Assessing the benefits of coupling hydrological and hydrodynamic model approaches for an improved simulation of flash floods

Heavy rainfall and resulting flash flood events have been in the focus of research and the public in recent years. The relevance of the topic will become more prominent with increasing temperatures due to climate change. Extreme rainfall events in Germany like 2014 in M&#252;nster (North Rhine-Westphalia) or 2016 in Simbach am Inn (Bavaria) and Braunsbach (Baden-Wurttemberg) have also raised public awareness.Hydrodynamic models for the simulation of fluvial events have been developed for a long time and are often used. However, the question arises to what extent these methods can be used for pluvial events. Hydrodynamic models allowing precipitation input are therefore well suited for the simulation of pluvial events, as they can display flow paths, depths, and velocities in high resolution. Nevertheless, defining precipitation without infiltration leads to an overestimation of the surface runoff. For this problem, an improved event simulation can be achieved by nesting hydrological processes into the hydrodynamic simulation procedure. In this study, we are using TELEMAC-2D as a hydrodynamic model because it uses precipitation in a spatially and temporally distributed manner and can be used very well by high-performance computing. LARSIM (Large Area Runoff Simulation Model) and WaSiM (Water Flow and Balance Simulation Model) are used as hydrological models.The methodology for simulating flash floods can be divided into two important processes: runoff generation and runoff concentration. These are divided according to the strength of the respective model types:<ul><li>Runoff generation: SCS-CN value method (TELEMAC-2D), Green Ampt method (LARSIM), layer-resolving Richards method (WaSiM)</li> <li>Runoff concentration: Strickler roughness approach (TELEMAC-2D), Kalinin-Miljukov method (LARSIM), flow time index method (WaSiM)</li> </ul>In this study, we examine three different types of couplings:<ul><li>(1) The runoff concentration is calculated using the hydrodynamic model, the runoff generation is carried out using the CN value method.</li> <li>(2) The runoff generation in the entire catchment is calculated using the hydrological processes (LARSIM/WaSiM). The runoff concentration is still generated by the hydrodynamic model.</li> <li>(3) The runoff concentration in the upper catchment area is also calculated using hydrological methods, only the urban area is calculated hydrodynamically.</li> </ul>We compare the different coupling types with each other using some real flash flood events. The results are presented with the aim to identify which approach is necessary for a good representation of the flash flood event. This depends mainly on the local conditions in the catchment area (e.g.&#160; culverts, land use) and the rainfall event (e.g. rainfall intensity and duration). The findings from this study will be transferred to unobserved catchments in the further course.

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Hydrodynamic rainfall-runoff modeling using different approaches for runoff creation

10.5194/egusphere-egu2020-21732 ◽

2020 ◽

Author(s):

Karl Broich ◽

Thomas Pflugbeil ◽

Johannes Mitterer ◽

Markus Disse

Keyword(s):

