The project SEVERE investigates the physical processes and scale dependency of very extreme precipitation events in a warming climate. Very extreme precipitation events with very long return periods (e.g., 100 years) can potentially cause large damages, especially when followed by regional or large-scale flooding. Thus, it is crucial to investigate such processes in a warming climate, since warmer air can contain more water vapour than colder air (as described in the Clausius-Clapeyron equation). Given the adequate forcing and triggering mechanisms, the larger airmass water content implies an increased potential for precipitation extremes. However, this effect is not the only factor, since the future development depends as well on the large- and regional-scale evaporation, atmospheric static-stability conditions and large-dynamics dynamics and other triggering factors. An important caveat is that the period for which reliable observations exist is too short (~ 70 years) to derive robust estimates for very extreme and therefore rare events.

Therefore, SEVERE uses data from large ensembles of climate simulations from global- to kilometre-scale resolution to improve the assessment of extreme precipitation events. In the first phase of ClimXtreme, SEVERE developed a scale independent precipitation severity index (PSI; Caldas-Alvarez et al., 2023) This index was used to assess the return periods of observed events like the Ahr/Erft flood in July 2021 (Mohr et al., 2023, Ludwig et al., 2023) or an event on 29th June 2017 in the Berlin area (Caldas-Alvarez et al., 2022). In addition, the LAERTES-EU large regional ensemble (Ehmele et al., 2020) was used to estimate robust flood return levels up to ~1000 years for major European river catchments (Ehmele et al., 2022).

In the second phase, the focus of SEVERE lies primarily on climate change and its implications. Hundhausen et al. (2024) estimated the increase of extreme precipitation intensities per degree of global warming over a wide range event durations and return periods and found a strong increase for short, sub-daily events. For long events up to several days, the changes in precipitation characteristics can be linked to the representation and modifications of the large-scale atmospheric dynamics, whose possible changes more uncertain. Large GCM ensembles are thus applied to distinguish between the natural variability and the forced response. Furthermore, dynamical downscaling of the most extreme events detected via the PSI in the coarse GCM simulations to the kilometre-scale is performed to study the scale dependency and regional-to-local feedbacks.

Website: SEVERE

Institution: Institute for Meteorology and Climate Research, Karlsruhe Institute of Technology

Contact: Hendrik Feldmann, Prof. Joaquim G. Pinto