Global vegetation dynamics under decreased terrestrial water storage: Insights into water stress response

Terrestrial water storage (TWS) plays a critical role in regulating global water-energy budget, significantly influencing water availability and carbon sequestration dynamics. However, how decreased TWS affect terrestrial carbon assimilation under climate change remains poorly understood. This study explores the influence of TWS on vegetation productivity across diverse ecosystems by synthesizing satellite observations, reanalysis datasets, field measurements, and long-term TWS reconstructions. We apply a supervised machine learning model and path analysis to examine how dominant water-heat factors—such as soil moisture, vapor pressure deficit, precipitation and temperature—regulate vegetation photosynthesis under varying levels of water stress. Moreover, we employ a large set of hydro-climate models to project future TWS scenarios, and quantify their impacts on vegetation productivity in a warming climate. Our findings indicate that intensifying drought conditions, indicated by decreased TWS, lead to increasingly severe reductions in vegetation productivity, particularly in water-limited regions. The integrated model framework projects that climate warming could significantly worsen drought impacts on vegetation productivity. As drought severity escalates from moderate drought to exceptional drought, the global average gross primary productivity decreases from -3.20 $g{m}^{-2}da{y}^{-1}$to -7.10$g{m}^{-2}da{y}^{-1}$under low carbon emission scenarios. These insights highlight the critical need to develop robust strategies to enhance ecosystem resilience against worsening drought conditions, underscoring a key aspect of climate adaptation efforts.