Divergent Causes of Terrestrial Water Storage Decline Between Drylands and Humid Regions Globally.

Declines in terrestrial water storage (TWS) exacerbate regional water scarcity and global sea level rise. Increasing evidence has shown that recent TWS declines are substantial in ecologically fragile drylands, but the mechanism remains unclear. Here, by synergizing satellite observations and model simulations, we quantitatively attribute TWS trends during 2002–2016 in major climate zones to three mechanistic drivers: climate variability, climate change, and direct human activities. We reveal that climate variability had transitory and limited impacts (<20%), whereas warming‐induced glacier loss and direct human activities dominate the TWS loss in humid regions (∼103%) and drylands (∼64%), respectively. In non‐glacierized humid areas, climate variability generated regional water gains that offset synchronous TWS declines. Yet in drylands, TWS losses are enduring and more widespread with direct human activities, particularly unsustainable groundwater abstraction. Our findings highlight the substantive human footprints on the already vulnerable arid regions and an imperative need for improved dryland water conservation. Plain Language Summary: Terrestrial water storage (TWS) losses are increasingly prominent in both global and regional scales, particularly in vulnerable drylands. An accurate attribution of TWS changes is essential for the sustainability and conservation of water resources. We provide a comprehensive interpretation of recent satellite‐observed TWS changes in each climate zone through quantitative attributions to natural and anthropogenic factors. We found climate change and direct human activities are the dominant drivers of zonal TWS changes but their impacts are considerably divergent between drylands and humid regions. In humid regions, TWS losses are primarily concentrated on glacierized regions and the net TWS budget in the non‐glacierized humid regions exhibits an equilibrium. Contrastively, TWS declines in drylands are more widespread and enduring with human groundwater depletion. Our analysis highlights a pressing need for improving water conservation strategies in global drylands. Key Points: Recent zonal terrestrial water storage (TWS) losses are primary results of climate change and human activities, instead of climate variabilityIn humid regions, glacier loss fully explains the net TWS decline, meaning a water budget equilibrium in non‐glacierized humid regionsIn drylands, widespread TWS losses are mainly attributed to direct human activities [ABSTRACT FROM AUTHOR]