Water Depth ◽

Surface Runoff ◽

Flash Flood ◽

Flash Floods ◽

Rainfall Runoff ◽

Runoff Generation ◽

Hydrodynamic Models ◽

Additional Advantage ◽

Runoff Modeling ◽

Scs Cn

After extreme flash floods events 2016 in Bavaria, the cooperation project HiOS (reference map for surface runoff and flash floods) was started aiming at the detailed analysis of risk generated by flash floods using GIS methods as well as hydrological and hydrodynamic models. Part of the risk analysis is done using hydrodynamic rainfall-runoff modeling (HDRRM). HDRRM gets more and more popular since hydrodynamic models are able to accept rainfall as input. But most of the known hydrodynamic models have no integrated precipitation modules and therefore cannot be used uniquely for rainfall-runoff modeling. In this study, TELEMAC-2D is used for HDRRM because it already contains the SCS-CN-method and offers the possibility to implement new precipitation modules due to its open source license. An additional advantage of TELEMAC-2D is the good scaling on HPC cluster systems.In this study, two different approaches for runoff creation will be compared. (1) The well-proven SCS-CN method calculates effective rain. Due to its simple structure, the process of runoff generation is completely decoupled from runoff concentration. Consequently, SCS-CN cannot account for re-infiltration due to surface runoff. (2) However, the Green-Ampt infiltration (GAI) is coupled to surface runoff as long as the water depth is non-zero. GAI is implemented recently and thus will be described in more detail. Both approaches are first tested using a simple model setup. The general model performance of the enhanced hydrodynamic rainfall-runoff modeling (EHDRRM) is verified using the case study Simbach/Triftern in Bavaria. This extreme flash flood event from 1st June 2016 hit the townships Simbach am Inn and Triftern. It is well documented and all necessary data is available in good quality. The main setup for the catchment area of 47&#160;km&#178; resp. 90&#160;km&#178; is built on a 1x1&#160;m DEM, land use data, hydrological soil group data and 5&#160;min-RADOLAN precipitation data. The calculated catchment outflow can be verified by measured data at the gauging stations in Simbach am Inn resp. Triftern. All comparisons include as reference results for precipitation without losses by infiltration.The hydrodynamic precipitation runoff modeling HDRRM has proven to be a useful method for calculating flow paths, depths and velocities with a high spatial resolution during flash flood events. If the process of runoff generation is performed by the hydrodynamic model EHDRRM then the quality of results is improved significantly while keeping the modeling procedure simple. Concerning infiltration, EHDRRM allows for a physically correct representation taking the actual local water depth into consideration.

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Characteristics and influencing factors of flash floods in Bavaria (Germany) – an analysis using a hydrological-hydraulic model ensemble

10.5194/egusphere-egu2020-13267 ◽

2020 ◽

Author(s):

Johannes Mitterer ◽

Karl Broich ◽

Thomas Pflugbeil ◽

Fabian von Trentini ◽

Florian Willkofer ◽

...

Keyword(s):

Water Balance ◽

Hydrodynamic Model ◽

Flash Flood ◽

Flash Floods ◽

Individual Characteristics ◽

Runoff Generation ◽

Retention Capacity ◽

Index Method ◽

Area Of Interest ◽

Water Balance Models

In recent years, heavy precipitation and flash flood events frequently occurred in Germany. The project HiOS (reference map for surface runoff and flash floods) focusses on the analysis of these events using conceptual lumped precipitation runoff models, distributed raster-based water balance models (LARSIM and WaSiM), as well as a hydrodynamic model internally coupled with infiltration routines (TELEMAC-2D). The objective of our research is to analyze which factors and processes foster flash floods, and how they may be represented in models. We show a comprehensive methodological comparison using simulation results of some events in Bavaria. These do not include erosion and log jam scenarios.The catchments distributed across whole Bavaria considering a variety of catchment characteristics and varying in size between 1.2 and 164km&#178;. All models are driven by 5 minute pseudo-calibrated radar precipitation data of the German Weather Service (YW product), which are available for entire Germany in a 1km&#178; raster. The distributed water balance models are available using high-resolution cell grids. WaSiM uses a regular grid size of 50m, whereas LARSIM is run using 100m cells and an embedded hydrological response unit scheme. All TELEMAC-2D meshes are built with a standard mesh size of 5m in the catchment and 2m in the settled area of interest, while important hydrodynamic structures are resolved more in detail.We want to highlight the variety of applied hydrological and hydrodynamic model approaches of runoff generation and concentration, whereby both, simple conceptual and complex physical methods are included. Runoff generation processes are represented using the SCS-CN method, a modified Lutz-S&#252;dbayern approach, a Xinjiang-bucket model combined with a Green&Ampt infiltration routine, as well as a layer-resolving Richards model. Beyond that, some of these consider silting up and soil crack formation. Runoff concentration processes are assessed by constant translation, Strickler flow time index method, a combination of Williams and Kalinin-Miljukov method, as well as finally with two-dimensionally resolved shallow water equations.As expected, runoff generation is influenced by land use and soil parametrization. However, the amount of created runoff differs a lot changing the method of simulation. Furthermore, the runoff volume reacts quite sensitive to small changes in the preceding saturation conditions. Runoff concentration is influenced by slope, retention capacity of the flood plain, the network of drainages, as well as the formation of polders by water-crossing structures such as traffic infrastructure. Our results therefore clearly show the individual characteristics of extreme events depending on the catchment properties, which are reflected by the demands concerning the modelling techniques. The findings of this study illustrate the importance of improved radar-derived precipitation observations as well as the need for a spatially distributed and layered soil moisture product to enhance flash flood modelling using hydrological models.

