governing factors. Two differentmodelling approaches to describe soil temperatures at two sitesincluding hydrological transects were tested (I). The approachin which both canopy and soil were considered proved to be amore flexible tool to describe soil temperatures, especiallyduring snow-free winter periods. Five sites along a climatetransect covering Sweden were used to describe soil carbon poolchanges during an 80-year period simulation (II). The dynamicmodelling approach, with a feedback between abiotic and bioticsub-models, was successful in describing simplified patterns offorest stand dynamics and furthermore in differentiatingbetween climate and nitrogen availability factors. The largereffect of nitrogen availability compared to climate on soilcarbon pool changes was clearly shown.

Keywords:SPAC; soil surface energy balance; Norwayspruce; canopy; LAI; climate; nitrogen; CoupModel

In order to improve our knowledge on the current state and variability of the Greenland ice sheet surface mass balance (SMB), a 27-year simulation (1979-2005) has been performed with the coupled atmosphere-snow regional model MAR. This simulation reveals an increase in the main factors of the SMB which are, on the one hand, the snowfall (+ 1.6 ± 1.8 km3 yr-1) in winter and on the other hand, the run-off (+ 4.2 ± 1.9 km3 yr-1) in summer. The net effect of these two competing factors leads to a SMB loss rate of – 2.7 ± 3.0 km3 yr-1, which has a significance of 87%. The melt extent derived from the passive microwave satellite data since 1979 also shows this trend. The melt water supply has increased because the Greenland ice sheet has been warming up by + 0.09 ± 0.04 °C yr-1 since 1979. This warming comes from a uniform increase of downward infra-red radiation which can not be explained by the natural variability. These changes result very likely from the global warming induced by human activities. As a result, it seems that: i) increased melting dominates over increased accumulation in a warming scenario, ii) the Greenland ice sheet has been significantly losing mass since the beginning of the 1980's by an increasing melt water run-off as well as by a probable increase of iceberg discharge into the ocean due to the "Zwally effect" (the melt water-induced ice sheet flow acceleration) and iii) the Greenland ice sheet is projected to continue to lose mass in the future. The Greenland ice sheet melting could have an effect on the stability of the thermohaline circulation (THC) and the global sea level rise. On the one hand, increases in the freshwater flux from the Greenland ice sheet (glacier discharge and run-off) could perturb the THC by reducing the density contrast driving it. On the other hand, the melting of the whole Greenland ice sheet would account for a global mean sea level rise of 7.4 m.

This thesis presents models applicable for aquatic ecosystems. Geographical Information Systems (GIS) form an important part of the thesis. The dynamic mass balance models focus on nutrient fluxes, biotic/abiotic interactions and operate on different temporal and spatial scales (site, local, regional and international). The relevance and role of scale in mass balance modelling is a focal point of the thesis.

A mesocosm experiment was used to construct a model to estimate the nutrient load of phosphorus and nitrogen from net cage fish farming (i.e., the site scale). The model was used to estimate what feeding conditions that are required for a sustainable aquaculture scenario, i.e., a zero nutrient load situation (a linkage between the site scale and the regional scale).

A dynamic model was constructed for suspended particulate matter (SPM) and sedimentation in coastal areas (i.e., the local scale) with different morphometric characteristics and distances to the Sea. The results demonstrate that the conditions in the Sea (the regional and international scale) are of fundamental importance, also for the most enclosed coastal areas.

A foodweb model for lakes was transformed and recalibrated for Baltic Sea conditions (i.e., the international scale). The model also includes a mass balance model for phosphorus and accounts for key environmental factors that regulate the presuppositions for production and biomasses of key functional groups of organisms. The potential use of the new model for setting fish quotas of cod was examined.

For the intermittent (i.e., regional) scale, topographically complex areas can be difficult to define and model. Therefore, an attempt was made to construct a waterscape subbasin identification program (WASUBI). The method was tested for the Finnish Archipelago Sea and the Okavango Delta in Botswana. A comparison to results from a semi-random delineation method showed that more enclosed basins was created with the WASUBI method.

This research project investigated the option of steelmaking with the ESS furnace by using computational modelling to estimate steady state decarburisation rates. It focused on understanding metallurgical phenomena that would dictate refining rates of molten pig iron with iron ore. The results obtained are aimed at designers and potential users of the furnace technology to improve their understanding of the expected steady-state process behaviour. A mass-and-energy-balance model with a decarburisation sub-model was developed to estimate feed material requirements for steady state operation. Modelling and simulation results suggest that it may not be possible to produce steel under the conditions proposed. However, the furnace still holds potential if ideal operational conditions are understood and applied. Modelling also gave insight into which areas areas of concern, such as bubble formation in the furnace’s channel induction heaters, and necessity for a well designed refractory lining to contain heat and allow the process to operate at a stable condition under the conditions proposed. Keywords: ESS furnace, steelmaking, metallurgical analysis, modelling, mass and energy balance, decarburisation kinetics
Dissertation (MEng)--University of Pretoria, 2020.
Materials Science and Metallurgical Engineering
MEng
Unrestricted

This thesis focused on the modelling of a pulping process. The purpose was to see if an accurate model can be crated based on relatively simple premises and if the errors can be identified or analysed. To realise this, the authors conducted a literature study to identify the current state of the art regarding the chemical pulping process. In addition, flow charts and sample data from a case study were examined. Based on the literature review and case study, model assumptions were derived. The model is divided into sixteen components. Where mixing occurs, lumped conditions are assumed. The model has five validation points, four of which are temperatures and a mass flowrate. These are shown as deviations from the measured values. In conclusions, it was the model could produce stable results over a narrow time frame. More so if the transition period at the start of the simulation is overlooked. Several new model assumptions are presented with the purpose to increase accuracy e.g. account for the components ability to store mass.

Naturvårdsverket rankar övergödningen som det allvarligaste hotet mot Östersjön. Strategin för att bekämpa övergödningen i Östersjön har varit att reducera antropogena utsläpp av fosfor och kväve från punktkällor och diffusa källor. Många forskare anser att primärproduktionen i egentliga Östersjön huvudsakligen är begränsad av kväve varför Sverige har infört ett ambitiöst och kostsamt program för avancerad kväverening på reningsverk. Andra experter hävdar istället att reducerade kväveutsläpp är meningslösa eller rent av skadliga.

I ljuset av dessa fundamentalt olika åsikter och de helt motsatta strategier de innebär syftar denna studie till att försöka klargöra vilka åtgärder som borde vidtas för att minska övergödningen genom att undersöka området Himmerfjärden som ofta används som ett exempel på lyckad kväverening. Området har också studerats intensivt sedan 1970-talet.

Detta arbete har använt en processbaserad dynamisk massbalansmodell för salt för att beräkna vattenutbytestider i Himmerfjärden. Flöden av vatten och näringsämnen till och från fjärden har beräknats och det har visats att bidraget av kväve och fosfor till Himmerfjärden från reningsverket är mycket marginellt jämfört med bidraget från Östersjön.

Denna studie har också genom att granska litteratur och mätdata från Himmerfjärden visat att det finns goda skäl att ifrågasätta hypotesen om att primärproduktionen i Himmerfjärden skulle vara långsiktigt begränsad av kväve. Resultaten av denna studie kommer att användas i framtida massbalansmodelleringar av fosfor, kväve och cyanobakterier i Himmerfjärden.

