Flash drought drives rapid vegetation stress in arid regions in Europe

Flash droughts are characterised by rapid onset, combined with the potential to severely impact agriculture and ecosystems. However, assessments of the ecological impacts of flash droughts, especially in Europe, are largely lacking. Here we investigate ecosystem responses to flash droughts in Europe between 2001 and 2019 using diverse observational data, including gross primary production (GPP) and leaf area index (LAI). We find that in arid regions an abrupt transition to water-stressed conditions occurs within a few weeks, which negatively affects vegetation status and reduces carbon uptake in the initial stages of drought; normalised anomalies of LAI and GPP decrease to about −0.5. By contrast, vegetation in humid regions is not as severely affected, given that soil moisture recovers relatively quickly. We also show that soil moisture status before the onset of drought significantly impacts the timing (1-5 pentads) and degree (−0.33 to −0.71 of normalised LAI and GPP anomalies) of drought-induced vegetation stress, particularly in arid regions. Our results highlight the regional characteristics of flash drought impacts for more informative monitoring and early warning systems.