Academic literature on the topic 'Flash flood'

Abstract. The data sets described in this paper provide a basis for developing and testing new methods for monitoring and modelling urban pluvial flash floods. Pluvial flash floods are a growing hazard to property and inhabitants' well-being in urban areas. However, the lack of appropriate data collection methods is often cited as an impediment for reliable flood modelling, thereby hindering the improvement of flood risk mapping and early warning systems. The potential of surveillance infrastructure and social media is starting to draw attention for this purpose. In the floodX project, 22 controlled urban flash floods were generated in a flood response training facility and monitored with state-of-the-art sensors as well as standard surveillance cameras. With these data, it is possible to explore the use of video data and computer vision for urban flood monitoring and modelling. The floodX project stands out as the largest documented flood experiment of its kind, providing both conventional measurements and video data in parallel and at high temporal resolution. The data set used in this paper is available at https://doi.org/10.5281/zenodo.830513.

Abstract. Flash floods constitute one of the deadliest and costliest natural disasters worldwide. This paper explains the karst flash flood phenomenon, which represents a special kind of flash flood. As the majority of flash floods karst flash floods are caused by intensive short-term precipitation in an area whose surface rarely exceeds a few square kilometres. The characteristics of all flash floods are their short duration, small areal extent, high flood peaks and rapid flows, and heavy loss of life and property. Karst flash floods have specific characteristics due to special conditions for water circulation, which exist in karst terrains. During karst flash floods a sudden rise of groundwater levels occurs, which causes the appearance of numerous, unexpected, abundant and temporary karst springs. This paper presents in detail an example of a karst flash flood in the Marina bay (Dinaric karst region of Croatia), which occurred in December 2004.

Abstract Flash floods reported for the forecast area of the National Weather Service Forecast Office at Binghamton, New York (BGM), are compared with similar significant precipitation and flash flood watch events not corresponding to flash flood reports. These event types are characterized by measures of surface hydrological conditions, surface and upper-air variables, thermodynamic properties, and proxies for synoptic-scale features. Flash flood and nonflood events are compared quantitatively via discriminant analysis and cross validation, and qualitatively via scatterplots and composite soundings. Results are presented in the context of a flash flood checklist used at BGM prior to this study. Flash floods and nonfloods are found to differ most significantly in antecedent soil moisture. The wind direction at 850 hPa shows differences between flood and nonflood events, with flooding more common for an easterly to southeasterly direction and nonflooding more common for a northwesterly direction. Southwesterly wind direction is characteristic of both types. In general, nonflooding significant precipitation events are more commonly associated with a better-defined ridge axis of relatively high 850-hPa equivalent potential temperature and larger convective available potential energy as compared to the flash flood events. Several parameters included on the BGM flash flood checklist, though effective at distinguishing significant precipitation events and flash floods from random events, were found to be unable to separate flash floods from nonflooding significant rain events.

An early warning of a flash flood is essential to prevent the general public from the hazardous flooding events, however, the rapid variation of human activities has led to the uncertainty of risk in prone areas. The lack of a systematic record of flash flood events introduces challenges to flash flood-related research. Herein, we map spatial and temporal variations in flash floods in China from 1950 to 2015 and establish a general ordered logit model in a geographic information environment to estimate the association between the occurrence of flash flood events and natural conditions and the variation of human activities at the watershed level. The results showed that precipitation is an important cause of flash flooding, and demonstrate that anthropogenic intervention (heavy rainfall, density of villages, and vegetation cover) in the environment affect the likelihood of flash floods. We found that the likelihood of flash floods in China may increase with the air quality worsening and that the occurrence of flash floods is strongly correlated with vegetation cover. Our findings suggest a need for further investigation of the link between air quality and flash flooding in flood-prone areas.

Hydrometeorological disasters are showing an increasing trend in Indonesia. Flash floods are part of a hydrometeorological disaster that has a significant livelihood impact. Flash Flood is triggered by the intensity of extreme rain, several actions of mitigation can be taken by early warning systems, hazard and risk mapping, community preparedness, and climate change adaptation. So, how does future land use have an impact, and how much loss will result from the flash flood disaster in Batu City? The hydrometeorological disaster that occurred in Indonesia was the Batu Flash Flood. The Flash Flood occurred on November 4, 2021. The flash flood has a lot of impact on many locations, including the Bumiaji District and Junrejo District. Based on the disaster history recorded, the flash flood in Batu has only happened once, but the impact was quite big because there are many houses in the midstream of Bulukerto. Based on the losses caused, this can be the basis for efforts to control the spatial pattern of Batu City in the future. The methodology used in this study is risk assessment. While the risk study related to delta (Δ) the study of flash floods risk in spatiotemporal prevention uses the 2030 spatial plan for delta prediction (Δ), which can later predict the consequences of climate change and meteorological disasters from flash floods in Batu. The results of this study are the delta (Δ) of flash flood risk and the damage assessment of the flash flood that occurred in Batu.

The objective of this research is (1) to raise awareness and prepare for flash flooding among people in the Mekong region which promotes inequality reduction from disasters by using Muang Nong Khai District, Nong Khai Province as a model area, and (2) To develop a policy proposal by designing a joint policy for flash flood preparedness in the Mekong region to promote inequality reduction from disasters. This research is action research in conjunction with policy design focusing on brainstorming. Group discussions with in-depth interviews. The research results were found that: [A] People have a basic understanding of (1) the nature of the disaster, and (2) the experience of the flash flood disaster encountered by the WiangKhuk Sub-district people is about remembering the severity Looking at the floods that have been associated, but in terms of preparation, community leaders see together that they want to develop into a system and plan for a joint rehearsal in the future. [B] Flash flood response weaknesses are (1) Weaknesses for early warning, evacuation, and flash flood drills, (2) Weaknesses of flash flood plans for areas that have not yet been formally planned, And (3) weaknesses in communication. [C] The interesting common policy design guidelines that should be developed are (1) Flash flood knowledge development, (2) direction and coordination for emergency operations, (3) agreements that Formal and informal for flash flood response, (4) resource mobilization focused on the certainty of emergency work. [D] The policy recommendations are: (1) Appropriate policy guidelines for flash flood preparedness in the Mekong River Basin should include precautions, evacuation, flash flood drills, and community-level plans to tackle flash floods. (2) The public sector, civil society, and communities should jointly develop policies to prepare for flash floods, that is, to develop flash flood knowledge to keep up with the changing circumstances of the local context. (3) The key policy to deal with flash floods to help reduce inequality is to develop community capacity or community potential. This is a collaboration of community organizations, the government sector, civil society in the area, which together with driving a community-level response plan. [E] The operation recommendations include (1) the community must be the host to invite government organizations such as the Provincial Disaster Prevention and Mitigation and the Mekong Community Organization Council to drive community-level planning. (2) Organizing a network meeting on flash flood response such as communities, Provincial Disaster Prevention and Mitigation Agency, and Mekong Community Organization Council should hold meetings at least twice a year to understand the situation and implement measures to deal with flash floods in a timely manner. (3) Flash flood drills should be conducted at least once a year in order to build mutual learning among communities and networks in flash flood preparedness, it is also an analysis of the weaknesses each year and can be used to develop the capacity and capacity of the community to handle the flash flood in the future.