The Swedish Environmental Protection Agency has ranked eutrophication as the most severe threat to the Baltic Sea. The strategy to combat the eutrophication in the Baltic has been to reduce antrophogenous emissions of phosphorus and nitrogen from point and diffuse sources. Many scientists argue that the primary production in the Baltic proper is primarily limited by nitrogen which is why Sweden and other countries have implemented an ambitious and expensive program of advanced nitrogen removal in sewage treatment plants. Other experts argue that reduced nitrogen load to the Baltic Sea is either pointless or even harmful.

In the light of these fundamentally different views and the very opposite management strategies they imply, this study aims to more bring clarity to which measures should be taken to reduce eutrophiction by investigating the area of Himmerfjärden. Himmerfjärden is often used as an example of successful removal of nitrogen and the area has been intensively monitored since the 1970’s.

This work used a process-based dynamic mass balance model for salt to calculate water retention times in Himmerfjärden. Water and nutrient flows to and from the bay have been calculated. It was shown that the contribution of nutrients to Himmerfjärden from the treatment plant is small compared to the contribution from the Baltic Sea.

This study showed by reviewing literature on Himmerfjärden that there are good reasons to question the hypothesis of Himmerfjärden being nitrogen limited in the long-run. The findings of this study will be used in future mass balance modelling of phosphorus, nitrogen and cyanobacteria in Himmerfjärden.

Antarctic mass balance is mainly controlled by surface mass balance (SMB, i.e. the net effect of precipitations at the surface of the ice sheet) and ice discharge at its margins, mostly through ice shelves. These floating ice bodies made from ice flowing from the continent to the ocean are buttressed by ice rises (elevation of the sea floor on which ice shelf re-grounds) such as the Derwael Ice Rise (DIR) in Dronning Maud Land (DML). In addition to this role important to consider in the future contribution of Antarctica to sea level rise, ice rises are also “climate dipsticks” helping to reconstruct the climate of the past centuries to millennia at high resolution. Due to their coastal location, they witness the changes happening there more rapidly than inland. Furthermore, their internal stratigraphy forms arches that allow to assess their stability, to date their own formation and therefore, in some cases, to constrain the past extension of the ice sheet at the scale of several millennia. As part of the IceCon project :Constraining ice mass changes in Antarctica, this thesis aimed to drill a 120 m ice core (named IC12 for the IceCon project, 2012) at the divide of the DIR and perform physico-chemical analyses to study its density and its internal annual layering with the aim of reconstructing SMB of the last two centuries. We also recorded a virtual image of the borehole using an optical televiewer (OPTV) to assess the ability of this instrument to reconstruct a density profile and measure vertical strain rates when the logging is repeated in the same borehole after a sufficient period of time (here, 2 years).The results show a general increase in snow accumulation rates (SMB) of 30-40% during the 20th century, particularly marked during the last 20-50 years. SMB variability is governed to a large extent by atmospheric circulation and to a lesser extent by variations in sea ice cover. The vertical velocity profile measured from repeat borehole OPTV was applied to refine SMB correction and the results fall in the error range of the corrections made using a model previously developed to study the DIR’s stability. This thesis also contributed to characterizing the spatial variability of SMB across the DIR by dating internal reflection horizons (IRHs), former surfaces of the DIR buried under subsequent snow layers and detected using radio-echo-sounding, and by measuring the density profile of IC12. SMB is found to be 2.5 times higher on the upwind slope than on the downwind slope due to the orographic effect. This pattern is regularly observed on ice rises in DML and stresses the importance of adopting a sufficient spatial resolution (5 km) in climate models.Finally, the technical developments allowing to rapidly reconstruct a density profile from the OPTV image of a borehole contributed to improving our knowledge of two features of Antarctic ice shelves, namely melt ponds, influencing surface mass balance and subglacial channels, influencing basal mass balance. Specifically, the results show that density is 5 % higher in surface trenches associated with subglacial channels, and that ice below melt ponds can reach the density of bubble-free ice due to melting and refreezing processes, with implications on ice shelf viscosity.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished

Antarctic mass balance is mainly controlled by surface mass balance (SMB, i.e. the net effect of precipitations at the surface of the ice sheet) and ice discharge at its margins, mostly through ice shelves. These floating ice bodies made from ice flowing from the continent to the ocean are buttressed by ice rises (elevation of the sea floor on which ice shelf re-grounds) such as the Derwael Ice Rise (DIR) in Dronning Maud Land (DML). In addition to this role important to consider in the future contribution of Antarctica to sea level rise, ice rises are also “climate dipsticks” helping to reconstruct the climate of the past centuries to millennia at high resolution. Due to their coastal location, they witness the changes happening there more rapidly than inland. Furthermore, their internal stratigraphy forms arches that allow to assess their stability, to date their own formation and therefore, in some cases, to constrain the past extension of the ice sheet at the scale of several millennia. As part of the IceCon project :Constraining ice mass changes in Antarctica, this thesis aimed to drill a 120 m ice core (named IC12 for the IceCon project, 2012) at the divide of the DIR and perform physico-chemical analyses to study its density and its internal annual layering with the aim of reconstructing SMB of the last two centuries. We also recorded a virtual image of the borehole using an optical televiewer (OPTV) to assess the ability of this instrument to reconstruct a density profile and measure vertical strain rates when the logging is repeated in the same borehole after a sufficient period of time (here, 2 years).The results show a general increase in snow accumulation rates (SMB) of 30-40% during the 20th century, particularly marked during the last 20-50 years. SMB variability is governed to a large extent by atmospheric circulation and to a lesser extent by variations in sea ice cover. The vertical velocity profile measured from repeat borehole OPTV was applied to refine SMB correction and the results fall in the error range of the corrections made using a model previously developed to study the DIR’s stability. This thesis also contributed to characterizing the spatial variability of SMB across the DIR by dating internal reflection horizons (IRHs), former surfaces of the DIR buried under subsequent snow layers and detected using radio-echo-sounding, and by measuring the density profile of IC12. SMB is found to be 2.5 times higher on the upwind slope than on the downwind slope due to the orographic effect. This pattern is regularly observed on ice rises in DML and stresses the importance of adopting a sufficient spatial resolution (5 km) in climate models.Finally, the technical developments allowing to rapidly reconstruct a density profile from the OPTV image of a borehole contributed to improving our knowledge of two features of Antarctic ice shelves, namely melt ponds, influencing surface mass balance and subglacial channels, influencing basal mass balance. Specifically, the results show that density is 5 % higher in surface trenches associated with subglacial channels, and that ice below melt ponds can reach the density of bubble-free ice due to melting and refreezing processes, with implications on ice shelf viscosity.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished

