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1
Driver, Penny Meredith. "Rainfall variability over southern Africa." Doctoral thesis, University of Cape Town, 2014. http://hdl.handle.net/11427/12830.
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Includes bibliographical references.Southern Africa is subject to high inter annual rainfall variability and the factors influencing southern African rainfall are not fully understood. The variability has been linked with various sea surface temperature anomalies (SSTAs) in each of the three major ocean basins as well as variability in the strength and position of regional atmospheric features. One of the atmospheric factors that may play a substantial role in southern African rainfall variability is the Botswana high, a high pressure cell which exists at the 500hPa level and is centred over central Namibia and western Botswana during austral summer. 20th Century reanalysis data is used to further investigate this feature and analysis reveals an association between the strength of the Botswana high and ENSO. Further analysis indicates that a connection between the Botswana high and rainfall over southern Africa not only exists during ENSO years, but is also apparent during neutral years that display ENSO-like characteristics in the Botswana high. This result may assist in producing better rainfall forecasts for non-ENSO years. The frequency of dry days over southern Africa during austral summer is investigated using GPCP observational data. Correlation analysis is generally in agreement with previous studies and showed that dry day frequency(DDF) over the Limpopo and North East Zambia regions is correlated with ENSO, while DDF over coastal northern Angola and central South Africa is correlated with SSTs in the Indian and Atlantic Oceans. The possible role played by DDF during JFM 1998 and JFM 2010 is investigated and results indicate that the distribution of DDF over southern Africa was notably different during these two seasons and may have contributed to the unexpected rainfall experienced over southern Africa.
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Preece, David John. "Decadal rainfall variability over Southern Africa." Thesis, University College London (University of London), 2008. http://discovery.ucl.ac.uk/17232/.
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Southern Africa is a region of vulnerability, with high seasonal and interannual rainfall variability combined with rain-dependent agriculture. This variability is underpinned by influences from ENSO and other oceanic forcing, and known to exhibit quasi-decadal variability at 16-20 years (Tyson, 1975). This study uses a combination of proxy, observed and climate model data to explore the nature, mechanisms and anthropogenic forcing of rainfall variability at decadal scales. The spatial nature of rainfall variability, demonstrated through EOF analysis and composite decadal events, is similar to that at interannual scales. Spectral analysis of observed data confirms the presence of variability at ENSO-related timescales, combined with influences in the 10-12 year and 16-20 year band. Subtle differences appear in model simulated rainfall. The mechanisms of quasi-decadal variability are also shown to be similar to interannual forcing patterns: showing links to ENSO, the tropical and South Atlantic oceans, and the South West Indian Ocean. Rainfall correlation at decadal scales is dominated by the SW Indian Ocean, but the ‘dipole’ like forcing observed at interannual timescales is notable less coherent at quasi-decadal scales. Model-specific differences are explored, and though to be the result of the interaction between a weak (strong) decadal ENSO signal and a strong (weak) Southern Annular Mode influence at multi-decadal timescales. Using state of the art model simulations (Gonzales-Rouco et al., 2003; Tett et al., 2007) that incorporate anthropogenic forcings, the study also explores the impact of climate change on the quasi-decadal signals over the region. Results show that quasi-decadal variability is damped under anthropogenic forcing. The spatial structure appears unaltered, and many of the mechanisms are consistent with those in unforced simulations. A key change occurs in the tropical Indian Ocean, which substantially alters in relationship with the southern African rainfall. Implications for decadal predictability over the region are discussed and evaluated.
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Washington, Richard. "Interannual and interdecadal variability of African rainfall." Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.396138.
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Williams, Charles Jonathan Roger. "Rainfall variability and extremes over southern Africa." Thesis, University of Sussex, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.437453.
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Randriamahefasoa, Tsinampoizina Marie Sophie. "Variability of summer rainfall over southwestern Madagascar." Master's thesis, University of Cape Town, 2013. http://hdl.handle.net/11427/9809.
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Includes bibliographical references.This study investigates the interannual variability of the frequency of wet days during the rainy season over southwestern Madagascar, and its associated regional and global circulation patterns. The number of wet days was counted for each summer season (December to March) of the period 1971 to 2000 at four rainfall stations in southwestern Madagascar. For each station, the frequency of wet days was correlated with ENSO indices, SIOD index, SST, 850 hPa geopotential height, zonal and meridional winds at the surface. Composite anomalies of moisture flux and moisture flux convergence at 850 hPa, 500 hPa omega and velocity potential at .995 sigma level, using NCEP/NCAR reanalysis data, associated with El Niño events, La Niña events that occurred during the period of study were examined. Also, circulation anomalies during neutral years having anomalously high frequency of wet days or anomalously low frequency of wet days were analysed separately. It was found that the number of wet days rarely exceeds half of the total days in summer for each station. Inverse relationship between the equatorial Pacific SST anomalies and the frequency of wet days anomalies was identified. Statistics showed that years characterised by high frequency of wet days often occur with La Niña seasons whereas years having low frequency of wet days tend to occur with El Niño seasons. A strong relationship between the southern Indian Ocean SST and the frequency of wet days was found at Ranohira (45.3° E, 22.5° S) and Toliara (43.72° E, 23.38° S). Increased number of wet days over southwestern Madagascar is associated with low atmospheric pressure over the southern Mozambique Channel. Neutral years having anomalously high (low) frequency of wet days are marked by northwesterly (southeasterly) moisture flux anomalies at 850 hPa over southwestern Madagascar.
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Gamoyo, Majambo Jarumani. "Rainfall variability characteristics over the East African coast." Master's thesis, University of Cape Town, 2012. http://hdl.handle.net/11427/10571.
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Includes bibliographical references.This study explores inter-annual rainfall variability over the East African coast region (Kenya and Tanzania) for the period 1980-2010 and focuses on dry and wet spell characteristics during the two rainy seasons. The atmospheric and ocean conditions associated with the rainfall variability are also considered. Extreme occurrences of rainfall variable can result in droughts and floods which in turn may lead to socioeconomic disruptions. East Africa is highly dependent and vulnerable to the amounts and timing of rainfall.
7
Owusu, Kwadwo. "Analysis of rainfall variability in sub-humid Ghana." [Gainesville, Fla.] : University of Florida, 2004. http://purl.fcla.edu/fcla/etd/UFE0007041.
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Potts, Daniel Lawrence. "Rainfall Variability and Carbon Cycling in Semi-Arid Ecosystems." Diss., Tucson, Arizona : University of Arizona, 2005. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu%5Fetd%5F1338%5F1%5Fm.pdf&type=application/pdf.
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Lei, Yonghui. "Decadal variability in Chinese summer rainfall and climate change." Thesis, University of Reading, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.515737.
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Courtney, Shaun. "Latent heat flux and South African summer rainfall variability." Master's thesis, University of Cape Town, 1997. http://hdl.handle.net/11427/19252.
