Revegetation and increased precipitation lead to a drying-to-wetting hydrological regime shift in the Loess Plateau of China

The hydrological cycle has been intensifying globally during the past decades, causing long-term irreversible impacts on the social ecological system. However, research on hydrological regime shifts and their driving mechanisms remains limited. In this study, we selected 13 basins across the Loess Plateau and classified their hydrological regimes from 1990 to 2020 into distinct types using combined indicators of extreme drought and flood flows. Our analysis identified 2005 as the turning point for extreme flows. Hydrological regimes transitioned from a drying trend phase (1990-2005) to a wetting trend phase (2005-2020), characterized by decreasing drought and flood flows before 2005 but increasing trends thereafter across all basins. This shift exhibits a distinct north–south contrast, with larger changes in extreme flows in the northern region than in the southern region. During the drying phase, increased vegetation cover and water use, coupled with reduced mean available water (Mean P-ET, precipitation minus evapotranspiration), were the primary drivers of intensified drying. The wetting phase was triggered by elevated vegetation cover and maximum 14-day available water (Max. P-ET).​​ Notably, vegetation cover emerged as key driver of the drought flows in both periods (p < 0.001), though its regulatory mechanisms shifted between the two phases. Flood flows were influenced by water use and water availability, showing particular sensitivity to variations in Max. P-ET. The shift in hydrological regime suggests that priority should be given to enhancing flood prevention and regulation in future basin management, especially for the northern regions where they are more susceptible to climate change and human activities.