Abstract Flash flood is defined as “a flood of short duration with a relatively high peak discharge,” which leaves little time to take action to reduce property damage and the risk to life. Flash floods occur not only because of heavy rainfall but some co-factors that can trigger it. This study aims to determine the co-factors that trigger the flash flood. Observations are carried out using a descriptive-qualitative approach of five small catchments in Indonesia, namely Bahorok Catchment (Langkat, North Sumatra), Kalijompo, and Kalipakis Catchment (Jember, East Java), Nasiri Catchment (Western Seram, Maluku), Wasior Catchment (Wondama Bay, West Papua). The dominant co-factors are related to rainfall IDF, morphological characteristics (slope, channel properties, flow pattern), geological conditions (rock, soil, structure, geohydrology), catchment conditions (vegetation, land use). Flash floods generally occur due to landslides in the upstream part of the river. Debris consisting of water, rock, and tree trunks can stem the river’s flow and form natural dams. In five flash flood cases under investigation, the causes of a flash flood triggered by heavy rainfall and the morphological characteristics are 60% and 40%, respectively. The quantitative measure of each co-factor that triggers flash floods is essential for further research to identify flash flood symptoms.

The importance of identifying the areas vulnerable for both floods and flash-floods is an important component of risk management. The assessment of vulnerable areas is a major challenge in the scientific world. The aim of this study is to provide a methodology-oriented study of how to identify the areas vulnerable to floods and flash-floods in the Buzău river catchment by computing two indices: the Flash-Flood Potential Index (FFPI) for the mountainous and the Sub-Carpathian areas, and the Flood Potential Index (FPI) for the low-altitude areas, using the frequency ratio (FR), a bivariate statistical model, the Multilayer Perceptron Neural Networks (MLP), and the ensemble model MLP–FR. A database containing historical flood locations (168 flood locations) and the areas with torrentiality (172 locations with torrentiality) was created and used to train and test the models. The resulting models were computed using GIS techniques, thus resulting the flood and flash-flood vulnerability maps. The results show that the MLP–FR hybrid model had the most performance. The use of the two indices represents a preliminary step in creating flood vulnerability maps, which could represent an important tool for local authorities and a support for flood risk management policies.

AbstractThe Mississippi River basin (MRB) is a flash flood hotspot receiving the most frequent flash floods and highest average rainfall accumulation of any region in the United States. Given the destruction flash floods cause in the current climate in the MRB, it is critical to understand how they will change in a future, warmer climate in order to prepare for these impacts. Recent work utilizing convection-permitting climate simulations to analyze future precipitation changes in flash flood–producing storms in the United States shows that the MRB experiences the greatest future increase in flash flood rainfall. This result motivates the goal of the present study to better understand the changes to precipitation characteristics and vertical velocity in flash flood–producing storms in the MRB. Specifically, the variations in flash flood–producing storm characteristics related to changes in vertical velocity in the MRB are examined by identifying 484 historical flash flood–producing storms from 2002 and 2013 and studying how they change in a future climate using 4-km convection-permitting simulations under a pseudo–global warming framework. In a future climate, precipitation and runoff increase by 17% and 32%, respectively, in flash flood–producing storms in the MRB. While rainfall increases in all flash flood–producing storms due to similar increases in moisture, it increases the most in storms with the strongest vertical velocity, suggesting that storm dynamics might modulate future changes in rainfall. These results are necessary to predict and prepare for the multifaceted impacts of climate change on flash flood–producing storms in order to create more resilient communities.

Tuyen Quang is one of the provinces at high risk of flash floods in the Northern Midlands and Mountains of Vietnam. In the rainy season, like other localities in the region, Tuyen Quang has a long, concentrated rainfall combined with steep hills and mountains, large divisions, many rivers, and streams; In addition, the thinning of the vegetation cover due to excessive exploitation of the forest by the local people causes flash floods to appear more and more. Applying GIS and remote sensing to establish a map of flash flood risk is a quantitative approach and high reliability. This article has established a flash flood hazard map at a scale of 1/100,000 in Tuyen Quang province. In the map database, districts with a high risk of flash flood were identified, including Na Hang, Chiem Hoa, Ham Yen, and Lam Binh, the average flash flood hazard level included districts: Yen Son, Son Duong; Tuyen Quang city has a low risk of flash floods.

A major area targeted for hydrometeorological forecast service improvements is in flash flood forecasting. Verification data show that general public service products of flash flood forecasts do not provide enough lead time in order for the public to make effective response. Sophisticated users of flash flood forecasts could use forecast probabilities of flash flooding in order to make decisions in preparation for the predicted event. To this end, a systematic probabilistic approach to flash flood forecasting is presented. The work first describes a deterministic system which serves as a conceptual basis for the probability system. The approach uses accumulated rainfall plus potential rainfall over a specified area and time period, and assesses this amount against the water holding capacity of the affected basin. These parameters are modeled as random variables in the probabilistic approach. The effects of uncertain measurements of rainfall and forecasts of precipitation from multiple information sources within a time period and moving forward in time are resolved through the use of Bayes' Theorem. The effect of uncertain inflows and outflows of atmospheric moisture on the states of the system, the transformation of variables, is resolved by use of convolution. Requirements for probability distributions to satisfy Bayes' Theorem are discussed in terms of the types and physical basis of meteorological data needed. The feasibility of obtaining the data is evaluated. Two alternatives for calculating the soil moisture deficit are presented--one, an online automatic rainfall/runoff model, the other an approximation. Using the soil moisture approximation, a software program was developed to test the probabilistic approach. A storm event was simulated and compared against an actual flash flood event. Results of the simulation improved forecast lead time by 3-5 hours over the actual forecasts issued at the time of the event.