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The main purpose of this study was to determine if a relationship exists between oceanic latent heat flux and the summer rainfall of South Africa. Such a link would be useful for a better understanding and the prediction of monthly variability in the summer rainfall for South Africa. In order to investigate possible relationships between oceanic latent heat flux and summer rainfall in South Africa, point to point and point to field statistical correlations were made between gridded monthly COADS derived bulk oceanic heat fluxes and area averaged rainfall for the period 1950 to 1988. Correlations with the oceanic latent heat flux were not significant when the summer area averaged rainfall was divided into early and late summer seasons. This is due to the fact that different oceanic latent heat flux regions correlate with a different rainfall region each month. The results of monthly latent heat flux and summer rainfall demonstrated that there exists a statistical link between oceanic latent heat flux and summer rainfall and that this link could prove useful in the prediction of summer rainfall patterns. These results of the correlation between monthly latent heat flux and summer rainfall show that summer rainfall can be grouped into an all-area index that can be used as a proxy for the entire summer rainfall region. Results of these correlations further show that there are three major mechanisms that are at work over the six month summer rainfall period. These mechanisms show a link between the oceanic latent heat flux and summer rainfall variability. This study has shown that various oceanographic areas in the surrounding oceans correlate at different lags with South African summer rainfall. These correlations can be useful as precursors in predicting wetter or dryer rainfall events. Areas identified by correlation of oceanic latent heat flux regions as important as precursors for summer rainfall prediction are similar to those areas other researchers have identified in studies using OLR, SST and upper level winds (Jury 1995). This study adds weight to the already existing knowledge of these precursors of rainfall predictability.
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Tian, Daquan. "Rainfall spatial and seasonal variability analysis in semi-arid watersheds." Thesis, The University of Arizona, 1993. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu_etd_hy0256_sip1_w.pdf&type=application/pdf.
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Pechlivanidis, Ilias. "The significance of spatial variability of rainfall on runoff generation." Thesis, Imperial College London, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.508445.
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Kay, Gillian. "Mechanisms of southern African rainfall variability in coupled climate models." Thesis, University of Oxford, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.496573.
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Steel, Michael Edward. "Historic rainfall, climatic variability, and flood risk estimation for Scotland." Thesis, University of Dundee, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.311069.
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Ayabaca, Marcelo Vicente. "Rainfall variability in the upper Napo River Basin, Ecuadorian Amazon." FIU Digital Commons, 2004. http://digitalcommons.fiu.edu/etd/1348.
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The purpose of this research was to investigate the influence of elevation and other terrain characteristics over the spatial and temporal distribution of rainfall. A comparative analysis was conducted between several methods of spatial interpolations using mean monthly precipitation values in order to select the best. Following those previous results it was possible to fit an Artificial Neural Network model for interpolation of monthly precipitation values for a period of 20 years, with input values such as longitude, latitude, elevation, four geomorphologic characteristics and anchored by seven weather stations, it reached a high correlation coefficient (r=0.85). This research demonstrated a strong influence of elevation and other geomorphologic variables over the spatial distribution of precipitation and the agreement that there are nonlinear relationships. This model will be used to fill gaps in time-series of monthly precipitation, and to generate maps of spatial distribution of monthly precipitation at a resolution of 1km2.
16
Botha, Susan. "The influence of rainfall variability on savanna tree seedling establishment." Master's thesis, University of Cape Town, 2006. http://hdl.handle.net/11427/6238.
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Includes bibliographical references (leaves 111-114).My thesis investigates the rainfall requirements necessary for tree seedling survival of different savanna species in the first year of growth. Results from a field drought experiment showed that dry season survival for seedlings of Acacia nigrescens and Philenaptera vialacea was not related to wet season length. Instead mortality was highest immediately after germination despite irrigation to minimize dry spells. Furthermore there was no relationship between seedling size and the length of the dry spell seedlings of Acacia nigrescens and Philenaptera vialacea grown in basalt clay in the greenhouse, could survive. This was in contrast to seedlings of Scleracarya birrea and Terminalia sericea grown in granite sand, where number of dry days survived increased with number of growth days received. There was no significant differences in rainfall variability (t-test: tL III = 1.56, P = 0.121, F-ratio = 1.13) between a semi-arid (Satara) and semi-mesic (Pretoriuskop) site within the Kruger National Park despite significant differences in rainfall totals (t-test: tl, III = 4.40, P < 0.000, F-ratio 3.41). Results from a soil-water model show that seedling recruitment can occur at least twice a decade in the Satara area, which should be frequent enough to allow a transition to a woodland state over time. These results suggest that a mechanism other than the effect of rainfall variability on seedling establishment is required to explain the co-existence of trees and grasses at Satara. The lack of field germination, the absence of a seed bank and the germination of added seed at the field experiment site after rainfall emphasizes seed limitation as an important bottleneck at Satara. Higher herbivore biomass at Satara compared to Pretoriuskop may limit seedling establishment opportunities by destroying seed and seedlings of tree species.
17
Loisulie, Saiguran. "A model study of the interannual variability of Tanzanian rainfall." Master's thesis, University of Cape Town, 2006. http://hdl.handle.net/11427/6488.
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Includes bibliographical references (leaves 41-46)The ability of the Hadley Centre Atmospheric Model version 3 (HadAM3) to capturerainfall variability patterns over Eastern Africa and the western tropical Indian Oceanduring the rainy seasons (October to December (OND) and March to May (MAM)) isassessed against data derived from National Centre for Environmental Prediction (NCEP)model and Global Precipitation Climatology Project (GPCP). The vector windsclimatology at 850hPa and 200hPa reveals some comparable patterns in both HadAM3 andNCEP. However, there are indications that the Somali Jet appears earlier and the monsooneasterly winds over the western Indian Ocean are weaker in HadAM3 than in NCEP.Empirical Orthogonal Functions (EOF) and Principal Component Analysis (PCA) derivedfrom the GPCP precipitation and NCEP Outgoing Longwave Radiation (OLR) andgeopotential anomalies were also compared to those from the HadAM3 model.
18
Brinson, Kevin R. "An examination of precipitation variability with respect to frontal boundaries." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 113 p, 2007. http://proquest.umi.com/pqdweb?did=1251900241&sid=5&Fmt=2&clientId=8331&RQT=309&VName=PQD.
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Toomey, Michael R., Jeffrey P. Donnelly, and Jessica E. Tierney. "South Pacific hydrologic and cyclone variability during the last 3000 years." AMER GEOPHYSICAL UNION, 2016. http://hdl.handle.net/10150/614773.
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Major excursions in the position of the South Pacific Convergence Zone (SPCZ) and/or changes in its intensity are thought to drive tropical cyclone (TC) and precipitation variability across much of the central South Pacific. A lack of conventional sites typically used for multimillennial proxy reconstructions has limited efforts to extend observational rainfall/TC data sets and our ability to fully assess the risks posed to central Pacific islands by future changes in fresh water availability or the frequency of storm landfalls. Here we use the sedimentary record of Apu Bay, offshore the island of Tahaa, French Polynesia, to explore the relationship between SPCZ position/intensity and tropical cyclone overwash, resolved at decadal time scales, since 3200years B.P. Changes in orbital precession and Pacific sea surface temperatures best explain evidence for a coordinated pattern of rainfall variability at Tahaa and across the Pacific over the late Holocene. Our companion record of tropical cyclone activity from Tahaa suggests major storm activity was higher between 2600-1500years B.P., when decadal scale SPCZ variability may also have been stronger. A transition to lower storm frequency and a shift or expansion of the SPCZ toward French Polynesia around 1000years B.P. may have prompted Polynesian migration into the central Pacific.
20
Shah, Syed Mohammad Saeed. "The influence of spatial variability in rainfall on the catchment response." Thesis, University of Newcastle Upon Tyne, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.244892.