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Automating the creation of channel cross section data from aerial laser scanning and hydrological surveying for modeling flood events / Automatická tvorba geometrie vodních toků na základě syntézy dat z leteckého laserového skenování a hydrologického měření pro modelování povodňových událostí. j. hydrol., hydromech., 60, 2012, 4; 25 lit., 8 obr., 5 tab.

Journal of Hydrology and Hydromechanics ◽

10.2478/v10098-012-0020-5 ◽

2012 ◽

Vol 60 (4) ◽

pp. 227-241 ◽

Cited By ~ 5

Author(s):

Radek Roub ◽

Tomáš Hejduk ◽

Pavel Novák

Keyword(s):

Flow Rate ◽

Hydrodynamic Model ◽

Input Data ◽

Laser Scanning ◽

Digital Terrain Model ◽

Flood Events ◽

Hydrodynamic Models ◽

Terrain Model ◽

Aerial Laser Scanning ◽

Digital Terrain

Knowing the extent of inundation areas for individual N-year flood events, the specific flood scenarios, and having an idea about the depths and velocities in the longitudinal or transverse water course profile provided by hydrodynamic models is of key importance for protecting peoples’ lives and mitigating damage to property. Input data for creating the watercourse computational geometry are crucial for hydrodynamic models. Requirements for input data vary with respect to the hydrodynamic model used. One-dimensional (1D) hydrodynamic models in which the computing track is formed by cross-sectional profiles of the channel are characterized by lower requirements for input data. In two-dimensional (2D) hydrodynamic models, a digital terrain model is needed for the entire area studied. Financial requirements of the project increase with regard to the input data and the model used. The increase is mainly due to the high cost of the geodetic surveying of the stream channel. The paper aims at a verification and presentation of the suitability of using hydrological measurements in developing a schematization (geometry) of water courses based on topographic data gained from aerial laser scanning provided by the Czech Office for Surveying, Mapping and Cadastre. Taking into account the hydrological measurement during the schematization of the water course into the hydrodynamic model consists in the derivation of flow rate achieved at the time of data acquisition using the method of aerial laser scanning by means of hydrological analogy and in using the established flow rate values as a basis for deepening of the digital terrain model from aerial laser scanning data. Thus, the given principle helps to capture precisely the remaining part of the channel profile which is not reflected in the digital terrain model prepared by the method of aerial laser scanning and fully correct geometry is achieved for the hydrodynamic model.

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Post-event analysis and flash flood hydrology in Slovakia

Journal of Hydrology and Hydromechanics ◽

10.1515/johh-2016-0041 ◽

2016 ◽

Vol 64 (4) ◽

pp. 304-315 ◽

Cited By ~ 8

Author(s):

Kamila Hlavčová ◽

Silvia Kohnová ◽

Marco Borga ◽

Oliver Horvát ◽

Pavel Šťastný ◽

...

Keyword(s):

