Clarifying the impacts of climate and vegetation changes on hydrological drought in the Yellow River Basin, China

The Yellow River Basin (YRB). This study constructed a Standardized Water Availability Index (SWAI) based on surface water availability (Pr-ET, precipitation minus evapotranspiration), highlighting the feasibility of assessing hydrological drought in YRB through surface water balance mechanism. The ET for SWAI calculation was simulated by the Priestley-Taylor Jet Propulsion Laboratory (PT-JPL) model, which allowed quantifying the impacts of basin climate and vegetation changes on hydrological drought from 2001 to 2022 by controlling vegetation variation scenario. (1) Verification using observed runoff in YRB indicated that Pr-ET based drought index better capture surface water scarcity than conventional Pr-PET (PET, potential evapotranspiration) approaches. (2) The inclusion of vegetation change increased the area of hydrological drought in YRB by 11.3 % under climate change. Vegetation change primarily exacerbated SWAI decline in middle reaches, while the relatively humid upstream and downstream were mainly affected by climate change. (3) Precipitation (Pr), temperature (Ta), leaf area index (LAI) were primarily drivers of SWAI variation. Within the delineated sub-basins of YRB, SWAI correlated positively with Pr (r ≤ 0.83) and negatively with Ta (r ≥ -0.63). The introduction of LAI amplified the negative impact of Ta (r ≥ -0.76) and mitigated the positive impact of Pr (r ≤ 0.75). The above findings can provide scientific references for ecohydrological regulation at the basin scale. • SWAI calculated by Pr-ET better captured the hydrological drought variation of YRB. • The inclusion of vegetation change increased hydrological drought area in YRB under climate change. • Vegetation showed a significant recovery trend in the midstream of YRB, causing heightened hydrological drought in the region. • The correlation between Pr, Ta, and LAI with SWAI in YRB was more significant than other factors. • Vegetation change in YRB altered the original correlation between climatic factors and SWAI.