Attributing heavy rainfall event in Berchtesgadener Land to recent climate change – Further rainfall intensification projected for the future

Abstract

On 17 July 2021, storm “Bernd” hit the alpine region of Berchtesgadener Land inducing short-duration heavy rainfall, which triggered flash floods, debris flows, landslides, and flooding. Based on the observed precipitation data and an analysis of the runoff measurements, the driver of the event is defined as a 3-h rainfall. The 50-member single model initial-condition large ensemble of the Canadian Regional Climate Model version 5 under the emission scenario RCP 8.5 is employed to explore the occurrence probability of the event under historic, current, and future climate conditions. For the rainfall event, a return period of 21 years (17–25 years) is found for the current climate (2006-2035). Under historic climate (1970-1999) the event is estimated to be 3.1 (1.9–5.2) times less likely equalling a return period of 64 years (48–90 years). This is particularly critical as experience and observational data from the recent past have been crucial to the design of infrastructure and still influence current planning. For future climate conditions, the event probability is projected to increase resulting in return periods of 7.8 years (7.1–8.8 years; 2040-2069) and 4.9 years (4.6–5.4 years; 2070-2099), respectively. The future shifts in extreme precipitation must be urgently taken into account for appropriate adaptation measures.