Rapid attribution of heavy rainfall events leading to the severe flooding in Western Europe during July 2021

The July 2021 floods in Western Europe were driven by extreme rainfall from the low-pressure system 'Bernd', compounded by pre-existing wet soil conditions. While attribution for small catchments like the Ahr and Erft is challenging due to high natural variability, a broader 'Pooling Region' analysis indicates that climate change increased the intensity of maximum 1-day rainfall by 3-19% and its likelihood by a factor of 1.2 to 9 compared to a climate 1.2 °C cooler. Future projections suggest further increases in intensity and frequency in a 2 °C warmer climate.

• The severe flooding was driven by a combination of very heavy rainfall over 1-2 days, pre-existing wet soil conditions, and local hydrological factors.
• Rainfall amounts in the Belgian part of the Meuse catchment and the Ahr/Erft regions significantly exceeded historical records.
• In a larger 'Pooling Region' spanning from the north of the Alps to the Netherlands, an event of this magnitude is expected on average once every 400 years in the current climate.
• Compared to a global climate 1.2 °C cooler than today, climate change increased the intensity of the maximum 1-day and 2-day rainfall events in the Pooling Region by approximately 3% to 19%.
• The likelihood of such an event occurring in the Pooling Region has increased by a factor of 1.2 to 9 for 1-day events, with similar increases for 2-day events, compared to a 1.2 °C cooler climate.
• Observation-based assessments show larger changes in intensity and likelihood than those produced by regional and convection-permitting climate models.
• In a climate 2 °C warmer than preindustrial times, models project a further increase in 1-day event intensity of 0.8% to 6% and a likelihood increase by a factor of 1.2 to 1.4.
• The July 2021 event caused extreme impacts, including over 200 deaths and significant infrastructure damage, with costs estimated at €4.5 to €5.5 billion for Germany and over €0.35 billion for Belgium.
• Hydrological attribution for specific small catchments is currently not possible due to the destruction of gauging stations and the complexity of local drivers.

APA

Kreienkamp, F., Philip, S. Y., Tradowsky, J. S., Kew, S. F., Lorenz, P., Arrighi, J., Belleflamme, A., Bettmann, T., Caluwaerts, S., Chan, S. C., Ciavarella, A., De Cruz, L., de Vries, H., Demuth, N., Ferrone, A., Fischer, E. M., Fowler, H. J., Goergen, K., Heinrich, D., ... Wanders, N. (2021). Rapid attribution of heavy rainfall events leading to the severe flooding in Western Europe during July 2021. World Weather Attribution. https://www.worldweatherattribution.org/wp-content/uploads/Scientific-report-Western-Europe-floods-2021-attribution.pdf

Chicago

Kreienkamp, Frank, Sjoukje Y. Philip, Jordis S. Tradowsky, Sarah F. Kew, Philip Lorenz, Julie Arrighi, Alexandre Belleflamme, et al. Rapid attribution of heavy rainfall events leading to the severe flooding in Western Europe during July 2021. World Weather Attribution, 2021. https://www.worldweatherattribution.org/wp-content/uploads/Scientific-report-Western-Europe-floods-2021-attribution.pdf.

Wikipedia

{{cite report |last1=Kreienkamp |first1=Frank |last2=Philip |first2=Sjoukje Y. |last3=Tradowsky |first3=Jordis S. |last4=Kew |first4=Sarah F. |last5=Lorenz |first5=Philip |last6=Arrighi |first6=Julie |last7=Belleflamme |first7=Alexandre |last8=Bettmann |first8=Thomas |last9=Caluwaerts |first9=Steven |display-authors=etal |title=Rapid attribution of heavy rainfall events leading to the severe flooding in Western Europe during July 2021 |publisher=World Weather Attribution |date=2021 |url=https://www.worldweatherattribution.org/wp-content/uploads/Scientific-report-Western-Europe-floods-2021-attribution.pdf |access-date=23 October 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{kreienkamp2021rapid, author = {Kreienkamp, Frank and Philip, Sjoukje Y. and Tradowsky, Jordis S. and Kew, Sarah F. and Lorenz, Philip and Arrighi, Julie and Belleflamme, Alexandre and Bettmann, Thomas and Caluwaerts, Steven and Chan, Steven C. and Ciavarella, Andrew and De Cruz, Lesley and de Vries, Hylke and Demuth, Norbert and Ferrone, Andrew and Fischer, Erich M. and Fowler, Hayley J. and Goergen, Klaus and Heinrich, Dorothy and Henrichs, Yvonne and Lenderink, Geert and Kaspar, Frank and Nilson, Enno and Otto, Friederike E L and Ragone, Francesco and Seneviratne, Sonia I. and Singh, Roop K. and Skålevåg, Amalie and Termonia, Piet and Thalheimer, Lisa and van Aalst, Maarten and Van den Bergh, Joris and Van de Vyver, Hans and Vannitsem, Stéphane and van Oldenborgh, Geert Jan and Van Schaeybroeck, Bert and Vautard, Robert and Vonk, Demi and Wanders, Niko}, title = {{Rapid attribution of heavy rainfall events leading to the severe flooding in Western Europe during July 2021}}, institution = {World Weather Attribution}, year = {2021}, url = {https://www.worldweatherattribution.org/wp-content/uploads/Scientific-report-Western-Europe-floods-2021-attribution.pdf}, urldate = {2026-10-23}, note = {Indexed by Climate Insights Directory} }