Dominant Role of Soil Moisture Regulating Vegetation Water Content During Flash Drought Evolution

Abstract

Increasing flash drought exposure raises global concerns regarding terrestrial ecosystem responses. We investigate the effect of concurrent and past rootzone soil moisture (SM) and vapor pressure deficit (VPD) on vegetation optical depth (VOD), a satellite-based proxy of vegetation-water content, during flash drought evolution. Analysis reveals greater importance of SM than VPD across drought phases, driving global ecosystem responses. We observe contrasting VOD sensitivity to simultaneous SM and VPD fluctuations, which decrease (increase) in natural ecosystems (croplands) as drought evolves. VOD declines most over grasslands-shrublands, while its recovery is relatively slow (fast) over croplands (forests). Concurrent SM has the strongest influence over grasslands-shrublands in dry anisohydric regions, while antecedent SM plays the weakest role in humid, isohydric forests. Thus, divergent responses across ecosystems, shaped by varying water-use strategies and adaptability to background aridity, and their phase-wise variations underscore the necessity of region-specific studies focusing on plant-functional-traits for flash drought mitigation strategies.