Will extreme precipitation events like July 2021 become more frequent in the future? Insights from Belgium using MAR

The July 2021 rainfall event that affected western Germany, the Netherlands and Belgium was of unprecedented intensity, reaching 170 mm of daily totals in some places. To estimate the probability of such events in the near and far future (up to 2100), the regional climate model MAR is used to run simulations at a resolution of 5 km. For this purpose, MAR is coupled with a set of 4 CMIP6 Earth System Models (ESMs) for 4 IPCC SSP scenarios over an area encompassing Belgium and Luxembourg.

An extreme value analysis is applied to the output for the period 1980-2100 for different rainfall durations (1 to 5 days). Our results show that such extreme precipitation events remain extreme throughout the century, but the probability of their occurrence increases by an order of 10 or more in the most pessimistic scenario. However, our analysis suggests that methodological choices can have a major impact on the results. In particular, the Peak Over Threshold approach shows larger changes in frequency than the Annual Maxima  approach, with less uncertainty in the results due to larger sample sizes of extreme events.