Widespread and complex drought effects on vegetation physiology inferred from space

The response of vegetation physiology to drought at large spatial scales is poorly understood due to a lack of direct observations. This study analyzes drought responses related to photosynthesis, evaporation, and vegetation water content using satellite data, isolating physiological responses with a machine learning approach. Results show that decreases in ecosystem functioning are largely driven by downregulation of vegetation physiology (e.g., stomatal conductance, light use efficiency), strongest in water-limited regions. In wet regions, physiological decreases lead to discrepancies between functional and structural changes under severe drought. Similar spatial patterns are found using simulations from a soil-plant-atmosphere continuum model coupled with a radiative transfer model. Observation-derived physiological responses are mainly controlled by aridity and additionally modulated by abnormal hydrometeorological conditions and vegetation types. Quantifying vegetation physiological responses to drought improves understanding of ecosystem biogeochemical and biophysical feedbacks in modulating climate change.