The representation of high-latitude surface processes and quantifying surface-climate feedbacks are some of the most serious shortcomings of present day Arctic land surface modelling. The energy balance of seasonally snow-covered sparse deciduous forests at high latitudes is poorly understood and inaccurately represented within hydrological and climate models. Snow cover plays an important role in wintertime fluxes of energy, water and carbon, controlling the length of the active growing season and hence the overall carbon balance of Arctic ecosystems. Snow cover is non-uniform and spatially variable, as wind redistributes snow from areas of exposed open tundra to sheltered areas within the forest, where a deeper snowpack develops. Low solar zenith angles, coupled with sparse deciduous leafless trees, cast shadows across the snow surface. The spatial distribution of canopy gaps determines the timing of direct radiation which penetrates down through the canopy to the snow surface. The forest canopy also excludes incoming longwave radiation and yet also emits longwave radiation to the snow surface. Consequently the forest canopy plays a key role in the radiation balance of sparse forests. To improve our knowledge of these complex processes, meteorological and field observations were taken in an area of highly heterogeneous birch Betula pubescens ssp. czerepanovii forest in Abisko, Sweden during the spring of 2008 and 2009. Detailed measurements of short and longwave radiation above and below the canopy, hemispherical photographs, tree temperatures and snow surveys were conducted to quantify the radiation balance of the sparse deciduous forest. An array of below canopy pyranometers found the mean canopy transmissivity to be 74 % in 2008 and 76 % in 2009. Hemispherical photographs taken at the pyranometer locations analysed with Gap Light Analyzer (GLA) showed reasonable agreement with a mean canopy transmissivity of 75 % in 2008 and 74 % in 2009. The canopy transmissivity was found to be independent of the diffuse fraction of radiation as the canopy is very sparse. A series of survey grids and transects were established to scale up from the below canopy pyranometers to the landscape scale. Hemispherical photographs analysed with GLA showed the sparse forest canopy had a mean transmissivity of 78 % and a mean LAI of 0.25, whereas the open tundra had a mean transmissivity of 97 % and a mean LAI of < 0.01. Snow surveys showed the sparse forest snow depth to vary between 0.34 and 0.55 m, whereas the snow depth in the open tundra varied between 0.12 and 0.18 m. Observations of canopy temperatures showed a strong influence of incident shortwave radiation warming the tree branches to temperatures up to 15 °C warmer than ambient air temperature on the south facing sides of the trees, and up to 6 °C on the north facing sides of the trees. To reproduce the observed radiation balance, two canopy models (Homogenous and Clumped) were developed. The Homogeneous canopy model assumes a single tree tile with a uniform sparse canopy. The Clumped canopy model assumes a tree and a grass tile, where the tree tile is permanently in shade from the canopy and the grass tile receives all the incoming radiation. These canopy models identified the need for a parameter that accounts for the spatial and temporal variation of the shaded gaps within the sparse forest. JULES (Joint UK Land Environment Simulator) is the community land surface model used in the UK Hadley Centre GCM suite. Modifications of the land-surface interactions were included in JULES to represent the shaded gaps within the sparse deciduous forest. New parameterisations were developed for the time-varying sunlit fractions of the gap (flit), the sky-view fraction (fv), and the longwave radiation emitted from the canopy (LWtree). These model developments were informed by field observations of the forest canopy and evaluated against the below canopy short and longwave radiation observed data sets. The JULES Shaded gap model output showed a strong positive relationship with the observations of below canopy shortwave and longwave radiation. The JULES Shaded gap model improves the ratio of observed to modelled short and longwave radiation on sunny days compared to the JULES model. The JULES Shaded gap model reduces the time to snow melt by 2 to 4 days compared to the JULES model, making the model output more aligned with in-situ observational data. This shortening of the modelled snow-season directly impacts on the simulated carbon and water balance regionally and has wider relevance at the pan-Arctic scale. When JULES Shaded Gap was evaluated on the global scale, it improved the modelled snowmass across large areas of sparse forest in northern Canada, Scandinavia and Northern Russia with respect to GlobSnow. The performance of the land surface-snow-vegetation interactions of JULES was improved by using the Shaded gap to model the radiation balance of sparse forests in climate-sensitive Arctic regions. Furthermore these observational data can be used to develop and evaluate high latitude land-surface processes and biogeochemical feedbacks in other earth system models.

This thesis aims to study the recent and past behaviours of the lowermost Italian glacier, a very small glacier (<0.5 km2) known as Ghiacciaio Occidentale del Montasio (Julian Alps), which is located far below the regional equilibrium-line altitude. Glacier elevation changes, mass balances, surface displacements and change in surface cover were monitored using high resolution techniques (in particular Structure from Motion Multi-View Stereo, SfM-MVS) and reconstructing Digital Elevation Models (DEMs) from historical images and maps. Glacier changes were correlated to air temperature and precipitation trends to better characterise and understand its climatic response. The first object of the thesis was to investigate the reliability of the SfM-MVS technique for monitoring elevation changes in debris covered areas such as the lower half of the Montasio Glacier. The technique was tested over easy-to-access riverbeds with different morphologies and patterns, to point out critical aspects and minimise errors in the acquisition and processing phases. SfM-MVS proved to have high repeatability with unchanged acquisition setup, while surveys performed with different sensors might introduce systematic errors in the elevation change detection analysis. Overall, this technique was considered adequately accurate and precise for monitoring small debris covered areas, such as the Montasio Glacier. Bases on these results, the focus moved to the recent (2006-2019) dynamics of the Montasio Glacier. Data acquired with both SfM-MVS and laser scanning (terrestrial and aerial) techniques were used to analyse the annual mass balance of the glacier. The study confirmed a complex relationship between the glacier mass balance and the extent of the debris-covered area. It also highlighted the unusual behaviour of this glacier, characterised by: i) a remarkably lower imbalance compared to others Alpine reference glaciers, ii) a nonsignificant correlation of mass balance with air temperature, and iii) a high sensitivity to precipitations during the accumulation season. The analysis of the recent dynamics opened new questions regarding the long-term climatic sensitivity of the glacier and its relationship with the debris cover, at the secular time scale. Therefore, an historical analysis was performed reconstructing glacier DEMs for five different years (1920,1948,1982,2006,2020), which enabled the calculation of the geodetic mass balance rate in the last century. The Montasio Glacier behaviour was comparable with the other alpine glaciers trough the 20th Century until the early 1980s. In the recent decades, however, it progressively decoupled from the typical response of alpine glaciers, showing increasing departure and much lower imbalance. The progressively increase in thickness and extent of the debris layer observed after the 1940s, in association with the avalanche feeding and the shadowing effect of the Mt. Jof di Montasio, were confirmed as the main causes of the current minor imbalance and low sensitivity to air temperature fluctuations. This thesis demonstrates that high-resolution SfM-MVS represents a cost-effective method, which can be successfully adopted for monitoring the response of glaciers with characteristics similar to the Montasio Glacier.The study provides a full characterisation of the current and past dynamics and behaviour of the Montasio Glacier, from both climatic and glaciological perspectives. Based on the results of this study, it can be assumed that a transition to periglacial conditioning (i.e.transformation to a rock glacier) is improbable, and that the glacier should not quickly disappear in the near future.
This thesis aims to study the recent and past behaviours of the lowermost Italian glacier, a very small glacier (<0.5 km2) known as Ghiacciaio Occidentale del Montasio (Julian Alps), which is located far below the regional equilibrium-line altitude. Glacier elevation changes, mass balances, surface displacements and change in surface cover were monitored using high resolution techniques (in particular Structure from Motion Multi-View Stereo, SfM-MVS) and reconstructing Digital Elevation Models (DEMs) from historical images and maps. Glacier changes were correlated to air temperature and precipitation trends to better characterise and understand its climatic response. The first object of the thesis was to investigate the reliability of the SfM-MVS technique for monitoring elevation changes in debris covered areas such as the lower half of the Montasio Glacier. The technique was tested over easy-to-access riverbeds with different morphologies and patterns, to point out critical aspects and minimise errors in the acquisition and processing phases. SfM-MVS proved to have high repeatability with unchanged acquisition setup, while surveys performed with different sensors might introduce systematic errors in the elevation change detection analysis. Overall, this technique was considered adequately accurate and precise for monitoring small debris covered areas, such as the Montasio Glacier. Bases on these results, the focus moved to the recent (2006-2019) dynamics of the Montasio Glacier. Data acquired with both SfM-MVS and laser scanning (terrestrial and aerial) techniques were used to analyse the annual mass balance of the glacier. The study confirmed a complex relationship between the glacier mass balance and the extent of the debris-covered area. It also highlighted the unusual behaviour of this glacier, characterised by: i) a remarkably lower imbalance compared to others Alpine reference glaciers, ii) a nonsignificant correlation of mass balance with air temperature, and iii) a high sensitivity to precipitations during the accumulation season. The analysis of the recent dynamics opened new questions regarding the long-term climatic sensitivity of the glacier and its relationship with the debris cover, at the secular time scale. Therefore, an historical analysis was performed reconstructing glacier DEMs for five different years (1920,1948,1982,2006,2020), which enabled the calculation of the geodetic mass balance rate in the last century. The Montasio Glacier behaviour was comparable with the other alpine glaciers trough the 20th Century until the early 1980s. In the recent decades, however, it progressively decoupled from the typical response of alpine glaciers, showing increasing departure and much lower imbalance. The progressively increase in thickness and extent of the debris layer observed after the 1940s, in association with the avalanche feeding and the shadowing effect of the Mt. Jof di Montasio, were confirmed as the main causes of the current minor imbalance and low sensitivity to air temperature fluctuations. This thesis demonstrates that high-resolution SfM-MVS represents a cost-effective method, which can be successfully adopted for monitoring the response of glaciers with characteristics similar to the Montasio Glacier.The study provides a full characterisation of the current and past dynamics and behaviour of the Montasio Glacier, from both climatic and glaciological perspectives. Based on the results of this study, it can be assumed that a transition to periglacial conditioning (i.e.transformation to a rock glacier) is improbable, and that the glacier should not quickly disappear in the near future.