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A new stochastic rainfall field model is described which employs the Turning Bands Method (TBM) to transform a unidimensional Gaussian process, generated by the fractional differencing process along a line, into a multidimensional space-time Gaussian process with a specified space-time correlation structure. Transformations are applied to give the rainfall process a non-Gaussian and non-stationary structure. A correction factor is introduced into the model to take account of the effect of topography on rainfall. The model has been applied to the small upland Wye catchment in mid Wales (area 10.55 km2) and shown to reproduce satisfactorily the statistics and correlation structure of observed hourly point rainfall. As an extension to the rainfall field model, a new technique of conditional simulation has been used to generate the rainfall fields. The conditionally simulated rainfall fields reproduce exactly the observed point rainfalls at measurement points and likely realizations of rainfall fields between points. Rainfall fields generated by the above mentioned rainfall field model and the conditional simulation technique are fed directly into the Systeme Hydrologique European (SHE) model and the sensitivity of runoff prediction errors to (i) level of space-time correlation (ii) sampling of rainfall with different schemes in space and (iii) antecedent conditions are explored. It is found that in case of Wye catchment the errors deriving from sampling procedure used are generally small when rainfall fields were based on observed correlation structure. Sensitivity of errors to different correlation levels give the impression that errors increase with a decrease in correlation level. Further it is noticed that this trend of errors is more pronounced in `dry' catchment conditions as compared to `wet' catchment conditions. Overall the results for the small Wye catchment illustrate that the catchment acts as a smoother of the spatially distributed rainfall input at this spatial scale and for the rainfall regime in question. However, the results imply that for the typical raingauge densities encountered for larger catchments, significant errors may occur.
21
Mandapaka, Venkata Pradeep Krajewski Witold F. "Role of rainfall variability in the statistical structure of peak flows." [Iowa City, Iowa] : University of Iowa, 2009. http://ir.uiowa.edu/etd/403.
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Turner, Barry John. "Spatial sampling and vertical variability effects on microwave radiometer rainfall estimates." Thesis, McGill University, 1991. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=59910.
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Three-dimensional radar data for three Florida storms are used with a radiative transfer model to simulate observations at 19 GHz by a nadir pointing, satellite bourne microwave radiometer. Estimates were made of spatial sampling errors due to both horizontal and vertical variability of the precipitation. Calibrated radar data were taken as realistic representations of rainfall fields.The optimal conversion between microwave brightness temperature and rainfall rate was highly sensitive to the spatial resolution of observations. Retrievals were made from the simulated microwave measurements using rainfall retrieval functions optimized for each resolution and for each storm case.
There is potential for microwave radiometer measurements from the planned TRMM satellite to provide better 'snapshot' estimates than area-threshold VIS/IR methods. Variability of the vertical profile of precipitation did not seriously reduce accuracy. However, it is crucial that calibration of retrieval methods be done with ground truth of the same spatial resolution.
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Mandapaka, Venkata Pradeep. "Role of rainfall variability in the statistical structure of peak flows." Diss., University of Iowa, 2009. https://ir.uiowa.edu/etd/403.
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This thesis examines the role of rainfall variability and uncertainties on the spatial scaling structure of peak flows using the Whitewater River basin in Kansas, and Iowa River basin in Iowa as illustrations. We illustrate why considering individual hydrographs at the outlet of a basin can lead to misleading interpretations of the effects of rainfall variability. The variability of rainfall is characterized in terms of storm intensity, duration, advection velocity, zero-rain intermittency, variance and spatial correlation structure. We begin with the simple scenario of a basin receiving spatially uniform rainfall of varying intensities and durations, and advection velocities. We then use a realistic space-time rainfall field obtained from a popular rainfall model that can reproduce desired storm variability and spatial structure. We employ a recent formulation of flow velocity for a network of channels and calculate peak flow scaling exponents, which are then compared to the scaling exponent of the channel network width function maxima. The study then investigates the role of hillslope characteristics on the peak flow scaling structure. The basin response at the smaller scales is driven by the rainfall intensities (and spatial variability), while the larger scale response is dominated by the rainfall volume as the river network aggregates the variability at the smaller scales. The results obtained from simulation scenarios can be used to make rigorous interpretations of the peak flow scaling structure obtained from actual space-time model, and actual radar-rainfall events measured by the NEXRAD weather radar network.
An ensemble of probable rainfall fields conditioned on the given radar-rainfall field is then generated using a radar-rainfall error model and probable rainfall generator. The statistical structure of ensemble fields is then compared with that of given radar-rainfall field to quantify the impact of radar-rainfall errors on 1) spatial characterization of the rainfall events and 2) scaling structure of the peak flows. The effect of radar-rainfall errors is to introduce spurious correlations in the radar-rainfall fields, particularly at the smaller scales. However, preliminary results indicated that the radar-rainfall errors do not significantly affect the peak flow scaling exponents.
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Achuthavarier, Deepthi. "Role of the Indian and Pacific Oceans in the Indian summer monsoon variability." Fairfax, VA : George Mason University, 2009. http://hdl.handle.net/1920/4524.
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Thesis (Ph.D.)--George Mason University, 2009.Vita: p. 179. Thesis director: V. Krishnamurthy. Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Climate Dynamics. Title from PDF t.p. (viewed June 10, 2009). Includes bibliographical references (p. 171-178). Also issued in print.
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Fowler, Hayley Jane. "The impacts of climatic change and variability on water resources in Yorkshire." Thesis, University of Newcastle Upon Tyne, 2000. http://hdl.handle.net/10443/432.
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Observational evidence and future climate change scenarios suggest an amplification of climatic contrasts across the UK. This is seen most prominently in the marked increase in notable flood events and drought episodes and may profoundly affect water resource systems in vulnerable areas, as exemplified by the 1995 Yorkshire drought. The 1995-96 drought resulted in severe stress to the Yorkshire water supply, necessitating the emergency measure of tanking in water from outside the region, and was caused by an unusual pattern of weather and precipitation. This research is an investigation into both natural climatic variability and possible future climate change in Yorkshire aiming to quantify the risk of future occurrence of severe drought events, such as that of 1995. Historical drought characteristics and spatial-temporal precipitation variability in Yorkshire are examined and linked to synoptic weather patterns. A multi-site stochastic rainfall model is then developed using conditioning by synoptic weather types. The model can account for spatial variability and allows the concurrent simulation of precipitation time-series for very different climatological sub-regions within the same water resource area. This model is used to investigate the impact of natural climatic variability and possible future climate change upon water resource reliability, resilience and vulnerability in Yorkshire. The structure of the stochastic rainfall model enables the impact of variations in weather type persistence or frequency to be investigated. In addition, rainfall model statistics can be altered to simulate instances of increased precipitation intensity or proportion dry days for example, for individual weather groups. The UKCIP98 Medium-High climate change scenarios for 2021- 2050 and 205 1-2080 are investigated using modifications to weather type frequency, precipitation and potential evapotranspiration. Results indicate that water resources in Yorkshire are likely to become more reliable on average under the examined climate change scenarios due to increased winter precipitation. However, model simulations also suggest a reduction in resource resilience and increased vulnerability to drought. Severe droughts comparable to that of 1995 show only a slight increase in frequency by 2080. However, there will be a significant increase in both magnitude and duration of severe drought, as a consequence of summer precipitation reductions and increased climatic variability. This methodology of simulating the impacts of potential atmospheric circulation change on precipitation regimes can provide a basis for the future planning and management of water resource systems.
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Farnsworth, Alexander James. "Rainfall variability and the impact of land cover change over central Africa." Thesis, University of Reading, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.654486.
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Muthusamy, Manoranjan. "Accounting for rainfall variability in sediment wash-off modelling using uncertainty propagation." Thesis, University of Sheffield, 2018. http://etheses.whiterose.ac.uk/20905/.
