Many extreme impacts on society are caused by compound events, which were recently defined as a combination of multiple drivers and/or hazards contributing to societal or environmental risk. Compound events include, for example, concurring precipitations and storm surges causing flooding along low-lying coastal areas; heatwaves enhanced by drought conditions; strong wind episodes combined with drought conditions that together increase the wildfires probability.

In the last few years, it has become clear that compound events can lead to serious impacts on our society. Research oriented towards compound events can, therefore, be helpful for improving weather and climate risk estimates.

However, given the large variety of compound events types, researchers would benefit from a compound event categorization and from guidelines on how to study them.

Providing researchers with these guidelines is one of the goals of the COST action DAMOCLES. In March 2019, a one-week short term scientific mission (STSM) has been set-up within DAMOCLES to advance in this direction. We (Emanuele Bevacqua from University of Reading and Edoardo Vignotto from University of Geneva) visited Aglaé Jézéquel, leader of the DAMOCLES working group 4, at the Laboratoire de Météorologie Dynamique (LMD) in Paris.

During the STSM, in collaboration with other DAMOCLES members, we discussed the categorization of compound events started by working group 1. This served as a basis for selecting the relevant statistical approaches associated with the main compound event categories. In addition, a workshop on compound events, organised at LMD in Paris, led to very interesting discussions with the local researchers working in climate science and experts in statistics. This discussion was beneficial to the success of the mission and pointed out, for example, that a better understanding of compound event impacts requires to disentangle the involved physical drivers. A deep physical understanding of compound events is especially relevant in the current climate change context, which can alter the physical processes leading to extreme impacts.

The results of this STSM will contribute to achieving the goals of DAMOCLES, including raising awareness of the relevance of compound events, which will ultimately lead to improved risk assessments with a direct benefit for society.

Emanuele Bevacqua, University of Reading, UK.

Edoardo Vignotto, University of Geneva, Switzerland.

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