Search

Today, erosion is increasing in many intensively used agricultural regions with fertile soils. At the same time, scientists expect that the intensity of heavy precipitation events, their erosivity, drought intensity and persistance will increase significantly through climate change. In combination with more strict regulations to protect the natural environment from nutrients and hazardous substances (such as herbicides and micro-plastics), it is challenging to balance the interests of food (and energy) production and environmental protection.Therefore, we design and establish a worldwide unique measurement plot at the Bavarian Agricultural Institute (LfL) to assess different combinations of four- and six-year crop rotation schemes and machining methods concerning their long-term soil fertility, stability and resilience against climate change effects and environmental impacts, focusing on compound effects. The plot to measure and compare soil-water retention, nutrient fluxes, surface runoff, and erosion masses has an area of four acres and 14 parallel crop strips. Crop cultivation, experiments and measurements with and without artificial rain will be performed for more than ten years after a three-year set-up phase, will have a 4D (3D spatial plus temporal) high-resolution design and combine established and innovative measurement and management techniques, such as artificial intelligence, neural networks, deep learning, and robotics. Finally, up-to-date process-based hydrological modelling will incorporate the measurement data to increase our process understanding and enable upscaling to catchment scales.This contribution to EGU 2022 will inform and include the scientific community during the set-up phase about the running and planned activities to build an international scientific network, discuss our approaches, efficiently use the existing scientific knowledge, and initiate future collaborations around the measurement financed by the German federal state of Bavaria.

As the built-up areas extend and become denser with time, high-resolution land use and especially imperviousness data is of increasing importance, e.g., for detailed studies on settlement and landscape water retention to provide for extremes such as (flash) floods, heatwaves, and droughts.The open-source COPERNICUS imperviousness density dataset covers 2006 until 2018 with a three-year timestep with incremental raster resolution (2018: ten meters). On the other hand, there is an accurate object-oriented cadastre dataset of German authorities called ATKIS. It describes the geometries of buildings and all types of traffic routes from airports to dirt roads with an increasing amount of attributes like shape, area, width, or material. While both datasets are very detailed, they have specific (dis-)advantages due to their very different data and surveying type.We used the information stored in the ATKIS database of 2020 to create an alternative object-based imperviousness map of the German state Bavaria with roughly 70,000 km² to contrast and compare it with the COPERNICUS imperviousness density dataset of 2018 in several different (urban and rural) areas. We found that COPERNICUS indicates much higher imperviousness for densely settled areas as city centres and commercial and industrial zones and can describe even complex types of significant extent (such as golf courses, transhipment stations, and allot settlements) better. Vice versa, ATKIS could resolve even linear traffic elements in rural areas and detached house settlements to an outstanding level of detail, which COPERNICUS cannot afford due to its limited resolution. Both products cannot distinguish clearly between sealed concrete and loose stony material (e.g., from construction or mining sites), nor give indications on sub-surface water retention or sewage infrastructure.Overall, we can name both methods' (dis-)advantages, relate them to surprisingly distinct land use classes, and give guidance, where additional object-oriented information can significantly improve COPERNICUS imperviousness data. Finally, the resulting maps highlight the hotspots of extreme building-independent imperviousness. They can serve as a tool to prioritize areal and building-centred measures to prevent large amounts of fast runoff.

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 164km². 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 1km² 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-Südbayern 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.

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 Münster (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:Runoff generation: SCS-CN value method (TELEMAC-2D), Green Ampt method (LARSIM), layer-resolving Richards method (WaSiM) Runoff concentration: Strickler roughness approach (TELEMAC-2D), Kalinin-Miljukov method (LARSIM), flow time index method (WaSiM) In this study, we examine three different types of couplings:(1) The runoff concentration is calculated using the hydrodynamic model, the runoff generation is carried out using the CN value method. (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. (3) The runoff concentration in the upper catchment area is also calculated using hydrological methods, only the urban area is calculated hydrodynamically. 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. 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.