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<strong class="journal-contentHeaderColor">Abstract.</strong> In recent years, flash floods repeatedly occurred in temperate regions of central western Europe. Unlike in Mediterranean catchments, this flooding behaviour is unusual. In the past, and especially in the 1990s, floods were characterized by predictable, slowly rising water levels during winter and driven by westerly atmospheric fluxes (Pfister et al., 2004). The intention of this study is to link the recent occurrence of flash floods in central western Europe to extreme precipitation and specific atmospheric conditions to identify the cause for this apparent shift. Therefore, we hypothesise that an increase in extreme precipitation events has subsequently led to an increase in the occurrence of flash flood events in central western Europe and all that being caused by a change in the occurrence of flash flood favouring atmospheric conditions. To test this hypothesis, we compiled data on flash floods in central western Europe and selected precipitation events above 40 mm h^&minus;1 from radar data (RADOLAN, DWD). Moreover, we identified proxy parameters representative for flash flood favouring atmospheric conditions from the ERA5 reanalysis dataset. High specific humidity in the lower troposphere (q &ge; 0.004 kg kg^&minus;1), sufficient latent instability (CAPE &ge; 100 J kg^&minus;1) and weak deep-layer wind shear (DLS &le; 10 m s^&minus;1) proved to be characteristic for long-lasting intense rainfall that can potentially trigger flash floods. These atmospheric parameters, as well as the flash flood and precipitation events were then analysed using linear models. Thereby we found significant increases in atmospheric moisture contents and increases in atmospheric instability. Parameters representing the motion and organisation of convective systems occurred slightly more often or remained unchanged in the time period from 1981&ndash;2020. Moreover, a trend in the occurrence of flash floods was confirmed. The number of precipitation events, their maximum 5-minute intensities as well as their hourly sums were however characterized by large inter-annual variations and no trends could be identified between 2002&ndash;2020. This study therefore shows that the link from atmospheric conditions via precipitation to flash floods cannot be traced down in an isolated way. The complexity of interactions is likely higher and future analyses should include other potentially relevant factors such as intra-annual precipitation patterns or catchment specific parameters.

In recent years, flash floods repeatedly occurred in temperate regions of central western Europe. Unlike in Mediterranean catchments, this flooding behaviour is unusual. In the past, and especially in the 1990s, floods were characterized by predictable, slowly rising water levels during winter and driven by westerly atmospheric fluxes (Pfister et al., 2004). The intention of this study is to link the recent occurrence of flash floods in central western Europe to extreme precipitation and specific atmospheric conditions to identify the cause for this apparent shift. Therefore, we hypothesise that an increase in extreme precipitation events has subsequently led to an increase in the occurrence of flash flood events in central western Europe and all that being caused by a change in the occurrence of flash flood favouring atmospheric conditions. To test this hypothesis, we compiled data on flash floods in central western Europe and selected precipitation events above 40 mm h−1 from radar data (RADOLAN, DWD). Moreover, we identified proxy parameters representative for flash flood favouring atmospheric conditions from the ERA5 reanalysis dataset. High specific humidity in the lower troposphere (q ≥ 0.004 kg kg−1), sufficient latent instability (CAPE ≥ 100 J kg−1) and weak deep-layer wind shear (DLS ≤ 10 m s−1) proved to be characteristic for long-lasting intense rainfall that can potentially trigger flash floods. These atmospheric parameters, as well as the flash flood and precipitation events were then analysed using linear models. Thereby we found significant increases in atmospheric moisture contents and increases in atmospheric instability. Parameters representing the motion and organisation of convective systems occurred slightly more often or remained unchanged in the time period from 1981–2020. Moreover, a trend in the occurrence of flash floods was confirmed. The number of precipitation events, their maximum 5-minute intensities as well as their hourly sums were however characterized by large inter-annual variations and no trends could be identified between 2002–2020. This study therefore shows that the link from atmospheric conditions via precipitation to flash floods cannot be traced down in an isolated way. The complexity of interactions is likely higher and future analyses should include other potentially relevant factors such as intra-annual precipitation patterns or catchment specific parameters.