Hydrological Model ◽

Flash Flood ◽

Flash Floods ◽

Event Analysis ◽

Distributed Hydrological Model ◽

Rainfall Runoff ◽

Flood Events ◽

Spatially Distributed ◽

Catchment Size ◽

Flood Peaks

Abstract This work examines the main features of the flash flood regime in Central Europe as revealed by an analysis of flash floods that have occurred in Slovakia. The work is organized into the following two parts: The first part focuses on estimating the rainfall-runoff relationships for 3 major flash flood events, which were among the most severe events since 1998 and caused a loss of lives and a large amount of damage. The selected flash floods occurred on the 20th of July, 1998, in the Malá Svinka and Dubovický Creek basins; the 24th of July, 2001, at Štrbský Creek; and the 19th of June, 2004, at Turniansky Creek. The analysis aims to assess the flash flood peaks and rainfall-runoff properties by combining post-flood surveys and the application of hydrological and hydraulic post-event analyses. Next, a spatially-distributed hydrological model based on the availability of the raster information of the landscape’s topography, soil and vegetation properties, and rainfall data was used to simulate the runoff. The results from the application of the distributed hydrological model were used to analyse the consistency of the surveyed peak discharges with respect to the estimated rainfall properties and drainage basins. In the second part these data were combined with observations from flash flood events which were observed during the last 100 years and are focused on an analysis of the relationship between the flood peaks and the catchment area. The envelope curve was shown to exhibit a more pronounced decrease with the catchment size with respect to other flash flood relationships found in the Mediterranean region. The differences between the two relationships mainly reflect changes in the coverage of the storm sizes and hydrological characteristics between the two regions.

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Effectiveness of the Submersible Embankment in Haor Area in Bangladesh

Journal of Disaster Research ◽

10.20965/jdr.2018.p0780 ◽

2018 ◽

Vol 13 (4) ◽

pp. 780-792

Author(s):

Mohammad Hossain Mahtab ◽

Miho Ohara ◽

Mohamed Rasmy ◽

◽

Keyword(s):

Flash Flood ◽

Flash Floods ◽

Rainfall Runoff ◽

Flood Events ◽

Monsoon Period ◽

Flash Flooding ◽

The North ◽

North Eastern ◽

Embankment Height ◽

North Eastern Part

The north-eastern part of Bangladesh is very productive for agriculture and fishing, and the region involves several depressed (haor) areas. Flash floods during the pre-monsoon period bring devastating damage to agriculture in the haor region recurrently. To protect crops from flash floods, the Bangladesh Water Development Board constructed several ring-type submersible embankments. In this research, we have investigated the effectiveness of submersible embankments in controlling flash flooding in the Matian and Shanir haors in the Sunamganj district. A two-dimensional rainfall runoff inundation model was applied considering several scenarios for simulating heavy flash flood events in 2004, 2010, and 2016. Without an embankment, the river overflow would have entered the Matian haor 3 days, 22 days, and 9 days earlier in 2004, 2010, and 2016, respectively, whereas it would have been 7 days and 23 days earlier in 2004 and 2010 for the Shanir haor. The event in 2016 was successfully stopped by the Shanir haor embankment. To avoid river overflow entering into the Matian and Shanir haor completely, the embankment height must be elevated further by 1 m and 0.7 m, respectively. Providing proper drainage facilities for the accumulated rain water inside the hoar is still an important issue for protecting the crops effectively.

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Impact of Flash Flood Events on the Coastal Waters Around Madeira Island: The “Land Mass Effect”

Frontiers in Marine Science ◽

10.3389/fmars.2021.749638 ◽

2022 ◽

Vol 8 ◽

Author(s):

Alexandra Rosa ◽

Cláudio Cardoso ◽

Rui Vieira ◽

Ricardo Faria ◽

Ana R. Oliveira ◽

...

Keyword(s):