Depuis les années 90, l’Antarctique de l’Ouest, dont le secteur d’Amundsen, affiche une importante perte de masse provenant principalement de l’accélération des glaciers côtiers en réponse à une fonte océanique plus conséquente sous les plateformes de glace. Ces plateformes sont généralement confinées est agissent comme un verrou pour l’écoulement. En subissant davantage de fonte basale, les plateformes deviennent fragiles et les glaciers en amont s’accélèrent, contribuant ainsi à augmenter le niveau des mers. L’avenir de l’Antarctique de l’Ouest est particulièrement préoccupant car sa configuration rend la calotte sujette à une instabilité marine. Par ailleurs, ces plateformes pourraient s’affaiblir sous l’effet d’une augmentation de la fonte de surface dans un climat plus chaud (hydrofracturation), rendant là aussi une instabilité possible. L’arrivée de ces instabilités pourrait être freinée ou compensée par l’évolution du bilan de masse de surface qui se compose majoritairement de précipitations neigeuses, sporadiquement augmenté par la pluie, et légèrement amoindri par la sublimation et le runoff. Cette thèse porte sur la modélisation de l’ensemble des processus atmosphériques et océaniques pouvant faire évoluer la contribution de l’Antarctique de l’Ouest au niveau des mers.Pour cela une projection océanique représentant les cavités sous-glaciaires a d’abord été réalisée avec le modèle NEMO. La circulation induite par la fonte océanique modifie la réponse de l’océan côtier à un futur changement de circulation atmosphérique, si bien qu’utiliser des modèles de climat ne représentant pas les cavités donne une indication faussée du réchauffement de l’océan autour de la calotte. Nous avons également mis en évidence une rétroaction positive entre la fonte sous-glaciaire et le retrait de la ligne d’échouage, entraînant une augmentation de la fonte jusqu’à 2.5 fois. Ces résultats indiquent la nécessité de coupler des modèles de calotte et d’océan pour établir des projections futures, même si les projections envisagées dans cette thèse restent relativement idéalisées.Pour établir des projections de bilan de masse de surface, il est nécessaire d’utiliser un modèle atmosphérique avec une représentation fine des processus polaires, notamment ceux liés au manteau neigeux. Ainsi nous avons utilisé le modèle atmosphérique régional MAR pour établir des projections dans le secteur d’Amundsen. Nous avons d’abord montré que MAR est approprié pour représenter le climat de surface observé en Antarctique de l’Ouest. Nous avons trouvé qu’aucun des modes climatiques (ASL, SAM, ENSO) n’expliquent plus de 50% de la variance de la fonte et du SMB en été à l’échelle interannuelle, et il est donc difficile d’utiliser des projections des modes climatiques comme indication de l’évolution du climat de surface.Forcé par le signal multi-modèle CMIP5 dans le scénario rcp85, MAR prévoit une augmentation du bilan de masse de surface de 30-40% d’ici 2100. Cette augmentation est équivalente à une baisse de 0.33 mm/an de niveau des mers, ce qui compenserait l’effet de la dynamique si celle-ci restait à son niveau actuel (0.26 mm/an). Ces projections indiquent également 5 à 15 fois plus de fonte de surface sur les plateformes du secteur Amundsen, mais la quasi-totalité de la fonte produite chaque année continue à regeler dans la couche de neige annuelle, et ne devrait donc contribuer de manière importante ni au bilan de masse de surface ni à l’hydrofracturation.Il ressort de ces travaux qu’un couplage océan/calotte dans les modèles de climat est primordial pour simuler le futur de l’Antarctique et de l’océan Austral. Une représentation fine des processus liés à la fonte de surface et au regel dans le névé est également essentielle car la possibilité d’hydrofracturation des plateformes dans un climat plus chaud relève d’un équilibre subtil entre l’augmentation de l’accumulation, de la température, et les rétroactions liées à l’albédo et à l’humidité
West Antarctica, and particularly the Amundsen sector, has shown since the 1990s a large increase of mass loss related to coastal glacier acceleration in response to an increase of oceanic melt underneath ice shelves. Ice shelves play a buttressing role for ice-stream and increased oceanic melt therefore lead to ice shelves thinning and glacier acceleration, which contributes to sea level rise. West Antarctica is of particular concern because its configuration is prone to marine ice-sheet instability. It has been suggested that ice shelves weaken under large surface melt in a warmer climate (hydrofracturing), possibly leading to another kind of instability. Instabilities could be slowed down or compensated by future Surface Mass Balance (SMB) that consists mainly of snowfall, sporadic rainfall, and is slightly reduced by sublimation and runoff. The main objective of this PhD work is to model the atmospheric and oceanic processes that will most likely affect the future West Antarctic contribution to sea level rise.First, oceanic projections have been developed using the NEMO ocean model. The ocean circulation induced by ice-shelf basal melting affects the ocean response to future changes in surface winds. Therefore, models that do not represent ice-shelf cavities produce wrong warming patterns around Antarctica. A positive feedback between oceanic melting and grounding-line retreat has been identified and can increase melt rates by a factor of 2.5. These results are strong incentive to couple ocean and ice sheet models, although the projections proposed here are relatively idealized.To run SMB and surface melting projections, an atmospheric model with a fine representation of polar processes, including those related to the snowpack, is needed. MAR is found to be an appropriate tool to simulate the present-day surface climate in the Amundsen region. We find that none of the large climate modes of variability (ASL, SAM, ENSO) explains more than 50% of surface melt and SMB summer variance at the interannual timescale. The use of climate mode variability projections to estimate the future surface climate of West Antarctica is therefore not trivial.Forced by the CMIP5 multi-model mean under the RCP8.5 scenario, MAR predicts an increase of SMB by 30-40% for the end of the 21st century. This increase corresponds to 0.33 mm yr-1 of sea level drop down, which is higher than the current West Antarctic contribution of ~0.26 mm yr-1 from ice dynamics. Surface melt is also projected to increase by a factor of 5 to 15 over the Amundsen ice shelves, but most of it is projected to refreeze in the annual snow layer, so future melting should not have a strong contribution to SMB or hydrofracturing.To conclude we show that coupled ocean and ice sheet climate models are essential to simulate the future of Antarctica and Southern Ocean. A fine representation of surface melt and refreezing processes within the snowpack is also crucial as possible hydrofracturing is threatening in a warmer climate and it comes within a delicate equilibrium between snowfall, air temperature, and feedback related to albedo and humidity

