Worse Case Scenarios of the July 2021 Western European Rainfall 

Abstract: In July 2021 a cut-off low-pressure system brought extreme precipitation to Western Europe. Record daily rainfall totals led to flooding that caused loss of life and substantial damage to infrastructure.  
We use ensemble boosting to investigate possible alternative storylines of the event, given the observed dynamical situation and current climate. We use the fully-coupled free-running climate model (CESM2), identifying atmospheric flow analogues of the July 2021 event in an initial-condition large ensemble of the present climate. These analogues are re-initialized with slightly perturbed atmospheric initial conditions to generate a set of alternative storylines, dynamically similar to the July 2021 event.  
The set of storylines are used to identify physically plausible worse case scenarios. We do not assess for more intense events, but instead investigate different metrics which could lead to greater impacts to society and ecosystems. We find generated storylines of similar events that persisted longer and covered a larger region – but also show that the observed event was towards the upper end of what is plausible in the current climate. 
Authors - Vikki Thompson1, Dim Coumou2, Erich Fischer3, Urs Beyerle3 
1 Royal Netherlands Meteorological Institute (KNMI), De Bilt, Netherlands.  
2 Institute for Environmental Studies, Vrije Universiteit Amsterdam, Amsterdam, Netherlands   
3 Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland

Biography: Vikki is a scientist at the Royal Netherlands Meteorological Institute and visiting researcher at the Institute of Environmental Studies, VU Amsterdam. Her research focuses on climate extremes, such as heavy rainfall events and heatwaves. She aims to improve understanding of how extreme events are changing and what is driving the changes. 
Vikki has previously worked on extreme heat at the Cabot Institute, University of Bristol; in flood risk at the Scottish Environment Protection Agency; and as a research scientist at the Met Office Hadley Centre. She has a PhD in Meteorology from Reading University.