Compounding extreme rainfall and heatwaves: how important are large scale dynamics in generating extreme floods?

Weather extremes carry immense importance for society due to their potential to endanger human lives and cause extensive economic damages.

In Europe, heatwaves rank among the most dangerous natural disasters for low of life, while economic damages from storms and flooding events are significant. Heatwaves often coincide with droughts, with severe agricultural consequences. Recently, droughts with rapid onset and intensification, known as 'flash droughts,' have been identified.

This type of drought is primarily characterized by extremely high air temperatures and soil moisture deficits and is usually accompanied by heatwaves.

In general, compound dry-hot (e.g., heatwave/flash drought) events amplify the risks associated with public health concerns, and agricultural losses, while compound pluvial-hot (e.g., heatwave/extreme precipitation) events heighten the chances of flash floods, and storms.

These extremes are closely linked to large-scale atmospheric flow patterns in the troposphere, particularly atmospheric blocking, which significantly influences the duration and intensity of dry-hot events.

Recent observations have also highlighted connections between heatwaves, atmospheric instability, and extreme rainfall in mid and high latitudes.

However, the mechanisms driving extreme rainfall or wildfires following compound heatwave/flash drought events, and their behaviour in a warming climate, remain unclear.

This research seeks to deepen our understanding of the drivers and characteristics of compound dry-hot and pluvial-hot extremes, focusing on the role of atmospheric blocking.

We aim to investigate the changing frequencies, intensities, and characteristics of flash droughts and heatwaves, as well as their links to extreme rainfall and/or wildfire, by using reanalysis data, high-resolution observations, and the latest climate model projections, including convection-permitting simulations.

Additionally, the project will identify key factors for improving forecasts of extreme rainfall events that follow compound dry-hot conditions, ultimately enhancing societal preparedness and mitigation strategies.