Chlorophyll A ◽

Coastal Waters ◽

Flash Flood ◽

Mass Effect ◽

Flash Floods ◽

River Plume ◽

Flood Events ◽

Madeira Island ◽

The Impact ◽

Land Runoff

The Island Mass Effect has been primarily attributed to nutrient enhancement of waters surrounding oceanic islands due to physical processes, whereas the role of land runoff has seldom been considered. Land runoff can be particularly relevant in mountainous islands, highly susceptible to torrential rainfall that rapidly leads to flash floods. Madeira Island, located in the Northeast Atlantic Ocean, is historically known for its flash flood events, when steep streams transport high volumes of water and terrigenous material downstream. A 22-year analysis of satellite data revealed that a recent catastrophic flash flood (20 February 2010) was responsible for the most significant concentration of non-algal Suspended Particulate Matter (SPM) and Chlorophyll-a at the coast. In this context, our study aims to understand the impact of the February 2010 flash flood events on coastal waters, by assessing the impact of spatial and temporal variability of wind, precipitation, and river discharges. Two specific flash floods events are investigated in detail (2 and 20 February 2010), which coincided with northeasterly and southwesterly winds, respectively. Given the lack of in situ data documenting these events, a coupled air-sea-land numerical framework was used, including hydrological modeling. The dynamics of the modeled river plumes induced by flash floods were strongly influenced by the wind regimes subsequently affecting coastal circulation, which may help to explain the differences between observed SPM and Chlorophyll-a distributions. Model simulations showed that during northeasterly winds, coastal confinement of the buoyant river plume persisted on the island’s north coast, preventing offshore transport of SPM. This mechanism may have contributed to favorable conditions for phytoplankton growth, as captured by satellite-derived Chlorophyll-a in the northeastern coastal waters. On the island’s south coast, strong ocean currents generated in the eastern island flank promoted strong vertical shear, contributing to vertical mixing. During southwesterly winds, coastal confinement of the plume with strong vertical density gradient was observed on the south side. The switch to eastward winds spread the south river plume offshore, forming a filament of high Chlorophyll-a extending 70 km offshore. Our framework demonstrates a novel methodology to investigate ocean productivity around remote islands with sparse or absent field observations.

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From Flash Flood Vulnerability and Risk Assessment to Property Damage Prediction: the Value of Machine Learning

10.5194/egusphere-egu2020-19057 ◽

2020 ◽

Author(s):

Atieh Alipour ◽

Peyman Abbaszadeh ◽

Ali Ahmadalipour ◽

Hamid Moradkhani

Keyword(s):

Machine Learning ◽

Flash Flood ◽

Rapid Onset ◽

Flash Floods ◽

Flood Damage ◽

Flood Events ◽

Property Damage ◽

Damage Prediction ◽

Financial Consequences

Flash floods, as a result of frequent torrential rainfalls caused by tropical storms, thunderstorms, and hurricanes, are a prevalent natural disaster in the southeast U.S. (SEUS), which frequently threaten human lives and properties in the region. According to the U.S. National Weather Service (NWS), flash floods generally initiate within less than six hours of an intense rainfall onset. Therefore, there is a limited chance for effective and timely decision-making. Due to the rapid onset of flash floods, they are costly events, such that only during 1996 to 2017 flash floods imposed 7.5 billion dollars property damage to the SEUS. Therefore, estimating the potential economic damages as a result of flash floods are crucial for flood risk management and financial appraisals for decision makers. A multitude of studies have focused on flood damage modeling, few of which investigated the issue on a large domain. Here, we propose a systematic framework that considers a variety of factors that explain different risk components (i.e., hazard, vulnerability, and exposure) and leverages Machine Learning (ML) for flood damage prediction. Over 14,000 flash flood events during 1996 to 2017 were assessed to analyze their characteristics including frequency, duration, and intensity. Also, different data sources were utilized to derive information related to each event. The most influential features are then selected using a multi criteria variable selection approach. Then, the ML model is implemented for not only binary classification of damage (i.e., whether a flash flood event caused any damage or not), but also for developing a model to predict the financial consequences associated with flash flood events. The results indicate a high accuracy for the classifier, significant correlation and relatively low bias between the predicted and observed property damages showing the effectiveness of proposed methodology for flash flood damage modeling applicable to variety of flood prone regions.

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Bias Correction of Satellite-Based Rainfall Estimates for Modeling Flash Floods in Semi-Arid regions: Application to Karpuz River, Turkey

10.5194/nhess-2016-339 ◽

2016 ◽

Cited By ~ 7

Author(s):

Mohamed Saber ◽

Koray Yilmaz

Keyword(s):

