Spatiotemporal pattern of terrestrial ecological drought based on ecological water deficit in the Yellow River Basin

ABSTRACT Ecological drought (ED) poses significant challenges to terrestrial ecosystems under environmental change. However, most existing remote sensing indices are merely descriptive, lacking a comprehensive ED assessment that integrates vegetation conditions, evapotranspiration, and water deficit. Therefore, the study developed a ‘Vegetation-Evapotranspiration-Water Balance’ framework that captures the complete process in water supply and demand balance and reflects the combined effects of meteorological conditions, soil moisture, and vegetation physiological status, revealing ED's physio-ecological mechanisms. The study applied this framework to assess ED spatiotemporal patterns across the Yellow River Basin (YRB) from 1982 to 2020 using an eight-subregion division. Key findings include: (1) normalized difference vegetation index showed an abrupt circa around 2003, with 95.3% area of YRB exhibiting increases. (2) Crop coefficients increased in northern subregions but decreased in southern, reflecting divergent ecological responses; (3) ecological water metrics exhibited strong spatial gradients, with ecological water requirement (EWR) decreasing southward and ecological water consumption (EWC) and ecological water deficit (EWD) increasing from north to south; (4) despite rising EWR and EWC, EWD decreased in 54.6% area of YRB. Spatially, terrestrial ED was slightly alleviated in the upper reaches (loop irrigation area), remained stable in the middle reaches (Loess Plateau core), and was significantly alleviated across the downstream.