&amp;lt;p&amp;gt;In the second half of the 20&amp;lt;sup&amp;gt;th&amp;lt;/sup&amp;gt; century, hydrological regimes in central Western Europe were largely characterised by large-scale winter floods. This type of event was predominantly triggered by westerly atmospheric fluxes, bringing moist and mild air masses from the Atlantic Ocean to the European continent. Since the late 1990&amp;amp;#8217;s, major flooding events seem to have shifted in time and magnitude. Flash flood events, while being a well-known phenomenon in Mediterranean catchments, are increasingly also reported at higher latitudes. Unlike the large-scale winter flood events, flash floods are of very narrow spatial extension and triggered by rather short, but highly intense rainfall events.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Here, we focus on the specific case of rivers in Luxembourg that have experienced several flash flood events in recent years, while only small to moderate winter flood events have been reported since the late 1990&amp;amp;#8217;s. National hydro-meteorological monitoring and flood forecasting systems have been designed for large-scale floods and are not suited for simulating local flash flood events. Therefore, there is a need to increase our understanding of the hydro-meteorological processes underlying flash flood occurrences in our area of interest.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;While increasing air temperature is known to allow a higher air moisture content that can lead to more intense rainfall events and possible flooding, we moreover hypothesize that the recent increase in flash flood occurrences in Luxembourg is reinforced by a change in atmospheric circulation patterns. To test this hypothesis, we analyse the prevailing atmospheric patterns on rainy days during summer and winter months over the period 1954 - 2019, with a particular focus on rainfall events that lead to moderate and extreme floods. In a next step, we intend to extend our findings for Luxembourg in a larger European context. This analysis should allow to better assess the current situation of hydrological extreme events in central Western Europe in order to take precaution measures and prepare for a diversifying hazard.&amp;lt;/p&amp;gt;

Introduction: Limited understanding exists regarding the association between extreme weather events and risk of Campylobacteriosis, particularly for communities in coastal regions. Methods: Laboratory culture-confirmed cases of Campylobacteriosis were obtained from the Maryland Foodborne Diseases Active Surveillance Network for Maryland from 2002 to 2012 along with clinical and demographic information. This data was combined with location and calendar day specific extreme temperature and precipitation events calculated using a 30-year baseline (1960-1989). Multivariate negative binomial regression utilizing generalized estimation equations was used to investigate the associations between Campylobacteriosis and extreme weather events. Results: There were 4,804 cases of Campylobacteriosis from 2002-2012 in Maryland. Through stratified analysis, we observed a 2% increase in risk of Campylobacteriosis for Non-Hispanic Whites associated with a one-unit increase in extreme precipitation events, but a marginally significant decrease in risk for extreme temperature events (IRR 0.98, 95% CI: 0.97, 1.00). For a one-unit increase in extreme precipitation events, this risk was considerably higher in the Eastern Shore region (IRR 1.05, 95% CI: 1.01, 1.09), and during the El Niño period (IRR 1.10, 95% CI: 1.06, 1.14). Discussion: Our data suggest that Campylobacteriosis is associated with extreme precipitation events in Maryland. The risk was more pronounced in the coastal areas and during El Niño periods. Extreme precipitation related flooding in coastal areas could bring water contaminated with bacterial pathogens (originating from point sources such as municipal wastewater treatment plants and animal feeding operations) into close proximity with individuals, where frequency of contact (via swimming or recreation) may be higher. Increased risk associated with the El Niño period could be related to the more intense precipitation events during this time period.