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Urban surface sediment is a major source of pollution as it acts as a transport medium for many contaminants. Accurate modelling of sediment wash-off from urban surfaces requires an understanding of the effect of variability in the external drivers such as rainfall on the wash-off process. This study investigates the uncertainty created due to the urban-scale variability of rainfall, in sediment wash-off predictions. Firstly, a rigorous geostatistical method was developed that quantifies uncertainty due to spatial rainfall variability of rainfall at an urban scale. The new method was applied to a unique high-resolution rainfall dataset collected with multiple paired gauges for a study designed to quantify rainfall uncertainty. Secondly, the correlation between calibration parameters and external drivers - rainfall intensity, surface slope and initial load- was established for a widely used exponential wash-off model using data obtained from new detailed laboratory experiments. Based on this, a new wash-off model where the calibration parameters are replaced with functions of these external drivers was derived. Finally, this new wash-off model was used to investigate the propagation of rainfall uncertainty in wash-off predictions. This work produced for the first time quantitative predictions of the variation in wash-off load that can be linked to the rainfall variability observed at an urban scale. The results show that (1) the assumption of constant spatial rainfall variability across rainfall intensity ranges is invalid for small spatial and temporal scales, (2) wash-off load is sensitive to initial loads and using a constant initial load in wash-off modelling is not valid, (3) the level of uncertainty in predicted wash-off load due to rainfall uncertainty depends on the rainfall intensity range and the “first-flush” effect. The maximum uncertainty in the prediction of peak wash-off load due to rainfall uncertainty within an 8-ha catchment was found to be ~15%.
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Manhique, Atanásio João. "The South Indian Convergence Zone and relationship with rainfall variability in Mozambique." Doctoral thesis, University of Cape Town, 2008. http://hdl.handle.net/11427/6492.
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Includes abstract.Includes bibliographical references (leaves 137-145).
Southern Hemisphere atmospheric circulation and sea surface temperatures in the South Indian Ocean, associated with the South Indian Convergence Zone (SICZ), the main rain producing system over southern Africa, and links with rainfall over Mozambique, are analysed. Cluster analysis applied to gridded outgoing long-wave radiation data, were used to identify convective activity related to the tropical temperate troughs that collectively form the SICZ. Intraseasonal and inter-annual variability of these systems and their contribution to the anomalies of rainfall over Mozambique were explored using composite, correlation and regression analyses for both the early (October to December) and the late (January to March) summer.
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Zhu, Chunmei. "Role of antecedent land surface conditions on North American monsoon rainfall variability /." Thesis, Connect to this title online; UW restricted, 2007. http://hdl.handle.net/1773/10140.
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Tanaka, Tomohiro. "Extreme flood frequency analysis and flood risk curve development considering spatiotemporal rainfall variability." 京都大学 (Kyoto University), 2016. http://hdl.handle.net/2433/217150.
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Palanisamy, Bakkiyalakshmi. "Evaluation of SWAT model - subdaily runoff prediction in Texas watersheds." Texas A&M University, 2003. http://hdl.handle.net/1969.1/5921.
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Spatial variability of rainfall is a significant factor in hydrologic and water
quality modeling. In recent years, characterizing and analyzing the effect of spatial
variability of rainfall in hydrologic applications has become vital with the advent of
remotely sensed precipitation estimates that have high spatial resolution. In this study,
the effect of spatial variability of rainfall in hourly runoff generation was analyzed using
the Soil and Water Assessment Tool (SWAT) for Big Sandy Creek and Walnut Creek
Watersheds in North Central Texas. The area of the study catchments was 808 km2 and
196 km2 for Big Sandy Creek and Walnut Creek Watersheds respectively. Hourly
rainfall measurements obtained from raingauges and weather radars were used to
estimate runoff for the years 1999 to 2003. Results from the study indicated that
generated runoff from SWAT showed enormous volume bias when compared against
observed runoff. The magnitude of bias increased as the area of the watershed increased
and the spatial variability of rainfall diminished. Regardless of high spatial variability,
rainfall estimates from weather radars resulted in increased volume of simulated runoff.
Therefore, weather radar estimates were corrected for various systematic, range-dependent
biases using three different interpolation methods: Inverse Distance
Weighting (IDW), Spline, and Thiessen polygon. Runoff simulated using these bias adjusted radar rainfall estimates showed less volume bias compared to simulations using
uncorrected radar rainfall. In addition to spatial variability of rainfall, SWAT model
structures, such as overland flow, groundwater flow routing, and hourly
evapotranspiration distribution, played vital roles in the accuracy of simulated runoff.
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Zahid. "The influence of Asian monsoon variability on precipitation patterns over the Maldives." Thesis, University of Canterbury. Department of Geography, 2011. http://hdl.handle.net/10092/5891.
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Asian climate varies on various spatial and temporal scales and has a wide spectrum of climatic characteristics. Climate variability, especially decadal to inter-annual scale rainfall variability across Asia has gained considerable attention of climatologists over the last century due to the fact that rainfall variability is known to have caused considerable damage to southern Asian nations. Until recent, much of the existing literature on southern Asian climate focused on India and it is only recently that studies have focused on countries other than India. Although the Maldives is a nation within southern Asia (lying in the Indian Ocean southwest of India), literature on precipitation patterns over the Maldives and its connection to the Asian monsoon is lacking.
This thesis examines the variability of precipitation over the Maldives in relation to the Asian monsoon, since proper knowledge of the spatial and temporal variations of precipitation is essential for managing the water resources and agricultural sector of the Maldives. Yearly and monthly rainfall across the Maldives indicates that the rainfall varies temporally and spatially. Despite spatial variability of mean annual rainfall (January-December total) showing rainfall increasing from north to south, it was found that on average the northern and southern parts of the Maldives have received less rainfall during the monsoon season (May-November). This suggests that the mean annual rainfall maximum for the Maldives occurs between central and southern parts of the Maldives during the monsoon season. The Maldives monsoon rainfall is characterised by inter-decadal and inter-annual periodicities with a frequency of 12.9 and 2.5-4 years, and intra-seasonal periodicities (10-20 days and 30-60 day) in daily time series of monsoon rainfall for different regions of Asia. The fact that no objective criteria previously existed to identify monsoon onset and withdrawal dates in the Maldives, the criteria developed here for defining the monsoon season objectively for this region indicates that on average the rainy season or monsoon commences between 4 May and 13 May (mean onset dates based on outward longwave radiation (OLR) index and rain and wind criteria, respectively) and terminates in late November (21 and 23 November: mean withdrawal dates based on rain and wind, and OLR index criteria, respectively) for the Maldives. The mean length of the rainy season (LRS) based on the OLR index is 204 days, the mean LRS based on rain and wind is 11 days shorter (193 days). Results also demonstrate that the earliest monsoon onset for the Asian region occurs in the south of the Maldives in April.
Correlation coefficient maps generated between Maldives monsoon rainfall and meteorological parameters suggest that the most significant parameters that influence the interannual variability of the Maldives monsoon rainfall (MMR) are mean sea level pressure, surface air temperature, OLR, sea surface temperature (SST), and the zonal wind and relative humidity at various levels. Temporal consistency checks carried out for these parameters with the MMR led to the elimination of some of these predictors (which have less influence in the variance of MMR). The predictors which explained a significant amount of variance in the MMR were retained, including surface relative humidity during April (SRHAPR), 850 hPa level relative humidity during May (850RHMAY) and 500 hPa relative humidity for May (500RHMAY). These parameters were then used to formulate a regression model (using backward regression) for the prediction of Maldives monsoon rainfall. The predictors included in the model account for a significant part of the variance (76.6%, with a correlation coefficient, CC = 0.9) in MMR, indicating the usefulness of the model for medium-range prediction of MMR before the core monsoon season commences.