A flash flood is a flood that follows the causative storm event in a short period of time. The term “flash” reflects a rapid response, with water levels in the drainage network reaching a crest within minutes to a few hours after the onset of the rain event, leaving extremely short time for warning [Creutin and Borga, 2003; Borga et al., 2008]. Flash floods are localized phenomena that occur in watersheds of few hundred kilometres or less, with response times of a few hours or less [Creutin and Borga, 2003; O’Connor and Costa, 2004]. Such basins respond rapidly to intense rainfall because of steep slopes and impermeable surfaces, saturated soils, or because of human (i.e., urbanization) or fire-induced alterations to the natural drainage. Causative events are generally excessive storms, but can also be the sudden release of water impounded by a natural jam (i.e., formed by ice or rock, mud, and wood debris) or human-made dam or levee. This thesis focuses on flash flood events associated with heavy rainfall. Europe experienced several catastrophic flash floods in the last decades. Data concerning a number of these floods occurred during the last 15 years have been reported in Marchi et al. (2010). Examination of these data and references therein shows that: Flash floods occur in any of the hydroclimatic regions of Europe, even though three regions appear to be characterized by high flash flood potential: Mediterranean, Alpine Mediterranean, and Inland Continental Europe; Heavy rainfall accumulation is a necessary but not sufficient condition for flash floods, since hydrology critically controls flash-flood-triggering. Without hydrological analysis, it is impossible to evaluate the flood potential of storms, particularly in the fringe of the flood/no flood threshold; Flash flood hazard is related to both stream response (flood) and landscape response (landslide and erosion). The intense erosion and solid transport associated with these extreme events add to the hazard and strongly influence the quality of soils, waters and ecosystems. The twofold consequence of the above observations is that forecasting of flash-floods: Depends critically on meso-scale storm forecasting, with a specific attention to the processes leading to slow movement of the precipitation system; Necessitates real time hydrological modelling, with a specific attention to the runoff generation processes over a wide range of scales. Although they are seldom all deployed at the same time, the technical requirements for a hydrometeorological flash flood forecasting system include: A numerical weather prediction (NWP) model, capable to provide short-range Quantitative Precipitation Forecasts (QPF); A remote sensing based (radar, satellites) precipitation detection system, for storm monitoring and for the possible initialization and conditioning of the NWP model, and A hydrological-hydraulic forecasting model, capable to forecast the stream response from the rain input. These requirements are similar to those of more common riverine flood forecasting systems. However, some features characterise flash flood forecasting with respect to riverine flood forecasting and point out to their larger uncertainty. These are: The short lead time, which implies both the integration of meteorological and hydrologic forecast, and the difficulties of using data assimilation procedures based on real time observed discharges to reduce uncertainty in hydrologic predictions; The need to provide local forecasts, which means that, on one hand, the rainfall must be monitored and forecasted on a wide range of space/time scales, and, on the other hand, every tributary of a monitored basin can be considered as a potential target for flood warning. Estimation of extreme rainfall rates by weather radar at the appropriate time and space scales is the cornerstone of flash flood analysis and forecasting. A large body of research work has greatly improved in the last two decades radar technology and algorithms for rain quantification. This work has shown that well maintained conventional radar systems can estimate rainfall at ground level provided that a number of precautions are taken, and in particular: The siting of the instrument and its scanning protocol must be carefully selected and analysed; The quality of the instrument must be routinely checked; The signal processing must take into account the physics of the instrument as well as the properties of the atmospheric and ground targets. A downstream control of the radar rainfall processing can rely on rain-gauge measurements at ground level using a variety of methods. When these precautions are taken, different studies have shown that radar-based rainfall estimates are reliable and may be used as input in rainfall-runoff models for flood modelling and forecasting [Borga et al., 2000; Delrieu et al., 2005; Borga et al., 2002]. These very positive results must not be hiding some weaknesses: Most of these results never had the opportunity to be coherently validated over a significant number of flash floods events. The use of specific experiments or of limited operational radar data sets is insufficient to test complex combinations of algorithms, especially if high rain intensities are of interest. Very few results have been translated into operational hydrologic applications. This thesis aims to investigate the use of weather radar for the purpose of understanding the hydrometeorological mechanisms leading to flash floods, and then for flash flood forecasting. The outline of the thesis work is as follows. Chapter 1 provides a literature review of the rainfall estimation by weather radar for flash flood-generating storms. Chapter 2 describes a number of procedures for the rainfall estimation at the ground during flash flood events in mountainous catchments. A metric for the analysis of the rainfall field spatial patterns is proposed in Chapter 3, in the context of the analysis of a number of Romenian flash floods. This metric is used for the analysis of two flash flood events, respectively occurred in 2003 in the Eastern Italian Alps (Chapter 4) and in Western Slovenia (Chapter 5). Major conclusions from the work are reported in Chapter 6.
Una piena improvvisa è una piena che segue l’evento precipitativo che la ha causata entro un breve periodo di tempo. Il termine “improvvisa o flash” riflette una risposta rapida, con il picco di piena che si verifica nella rete di drenaggio nel volgere di alcuni minuti fino a poche ore dopo l’inizio dell’evento di pioggia. Questo fatto lascia intendere quanto poco tempo ci sia per l’allerta [Creutin and Borga, 2003; Borga et al., 2008]. Questo tipo di bacini rispondo rapidamente ad una precipitazione intensa a causa di pendii ripidi e superfici impermeabili, terreni saturi, o a per fattori determinati dall’uomo (vedi per esempio l’urbanizzazione) o a causa di alterazioni del drenaggio naturale del terreno dovuto ad incendi. Gli eventi scatenanti le piene improvvise sono generalmente precipitazioni che portano all’eccesso di drenaggio, ma questo tipo di piene possono anche essere scatenate dal rilascio improvviso di acqua trattenuta da impedimenti naturali (per esempio formati da ghiaccio e roccia, fango e detriti di legno) o di tipo artificiale come dighe e argini. Questa tesi si concentra su eventi di piena improvvisa associati a precipitazioni intense. L’Europa ha conosciuto diverse inondazioni catastrofiche negli ultimi decenni. I dati relativi un certo numero di queste inondazioni che si sono verificate nel corso degli ultimi 15 anni sono riportati da Marchi et al. (2010). Dall’analisi di questi dati e di queste fonti risulta che: Una piena improvvisa si può verificare in qualsivoglia regione idroclimatica dell’Europa, anche se tre regioni sembrano essere caratterizzate da una grande incidenza di di piene improvvise: l’area Mediterranea, quella Alpino-Mediterranea, e quella Continentale; Una gran quantità di pioggia accumulata è una condizione necessaria ma non sufficiente al verificarsi di una piena improvvisa, dal momento che l’idrologia controlla in modo decisivo l’innesco della piena improvvisa. Senza un’analisi di tipo idrologico, risulta impossibile valutare la probabilità che una data precipitazione scateni una piena, in praticolare in termini di una soglia oltre la quale si verifica la piena; La pericolosià delle piene improvvise è collegata sia alla risposta del fiume (la piena) che alla risposta del terreno (fenomeni di tipo franoso ed erosivo). L’intensa erosione ed il trasporto solido associati a questi fenomeni estremi si aggiungono alla pericolosità ed influenzano in modo significativo la qualità dei terreni, delle acque e degli ecosistemi. La duplice conseguenza delle osservazioni appena fatte è che la previsione di piene improvvise: Dipende in modo determinante dalle previsioni delle precipitazioni che si sviluppano alla meso-scala, con una attenzione specifica ai processi che frenano la circolazione del sistema di precipitazione; Richiedone modelli idrologici che lavorino in tempo reale, con una particolare attenzione ai processi du generazione del deflusso a vasta scala. Anche se raramente sono tutti utilizzati contemporaneamente, i requisiti tecnici per un sistema di previsione idrometeorologica per le piene improvvise comprendono: Un modello numerico di previsione (NWP2), in grado di fornire previsioni quantitative di pioggia a corto raggio (QPF3); Un sistema di rilevamento in remoto per la pioggia (radar, satellite), per il monitoriraggio dei fenomeni temporaleschi e la possibilie inizializzazione e condizionamento del modello NWP, e Un modello di previsione idrologico-idraulico, in grado di prevedere la risposta del corso d’acqua all’input pioggia. Tali requisiti sono simili a quelli più comuni utilizzati per la previsione delle alluvioni dei sistemi fluviali. Tuttavia, alcuni elementi caratterizzano la previsione delle piene improvvise rispetto alla previsione delle alluvioni e ne sottolineano la grande incertezza. Questi sono: Il breve periodo durante il quale questi processi si sviluppano, che implica sia l’integrazione di un sistema di previsione di tipo meteorologico e idrologico, che la difficoltà nell’utilizzo di procedure di assimilazione di dati basate sull’osservazione in tempo reale delle portate al fine di ridurre l’incertezza nelle previsioni idrologiche; La necessità di fornire previsioni a scala locale, il che significa da una parte che la pioggia deve essere monitorata e prevista su una vasta scala spazio-temporale, all’altra che ciascun tributario del bacino monitorato può essere considerato come un bersaglio potenziale per un allarme di piena. La stima di fenomeni precipitativi estremi tramite l’utilizzo del radar meteorologico alla appropriata scala spazio-temporale è una pietra miliare dell’analisi e della previsione delle piene improvvise. Una grande branca della ricerca in questo campo ha favorito un notevolmente migliorato, negli ultimi due decenni, delle tecnologie radar e degli algoritmi per la stima di pioggia. Questo lavoro ha dimostrato che anche utilizzando sistemi radar convenzionali si possono ottenere stime di precipitaziona a livello del suolo, a condizione che vengono adottate una serie di precauzioni, in particolare: L’ubicazione dello strumento e del suo protocollo di scansione devono essere attentamente selezionati ed analizzati; La qualità dello strumento deve essere sottoposta a controlli ordinari; L’elaborazione del segnale deve tener conto della fisica dello strumento così come delle proprietà atmosferiche e dei bersagli di terra. Un controllo a valle del trattamento delle precipitazioni radar può essere fatto tramite misurazioni da pluviometro a livello del suolo utilizzando una varietà di metodi. Quando si sono prese queste precauzioni, diversi studi hanno dimostrato che le stime di precipitazione basate su radar meteorologico sono affidabili e possono essere utilizzate come input di modelli afflussodeflusso per la modellazione e la previsione delle piene [Borga et al., 2000; Delrieu et al., 2005; Borga et al., 2002]. A fronte di questi risultati molto positivi non devono però essere nascosti alcuni punti deboli: La maggior parte di questi risultati non hanno mai la possibilità di essere coerentemente convalidati su un numero significativo di eventi di piena improvvisa. L’utilizzo di esperimenti specifici o di una banca dati limitata di dati radar è insufficiente a testare la combinazione complessa degli algoritmi utilizzati, specialmente se si è interessati ad intensità di pioggia elevata. Un numero molto limitato di risultati positivi è stato tradotto in applicazioni idrologiche operative. Questa tesi si propone di esaminare l’uso del radar meteorologico ai fini della comprensione dei meccanismi idrometeorologici che portano alla formazione di piene improvvise, e quindi alla loro previsione. L’organizzazione del lavoro di tesi è la seguente. Il Capitolo 1 fornisce una revisione della letteratura sul tema della stima di precipitazione tramite radar meteorologico per le precipitazioni che causano la formazione di piene improvvise. Il Capitolo 2 descrive una serie di procedure per la stima delle precipitazioni al suolo durante gli eventi di piena improvvisa in bacini montani. Una metrica per l’analisi spaziale del campo di pioggia viene proposta nel Capitolo 3, nel contesto dell’analisi di una serie di piene improvvise verificatesi in Romania. Questa metrica è utilizzata per l’analisi di due eventi di piena, accaduti rispettivamente nel 2003 nelle Alpi Italiane friulane e nella parte ovest della Slovenia (Capitolo 5). Le conclusioni principali del lavoro di tesi sono riportate nel Capitolo 6.