The Himalayan region, characterized by its substantial topographical scale and elevation, exhibits vulnerability to flash floods and landslides induced by natural and anthropogenic influences. The study focuses on the Himalayan region, emphasizing the pivotal role of geographical and atmospheric parameters in flash flood occurrences. Specifically, the investigation delves into the intricate interactions between atmospheric and surface parameters to elucidate their collective contribution to flash flooding within the Nainital region of Uttarakhand in the Himalayan terrain. Pre-flood parameters, including total aerosol optical depth, cloud cover thickness, and total precipitable water vapor, were systematically analyzed, revealing a noteworthy correlation with flash flooding event transpiring on October 17th, 18th, and 19th, 2021. Which resulted in a huge loss of life and property in the study area. Contrasting the October 2021 heavy rainfall with the time series data (2000–2021), the historical pattern indicates flash flooding predominantly during June to September. The rare occurrence of October flash flooding suggests a potential shift in the area's precipitation pattern, possibly influenced by climate change. Robust statistical analyses, specifically employing non-parametric tests including the Autocorrelation function (ACF), Mann–Kendall (MK) test, Modified Mann–Kendall, and Sen's slope (q) estimator, were applied to discern extreme precipitation characteristics from 2000 to 201. The findings revealed a general non-significant increasing trend, except for July, which exhibited a non-significant decreasing trend. Moreover, the results elucidate the application of Meteosat-8 data and remote sensing applications to analyze flash flood dynamics. Furthermore, the research extensively explores the substantial roles played by pre and post-atmospheric parameters with geographic parameters in heavy rainfall events that resulted flash flooding, presenting a comprehensive discussion. The findings describe the role of real time remote sensing and satellite and underscore the need for comprehensive approaches to tackle flash flooding, including mitigation. The study also highlights the significance of monitoring weather patterns and rainfall trends to improve disaster preparedness and minimize the impact of flash floods in the Himalayan region.

ABSTRACTThe present study aims to investigate how large‐scale atmospheric circulation may influence flash floods in Portugal. For this purpose, weather types (WTs) in a northeastern North Atlantic sector are used and flash floods between 1950 and 2003 were identified in six hydrographic basins: three in the north of Portugal and another three in the south of Portugal. An adapted methodology for flash flood detection on daily discharges is applied. A total of 131 flash floods were detected: 35 in the northern basins and 96 in the southern basins. WTs are identified using the National Oceanic and Atmospheric Administration 20th Century Reanalysis V2. The sea level pressure composites for flash flood days by WT reveal the large‐scale atmospheric patterns underlying their occurrence. The results show that the cyclonic (C) type was strongly associated with flash flood days in the northern basins. The C type pattern features deep low pressure systems north of Iberia, much stronger than average for this WT. For the southern basins, the C type still shows the highest relevance for flood occurrence, but to a lesser extent, since the easterly wind (E) and dual anticyclonic (AA) types also acquire some importance. The flash flood‐inducing AA‐type events are characterized by atypical largely zonal troughs extending towards Portugal. The flash flood‐inducing E type events hint at the occurrence of anomalously strong cut‐off low pressure systems over southern Portugal. Although the significance of these systems to precipitation in Portugal was addressed in previous studies, a systematized assessment of their role on flash flood occurrences is herein provided for the first time. The presented flash flood detection methodology can be applied to other regions where hourly flow discharge data are not available, thus being an alternative to the more conventional detection algorithms.

The present study aims to analyse the human perceptions and adaptations to recurrent devastating flash floods in Khyber Agency, FATA. The study is mainly based on both primary data sources including field observations, structured questionnaire survey and focus group discussions supported by secondary data sources. Three hundred adult residents in five sample villages along Chora River and its tributaries were interviewed by using a structured questionnaire which covered approximately 20% of the total households. Respondents’ perceptions were investigated about the occurrence of flash floods, flood damages, nature of affinity towards flood prone areas and adaptation strategies. Cartographic and statistical techniques were applied to process and analyze the data. As a result, the data were analytically discussed and presented in the form of tables, maps and plates. The analysis reveals that people of the area perceived about the recurrence of future flash floods during rainy season. Most of the people perceived the flash floods as it hit the study area with devastating impacts and the extent of flood damages. In spite of flood risk, the level of affinity towards living in the flood prone area was found high among the community as they have blood ties with the land, kith and kinship. In the study area, people had adopted various flood mitigation strategies to reduce the devastating impacts of flash floods. However, the resident had greater motivations and concern on socio-economic factors rather than adjustments to frequent flash flood.