This thesis focuses on the glaciation of the Late Saalian period (160 -140 ka) over Eurasia. The Quaternary Environment of the Eurasian North (QUEEN) project determined that during this period, the Eurasian ice sheet was substantially larger than during the entire Weichselian cycle and especially that of the Last Glacial Maximum (21 ka, LGM). The Late Saalian astronomical forcing was different than during the LGM while greenhouse gas concentrations were similar. To understand how this ice sheet could have grown so large over Eurasia during the Late Saalian, we use an Atmospherical General Circulation Model (AGCM) coupled to an oceanic mixed layer and a vegetation model to explore the influence of regional parameters, sea surface temperatures (SST) and orbital parameters on the surface mass balance (SMB) of the Late Saalian Eurasian ice sheet. At140 ka, proglacial lakes, vegetation and simulated Late Saalian SST cool the Eurasian climate, which reduce the ablation along the southern ice sheet margins. Dust deposition on snow has the opposite effect. The presence of a Canada Basin ice-shelf during MIS6 in the Arctic Ocean, does not affect the mass balance of the ice sheet. According to geological evidence, the Late Saalian Eurasian ice sheet reached its maximum extent before 160 ka. Northern Hemisphere high latitude summer insolation shows a large insolation peak near 150 ka. The simulated climate prior to 140 ka is milder and ablation is larger along the southern margins of the Eurasian ice sheet although the mean annual SMB is positive. The Late Saalian Eurasian ice sheet may have been large enough to generate its own cooling, thus maintaining itself over Eurasia.
Joint PhD Degree between Stockholm University and Université Joseph FourierAt the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Submitted. Paper 4: Submitted. Paper 5: Manuscript.

This thesis details the development and calibration of a model created by coupling a land surface simulation model named CLASS with a hydrologic model named WATFLOOD. The resulting model, known as WatCLASS, is able to serve as a lower boundary for an atmospheric model. In addition, WatCLASS can act independently of an atmospheric model to simulate fluxes of energy and moisture from the land surface including streamflow. These flux outputs are generated based on conservation equations for both heat and moisture ensuring result continuity. WatCLASS has been tested over both the data rich BOREAS domains at fine scales and the large but data poor domain of the Mackenzie River at coarse scale. The results, while encouraging, point to errors in the model physics related primarily to soil moisture transport in partially frozen soils and permafrost. Now that a fully coupled model has been developed, there is a need for continued research by refining model processes and test WatCLASS's robustness using new datasets that are beginning to emerge. Hydrologic models provide a mechanism for the improvement of atmospheric simulation though two important mechanisms. First, atmospheric inputs to the land surface, such as rainfall and temperature, are transformed by vegetation and soil systems into outputs of energy and mass. One of these mass outputs, which have been routinely measured with a high degree of accuracy, is streamflow. Through the use of hydrologic simulations, inputs from atmospheric models may be transformed to streamflow to assess reliability of precipitation and temperature. In this situation, hydrologic models act in an analogous way to a large rain gauge whose surface area is that of a watershed. WatCLASS has been shown to be able to fulfill this task by simulating streamflow from atmospheric forcing data over multi-year simulation periods and the large domains necessary to allow integration with limited area atmospheric models. A second, more important, role exists for hydrologic models within atmospheric simulations. The earth's surface acts as a boundary condition for the atmosphere. Besides the output of streamflow, which is not often considered in atmospheric modeling, the earth's surface also outputs fluxes of energy in the form of evaporation, known as latent heat and near surface heating, known as sensible heat. By simulating streamflow and hence soil moisture over the land surface, hydrologic models, when properly enabled with both energy and water balance capabilities, can influence the apportioning of the relative quantities of latent and sensible heat flux that are required by atmospheric models. WatCLASS has shown that by improving streamflow simulations, evaporation amounts are reduced by approximately 70% (1271mm to 740mm) during a three year simulation period in the BOREAS northern old black spruce site (NSA-OBS) as compared to the use of CLASS alone. To create a model that can act both as a lower boundary for the atmosphere and a hydrologic model, two choices are available. This model can be constructed from scratch with all the caveats and problems associated with proving a new model and having it accepted by the atmospheric community. An alternate mechanism, more likely to be successfully implemented, was chosen for the development of WatCLASS. Here, two proven and well tested models, WATFLOOD and CLASS, were coupled in a phased integration strategy that allowed development to proceed on model components independently. The ultimate goal of this implementation strategy, a fully coupled atmospheric - land surface - hydrologic model, was developed for MC2-CLASS-WATFLOOD. Initial testing of this model, over the Saguenay region of Quebec, has yet to show that adding WATFLOOD to CLASS produces significant impacts on atmospheric simulation. It is suspected, that this is due to the short term nature of the weather simulation that is dominated by initial conditions imposed on the atmospheric model during the data assimilation cycle. To model the hydrologic system, using the domain of an atmospheric model, requires that methods be developed to characterize land surface forms that influence hydrologic response. Methods, such as GRU (Grouped Response Unit) developed for WATFLOOD, need to be extended to taken advantage of alternate data forms, such as soil and topography, in a way that allows parameters to be selected a priori. Use of GIS (Geographical Information System) and large data bases to assist in development of these relationships has been started here. Some success in creating DEMs, (Digital Elevation Model) which are able to reproduce watershed areas, was achieved. These methods build on existing software implementations to include lake boundaries information as a topographic data source. Other data needs of hydrologic models will build on relationships between land cover, soil, and topography to assist in establishing grouping of these variables required to determine hydrologic similarity. This final aspect of the research is currently in its infancy but provides a platform from which to explore for future initiatives. Original contributions of this thesis are centered on the addition of a lateral flow generation mechanism within a land surface scheme. This addition has shown a positive impact on flux returns to the atmosphere when compared to measured values and also provide increased realism to the model since measured streamflow is reproduced. These contributions have been encapsulated into a computer model known as WatCLASS, which together with the implementation plan, as presented, should lead to future atmospheric simulation improvements.