ABSTRACT: “Flash flood analysis and modelling in mountain regions” Flash flood are rare and localized phenomena, triggered by meteorological event with a pronounced spatial variability, with a precipitation gradient, at event scale, up to 20-50 mm/km. The consequences of these features is that the scientific and operational communities working on flash flood analysis have to deal with an impressive lack of data. Even a dense raingauge network may not be able to represent spatial variability of rainfall patterns associated with convective storms that trigger flash floods. Radar rainfall estimations, when correctly elaborated, are able to represent spatial patterns, but quantitative precipitation volume estimations need to be validated. In addition, concerning discharge data, the majority of the upstream and larger catchments affected by flash floods are not gauged and stream gauges, where present, are often damaged, so that peak discharge distribution along main and secondary river network is even less known than precipitation fields. This study aims at covering the gap between needed and available data for flash flood event analysis, combining different methodologies. An Intense Post Event Campaign (IPEC) may be very useful to collect peak discharge estimations and time sequence of the flood in ungauged sections. Simplified hydrological model, based on rough runoff excess computation and set velocity propagation, can be used to cross validate quantitative distributed precipitation data from weather radar and peak discharge estimations collected during an IPEC. More complex and detailed model may help to improve the knowledge about flash flood associated phenomena, like debris flow. Another objective of this thesis is to investigate the role of rainfall spatial variability in flash flood triggering. First a standard procedure to describe the variability catchment scale is needed. It will be so possible to study the relationship between rainfall input distribution and flood propagation dynamics. Then a simplified hydrological model is used to investigate the role of spatial variability in precipitation patterns: systematic studies are carried to describe the accuracy of rainfall volumes at basin scale and the effect of spatial variability within the basin. Often the studies about flash flood dynamics are slow down or stopped because no measured data are directly to hand, or, if so, because they are not considered sufficiently accurate. This work shows the possibility to combine together data with an assured degree of uncertainty, the only available or collectable existing data, and processed them with simple statistical and hydrological tools to obtain a more precise knowledge about past flash floods. The remainder of this dissertation is organised as follows. Chapter 1 “Introduction”. The work starts with the aim to define what a “flash flood” is, underlying the importance to characterize such event according spatial and temporal proprieties. From this definition it follows that a generic flood can be classified according its own spatial and temporal proprieties and located in a specific point of a segment delimitated by the two ideal cases of “flash flood” and “flood at large scale”. Chapter 2 “Literature review”. Spatial and temporal characterization lead to describe typical features of flash flood in different climates. Meteorological conditions able to trigger this kind of events are described and analyzed, with particular care about convective cells system organized in mesoscale structures. Finally some literature examples are reported to show different possible approach and to underline usual uncertainty when dealing with flash flood. Chapter 3 “Materials an methods”. This chapter summarizes and describes the tools used in this thesis to carry on flash flood analysis. 3.1 Weather radar data are used to describe rainfall spatial distribution and obtain quantitative estimations of rainfall patterns. Data acquiring and processing are described and most common errors are summarized along with most common procedures and algorithms to avoid and correct them. It is finally shown how merging radar and conventional raingauge network information can provide a more exhaustive description of rainfall fields, with quantitative estimation. This data processing is very useful for further characterization and analysis of past flash flood events. 3.2 Post event surveys are presented as an essential tool to collect the richest possible documentation. Measure campaigns are valorised to obtain qualitative and quantitative description of past floods. The goal is to complete the spatial and temporal precipitation knowledge and dynamic description, focusing on discharge estimation along hydrological network in term of peak values and timing. 3.3 Hydrological models can be routed for a better comprehension of flood dynamics at event scale. Two hydrological models, then used for flash flood analysis, are described in detail. The first one is applied at large event scale and starts from a distributed precipitation input. Hortonian runoff generation is applied punctually and superficial flood propagation is computed basing on fixed hillslope and channel velocity. The second model is built to be applied at very small catchment scale and simulate infiltration and transport processes for surface and subsurface flow through uniform hypothesis equations. Chapter 4 “Analysis of past flash flood events”. Some specific post flood analysis are collected in three section. 4.1 Five flash flood events occurred in Romania are analysed with HYDRATE European project contribution. This study shows that even if the conventional hydrometeorological data are poor, weather radar information and hydrological modelling can help in understanding specific past flood dynamics. 4.2 HYDRATE project was also involved in the analysis of a flash flood occurred in Slovenia in September 2007, including radar processing and post event surveys. It is shown how this approach, characterize by time and cost significant efforts, is a precious tool to collect data and information for a detailed description that would be not possible through traditional hydrometeorological network. 4.3 A detailed model is used to describe surface and subsurface flow dynamics during the debris flow occurred in two small subcatchments in Fella river valley (North Est of Italy), hit by a flash flood on August 29, 2003. The study mainly consists on liquid and solid mass balance during the different phases of the event. Chapter 5 “Spatial variability in flash flood events”. An analysis on rainfall spatial distribution is carried with the same tools on two different basin interested by flash flood event. The studies includes a fist detailed analysis on rainfall spatial variability within selected subcatchments at different scales: spatial variability is described through time distance calculated in base of hydrological network. Then a simplified hydrological model is used to investigate spatial aggregation effects on mean areal rainfall and peak discharge value at subcatchment scale. 5.3 For Fella river basin (in Friuli Venezia Giulia region), ten subcatchments from 10.5 and 623km² are choosen. 5.4 For Cervo River (Piomente region, North West Italy) the study is applied to three flood events characterized by different rainfall spatial variability, and focused on four subcatchments (from 75 to 983km²). Chapter 6 “Conclusions”. Are here reported and summarized the main observations coming from the specific studies describe in the two previous chapters as long as recommendation for future research.