This study examines the potential impacts of climate change on the characteristics of precipitation over the Drakensberg Mountain Range (DMR) at different global warming levels (GWLs: 1.5, 2.0, 2.5 and 3.0°C) under the Representative Concentration Pathway 8.5 (RCP8.5) scenario, using dynamical and statistical downscaled datasets. The dynamical datasets consist of 19 multi‐model simulations datasets from the Coordinated Regional Climate Downscaling Experiment (CORDEX), whereas the statistical downscaled datasets comprise 19 multi‐model simulations from the National Aeronautics and Space Administration (NASA) Earth Exchange (NEX) Global Daily Downscaled Projections (NEX‐GDDP, hereafter NEX). The capacity of the CORDEX and NEX datasets to represent past characteristics of extreme precipitation over the DMR was evaluated against eight observation datasets. The precipitation characteristics were represented by eight precipitation indices. Both CORDEX and NEX realistically capture the characteristics of extreme precipitation over the Drakensberg and, in most cases, their biases lie within the observation uncertainty. However, NEX performs better than CORDEX in reproducing most of the precipitation characteristics, except in simulating the threshold of extreme rainfall. The ensemble means of CORDEX and NEX agree on a future increase in the intensity of normal precipitation, in the frequency and intensity of extreme precipitation, as well as an increase in widespread extreme events, with a decrease in the number of precipitation days and continuous wet days. However, they disagree on the projected changes of annual precipitation, for which CORDEX projects an increase over most parts of the DMR, whereas NEX indicates a decrease. The self‐organizing‐map analysis, which reveals diversity in the projection patterns hidden in the ensemble means, shows the most probable combinations of projected changes in the annual precipitation and extreme precipitation events (in terms of intensity and frequency): (a) increase in both annual precipitation and extreme precipitation events; (b) decrease in both annual precipitation and extreme precipitation events; (c) decrease in annual precipitation but increase in extreme precipitation events. The results of this study can thus provide a basis for developing climate change adaptation and mitigating strategies over the DMR.

An analysis of extreme daily precipitation events that occurred in the south-central United States during May and June 2010 is carried out using gridded station data and reanalysis products in use at the National Centers for Environmental Prediction (NCEP). Various aspects of the daily extremes are examined from a climate perspective using a 62-yr (1948–2010) period of record, including their historical ranking, common circulation features, moisture plumes, and the possible influence of ENSO. The analysis also considers how the frequency and intensity of daily extremes is changing in the United States. Each of the 2010 flash flood events examined here was associated with historic daily rainfall totals. Several of the events had meteorological conditions in common at upper and lower levels of the atmosphere, and all of the events fit well into an existing classification scheme for heavy precipitation events associated with flash flooding. Each case exhibited characteristics of the “Maya Express” flood events that link tropical moisture plumes from the Caribbean and Gulf of Mexico to midlatitude flooding over the central United States. Consistent with recent assessment reports, it is shown that extreme daily precipitation events in the United States have increased in frequency during the most recent 30-yr period (1980–2009) when compared to the previous 30-yr period (1950–79), though the increases are relatively small during May and June.

The geographical distribution of a flash flood's occurrence could be an important consideration in assessing its severity and social impacts. In this study, the spatial distribution of survey responses is analysed with respect to features such as the stream network (natural water path), the drainage network, buildings, and catchments. This provides information on both flash flood distribution causes in an urban setting and residents' perceptions of the hazard that would otherwise not be revealed. The study demonstrated the possibility of taking into account people's experience in detecting the location of potential flash flood hazards. It also illustrates the usefulness of GIS-supported spatial analysis of survey results in identifying factors that increase the occurrence of urban flash floods.

