Drought and flood disasters EXDIMUM joint project of TU Braunschweig investigates extreme water events
Global climate change is not only about an increase in average temperature, but above all about the intensification of extremes: even in the “temperate latitudes” of Central Europe, both drought, as in the drought summer of 2022, and heavy rainfall events, as in the flood disaster of the summer of 2021 in the Eifel and in the Ahr valley, are increasing dramatically. The research project EXDIMUM (Extreme Weather Management with Digital Multiscale Methods), launched this year under the auspices of Technische Universität Braunschweig, addresses a spectrum of complex challenges posed by these extreme weather situations. It is one of only 12 projects out of 160 submitted that are being funded by the Federal Ministry of Education and Research (BMBF) as part of the Wasser-Extremereignisse (WaX) (Hydrological extreme events) funding measure. It has a duration of three years and a funding volume of a good 3 million euros.
In addition to Prof. Sándor Fekete from the Algorithms Division Department and Prof. Jochen Steil from the Institute for Robotics and Process Control at TU Braunschweig, the TU Clausthal and the Kiel University are also involved, as well as partners from industry: Eurawasser Betriebsführungsgesellschaft mbH, Remondis Aqua Industries, DSI Aerospace Technologie GmbH, AMENO GmbH and Planet Labs PBC and SCALGO.
Opposing extremes do not balance each other out
“The development that extreme weather events are occurring more and more frequently is taking place simultaneously on different and often opposite scales,” explains Prof. Sándor Fekete. Extreme drought is a longer-term process that extends over larger regions. Floods, on the other hand, would often be short-term and more localised. Conversely, in the case of flooding, even small local differences in the terrain, for example a stream blocked by deadwood or a new dam to be built, could cause drastic differences in the runoff of precipitation for an entire region.
Opposing extremes do not balance each other out at all, but can further reinforce each other, according to Fekete: “Prolonged drought affects vegetation and the composition of the soil, which becomes less absorbent and resistant to erosion. During heavy rainfall, not only does more water run off the surface and cause damage to the soil, but less water remains in the soil, which in turn affects the regrowth of vegetation”. The same applies to the interaction of other opposites, for example when the death of local vegetation leads to increased evaporation of water.
Alarm signs visible in the Harz Mountains
In the Harz mountains, the highest low mountain range in northern Germany, these problems are particularly evident. While the average annual precipitation in Braunlage was still 1350 millimetres between 1990 and 1999 and 1360 millimetres from 2000 to 2009, it was only 983 millimetres between 2010 and 2019. “If you pay attention to them, the consequences are fully recognisable sooner in a natural landscape than in agricultural and cultivated areas, where the problem can be covered up and ignored for longer with intensive groundwater irrigation, for example,” says Prof. Fekete.
At the other end of the scale, there are also clear alarm signs in the Harz Mountains, the scientist explains: “Despite the possibility to protect against flood peaks with dams, flood waves that could no longer be controlled flooded the surrounding area in 2014 and 2017. As became clear with the flood catastrophe in the Eifel and in the Ahr valley in 2021, the specific location and time of such extreme weather situations can only be recognised at relatively short notice.” Even with functioning relief structures, major protective measures could hardly be implemented if suitable disaster mitigation measures had not been planned in advance. It is therefore correspondingly important to have comprehensive scenarios available in order to be able to react effectively in the event of an emergency. These are to be developed within the framework of EXDIMUM.
Simulation of possible extreme weather situations
In the project, methods of computer science and information technology are applied using different data sources. For example, the modelling of the spread of precipitation combines topographical information with data on land use, the condition of the vegetation and data on soil moisture. “We combine spatially and temporally high-resolution aerial images with reference values from ground-based sensors. With the digital image of reality generated in this way, novel artificial intelligence methods can not only identify existing relationships, but also map the respective system state with the help of a model working in different spatial and temporal dimensions,” says Fekete.
The researchers’ goal is to derive forecasts and recommendations for action for network operators and river basin managers. To this end, promising courses of action are to be identified and tested in advance by simulating possible extreme weather situations, such as large amounts of precipitation. In the future, this could help to better predict the course of flood disasters like the one in the Ahr valley and save human lives.