Understanding Extreme Weather in a Changing Climate

ClimaMeter is an experimental rapid framework for understanding extreme weather events in a changing climate based on looking at similar past weather situations. Find out more here and follow us on X

High Precipitation in Autumn 2023 France and Italy Floods likely enhanced by human-driven climate change and natural variability

In Autumn 2023, storms including Babet, Aline, and Ciaran caused severe flooding in Northern France, with nearly 250 millimeters of rainfall over three weeks. The Pas-de-Calais region experienced significant impact due to ground saturation and limited drainage, affecting 262 municipalities and prompting emergency responses. Simultaneously, Storm Ciaran led to a parallel catastrophe in Italy's Tuscany region, causing unprecedented floods, casualties, and a national state of emergency declaration.

Our analysis finds that events similar to the Autumn 2023 French and Italy floods led to wetter conditions, with an increase of 1 mm/day to 3 mm/day (equivalent to 15% to 30% more precipitation) along the French Atlantic coasts and the Italian Tyrrhenian coasts. We interpret the Autumn 2023 floods in France and Italy as an unusual event for which natural climate variability likely played an important role.

Photo:  Screenshot from an areal view by BFMTV

High temperatures during the Brazilian heatwave mostly strengthened by human-driven climate change

From November 13 to 19, 2023, central-southern Brazil experienced a severe heatwave. Temperatures soared to up to 44.8 °C, marking a new national temperature record despite the heatwave not having occurred during meteorological southern hemisphere summer. Red alerts were issued across the country due to the extreme heat.

Our analysis finds that events similar to the Brasil heatwave are between 1 ºC and 4 ºC hotter in the present than they would have been in the past. We interpret this heatwave as a largely unique event, for which natural climate variability played a role. For this event, we have low confidence in the robustness of our approach given the available climate data, as the event is largely unique in the data record.

Photo: A beach in Rio de Janeiro, Tomaz Silva/Agencia Brasil

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