Quantifying regional-scale flash flood susceptibility using watershed geomorphometry-based approach along the high range, west of Chiang Mai Basin, Northern Thailand

This paper was initially motivated by a flash flood index (FFI) study performed by Bhaskar et al. and others that explained flash floods using a runoff perspective by extracting a rising curve gradient, the flood magnitude ratio, and flood response time variables from runoff hydrograph. However, the runoff data are not sufficient to estimate a robust flood magnitude ratio in Korea. In addition, the existing model is not able to consider high rainfall intensity, which is an important flash flood characteristic in Korea. Flood magnitude ratio variables, thus, were replaced by rainfall intensity variables. Then, the results were compared with the existing FFI. The spatial distribution of the flood event in the Han River basin that occurred in July 2006 showed that a modified FFI, which reflects rainfall characteristics, outperformed in representing damaged (flash flood occurrence) areas in the past. Furthermore, the FFI for three different time windows (early, middle, and late periods) for the Han River basin during the localised intensive rainfall in July 2006 were analysed. Analysis of spatiotemporal distribution showed that sudden intensity was pronounced in the Seoul area during the first 10 days of July. During the second 10 days of July, a probable high‐intensity flash flood appeared in the Gangwon‐do area. Meanwhile, an onsite survey of the Gangwon‐do area showed that the actual occurrences of a high‐intensity flash flood were largely in agreement with the predictions made by the model.

Flash floods that hit parts of South Sulawesi on July 13, 2020, left 36 people dead, 18 people lost, 40 people missing, 58 injured, and a total of 14,483 people were affected. Around 14,000 people were evacuated to safer locations due to not having a home to live in. The disaster was caused by heavy rains. One of the areas affected was North Luwu. This phenomenon needs to be done research so that people can overcome the possibility of disasters that might occur. Air pressure and air temperature for 2 days before the occurrence of flash floods have the same relative patterns and anomalies occurred on the day of the incident. This research uses satellite image data interpretation method by processing the Himawari-8 infrared channel data and compared with rainfall data from the Andi Jemma meteorological station in North Luwu Regency on July 13, 2020. Interpretation and analysis of satellite imagery data shows the growth of strong convective clouds has the potential to cause rain in North Luwu around 07.00 UTC. So it was concluded that during a flash flood, unstable atmospheric conditions and the presence of Cumulonimbus (CB) cloud cover in the North Luwu region.

PurposeThe Ethiopian highlands are a fragile environment characterized by steep slopes, intense rainfall, a sparse vegetation cover, and the occurrence of flash floods. Although important efforts have been made to mitigate the ongoing soil erosion and land degradation problems, the sediment dynamics at medium-sized catchment scale (100–10,000 km2) are not fully understood. Therefore, this study aims to provide a better understanding of sediment export processes and the importance of flash flood events in semi-arid tropical catchments.Materials and methodsMeasuring campaigns were conducted in ten sub-catchments of the Geba, a tributary of the Tekeze, representative of the northern Ethiopian highlands. During two to four rainy seasons, the rivers were sampled for their suspended sediment concentration (SSC) and runoff discharge.Results and discussionVariations in SSC and sediment grain size distribution indicate changes in sediment supply during the rainy season due to the depletion of readily available sediments and the development of a vegetation cover. Also, during flood events, changes in sediment supply are observed. Sediment yields (i.e., 497–6,543 t km−2 year−1) are higher than suggested by previous studies and correlate with rainfall depth. The majority of sediment export occurs during a few short but intense flash floods. No clear effect of implemented soil and water conservation measures could be detected in the sediment yields of the catchments.ConclusionsSediment export rates in the Ethiopian highlands are high, are characterized by important changes in sediment supply, and are mainly controlled by the occurrence and magnitude of flash flood events. Mitigation measures to reduce sediment yield at the catchment scale should therefore not only focus on the reduction of hillslope erosion rates but also on the magnitude of these floods.

One of external factors which contribute to the occurrence of floods and flash floods at Garangwatersheds is socio hidraulic character (water culture). The inhabitants water culture of the Garangwatersheds belongs to the low category. It is reflected from several behaviors: they channels velocity thesurface runoff to the river, lack to act on environment and small river conservation, garbage disposal tothe river and they are not making every effort infiltrated the surface runoff. Keywords : Water culture, watersheds, infiltration, surface runoff, flash flood