Global scale processes such as the El Niño-Southern Oscillation (ENSO) phenomenon influence the weather and climate around the globe, with ENSO considered to be one of the strongest natural phenomena influencing the climate of Asia on inter-annual time-scales. The association between the Maldives monsoon rainfall and ENSO events demonstrates that deficient/excess monsoon rainfall over the Maldives and India region is linked to the strong/moderate El Niño and La Niña events, respectively. During strong/moderate El Niño events, about 71.4% of the time the Maldives/India region experiences deficiencies in monsoon rainfall, while the Maldives/India region experiences excessive monsoon rainfall about 75% of the time during strong/moderate La Niña events. One of the regional scale processes that influence the climate of Asia is Eurasian snow cover. No previous studies have directly examined possible relationships between Eurasian snow and Maldives monsoon rainfall. The possible relationship between Eurasian snow cover (ESC) and the Maldives monsoon rainfall, explored in this research for the first time, appears to be only very weak. The results also demonstrate that the inverse relationship between the ESC and the Indian monsoon has weakened over recent decades. The correlation coefficient (-0.34) between Indian monsoon rainfall and ESC obtained for the 1973-94 period dropped to -0.18 for the 1979-2007 period. The inter-annual variability of the Indian and Australian monsoon rainfall experiences a remarkable biennial oscillation, which has been referred to as the tropospheric biennial oscillation (TBO). It is believed that the land and ocean surface conditions in March-May (MAM) over the Indo-Pacific region play an important role in monsoon transitions. The Maldives monsoon rainfall transition from relatively strong/weak to relatively weak/strong in consecutive years demonstrates a TBO connection (via a biennial tendency in Maldives monsoon rainfall). In relation to the Maldives monsoon rainfall, TBO strong years occur about 47.1% of the time, while weak TBO years occur about 52.9% of the time. Only some of the El Niño and La Niña onset years correspond to strong TBO years, with El Niño onset years (1982, 1987 and 2002) corresponding to weak TBO years, while La Niña onset years (1988 and 2000) corresponding to strong TBO years. Variability (spatial and temporal) in Maldives precipitation associated with global and regional scale processes results in flood and drought events that have downstream impacts, such as on water resources and the agricultural sector of the Maldives. Excess (wet) or deficient rainfall years identified for the period 1992-2008 indicate that the central region is most vulnerable to flooding (5 years with excess rainfall: 27.8% of the time), while the southern region is least vulnerable to both flooding (2 years with excess rainfall: 11.1% of the time) and drought (2 years with deficit rainfall: 11.1% of the time). The northern and central regions show an equal number of years with deficit rainfall (3 years: 16.7% of the time), indicating that they are equally prone to drought events. Furthermore, field survey results demonstrate that about 23, 31 and 37% households (respondents) from the northern, central and southern regions experienced flood events. About 79, 58 and 77% of the farmers from the northern, central and southern areas also experienced floods on their farms. On the other hand, field survey results also suggest that the 49-63% of the households in outer islands of the Maldives and 48-62% of farmers experience shortage of rainwater.
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Nsubuga, F. W. N. (Francis Wasswa Nkugwa). "Climate variability and its implication for water resources and livelihoods in Uganda." Thesis, University of Pretoria, 2013. http://hdl.handle.net/2263/40256.
Full textAbstract:
This thesis examines the climatic trends of rainfall and temperature in Uganda using historical data. And because climate is an important aspect in water resources management and livelihoods formation, an attempt to explain how the interaction impacts on the two is made in the context of climate variability and change. The assumption is that climate change/variability has had an effect on water resources management and the way individual, households and society at large form livelihoods in Uganda. The rationale for the investigation is the number of climate and livelihood related studies that have been undertaken for Uganda over recent years, which have not focused specifically on the water resources management and livelihood formation.
The study is grounded by reviewing the theoretical perspectives of climate science which underpin the concepts of climate change, climate variability and impacts on livelihoods in the world, tropics, Africa, east Africa and Uganda in that order.
A cross sectional research design based on selected case studies from sub-counties located in the main sub-basins across the country is used. Both qualitative and quantitative data analysis techniques are applied independently or in combination on climatic data from Uganda‟s Department of Meteorology, data generated from field interviews and landsat images. The data sets are analysed using MS EXCEL, SPSS, MATLAB, ANCLIM, TREND TOOL, GIS and ENVI 4.8 to establish climatic trends and deduce evidence of change and variability. The impact on livelihood formation is investigated through the assets available to the households using the DFID framework.
The study therefore has investigated the characteristics of climate in Uganda especially by following up on the responses that arose from the field study. Through their own observations, respondents noticed changes in temperature and rainfall. Temperature variables like diurnal temperature range, maximum and minimum temperatures and rainfall (monthly, seasonal, annual) have been investigated, to establish whether these observations were impacting on livelihood formations and water resources which are central in the wellbeing of individual households.
Results show decadal variability of rainfall with marked seasonal cycles, temporal variability of drought patterns is detected; variations in annual rainfall are low with no significant trends observed in the main drainage sub-basins. Significant trends occur in October, November, December and January. A noticeable decrease in the annual total rainfall was observed mostly in north-western and south-western sub-basins. Rainfall trend in the second normal of June-July-August (JJA) is decreasing in all the main drainage sub-basins; highest rainfall was recorded in April, while January, June and July have the lowest rainfall. Spatial analysis results show that stations close to Lake Victoria recorded high amounts of rainfall. Average annual coefficient of variability was 19% signifying low variability. Rainfall distribution is bi-modal with maximums experienced in March- April- May and September- October- November seasons of the year. PCI values show a moderate to seasonal rainfall distribution.
FNW Nsubuga – University of Pretoria Page 11
Spectral analyses of the time components reveal the existence of a major period around 3, 6 and 10 years. Intra-annual temperature show reduced variability over recent decades, which is not statistically significant. Maximum temperatures are more variable compared to minimum temperatures in Uganda. An increasing trend in hot days, hot nights, warm nights and warm spells are also detected. At seven of the stations, annual temperature range and diurnal temperature range trends are negative. The finding that intra-annual and intra-monthly variance is declining suggests that fewer anomalously extreme temperature episodes occur. The gap between maximum and minimum extremes is reducing, which supports the observation that minimum temperatures are on the increase. At a micro-level analysis using Namulonge as a case study, total rainfall in March-May season decreased, while maximum temperatures increased between April and September, with statistically significant trends at 5% confidence level. The Mann-Kendall test revealed that the number of wet days reduced significantly. Temperatures are warmer and rainfall higher in the first climate normal compared to the recent 30 years. Direct rainfall, which is the most important source of water for water resources, recently, is experiencing variability, which is threatening the distribution of water resources in Uganda. The characteristics, availability, demand and importance of present day water resources in Uganda as well as the various issues, and challenges pertaining to management of water resources of the country are established. The present analysis reveals that surface-water area fluctuation is linked to rainfall variability. In particular, Lake Kyoga basin lakes experienced an increase in surface-water area in 2010 compared to 1986. This work has important implications to water resources management and people whose livelihoods depend on natural resources especially in this era of climate change. Evidence from the field survey validates what data analysis reveals from historical data. Respondents from the field study are aware of climate change, had noticed some changes in climatic variables and were adapting by changing lifestyle and diversifying to activities that are less prone to weather. Livelihoods in Uganda have evolved based on the availability of opportunity afforded by the natural resources base including water resources.Thesis (PhD)--University of Pretoria, 2013.
gm2014
Geography, Geoinformatics and Meteorology
unrestricted
34
Mya, Thandar Toe. "RAINFALL VARIABILITY, LAND COVER DYNAMICS AND LOCAL LIVELIHOOD IN DRY ZONE, CENTRAL MYANMAR." Kyoto University, 2016. http://hdl.handle.net/2433/215601.