En raison de l’augmentation de la pression de vapeur saturante avec la température, les précipitations en Antarctique sont censées augmenter au cours du prochain siècle. Cela conduirait à un accroissement de l’accumulation de neige sur le continent, atténuant ainsi en partie l’augmentation future du niveau des mers. Les tendances récentes de température et d’accumulation de neige en Antarctique ne reflète pas clairement ce processus. Le rôle joué par les intrusions d’humidité dans la variabilité des températures et des précipitations pourrait expliquer en partie ce paradoxe. Jusqu’à présent, seuls des événements épars de très forte intensité avaient été analysés. Une étude de 2014 portant sur la région de Dronning Maud Land avait montré la concordance des intrusions intenses avec l’occurrence de rivières atmosphériques (RA). Dans cette thèse, nous développons un algorithme de détection des rivières atmosphériques adapté aux régions polaires et créons une climatologie de ces événements à l’échelle de l’Antarctique. En utilisant les sorties du modèle à aire limitée MAR (Modèle Atmosphérique Régional), nous évaluons les impacts de rivières atmosphériques sur la fonte, la stabilité des plateformes de glace de la Péninsule Antarctique et sur les précipitations neigeuses en surface de la calotte.Chaque point de la calotte est concerné par des rivières trois jours par an en moyenne. Cette valeur est plus faible encore à l’intérieur du continent. Pourtant, les rivières contrôlent les processus de fonte de surface sur l’Antarctique de l’ouest et la variabilité des précipitations sur l'Antarctique de l’Est. A l’ouest, les RA qui pénètrent à l’intérieur du continent provoquent des anomalies positives du rayonnement de grande longueur d’onde incident et de vent, accompagné d’effet foehn marqué le long des pentes situées sous le vent. Entre 1979 et 2017, les rivières provoqué 40% de la fonte estivale sur la plateforme de Ross (près de 100% à plus haute altitude sur Marie Byrd Land) et 40 à 80% de la fonte hivernale le long des plateformes de la péninsule Antarctique. En été, ces RA contribuent aussi à la fonte des plateformes de glace de Larsen situées à l’est de la Péninsule. Les RA provoquent 60 à 80% des événements de fonte/ruissellement les plus intenses ainsi que les extrêmes de chaleur. Cette fonte est amplifiée par l’effet Foehn et par les anomalies positives des flux radiatifs incidents provoqués à l’Est de la Péninsule. L’eau de fonte s’accumule alors dans des lacs et des crevasses en surface des plateformes, étape préliminaire à la désintégration d’une plateforme par phénomène de fracturation hydraulique. Les RA repoussent aussi la glace de mer loin de la côte permettant à la houle d’abîmer les marges des plateformes de glace, permettant de déclencher leur désintégration. En particulier, la présence de RA a été découverte lors de la désintégration des plateformes de Larsen A fin janvier 1995 et de Larsen B fin février/début mars 2002. Dans l’ensemble, depuis 2000, 12 des 20 derniers événements de vêlage ou d’effondrement le long des plateformes de Larsen ont été précédés (dans la limite de 5 jours) par l’arrivée d’une RA. Enfin, les RA sont responsables de la majorité des précipitations les plus intenses en Antarctique. A l’Est, elles provoquent 20 à 30% de l’accumulation de neige et contrôlent les tendances et la variabilité interannuelle précipitations neigeuses sur cette partie du continent. Ce contrôle s’étend même à la majeure partie de la calotte glaciaire entre 1980 et 2018.En définitive, les RA jouent un rôle important du climat de l’Antarctique. Une évolution des conditions de blocage atmosphérique autour de l’Antarctique au cours du 21ème siècle engendrerait des changements du bilan de masse de surface de l’Antarctique. De telles évolutions sont actuellement ignorées dans le cadre des projections d’impact du changement climatique
Due to the increased ability of the air to hold moisture with temperature, precipitation in Antarctica is expected to increase significantly over the next century. This process will undoubtedly lead to an increase in snow accumulation on the continent, thereby partially mitigating future sea level rise. However, recent observed trends in temperature and snow accumulation in Antarctica are insignificant and paradoxical. The role played by moisture intrusions in temperature and precipitation variability could partly explain this phenomenon. These events are known to transport warm air masses from the oceans to the Antarctic continent, but only individual and unrelated intrusion events have been described so far. In an earlier study of the Dronning Maud Land region, the description of atmospheric rivers (ARs) provided an innovative view to describe high intensity moisture intrusions. In this thesis, we develop an atmospheric river detection algorithm adapted to the polar regions, in order to create a climatology of these events at the Antarctic scale. Using the outputs of the regional climate model, MAR (Regional Atmospheric Model), we evaluate the impacts of atmospheric rivers on the melting in West Antarctic, ice-shelf stability on the Antarctic Peninsula ice shelves, and on snowfall across the Antarctic ice sheet.Atmospheric rivers are infrequent events with coastal areas of Antarctica experiencing AR conditions around only three days per year on average and this value is even lower in Antarctic interior. However, ARs control surface melting processes on West Antarctica and precipitation variability on East Antarctica. In the west, ARs entering the interior of the continent cause positive anomalies in downward longwave radiation via highly liquid-laden clouds and wind, resulting in a marked foehn effect along leeward slopes. Between 1979 and 2017, rivers were thus associated with about 40% of the summer melt on the Ross Ice Shelf (nearly 100% at higher altitudes on Marie Byrd Land) and 40-80% of the winter melt along the ice shelves of the Antarctic Peninsula. In summer, these rivers also contribute to the melting of the Larsen ice shelves located east of the Peninsula. Their direct contribution to cumulative melting is more limited than in winter because the intense solar radiation in summer allows daily melting to occur. However, ARs caused 60-80% of the most intense melt/runoff events as well as high temperature extremes. This melting is linked to the Foehn effect and the positive longwave radiative fluxes anomalies over the eastern Peninsula during AR passages. The melt water accumulates in lakes and crevasses on the ice shelf surface, a preliminary step in ice shelf disintegration by hydraulic fracturing. ARs also push sea ice away from the coast, allowing swells to hit and apply strain to the ice-shelf margins. ARs can thus trigger the final disintegration of ice shelves. In particular, ARs were present during the disintegration of the Larsen A ice shelf in late January 1995 and the Larsen B ice shelf in late February/early March 2002. Overall, since 2000, 12 of the last 20 calving or collapse events along the Larsen Ice Shelves have been preceded (within 5 days) by the arrival of an AR. Finally, atmospheric rivers are responsible for the majority of the most intense precipitation in Antarctica. In eastern Antarctica, 20-30% of the snow accumulation occurred during of AR landfalls. Although this value remains modest, we observe that AR activity controls the trends and interannual variability of snowfall in this part of the continent. This control even extends to most of the ice sheet between 1980 and 2018.Ultimately, ARs play an important role in the Antarctic surface mass balance. Therefore, a change in atmospheric blocking conditions around Antarctica during the 21st century would lead to changes in the Antarctic surface mass balance. Such changes are currently ignored in climate change impact projections

A new surface aeration system for water and wastewater treatment has been studied. Its uniqueness lies in its ability to operate in two modes: aeration or simply blending (mixing) by just reversing the direction of rotation. An experimental plant has enabled to focus on mass transfer performance and hydrodynamics. The flow pattern and the velocity field measurements inside the agitated tank were performed by both the Laser Doppler Velocimetry (LDV) and the Particle Image Velocimetry (PIV) techniques for the single phase (Mixing) mode and for the two phases (Aeration) mode. The oxygen mass transfer occurs both in the water bulk and in the spray above water surface and has been independently investigated. Different configurations and operational conditions were tested during the experimental part in order to interpret phenomenon effect of the draft tube and RTP propeller, rotational speed, turbine blades submergence and else on the flow field and the oxygen mass transfer in the agitated system that produced mainly by a cone shape turbine. The experimental part dealing with hydrodynamics and flow field shows that the down-pumping operation mode with the draft tube has the most convenient results in the mixing mode with respect to turbulent flow field and mixing time. Whilst for the up-pumping aeration mode the hydrodynamics experimental results show the whole system configuration is the most convenient with regarded to mean velocities, turbulent flow intensity and mixing time. For the oxygen mass transfer experimental part, it is found that the highest standard liquid bulk aeration efficiency is achieved (SAEb = 2.65 kgO2 kw-1h-1) when the whole system configuration is used. The highest standard aeration efficiency at 20°C for the water spray zone is accomplished ((Esp)20 = 51.3 %) with the whole system configuration. Several correlations models have been derived for the oxygen mass transfer in water bulk and spray zones, power consumption and mixing time, on the basis of experimental results. They can be used as tools to estimate these parameters for geometrical and dynamical similar systems at industrial scales.