RIASSUNTO: “Analisi e modellazione di piene improvvise in zone montane” Le piene improvvise sono fenomeni rari e localizzati, causati da eventi meteorologici caratterizzati da una spiccata variabilità spaziale, con gradienti di precipitazione che possono raggiungere, a scala di evento, i 20-50 mm/km. La conseguenza di ciò è che la comunità scientifica e gli enti operativi interessati nell’analisi dei fenomeni di piena si relazionano quotidianamente con una carenza di dati. Anche una fitta rete di pluviometri non è in grado di rappresentare la variabilità spaziale dei campi di precipitazione associati a fenomeni convettivi che innescano piene improvvise. Le stime di precipitazione ottenute attraverso il radar meteorologico, opportunatamente elaborate, sono in grado di rappresentare i pattern spaziali, ma i valori di volumi di pioggia necessitano di essere validati. Inoltre, per quanto riguarda i dati di portata, la maggior parte dei bacini colpiti da piene improvvise non sono strumentati e gli strumenti, dove presenti, risultano spesso danneggiati, cosicché la conoscenza della distribuzione delle portate al picco, lungo la rete idrologica principale e secondaria, è persino più approssimativa di quella della distribuzione spaziale della precipitazione. Questo studio si prefigge di colmare la distanza tra i dati disponibili e quelli richiesti per un’analisi a scala di evento con riferimento a fenomeni di piena improvvisa. Un’approfondita campagna di rilievi post evento (in inglese Intense Post Event Campaign, IPEC) può risultare estremamente utile per raccogliere le stime di portate al picco e la sequenza cronologica dello svilupparsi della piena in sezioni non monitorate. Modelli idrologici semplificati, dotati di metodi elementari per la separazione dei deflussi e predeterminate velocità di propagazione, possono essere utilizzati per una validazione incrociata tra una descrizione quantitativa della distribuzione di precipitazione ottenuta attraverso il radar meteorologico e le stime di portate al picco raccolte durante un IPEC. Modelli più complessi e dettagliati possono migliorare il livello di conoscenza riguardo fenomeni associati alle piene improvvise, come le colate detritiche. Un altro obiettivo di questa tesi è quello di investigare il ruolo della variabilità spaziale della precipitazione nei fenomeni di piena improvvisa. In primo luogo è necessario impostare una procedura che permetta di caratterizzare tale variabilità all’interno di un particolare bacino idrografico, mettendo in relazione la distribuzione degli apporti meteorici con le modalità di propagazione della piena. In secondo luogo si vuole indagare, attraverso l’applicazione di modelli idrologici semplificati, il ruolo della risoluzione spaziale della precipitazione. A questo fine è necessario separare due aspetti: l’accuratezza della stima dei volumi piovuti a scala di bacino e l’influenza della variabilità spaziale all’interno del bacino stesso. Spesso gli studi che si concentrano sulle dinamiche delle piene improvvise sono rallentati o resi impossibili per il fatto che nessun dato misurato risulta utilizzabile così come disponibile, oppure perchè i dati di partenza non sono ritenuti sufficientemente accurati. Questo lavoro si prefigge di mostrare come sia possibile, partendo dai soli dati esistenti, disponibili o recuperabili, caratterizzati da un certo grado di incertezza, passare attraverso un’elaborazione tramite semplici strumenti statistici e idrologici al fine di ottenere una conoscenza più precisa riguardo passati eventi di piena improvvisa. Si riporta una breve descrizione del contenuto dei capitoli della tesi, che sarà elaborata in lingua inglese. Capitolo 1 “Introduction”. Introduzione alla tematica che comprende una definizione del termine “piena improvvisa”, convenendo sulla necessità di caratterizzare tali eventi in termini di proprietà spazio-temporali. Si nota che, a partire da questa definizione, è possibile classificare una generica piena in un punto di un segmento ai cui estremi ci sono i casi ideali di “piena improvvisa” e “piena a larga scala”. Capitolo 2 “Literature review”. Partendo dalla caratterizzazione spazio temporale si descrivono le caratteristiche tipiche delle piene improvvise nei diversi tipi di clima, si individuano le condizioni meteorologiche in grado di innescare tali fenomeni, quali le celle convettive organizzate in strutture di mesoscala. Si riportano, infine, alcuni esempi di studi in letteratura che mostrano diverse tipologie di approcci e che sono indicativi dell’incertezza in cui si è soliti lavorare quando si approfondiscono questi temi. Capitolo 3 “Materials an methods”. In questo capitolo vengono presentati i principali strumenti comuni a tutte le analisi di fenomeni di piena improvvisa presentati in questa tesi. 3.1 L’utilizzo del radar meteorologico per studiare, dal punto di vista quantitativo, la distribuzione spaziale della precipitazione. Vengono approfondite la modalità di acquisizione del dato, sottolineando le possibili fonti di errore ed i metodi più comuni per ovviare a questi inconvenienti. Viene anche mostrato come l’utilizzo combinato di radar e tradizionali pluviometri renda più completa la caratterizzazione della precipitazione ai fini di un analisi di una piena improvvisa. 3.2 Le indagini post evento, necessarie per raccogliere la maggior documentazione possibile, sono valorizzate al fine di una ricostruzione, anche qualitativa, delle dinamiche caratteristiche di una specifica piena. Queste, attraverso diverse metodologie, devono aiutare a descrivere la struttura spazio temporale della precipitazione e la stima di portata, distribuita lungo la rete idrica, in termini di valore al picco e di tempistica 3.3 L’uso della modellistica idrologica applicata ad una miglior comprensione delle dinamiche a scala di evento. In particolare vengono descritti i due modelli idrologici utilizzati. Il primo, da applicare a larga scala, parte da un input di precipitazione spazialmente distribuito e, attraverso un meccanismo hortoniano di separazione dei deflussi applicato puntualmente, propaga la piena in base a fissate velocità di versante e di canale. Il secondo, da applicare a bacini di piccolissima dimensione, simula i processi di trasporto superficiale e sottosuperficiale integrando le note equazioni di moto uniforme. Capitolo 4 “Analysis of past flash flood events”. Vengono qui presentate alcune analisi di eventi, distinte in tre sezioni. 4.1 Analisi di cinque eventi di piena improvvisa avvenuti in Romania nell’ambito del progetto europeo HYDRATE. Da questo studio risulta che, pur in presenza di scarsi dati provenienti dalle tradizionali fonti di monitoraggio idro-meteorologico, l’informazione proveniente da radar meteorologico e la modellistica idrologica possono aiutare nella ricostruzione delle dinamiche dell’evento preso in considerazione. 4.2 Analisi di una piena improvvisa avvenuta in Slovenia nel settembre 2007 per la quale, attraverso il progetto HYDRATE si è condotta un indagine post evento. La ricchezza di questo approccio, pur dispendioso in termini di tempo, mostra un possibile percorso per recuperare le maggior informazioni possibili per eventi di piena che non sono ricostruibili solo attraverso le normali reti di monitoraggio idrometeorologico. 4.3 Analisi attraverso un modello dettagliato di deflusso superficiale e sottosuperficiale della colata detritica avvenuta in due piccoli sottobacini nella valle del fiume Fella, colpita da una piena improvvisa il 29 agosto 2003. Lo studio consiste essenzialmente nel bilancio di massa liquido e solido durante le diverse fasi dell’evento. Capitolo 5 “Spatial variability in flash flood events”. Questa analisi sulla distribuzione spaziale della precipitazione è stata condotta con le medesime metodologie in due diversi bacini. Gli studi comprendono un primo approfondimento della variabilità spaziale della precipitazione all’interno di sottobacini di diversa estensione: la variabilità è descritta in funzione del reticolo idrografico del bacino preso in considerazione. Successivamente, attraverso un modello idrologico semplificato, si è valutata l’influenza della variabilità spaziale della precipitazione analizzando gli effetti dell’aggregazione spaziale in termini di precipitazione media su bacino e di portata al picco simulata. 5.3 Per l’analisi nel bacino del fiume Fella (FVG), colpito da una piena improvvisa il 29 agosto 2003, si sono scelti dieci sottobacini di dimensione variabile tra i 10.5 e i 623km². 5.4 Nel caso del fiume Cervo (Piemonte) lo studio ha riguardato tre eventi di piena con diversa variabilità spaziale della precipitazione e si è concentrato su quattro sottobacini (tra i 75 e i 983km²). Capitolo 6 “Conclusions”. Vengono riassunte le principali osservazioni ricavate dalle analisi descritte nei due capitoli precedenti e indicazioni per possibili future linee di ricerca.