Full textAbstract:
Kyoto University (京都大学)0048
新制・課程博士
博士(農学)
甲第19775号
農博第2171号
新制||農||1041(附属図書館)
学位論文||H28||N4991(農学部図書室)
32811
京都大学大学院農学研究科森林科学専攻
(主査)教授 神﨑 護, 教授 柴田 昌三, 教授 大澤 晃, 外国人教師 鄭 克聲
学位規則第4条第1項該当
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Breytenbach, Elvira. "Following the Rains: Evidence and Perceptions Relating to Rainfall Variability in Western Uganda." Digital Archive @ GSU, 2013. http://digitalarchive.gsu.edu/geosciences_theses/63.
Full textAbstract:
There have been reports that rainfall in East Africa is changing or becoming more variable. This can have significant implications for conservation initiatives and the food security of this populace region that is heavily reliant on the rain fed agricultural system. The perceptions of farmers regarding rainfall along with 30 years of satellite data and 16 years of ground level observations were analyzed in order to characterize rainfall in and around Kibale National Park, a protected area in the Ugandan portion of the Albertine Rift. Two homogenous rainfall regions exist in the area, and the onset, cessation, and amount of rainfall during seasons is highly variable. The perceptions of farmers align with the analysis of rainfall data, indicating that the season beginning in March shows the highest degree of variability. Decreases in the amount of rainfall are found for both rainy seasons.
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Haylock, Malcolm. "Interannual variability of mean and extreme rainfall and relationship with large-scale circulation." Thesis, University of East Anglia, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.427078.
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Gong, Cuiling 1964. "The role of land-atmosphere-ocean interactions in rainfall variability over West Africa." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/38753.
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Ambrosino, C. "Rainfall variability in southern Africa : drivers, climate change impacts and implications for agriculture." Thesis, University College London (University of London), 2011. http://discovery.ucl.ac.uk/1322446/.
Full textAbstract:
Southern Africa is characterised by a high degree of rainfall variability affecting agriculture among other sectors. The focus of this study is to investigate such variability and to identify stable relationships with its potential drivers in the climate system. These relationships are used as the basis for the statistical downscaling of climate model (GCM) outputs. From the simulated rainfall, indices representative of growing season characteristics are computed with the final purpose of studying the implications on maize cropping under a future climate change scenario. The analysis uses generalized linear models (GLMs), which allow the investigation of the relationships between different components of the climate system (geographical and climatic drivers) simultaneously. Initially, the effects of various climate indicators upon monthly regional (for all southern Africa) precipitation occurrences and amounts are characterised. Six climate factors are found to drive part of the rainfall variability in the region and their modelled effect upon rainfall occurrences and amounts agrees broadly with previous studies. Among the retained indices, relative humidity and El Niño accounted for the highest degree of explained variability. The location and intensity of the jet stream is also found to have a statistically significant and physically meaningful effect upon rainfall variability. Although effective for the analysis of monthly regional precipitation, and used to investigate future regional projections, the models do not perform adequately at more local spatial scales such as station locations or few km grids. The same methodology is, therefore, applied to characterise daily precipitation variability at multiple locations within a smaller region. The small scale statistical models capture adequately the seasonal and annual rainfall structure in the area. Indeed, the observations can not be distinguished from the simulated time series. However, the simulated rainfall values tend to be slightly too high throughout the seasons, possibly due to the spatial correlation structure not completely appropriate for such a complex region. From the simulated rainfall sequences, seven growing season indices (including the onset and length of the growing season, proportion of rainy days and total precipitation during the growing season) are derived and their projected change investigated under a climate change scenario. There is little consensus between the 18 selected GCMs, regarding changes in growing season indices between two investigated periods in the 20th and 21st centuries. For the next couple of decades the dominant source of variation in the indices appears to be the natural rainfall variability. Such information should therefore be taken into account when planning adaptation and mitigation strategies. The research presented here emerges as the first comprehensive assessment of different climatic factors linked to southern Africa rainfall variability as well as the first attempt to evaluate the GLMs suitability for the generation of rainfall sequences for agricultural impact studies.
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Engelbrecht, Johanna. "Dynamics of climate variability over the all-year rainfall region of South Africa." Thesis, University of Pretoria, 2015. http://hdl.handle.net/2263/53490.
Full textAbstract:
Climatologically, the Cape south coast is unique in the sense that it lacks the pronounced
seasonality observed over the remainder of South Africa. Here, rainfall occurs all-year round,
implying that rainfall-producing systems characteristic of both the winter and summer rainfall
regions contribute to rainfall over the Cape south coast. However, the relative contributions
of different rain-producing weather systems to annual rainfall have not been quantified to
date. This region has also not received as much attention as the winter and summer rainfall
regions of the country with regards to quantifying and understanding its interannual rainfall
variability. Furthermore, seasonal forecast skill over the Cape south coast region is generally
poorer and less well investigated than forecast skill over the summer rainfall region and to a
lesser extent the winter rainfall region. This study addresses these issues through objective
identification of the prevailing synoptic types of the Cape south coast region by application of
the self-organizing map (SOM) technique, with a subsequent analysis of their interannual
variability, intraseasonal variability, and predictability.
The relative contribution of different rain-producing systems to annual rainfall over the Cape
south coast is quantified. Ridging high pressure systems contribute most to the mean annual
rainfall (46%), followed by tropical-temperate troughs (28%) and cut-off lows (COLs).
COLs, co-occurring with ridging high pressure systems and tropical-temperate troughs
contribute to 16% of the mean annual rainfall. When extreme rainfall is considered, COLs
contribute to 29% of all extreme rainfall events along the Cape south coast. Particular
configurations of ridging high pressure systems and tropical-temperate troughs that are linked
to interannual variability of seasonal rainfall are identified. These systems are primarily
ridging high pressure systems, in particular those ridging from far south of the subcontinent,
and tropical-temperate troughs occurring during seasons with weaker zonal mid- and upper
air winds. COLs are also linked to interannual variability of seasonal rainfall, despite their
infrequent occurrence - highlighting the importance of COLs as high impact weather systems.
The COL link with rainfall variability is particularly strong during March-April-May (MAM)
and even more so for June-July-August (JJA). It is also shown that the interannual variability
in the frequency distribution of the occurrence of synoptic types within a season is linked to
the El Niño Southern Oscillation (ENSO) and the Southern Annular Mode (SAM),
suggesting potential predictability of intraseasonal variability at the seasonal time scale. The
predictability of intraseasonal characteristics over the Cape south coast at the seasonal time scale is subsequently assessed by utilizing an ensemble of simulations performed by an
atmosphere-ocean coupled global circulation model administered by the UK Met Office.
Hindcasts of 14 austral spring and summer seasons initialized at a 1-month lead time are used
to assess the model s ability to predict the intraseasonal characteristics of weather systems.
This assessment revealed that some skill exists in the predictability of the intraseasonal
characteristics of synoptic types over the Cape south coast region of South Africa at the
seasonal time scale. The result implies that there is potential to predict whether specific high
impact weather systems (e.g. COLs) or systems associated with good rainfall (e.g. ridging
highs ridging from anomalously far south of the subcontinent) will occur at anomalously high
or low frequencies during the next season, with associated benefits to the agricultural and
water sectors.Thesis (PhD)--University of Pretoria, 2015.
