The drought response of European ecosystem processes via multiple components of the hydrological cycle

Like those recently experienced in 2018 and 2022, European droughts significantly alter ecosystem processes, such as photosynthesis and evapotranspiration. Quantifying these large-scale alterations and understanding their drivers is essential to studying the drought impacts on ecosystem performance, water resource management, and carbon emission budgeting. However, to this date, because of differing definitions of drought events and complex interactions among eco-hydrological variables across multiple time scales, research has only painted a blurry picture of the impacts of droughts on ecosystems.

In this work, based on pan-European simulations of the land surface model CLM5-BGC, we identified drought events with a generalized clustering algorithm considering water deficits in multiple compartments of the hydrological cycle (groundwater, soil moisture, evapotranspiration, and vapor pressure deficit). Further, we distinguished these droughts' direct and lagged effects by aggregating water deficits across various time scales and their impacts on ecosystem processes by accounting for the absolute anomalies at the event locations.

We highlight statistics and trends of the identified drought events, their drivers, and their impact on photosynthesis and evapotranspiration, with increasingly severe soil moisture and vapor pressure deficits. In the shorter time scales, atmospheric droughts are the primary driver of photosynthesis and evapotranspiration anomalies. This study presents a novel multi-scale and multivariate approach to droughts, paving the way for holistic and more precise considerations of their impacts on ecosystems.