Sensitivity of observed changes in compound climate extremes across Europe to event definition

This article investigates the sensitivity of observed changes in compound climate extremes across Europe to the way these events are defined. The study examines three types of compound events: compound drought-heatwave (CDHW), compound heatwave-extreme precipitation (CHW-EP), and hydroclimatic whiplash events. A total of 39 combinations of drought metrics, accumulation periods, and heatwave definitions were tested using the E-OBS daily gridded observational dataset spanning 1950-2024. 

The key findings show that the frequency, intensity, and spatial distribution of compound climate extremes in Europe are highly sensitive to the adopted event definitions. Indices that account for evapotranspiration and incorporate nighttime temperatures detect larger and more widespread increases in compound events than definitions based only on precipitation or daytime temperatures. The authors recommend that future climate monitoring and hazard mapping carefully consider the choice of event definitions, accumulation periods, and underlying climatic variables, as these methodological choices significantly affect detected trends.