Geography, Geoinformatics and Meteorology
PhD
Unrestricted
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Hernandez, Tatiana X. "Rainfall-Runoff Modeling in Humid Shallow Water Table Environments." Scholar Commons, 2001. https://scholarcommons.usf.edu/etd/1537.
Full textAbstract:
Simulating the processes of rainfall and runoff are at the core of hydrologic modeling. Geomorphologic features, rainfall variability, soil types, and water table depths strongly influence hydrological process in Florida ecosystems. Topographic characteristics of the terrain define the stream paths and landscape. Alteration of these characteristics as a result of urban and/or agricultural developments, for example, can highly influence wetlands and river basin response. There are two predominant landforms in Florida: wetlands, where Variable Saturated Areas form near streams causing saturation excess runoff, and uplands where runoff is mainly generated by infiltration excess. The objective of this work is to analyze the impacts of geomorphologic and hydrologic characteristics on runoff mechanisms in humid environments such as Florida. In general, most research at the hillslope scale use hypothetical values of rainfall, sometimes non-realistic values, and single slope forms to explain the geomorphic and hydrologic process on Variable Saturated Areas. In this thesis, the complexity of hillslope processes on actual Florida topography is assessed by coupling a Digital Elevation Model with a two-dimensional variable saturated-unsaturated flow model called HYDRUS-2D. Actual rainfall records and soil parameters from the Characterization Data for Selected Florida Soils, Soil Survey were used to evaluate hydrologic impacts. A commercial software package, River Tools was used to display and extract topographic information from the Digital Elevation Models.
Results show that when inflitration excess runoff is dominant, infiltration and runoff are very sensitive to time resolution, especially for convective storms. When saturation excess occurs, runoff is not affected by rainfall intensity. However, saturated hydraulic conductivity, depth to the water table, slope and curvature highly influence the extent of Variable Saturated Areas. Results indicate runoff in shallow water table environments is produced mainly by subsurface storm runoff, running below the surface, except in hillslopes with concave curvature and mild slopes. Additionally, concave hillslopes generate more saturation excess runoff than straight and convex hillslopes.
41
Foxall, David William. "Daily rainfall variability in southern central Africa : an analysis of recent and future behaviour." Thesis, University of East Anglia, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.410311.
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Bhowmick, Mansi. "Impact of soil moisture variability on convective rainfall activity over the Indian sub-continent." Thesis, University of Leeds, 2016. http://etheses.whiterose.ac.uk/17015/.
Full textAbstract:
Soil moisture is an important geophysical parameter affecting land atmosphere processes, and hence free convection, by controlling the partitioning of the surface heat flux into latent and sensible heat flux. Interaction between these fluxes and the atmosphere gives rise to different types of soil moisture-precipitation feedback, namely “wet advantage” where rain is favoured over a wet (high latent heat flux) surface and “dry advantage” where rain is favoured over a dry (high sensible heat flux) surface. Previous studies over different parts of the world have shown that these feedback processes can take different pathways, according to one-dimensional and three-dimensional models. According to the one-dimensional model there is probability of rain initiation when the boundary layer top meets the level of free convection either by heating (increase in sensible heat flux over a dry surface) or by moistening (increase of latent heat flux over wet soil) of the boundary layer. On the other hand three-dimensional models explain convective triggering due to wind convergence near gradients in soil moisture. This is a first study to compare and evaluate the existing soil moisture-precipitation feedback theories presented in the literature, over the Indian sub-continent under a single environment, by using high resolution convection-permitting (non-parameterized, or “explicit” convection) EMBRACE model simulation. Initially, a brief synoptic observational study shows evidence of surface-atmosphere coupling. More detailed case studies from the model output show further evidence for the land-atmosphere interaction in this region. The model indicates that all the processes defined by different theoretical models do exist under different surface, and atmospheric conditions. The relative contribution of different processes under different soil moisture conditions prevailing over different climatic zones of the Indian sub-continent during the 20-day wet monsoon period from mid-July to early August is statistically studied. Dry-to-wet downwind soil moisture gradient is found to be the statistically significant pattern for initiation of the majority of afternoon convective initiation in the East, Centre and South study domains of India. It is also found that the so-called “CTP-HIlow” predictive framework is not sufficient to address the observed behaviour of convective initiation under the full three-dimensional modelling environment. The use of the parameter HIlow, which is defined as the sum of humidity within and just above the inversion, as a predictive parameter is not physically understandable. This framework also lacks generality and solutions are empirically derived based on one-dimensional modelling and observations, which vary from place to place. To offer a solution to these theoretical difficulties, this study provides a new quantitative model, using the basic idea behind the CTP-HIlow framework to find new predictive parameters depending on sound physical relationships instead of empirical solutions. The system is governed by two non-dimensional parameters, namely inversion Bowen ratio and a “stiffness ratio”, and a third, dimensional parameter ΔR. Analysis of the EMBRACE simulations shows occurrence of both the dry and wet advantage, but the majority of the morning profiles favour prediction of dry advantage. Thus, the equations derived from the new quantitative model offer a quantitative prediction of wet and dry advantage occurring systematically, which is a question of great importance to weather and climate prediction, especially over moisture-limited areas.
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Smart, Catherine Ann. "Rainfall variability and drought in the central and northern KwaZulu-Natal Drakensberg : 1955-2015." Diss., University of Pretoria, 2017. http://hdl.handle.net/2263/65946.
Full textAbstract:
This study assesses the temporal rainfall variability trends, the effects on river discharge and the identification of drought periods across the central and northern Drakensberg (1955 – 2015), as well as at a catchment scale, in the Sterkspruit Catchment. Records from five stations, covering the central and northern Drakensberg, indicate that there is a statistically significant decrease in rainfall over the recording period. The long-term trends in interannual variability show an increase in the variability of annual rainfall over the five stations. The mean annual rainfall in the Drakensberg is highly seasonal and an analysis of the monthly rainfall indicates an increase in the variability of the distribution of monthly rainfall and the strengthening of rainfall seasonality in the Drakensberg, which is shown by a statistically significant decrease in autumn rainfall. The El Nino Southern Oscillation (ENSO) influences summer rainfall variability in the Drakensberg and a strong correlation exists between the summer rainfall and the Southern Oscillation Index, for the preceding periods, suggesting that changes in the intensity and frequency of the ENSO should negatively affect the rainfall in the Drakensberg. A cyclicity of approximately 10 years between dry periods was found, from 1955-2015, and it is noted that the cycles are becoming increasingly variable over time. An analysis conducted across four stations in the Sterkspruit Catchment assessed valley-scale variability and how rainfall variability and drought conditions may affect agriculture in the area. The Sterkspruit Catchment has experienced an increase in rainfall variability and dry conditions in the 21st century. The assessment of meteorological droughts, at both study scales, using the Standard Precipitation Index, displayed a significant decreasing trend, indicating an increase in the number of dry years over time. Hydrological drought was assessed, using the Streamflow Drought Index for two rivers in the Drakensberg. Both drought indices found an increase in the number of dry years experienced over time, and they highlighted 1982, 1992, 1994, 2003, 2007 and 2015 as being the years with the lowest rainfall and experiencing drought conditions. Discharge in the Drakensberg reflects the rainfall and seasonal trends and the Little Tugela River, at the bottom of the Sterkspruit Catchment, shows decreasing discharge trends over time. Farmers in the Sterkspruit Catchment rely on the Bell Park farm dam water to irrigate crops throughout the year because the rainfall is unreliable, especially the early-seasonal and summer rain. However, in 2015, the dam ran dry for the first time since it was built. Thus, more insight into rainfall trends and cyclcity in the Drakensberg could help farmers to understand and plan for the periods with low rainfall conditions.Dissertation (MSc)--University of Pretoria, 2017.