An empirical method is developed for constructing likelihood functions required in a Bayesian probabilistic flash flood forecasting model using data on objective quantitative precipitation forecasts and their verification. Likelihoods based on categorical and probabilistic forecast information for several forecast periods, seasons, and locations are shown and compared. Data record length, forecast information type and magnitude, grid area, and discretized interval size are shown to affect probabilistic differentiation of amounts of potential rainfall. Use of these likelihoods in Bayes' Theorem to update prior probability distributions of potential rainfall, based on preliminary data, to posterior probability distributions, reflecting the latest forecast information, demonstrates that an abbreviated version of the flash flood forecasting methodology is currently practicable. For this application, likelihoods based on the categorical forecast are indicated. Apart from flash flood forecasting, it is shown that likelihoods can provide detailed insight into the value of information contained in particular forecast products.

Flash flooding in the semi-arid United States poses a significant danger to life and property. One effective way to mitigate flood risk is by implementing a rainfall-runoff model in a real-time forecast and warning system. This study investigated the feasibility of using the mechanistic, distributed semi-arid rainfall-runoff model KINEROS2 driven by high resolution radar rainfall input estimates obtained from the NEXRAD WSR-88D DHR reflectivity measurements in such a system. The original procedural paradigm-based KINEROS2 Fortran 77 code with space-time looping was recoded into an object-oriented Fortran 90 code with time-space looping for this purpose. The recoded form is now applicable to large basins, is easily future-extensible, and individual modules can be incorporated into other models.Sources of operational uncertainty in the above system were investigated for their influence over several events within a sub-basin of the USDA-ARS Walnut Gulch Experimental Watershed. Uncertainties considered were in the rainfall estimates, the model parameters, and the initial conditions. The variance-based Sobol' method of global sensitivity analysis conditioned on the observed streamflow showed that the uncertainty in the modeled response was heavily dominated by the operational variability of biases in the radar rainfall depth estimates. Sensitivities to KINEROS2 parameters indicates the need for improved representation of semi-arid hillslope hydrology in small basins, while pointing to specific influential, but poorly identified model parameters towards which field investigations should be directed. The significant influence of initial hillslope soil moisture showed the requirement of a sophisticated inter-storm model component for a continuous forecasting model.A synthetic study data was used to further explore the phenomena seen in the above real data study, of behavioral modifier set inconsistency across all events and of irreducibility in the spatial modifier ranges. The former was found to be attributable to wide uncertainty ranges in the sources of uncertainty, and the latter to the high distributed model non-linearity with associated interactions. These contribute towards a high predictive uncertainty in operational forecasting.Overall, the GLUE-based predictive uncertainty method with behavioral classification and accommodation of wide operational source uncertainty ranges is recommended as a simple and effective setup for operational flash flood forecasting.

