Minimizing uncertainties in climate projections and water budget reveals the vulnerability of freshwater to climate change

Global water scarcity threatens agriculture, food security, and human sustainability. Hence, understanding changes in terrestrial water storage (WS) is crucial. By utilizing climate models, reanalysis, and satellite data, we demonstrate the effectiveness of the multivariate bias correction technique in facilitating precise WS representation while ensuring robust water budget closure. Historical data indicate seasonal changes, where forested basins exhibit a WS surplus in the December-January-February season, with a reversal in the June-July-August-September season. Non-forested basins display varied patterns influenced by geographical location and land use type. Future projections indicate increased June-July-August-September deficits in most Southern Hemisphere basins under the middle-road (SSP 245) scenario and wetter December-January-February conditions under the regional rivalry (SSP 370) scenario. Weather and climate systems governing WS vary by season and basin, resulting in inconsistent moisture intake into basins. These findings underscore the intricate interplay between moisture transport, land characteristics, and the resulting WS, highlighting the need to understand these complex interactions for effective regional water resource management strategies in changing climates.