Lagoons are coastal waterbodies which are sensitive to meteorological and hydrological changes. This study focused on the spatial distribution of salinity in Gialova lagoon, Greece. The area in which the lagoon is located is under pressure from agriculture and truism in the area. Besides that, the lagoon is an important stop for migratory birds as well as the home for rare species. To investigate how salinity is distributed in the lagoon a salinity gradient was produced. Also, an attempt was made to model the salt and fresh water fluxes in the lagoon using a mass balance approach. The water fluxes are either from fresh water sources or influx of saline water from the sea. Manual electric conductivity measurements were taken during a field campaign to the lagoon. Time series data used in the model was obtained from stations in the lagoon and the surroundings. An investigation in how the lagoon measurement station differ in salinity was also performed in this study. Results from the gradient map and manual measurements show that the water in the lagoon is the freshest in the North-Eastern parts and the most saline to the South-West. The modelled water fluxes show an inverse relationship from each other. High fresh water fluxes correspond to precipitation events, lower salinity concentration. Whereas high salt water fluxes correspond to high salinity concentration and lowered precipitation. The stations concentrated to the middle lagoon show corresponding values in salinity whereas the station to the South-West differs. The canal surrounding the lagoon shows interactions since measurements show that the water is brackish. A longer time series could provide patterns in water fluxes over time. Trying to find the portions of terrestrial groundwater and surface water, and further investigation of the regional aquifer could provide new information to develop this model. The region is expected to experience water stress which makes further studies and monitoring important.

Les retenues collinaires sont des aménagements hydrauliques largement rencontrés en Afrique du Nord, et plus généralement dans les zones arides et semi-arides de la planète. Ils visent à la fois la conservation en eau dans les bassins versants amont et la rétention des matériaux issus de l'érosion afin d'éviter l'envasement des grands barrages en aval. L'implantation et la gestion de l'eau mobilisée par les retenues collinaires doit s'appuyer sur une connaissance de leur fonctionnement hydrologique. Or ce fonctionnement est encore peu connu, en particulier les processus et l'intensité des flux des échanges retenue-souterrain, constituent une question très ouverte. L'objectif de ce travail est de quantifier et d'analyser le fonctionnement des échanges retenue-souterrain sur un bassin versant agricole. L'étude a été menée sur la retenue collinaire du bassin versant expérimental de Kamech, appartenant à l'ORE OMERE. Dans la première partie de ce travail, une approche de bilan hydrologique a été développée et a permis de montrer que les échanges retenue-souterrain sont dominés par l'infiltration, qui représente environ 79 % des pertes à la retenue collinaire et dépasse largement les pertes par évaporation qui ne représente que 21 %.En revanche, l'analyse croisée des dynamiques hydrologiques dans la retenue et dans la nappe au voisinage de la retenue a mis en évidence des échanges qui se produisent dans les deux sens : des échanges dominés par un flux d'infiltration avec la nappe au pied du barrage, par contre, les échanges avec la nappe latérale des versants se produisent dans les deux sens mais restent très fugaces. Les résultats préliminaires de l'approche de modélisation développé dans ce travail a permis de souligner la complexité des échanges retenue-souterrain et montre que la relation entre la hauteur d'eau dans la retenue et le flux d'infiltration n'est pas univoque et présente des comportements différents entre la phase de montée et la phase de descente du niveau d'eau dans la retenue
Hill reservoirs are hydraulic infrastructures widely used in North Africa, generally in arid and semi arid zones of the planet. These infrastructures are used for both water conservation in the catchment scale and to reduce siltation of downstream dams. The implementation and the management of water resources mobilized in this infrastructure must be based on knowledge of their hydrological functioning. However, the hydrological functioning of this system is not very known, especially the water flux exchange processes and intensity between the reservoir and the subsurface is still an open question.The main purpose of this study is to quantify and analyse the hydrological functioning of the reservoir-subsurface exchange processes for an agricultural catchment. This study was conducted on the hill reservoir of the experimental observation site of Kamech belonging to the OMERE observatory. In the first part of this study, we develop a water balance approach to estimate reservoir-subsurface exchange flux. The results of this approach shows that reservoir-subsurface exchange flux is dominated by infiltration that represent about 79% of the water outflow, and largely exceeds the water loss by evaporation that represents only 21 % of the total water outflow. However, the cross-analysis of the hydrological dynamics of the hill reservoir and the aquifer in the vicinity of the reservoir revealed that infiltration can occur in both directions: reservoir-subsurface exchange dominated by infiltration with the aquifer located in the foot of the dam, however the water exchange with the lateral aquifer of the hill reservoir can occur in both directions but remain very fleeting. The preliminary results of the modeling approach developed in this work has highlighted the complexity of reservoir-subsurface exchange flux. In fact, the relationship between water level in the hill reservoir and the infiltration flux is not unique and can present different behavior between the rise and decrease phase of the water level in the hill reservoir

Předkládaná práce je zaměřena na numerické modelování spalování tuhých paliv na roštu metodami výpočtové dynamiky tekutin (CFD). Jelikož výsledky CFD simulací roštového spalování závisí na kvalitě vstupních dat, která zahrnují i údaje o teplotě, hmotnostním toku a chemickém složení spalin vystupujících z lože, pozornost je věnována především procesům, probíhajícím v loži během spalování na roštu. Velká část práce je věnována vývoji spolehlivého modelu spalování v sypaných ložích, jelikož může napomoci zkvalitnit výsledky simulací i rozšířit znalosti principů spalování tuhých paliv v sypaných ložích. V rámci práce byl vyvinut jednorozměrný nestacionární model spalování v experimentálním reaktoru a implementován do počítačového programu GRATECAL 1.3 včetně grafického uživatelského rozhraní. Zvláštní důraz byl kladen na konzervativnost modelu. Proto byla vyvinuta metoda pro kontrolu hmotnostní a energetické bilance systému a následně aplikována v řadě studií, v rámci nichž byly odhaleny některé chyby týkající se definic zdrojových členů, které byly převzaty z literatury a opraveny. Pomocí modelu byla provedena analýza šíření čela sušení a reakce hoření koksu po výšce lože pšeničné slámy. Na základě výsledků těchto analýz bylo doporučeno zahrnout i modelování změny porozity částic paliva, aby šířka reakční zóny byla predikována korektně v případě, že je uvažována změna porozity celého lože. Rovněž vyvinutá bilanční metoda byla použita k analýze vlivu kritérií konvergence na hmotnostní a energetickou nerovnováhu simulovaného systému. Bylo zjištěno, že škálovaná rezidua rovnic všech veličin by měla poklesnout aspoň na hodnotu $10^{-6}$, aby bylo dosaženo nízké hmotnostní a energetické nerovnováhy a tudíž uspokojivě přesných výsledků ze simulací v loži. Druhá část práce je věnována vývoji a implementaci knihovny uživatelem definovaných funkcí pro komerční CFD nástroj ANSYS FLUENT, které slouží k propojení modelu lože s modelem komory reálné spalovací jednotky, aby byla umožněna dynamická změna okrajových podmínek na vstupu do komory v závislosti na výstupech ze simulací v loži. Vytvořené rozhraní pro propojení těchto dvou modelů je dostatečně obecné pro aplikaci na širokou škálu modelů roštových kotlů. Popsané výsledky přispívají k lepšímu porozumění numerickému modelování spalování na roštu, a to zejména ve fázi sestavování numerického modelu a nastavení parametrů řešiče pro kontrolu konvergence.