Bias Correction ◽

Flash Flood ◽

Flash Floods ◽

Rainfall Rate ◽

Assessment Model ◽

Model Parameters ◽

Flood Events ◽

Rain Gauges ◽

Semi Arid ◽

Rainfall Estimates

Abstract. This study investigates the utility of gauge-corrected satellite-based rainfall estimates in simulating flash floods at Karpuz River - a semi-arid basin in Turkey. Global Satellite Mapping of Precipitation (GSMaP) product was evaluated with the rain gauge network at monthly and daily time-scales considering various time periods and rainfall rate thresholds. Statistical analysis indicated that GSMaP shows acceptable linear correlation coefficient with rain gauges however suffers from significant underestimation bias. A rainfall rate threshold of 1 mm/month was the best choice to improve the match between GSMaP and rain gauges implying that appropriate threshold selection is critically important for the bias correction. Multiplicative bias correction was applied to GSMaP data using the bias factors calculated between GSMaP and observed rainfall. Hydrological River Basin Environmental Assessment Model (Hydro-BEAM) was used to simulate flash floods at the hourly time scale driven by the corrected GSMaP rainfall data. The model parameters were calibrated for flash flood events during October-December 2007 and then validated for flash flood events during October-December 2009. The results show that the simulated surface runoff hydrographs reasonably coincide with the observed hydrographs.

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More frequent flash flood events and extreme precipitation favouring atmospheric conditions in temperate regions of Europe

10.5194/hess-2021-628 ◽

2021 ◽

Author(s):

Judith Meyer ◽

Malte Neuper ◽

Luca Mathias ◽

Erwin Zehe ◽

Laurent Pfister

Keyword(s):

Extreme Precipitation ◽

Western Europe ◽

Flash Flood ◽

Flash Floods ◽

Water Levels ◽

Specific Humidity ◽

Atmospheric Conditions ◽

Flood Events ◽

Extreme Precipitation Events ◽

Precipitation Events

Abstract. 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.

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Identifying and linking flash flood prone atmospheric conditions to flooding occurrences in central Western Europe

10.5194/egusphere-egu21-12522 ◽

2021 ◽

Author(s):

Judith Meyer ◽

Audrey Douinot ◽

Malte Neuper ◽

Luca Mathias ◽

Carol Tamez-Meléndez ◽

...

Keyword(s):

River Basin ◽

Western Europe ◽

Flash Flood ◽

Flash Floods ◽

Precipitation Data ◽

Atmospheric Conditions ◽

Flood Events ◽

Atmospheric Parameters ◽

Circulation Patterns ◽

Daily Precipitation Data

In recent years, flash floods occurred repeatedly in temperate regions of central Western Europe (e.g., Orlacher Bach (GER), Hupselsebeek (NL), White Ernz (LUX)). This type of extreme flood events is unusual for these regions, as opposed to Mediterranean catchments that are more prone to flash floods. In the second half of the 20th century, and more specifically in the 1990&#8217;s, westerly atmospheric fluxes were the dominating triggering factor of large scale (winter) floods in central Western Europe.With a view to gain a better understanding of the mechanisms controlling the recent flash flood events at higher latitudes, we explore various avenues related to the non-stationarity of environmental systems. We hypothesize that an increase in the occurrence of flash flood prone atmospheric conditions has recently led to higher precipitation totals and a subsequent increase in flash flood events in central Western Europe.Therefore, we first analysed relevant atmospheric parameters from the ERA 5 reanalysis dataset. Second, we linked the atmospheric parameters to the concept of general circulation patterns as per Hess and Brezowsky (1977). Third, we analysed precipitation data from a set of stations located in the Moselle river basin (35.000 km2). These three pillars build the base for identifying flash flood prone atmospheric conditions over space and time that are then compared to actual occurrences of extreme discharge events in streams within the Moselle river basin.To validate our hypothesis, spatial and temporal patterns in the occurrence of extreme precipitation and discharge events need to match atmospheric patterns. Preliminary results suggest that daily precipitation data and meridional circulation patterns do not show a clear trend towards an increased occurrence of precipitation events or higher precipitation amounts. Due to the limitations inherent to the available long-term dataset of daily data, the hypothesis can only be partly evaluated, and more detailed analyses are added. For that reason, discharge data with a 15-minute resolution, along with precipitation radar data of 5-minute time steps will be employed at a limited spatial extent in future analyses. In case of rejection of our working hypothesis this may pinpoint to other flash flood triggering mechanisms, such as changes in land use, soil moisture conditions or cultivation methods.

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