The dangerous hazard posed by flash flooding to upland communities is likely to increase due to climate change. The flood risk management policy approach has become predominant since the 1990s, with an emphasis on the public awareness of, and responses to, flood risks; however, the unpredictable nature of upland flash flooding means that responses to such hazards are uncertain. This thesis uses an integrated analysis of social and physical science datasets to study responses by local residents and the Environment Agency to flash flooding, using a case study of a major upland flood in North Yorkshire. Responses to flash flooding within upland communities were found to be mostly present as changes to individual behaviour and awareness. However, physical, damage reducing modifications were limited. Flash flood hazard perception was found to be linked to knowledge and experience of local flooding. Major flash flood events occurring in areas which have not experienced other recent floods are unlikely to increase perceptions or provoke responses. Although local awareness of changing weather patterns was found, supporting analyses of rainfall records, local flood risks were frequently framed in the context of river management, rather than climate change. The implementation of policy changes and responses to flash flooding by the Environment Agency will prove difficult at the local level, due to the nature of attitudes and perceptions encountered at the local level, including important differences in the perception of the flash flood hazard between local residents and representatives from nationwide organisations. Encouraging property-level modifications following flash floods, in accordance with national policies, is very difficult. In order to increase local perceptions of the flash flood hazard, the use of participatory work, focusing on long-term awareness raising and the sharing of locally held flood knowledge may be beneficial, alongside the support of existing resilience in upland communities.

This study was conducted at the mountainous catchment part of Batinah Region of the Sultanate of Oman called Al-Awabi watershed which is about 260km2 in area with about 40 Km long Wadi main channel. The study paper presents a proposed modeling approach and possible scenario analysis which uses 1D - hydraulic modeling for flood routing analysis; and the main tasks of this study work are (1) Model setup for Al-Awabi watershed area, (2) Sensitivity Analysis, and (3) Scenario Analysis on impacts of rainfall characteristics and transmission losses. The model was set for the lower 24 Km long of Al-Awabi main channel (Figure 13). Channel cross-sections were the main input to the 1D-Hydraulic Model used for the analysis of flash flood routing of the Al-Awabi watershed. As field measurements of the Wadi channel cross-sections are labor intensive and expensive activities, availability of measured channel cross-sections is barely found in this study area region of Batinah, Oman; thereby making it difficult to simulate the flood water level and discharge using MIKE 11 HD. Hence, a methodology for extracting the channel cross-sections from ASTER DEM (27mX27m) and Google Earth map were used in this study area. The performance of the model setup was assessed so as to simulate the flash flood routing analysis at different cross-sections of the modeled reach. And from this study, although there were major gap and problems in data as well as in the prevailing topography, slope and other Hydro Dynamic parameters, it was concluded that the 1D-Hydraulic Modelling utilized for flood routing analysis work can be applied for the Al-Awabi watershed. And from the simulated model results, it was observed that the model was sensitive to the type of Boundary Condition chosen and taken, channel cross sections and its roughness coefficient utilized throughout the model reach.

AbstractFloods are frequent hazard in Algeria. They cause severe casualties, destroy infrastructures, and impair economies. In the past decades, Algeria experienced devastating floods. The dominant type of occurring floods are flash floods, which tend to be not well documented and studied in Algeria. This chapter presents a brief introduction to the flood phenomena within the Algerian climatic and management context, based on databases, scientific publications, and local technical reports. Existing studies about floods are reviewed. It also provides an analysis of the most disastrous floods that occurred in the past decades. Of the most noteworthy flash floods, a highlight of the Bab El Oued flash flood occurring in a heavily urbanized setting and the M’zab Valley flash flood, which took place in a UNESCO World Heritage Site. The monitoring network in Algeria is presented and data availability is discussed. The implementation of the first forecasting and early warning system are also presented. Different aspects of flash floods were presented including the effect of the increase of urbanization, the influence of climate change and the adopted strategies of flood risk management. Heavy and increasing urbanization and population growth increased the flood vulnerability and this trend must be mitigated.

