Brief communication: On the extremeness of the July 2021 precipitation event in western Germany

The weather extremity index (WEI) and the cross-scale WEI (xWEI) are useful for determining the extremeness of precipitation events. Both require the estimation of return periods across different precipitation duration levels. For this purpose, previous studies determined annual precipitation maxima from radar composites in Germany and estimated the parameters of a generalized extreme value (GEV) distribution. Including the year 2021 in the estimation of GEV parameters, the devastating event in July 2021 drops from a rank of first to fourth regarding the WEI compared to all events between 2001 and 2020 but remains the most extreme regarding the xWEI. This emphasizes that it was extreme across multiple spatial and temporal scales and the importance of considering different scales to determine the extremeness of rainfall events.

Automated summary

The weather extremity index (WEI) and cross-scale WEI (xWEI) are useful tools for assessing the extremeness of precipitation events. Previous studies in Germany used radar composite data to estimate annual precipitation maxima and the parameters of a generalized extreme value (GEV) distribution. With the inclusion of data from 2021, the devastating event in July 2021 ranks fourth in terms of WEI compared to events between 2001 and 2020, but remains the most extreme in terms of xWEI. This highlights the importance of considering different spatial and temporal scales when evaluating the extremeness of rainfall events.