Does a changing climate lead to a higher flash flood hazard?

Does a changing climate lead to a higher flash flood hazard?

Flash floods pose a significant natural hazard and are triggered by high-intensity precipitation events occurring in small and steep catchments. The short lead time, high flow velocity, and transportation of debris and sediment of these floods can lead to devastating impacts. 

With the warming climate, the intensity and extent of precipitation events are likely to increase, consequently leading to an expected increase of flash flood hazard. But what do we have to expect, and how can we adapt to future climate scenarios? Simulating extreme rainfall is still highly uncertain under climate change. Because of their coarse spatio-temporal resolution, global circulation models are not suited to investigate the impacts of a warming climate on flash floods. However, new convection-permitting models (regional climate models) for the first time now offer an appropriate spatia-temporal resolution (3x3 km, 1 hour) for flash flood modelling. Based on the COSMO-CLM (COSMO model in CLimate Mode, Rockel et al., 2008; Sørland et al., 2021), we modelled the runoff in all small-scale catchments in Germany for the periods 1971-2000, 2001-2019, and for the period 2030-2100, which is based on the RCP8.5 scenario.

Our results reveal that half of the catchments would produce a flood peak of factor 1.5 or higher under the RCP8.5 scenario compared to the present period (2001-2019) and further enable us to estimate and compare return levels of flood peaks for the RCP8.5 scenario and shed light on regional differences within Germany. This study is the first comprehensive analysis of the (flash) flood response to a warmer climate in Germany.

References:

Rockel, B., A. Will, A. Hense, 2008: The regional climate nmodel COSMO-CLM (CCLM). Meteorol. Z. 17, 347–348, DOI: 10.1127/0941-2948/2008/0309.

Rybka, Harald, et al. "Convection-permitting climate simulations with COSMO-CLM for Germany: Analysis of present and future daily and sub-daily extreme precipitation; Convection-permitting climate simulations with COSMO-CLM for Germany: Analysis of present and future daily and sub-daily extreme precipitation." Meteorologische Zeitschrift 32.2 (2023): 91-111.

Sørland, S.L., C. Schär, D. Lüthi, E. Kjellström, 2018: Bias patterns and climate change signals in GCM-RCM model chains. Env. Res. Lett. 13, 074017, DOI:10.1088/1748-9326/aacc77.