Impacts of climate and land use changes on water retention in the transboundary Yuanjiang-Red River Basin: Historical attribution and future projections

Study region: the Yuanjiang–Red River Basin (YRRB), Southeast Asia. Study focus: Water retention (WR) capacity in the transboundary YRRB has been increasingly affected by combined climate and land-use changes. However, limited quantitative attribution of historical drivers and uncertain future projections hinder the development of effective cross-border adaptation strategies. This study integrated the Variable Infiltration Capacity model, a fixed-varying scenario design, and variable-specific Bayesian model averaging of bias-corrected, downscaled Coupled Model Intercomparison Project Phase 6 climate projections to attribute historical WR changes during 1973–2015 and project WR changes during 2016–2050 under three Shared Socioeconomic Pathway scenarios. New hydrological insights for the region: Historical WR averaged 572 mm and showed a nonsignificant decline of 18 mm decade⁻¹ , primarily attributable to climate change. Local buffering effects associated with land-use change were insufficient to offset this basin-wide decline. Future WR is projected to decline by 29.6%–33.5%. Empirical orthogonal function (EOF) analysis indicated a shift toward greater spatial heterogeneity. Relative to SSP126, EOF1 decreased from 79% to 64%–68%, whereas EOF2 increased from 7% to 12%–17% under SSP245 and SSP585. This overall shift was associated with the combined effects of declining precipitation and increasing evapotranspiration. These findings inform coordinated cross-border ecological restoration and spatially targeted water management between China and Vietnam.