The intensification of future extreme-rainfall events over Belgium and their dynamic and thermodynamic contributions

Climate change is expected to amplify extreme-rainfall intensity and frequency over Europe due to the increase in atmospheric moisture with warming, ensuing severe socio-economic impacts. The influence of future dynamic changes i.e. changes to atmospheric circulation patterns, on extreme-rainfall over Europe, on the other hand, remains unclear. Additionally, recent works point out that inadequate representation of regional circulation patterns by climate models may strongly impact their climate-change results over Europe (Vautard et al., 2023).

This study presents a methodology for assessing the dynamical and thermodynamical contributions to the changes in extreme daily rainfall based on the Lamb weather type classification and with an application over Belgium. Thereby, GCMs from CMIP6 are first sub-selected based on their ability to accurately represent the overall atmospheric circulation (Serras et al., 2024) and the atmospheric circulation during days of extreme rainfall. We find that models with a good circulation probability distribution do not necessarily feature a good circulation-probability representation when restricting to days with extreme rainfall events, and vice versa. This means that, for our purpose, additional to the model selection based on all days, a selection based on the circulation probability distribution during days of extreme rainfall is implemented. Additionally, the increase in extreme-rainfall intensity and likelihood at the end of century under the SSP3-7.0 scenario for Belgium, are driven by thermodynamic factors rather than dynamic changes. While the probability of extreme rainfall rises predominantly in fall and winter, the most significant intensity increases are projected for spring and summer. 

• Vautard, R., Cattiaux, J., Happé, T., Singh, J., Bonnet, R., Cassou, C., ... & Yiou, P. (2023). Heat extremes in Western Europe increasing faster than simulated due to atmospheric circulation trends. Nature Communications, 14(1), 6803.
• Serras, F., Vandelanotte, K., Borgers, R., Van Schaeybroeck, B., Termonia, P., Demuzere, M., & van Lipzig, N. P. (2024). Optimizing climate model selection in regional studies using an adaptive weather type based framework: a case study for extreme heat in Belgium. Climate Dynamics, 1-23.