This thesis reports on an investigation to develop an advanced and comprehensive milling process model of the raw sugar factory. Although the new model can be applied to both, the four-roller and six-roller milling units, it is primarily developed for the six-roller mills which are widely used in the Australian sugar industry. The approach taken was to gain an understanding of the previous milling process simulation model "MILSIM" developed at the University of Queensland nearly four decades ago. Although the MILSIM model was widely adopted in the Australian sugar industry for simulating the milling process it did have some incorrect assumptions. The study aimed to eliminate all the incorrect assumptions of the previous model and develop an advanced model that represents the milling process correctly and tracks the flow of other cane components in the milling process which have not been considered in the previous models. The development of the milling process model was done is three stages. Firstly, an enhanced milling unit extraction model (MILEX) was developed to access the mill performance parameters and predict the extraction performance of the milling process. New definitions for the milling performance parameters were developed and a complete milling train along with the juice screen was modelled. The MILEX model was validated with factory data and the variation in the mill performance parameters was observed and studied. Some case studies were undertaken to study the effect of fibre in juice streams, juice in cush return and imbibition% fibre on extraction performance of the milling process. It was concluded from the study that the empirical relations developed for the mill performance parameters in the MILSIM model were not applicable to the new model. New empirical relations have to be developed before the model is applied with confidence. Secondly, a soluble and insoluble solids model was developed using modelling theory and experimental data to track the flow of sucrose (pol), reducing sugars (glucose and fructose), soluble ash, true fibre and mud solids entering the milling train through the cane supply and their distribution in juice and bagasse streams.. The soluble impurities and mud solids in cane affect the performance of the milling train and further processing of juice and bagasse. New mill performance parameters were developed in the model to track the flow of cane components. The developed model is the first of its kind and provides some additional insight regarding the flow of soluble and insoluble cane components and the factors affecting their distribution in juice and bagasse. The model proved to be a good extension to the MILEX model to study the overall performance of the milling train. Thirdly, the developed models were incorporated in a proprietary software package "SysCAD’ for advanced operational efficiency and for availability in the ‘whole of factory’ model. The MILEX model was developed in SysCAD software to represent a single milling unit. Eventually the entire milling train and the juice screen were developed in SysCAD using series of different controllers and features of the software. The models developed in SysCAD can be run from macro enabled excel file and reports can be generated in excel sheets. The flexibility of the software, ease of use and other advantages are described broadly in the relevant chapter. The MILEX model is developed in static mode and dynamic mode. The application of the dynamic mode of the model is still under progress.

During the past few years a vast amount of research has been done to increase the understanding of the complex ecosystem of the Baltic Sea. Modelling and simulations are important tools to increase knowledge of the system. A suitable model must be simple to use and the parameters and variables needed in the model must be easy to access.

In this paper a dynamical mass-balance model, CoastMab, which is validated for smaller coastal areas, has been used to predict concentrations and transports of phosphorus in three large coastal areas - the Gulf of Finland, the Gulf of Gdansk and the Gulf of Riga. CoastMab uses ordinary differential equations to regulate inflow, outflow and internal flows. To reflect seasonal variations in temperature and different types of flows the model has a temporal resolution of a month. The main purposes of this paper have been to evaluate CoastMab, predict the concentrations and the transports of phosphorus in each coastal area and to analyse how much and why the results differ from empirical data.

The performed simulations show the importance of a correct calculation of the wave base. This is due to its influence on the division between surface and deep water as well as the division of areas of accumulation and areas of erosion and transport. The retention times of surface and deep water calculated by the model also is of great importance because of their direct influence on the flow of water between the study area and the sea outside the area. This together with the concentration of phosphorus determines the flow of phosphorus in and out of the study area.

The dynamical mass-balance model is considered to work well in the three studied areas even though the areas are outside the model domain in several respects. Even if the predictions of the phosphorus concentration in the gulf of Riga was less accurate than in the other study areas, the prediction was inside the interval of standard deviation that has been calculated from empirical data. The major flow of phosphorus in the model was in the cross section between the Baltic proper and the modelled coastal area.

Since the model is easy to use and requires only a small number of obligatory input variables it would be appealing to continue development of the model to handle coastal areas of the same size and larger than the study areas in this paper.

Under senare år har mycket forskning utförts för att öka förståelsen av det komplexa ekosystem Östersjön utgör. Viktiga redskap för att öka förståelsen för systemet är modellering och simulering. För att en modell ska vara lämplig att använda är det viktigt att den inte är för komplicerad och att de parametrar och variabler som används i modellen är lättillgängliga.

I detta arbete har en dynamisk massbalansmodell, CoastMab, som är validerad för mindre kustområden använts för att modellera fosforkoncentrationer och fosforflöden i tre större kustområden - Finska viken, Gdanskbukten och Rigabukten. CoastMab reglerar genom ordinära differentialekvationer inflöden, utflöden och interna flöden. För att kunna hantera säsongsvariationer i temperatur och olika typer av flöden har modellen en temporär upplösning på en månad. Syftet med arbetet har främst varit att se hur väl CoastMab predikterar fosforkoncentrationen och fosforflöden inom respektive område, samt att analysera hur mycket och varför prediktionerna skiljer sig från empiriska data.

De simuleringar som utfördes visade att djupet på den teoretiska vågbasen, som modellen beräknar, är av stor betydelse eftersom den i sin tur bestämmer fördelningen yt- och djupvatten samt fördelningen av ackumulationsbottnar och erosions- och transportbottnar. De utbytestider för yt- och djupvatten som modellen beräknar är också av största vikt eftersom de har en direkt inverkan på vattenflödet mellan studerat område och havet utanför, vilket i sin tur tillsammans med fosforkoncentrationen bestämmer fosforflöden in och ut ur det studerade området.

Den dynamiska massbalansmodellen kan anses fungera väl för samtliga tre studerade områden, trots att de ligger utanför modellens domän i flera avseenden. Även om prediktionen av fosforkoncentrationen i Rigabukten blev sämre än för de två övriga områdena, låg prediktionen inom det intervall för standardavvikelsen som beräknats utifrån empiriska data. De största fosforflödena i modellen förekom för samtliga områden i gränssnittet mellan egentliga Östersjön och det modellerade kustområdet.

Enkelheten i att använda modellen och det låga antalet obligatoriska drivvariabler gör att den är väl värd att utveckla för att hantera områden av samma eller större storlek än de nu studerade områdena.