Geography, Geoinformatics and Meteorology
MSc
Unrestricted
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Lo, Ping-kwong Paul, and 盧炳光. "Quantifying the climatic impacts on rainfall in South China and water discharge in the Pearl River (Zhujiang), China." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2014. http://hdl.handle.net/10722/206565.
Full textAbstract:
Monthly and annual changes in precipitation in South China during 1990-2011 are examined in this study. As located in the sub-tropical climate zone, the annual rainfall in South China is concentrated in the summer. During the same period of time, an average of 9 tropical cyclones approaching South China each year which also contribute ample of rainfall to South China during the tropical cyclone season (June-September). Since the climatic system is interconnected, so this study attempts to examine the combined effect on inter annual rainfall variations in South China due to El Nino Southern Oscillation (ENSO), tropical cyclones affecting South China and the Asian Monsoon. It is generally agreed that during the El Nino onset years, South China would be more wetter, but with less than average tropical cyclones affecting South China. As such, effects on precipitation in South China caused by these two factors offsetting each other and data indicate there is no consistent trend of either more or less rainfall recorded for the El Nino onset years during 1990-2011. On the other hand, the first half of the year right after the El Nino years are in general more wetter than normal. This can be due to the lagging effect of El Nino events normally happened in the winter time, plus the fact that the strength of winter monsoon during the El Nino years is weak, resulting in more rainfall in the following year. Furthermore, annual changes in precipitation in South China directly affect the surface runoff of the Pearl River and a strong positive correlation between the two variables exists for the period 2000-2011. The +/- 25% annual variations and the seasonal variations of rainfall in South China post a challenge to the water resource management in the Pearl River Delta Region. Therefore dams and reservoirs built along the Pearl River are necessary to store surplus rainwater in order to supply sufficient fresh water to the Pearl River Delta Region during the dry seasons or years. On the other hand, further studies and monitoring programs are recommended to continue assessing and evaluating impacts of dam constructions to the environment and the ecosystem of the Pearl River Delta Region.published_or_final_version
Applied Geosciences
Master
Master of Science
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Shi, Ge. "Variability and change of the Indo-Pacific climate system and their impacts upon Australia rainfall." University of Southern Queensland, Faculty of Sciences, 2008. http://eprints.usq.edu.au/archive/00004784/.
Full textAbstract:
[Abstract]: Australia is one of the driest continents in the world, and over the past decades, severe drought has plagued most of the country. Water security is an important national issue. The ultimate water supply, rainfall, however, is one of the most variable ones in theworld and is complicated by the fact that it is affected by several remote oceanatmospheric teleconnection systems simultaneously, including the El Niño-SouthernOscillation, the Indian Ocean Dipole and Southern Hemisphere oceanic and atmospheric variability. These three systems sometimes conspire to produce a severe impact, whereas sometimes they offset each other to produce a mild influence. The recent severe watershortage has generated a surge of investments with strong regional applications. The present study focuses on areas and issues outside the scope of these regional studies,aiming to provide an Australia-wide assessment of future Australian rainfall under climate change. Firstly, we unravel a process of the Indo-Pacific oceanic teleconnection and examine its role in influencing variability of the Indian Ocean, and hence Australianrainfall variations. An examination of their contribution to the warming structure of the Indian Ocean is carried out. Secondly, we explore dynamics of North West Australianrainfall variability and mechanisms of a rainfall increase over the past decades, and benchmark climate models in terms of their ability to reproduce the observed variability and trends, focusing on the role of increasing northern hemispheric aerosols in the rainfallincrease. Thirdly, we provide a dynamical explanation to the common future of a fast Tasman Sea warming rate under climate change, and identify the impacts of suchwarming on Australian rainfall. Finally, we examine the relative importance of the three systems, in addition to Tasman Sea warming, in driving rainfall changes undergreenhouse conditions. This project contributes to no less than six peer-reviewed journal publications.
46
Preston, Anthony. "Southern African rainfall variability and Indian Ocean sea surface temperatures : an observational and modelling study." Thesis, University of Oxford, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.411052.
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McSweeney, Carol Frances. "Daily rainfall variability at point and areal scales : evaluating simulations of present and future climate." Thesis, University of East Anglia, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.439921.
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Maldonado, Tito. "Inter-annual variability of rainfall in Central America : Connection with global and regional climate modulators." Doctoral thesis, Uppsala universitet, Luft-, vatten och landskapslära, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-304656.
Full textAbstract:
Central America is a region regularly affected by natural disasters, with most of them having a hydro-meteorological origin. Therefore, the understanding of annual changes of precipitation upon the region is relevant for planning and mitigation of natural disasters. This thesis focuses on studying the precipitation variability at annual scales in Central America within the framework of the Swedish Centre for Natural Disaster Science. The aims of this thesis are: i) to establish the main climate variability sources during the boreal winter, spring and summer by using different statistical techniques, and ii) to study the connection of sea surface temperature anomalies of the neighbouring oceans with extreme precipitation events in the region. Composites analysis is used to establish the variability sources during winter. Canonical correlation analysis is employed to explore the connection between the SST anomalies and extreme rainfall events during May-June and August-October. In addition, a global circulation model is used to replicate the results found with canonical correlation analysis, but also to study the relationship between the Caribbean Sea surface temperature and the Caribbean low-level jet. The results show that during winter both El Niño Southern Oscillation and the Pacific Decadal Oscillation, are associated with changes of the sea level pressure near the North Atlantic Subtropical High and the Aleutian low. In addition, the El Niño Southern Oscillation signal is intensified (destroyed) when El Niño and the Pacific Decadal Oscillation have the same (opposite) sign. Sea surface temperature anomalies have been related to changes in both the amount and temporal distribution of rainfall. Precipitation anomalies during May-June are associated with sea surface temperature anomalies over the Tropical North Atlantic region. Whereas, precipitation anomalies during August-September-October are associated with the sea surface temperature anomalies contrast between the Pacific Ocean and the Tropical North Atlantic region. Model outputs show no association between sea surface temperature gradients and the Caribbean low-level jet intensification. Canonical correlation analysis shows potential for prediction of extreme precipitation events, however, forecast validation shows that socio-economic variables must be included for more comprehensive natural disaster assessments.
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Seregina, Larisa [Verfasser], and J. [Akademischer Betreuer] Pinto. "Rainfall Variability and Trends over the Greater Horn of Africa / Larisa Seregina ; Betreuer: J. Pinto." Karlsruhe : KIT-Bibliothek, 2021. http://d-nb.info/1238148379/34.
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Faurés, Jean-Marc 1961. "Sensitivity of runoff to small scale spatial variability of observed rainfall in a distributed model." Thesis, The University of Arizona, 1990. http://hdl.handle.net/10150/192050.
Full textAbstract:
The spatial variability of rainfall is known to play an important role in the process of surface runoff generation. Yet, the typical assumption of uniform rainfall is still applied in modeling the hydrological behavior of small watersheds. To investigate the validity of this assumption, an experiment was conducted in a small catchment (4.4 ha) in a semi-arid environment. The distributed model KINEROS was used to assess the sensitivity of predicted runoff to rainfall variability. Uncertainties in estimating rainfall input were shown to have three major components: measurement errors, spatial variability of the rainfall field, and wind. Their relative importance is a function of the catchment scale, topography and physical properties of the storms. Computation of runoff based on the data from a unique raingage entails a high degree of uncertainty. Even at small scales, the number and location of raingages directly control the accuracy of runoff simulation.