AbstractFlash floods are unexpected, localized flood events that occur when an exceptional amount of rain falls happens over a short period of time. In South Asia, it is mostly disastrous, for example, in 2017 flash floods killed approximately 1200 people from India, Nepal, and Bangladesh. However, it is also common in Dhaka megacity, Bangladesh due to its geographic location, monsoon climatic condition and surrounding rivers. Though it is impossible to avoid them, the losses and damages of hazards can be reduced effectively by using appropriate techniques. This study aims to determine the responsible factors and measure the household vulnerability to flash flood as a tool of mitigation. The study has been conducted based on primary data. Therefore, data were collected from both slum and non-slum population to cover the entire urban habitats. Data were collected with a structured questionnaire based on five factors (social, economic, institutional, structural, and environmental) of vulnerability to flash flood. The key feature of this paper is to provide an insight into real picture of vulnerability to flash flood for urban habitants. Moreover, this practical approach is useful to quantify hazard-induced vulnerabilities not only for Dhaka megacity but also for other cities of the globe.

AbstractThe behaviors and impacts of flash floods (FF) are different based on the climatic regions. To understand such difference, two case studies were selected for the analysis: Wadi Uday, Oman and Sume Basin, Paraiba, Brazil. The rainfall-runoff inundation model (RRI) was used to simulate the discharge and flood inundation of the recent flood events to understand the severity and frequency of flash floods to better assess the current mitigation measures. The current FF situations in arid and semiarid basins were analyzed, and the hazards associated with flood phenomenon were assessed for various calculated rainfall return periods using RRI model. To this end, a flash flood index (average water depth per total basin area) was calculated as a basis to understand the impact of flash floods. A coupling of this index with the FF histories was included to provide a comprehensive overview of the FF vulnerability of arid and semiarid basins. We concluded that FFs tend to be more severe and extreme in arid regions than in semiarid regions, despite the lower frequency of FFs and the water scarcity in arid regions. Distributed dams also proved to be more effective in preventing FFs in arid regions than in semiarid regions.

AbstractIn the HKH region, large areas in Afghanistan, Bangladesh, China, India, Myanmar, Nepal, and Pakistan get inundated by floodwater during every rainy season. Among them, Bangladesh has been experiencing record-high floods where four types prevail: flash flood, local rainfall flood, monsoon river flood, and storm-surge flood; and these occur almost every year due to Bangladesh’s unique geographical setting as the most downstream country in the HKH region.

Flash floods are defined as rapidly developing extreme events caused by heavy or excessive amounts of rainfall. Flash floods usually occur over a relatively small area within six hours or less of the extreme event with quite a rapid streamflow rise and fall. Increased occurrence of flash flood events is expected due to climate change and increase in extreme precipitation events [1]. Flash flood forecasting is still a challenge for hydrologists and water professionals due to the complex nature of the event itself. Besides having sufficient background in hydrological and meteorological forecasting as well as information about local conditions yet an adequate approach for flash flood forecasting is needed. The Flash Flood Guidance System (FFGS) is widely recognized for enhancing the capacity to issue timely and accurate flash flood warnings by providing hydrological and meteorological forecasters with real-time information and products. FFGS is based on global data as well as national hydrometeorological data and analyses. In this paper the use of the Black Sea Middle East Flash Flood Guidance System (BSMEFFGS) products for flash flood forecasting by the hydrologists at the Hydrological Forecasting department at the National Institute of Meteorology and Hydrology, Bulgarian Academy of Sciences (NIMH) in Bulgaria is presented. An overview of the FFGS for Bulgaria with closer attention paid to the Flash Flood Guidance (FFG), Flash Flood Risk (FFR) and the Flash Flood Threat Products is introduced. Two case studies are also presented � a flash flood in the town of Shumen and another one in the area of the village of Popovitsa on September 28th 2015.

The flash flood forecasting remains one of the most difficult tasks in the operative hydrology worldwide. The torrential rainfalls bring high uncertainty included in both forecasted and measured part of the input rainfall data. The hydrological models must be capable to deal with such amount of uncertainty. The artificial intelligence methods work on the principles of adaptability and could represent a proper solution. The application of different methods, approaches, hydrological models and usage of various input data is necessary. The tool for real-time evaluation of the flash flood occurrence was assembled on the bases of the fuzzy logic. The model covers whole area of the Czech Republic and the nearest surroundings. The domain is divided into 3245 small catchments of the average size of 30 km2. Real flood episodes were used for the calibration and future flood events can be used for recalibration (principle of adaptability). The model consists of two fuzzy inference systems (FIS). The catchment predisposition for the flash flood occurrence is evaluated by the first FIS. The geomorphological characteristics and long-term meteorological statistics serve as the inputs. The second FIS evaluates real-time data. The inputs are: The predisposition for flash flood occurrence (gained from the first FIS), the rainfall intensity, the rainfall duration and the antecedent precipitation index. The meteorological radar measurement and the precipitation nowcasting serve as the precipitation data source. Various precipitation nowcasting methods are considered. The risk of the flash flood occurrence is evaluated for each small catchment every 5 or 10 minutes (the time step depends on the precipitation nowcasting method). The Fuzzy Flash Flood model is implemented in the Czech Hydrometeorological Institute (CHMI) – Brno Regional Office. The results are available for all forecasters at CHMI via web application for testing. The huge uncertainty inherent in the flash flood forecasting causes that fuzzy model outputs based on different nowcasting methods could vary significantly. The storms development is very dynamic and hydrological forecast could change a lot of every 5 minutes. That is why the fuzzy model estimates are intended to be used by experts only. The Fuzzy Flash Flood model is an alternative tool for the flash flood forecasting. It can provide the first hints of danger of flash flood occurrence within the whole territory of the Czech Republic. Its main advantage is very fast calculation and possibility of variant approach using various precipitation nowcasting inputs. However, the system produces large number of false alarms, therefore the long-term testing in operation is necessary and the warning releasing rules must be set.

Floods are one of the biggest natural disasters, causing significant economic and human losses. Regardless of the degree of development of urban or rural systems, floods account for about a third of all-natural disasters globally. Identifying areas vulnerable to floods is essential for better management and mitigation of their effects. The research aims to identify areas vulnerable to floods in the city of Codlea, Brașov County. Annually, the city records significant floods, one of the determining factors being its location, near the southern slope of the Perșani Mountains. The research proposes the Flash Flood Potential Index (FFPI) computation by combining GIS techniques with the Frequency Ration bivariate statistical model. The correlation of various flash-flood conditioning variables allowed us to compute the FFPI. The methodological approach could represent an essential tool for local authorities for better flood risk management.