In July 2021, heavy rainfall and flooding in western Europe caused the costliest weather disaster in European history. In IDEA, we study key atmospheric dynamical characteristics
In July 2021, heavy rainfall and flooding in western Europe caused the costliest weather disaster in European history. Anthropogenic global warming (AGW) increases the frequency of extreme summer rainfall, as also shown in a post event rapid attribution study. However, there is a stark discrepancy between observation-based estimates, suggesting a very strong influence of AGW (+900%), and model-based estimates, suggesting only a weak influence (+20%). This discrepancy originates from fundamental limitations of the classic attribution framework, which need to be overcome if KNMI is to provide accurate attribution of summertime rainfall extremes as well as other extremes governed by dynamical processes.
In IDEA, we will study two key atmospheric dynamical characteristics of the July flooding: 1) A persistent cut-off low, and 2) strong regional moisture convergence. Using very-large ensemble simulations, convection-permitting models, and novel data-driven techniques, we want to understand the role of dynamics in the 2021 flooding and develop more-confident, physics-informed attribution statements. This provides essential information for well-designed flood-risk reduction measures. We will develop a set of tools and best practices for improved attribution of dynamical aspects of extremes, that can be applied in future rapid attribution studies, ensuring that KNMI remains at the forefront of attribution science.
