Spatiotemporal heterogeneity and mechanisms of mountain-outlet runoff change on the northern slope of the Qilian Mountains during 1960–2020

Study region: Five major mountain-outlet basins on the northern slope of the Qilian Mountains, northwestern China: Shiyang (SY), Heihe (HH), Beida (BD), Shule (SL), and Danghe (DH). Study focus: This study examines the spatiotemporal heterogeneity of mountain-outlet runoff changes during 1960–2020 and their statistically associated pathways using hydrological, meteorological, atmospheric circulation, glacier, and snow data. OPGD and PLS-SEM were used to identify dominant explanatory factors and statistical pathways linking atmospheric circulation, meteorological factors, glacier and snow water storage (GSWS), and runoff (Q). New hydrological insights for the region: Mean runoff in 2000–2020 was 2.8–58.8% higher than in 1960–1999, while basin-specific abrupt-change years ranged from 1987 to 2009. Long-term increasing trends were significant only in HH, SL, and DH. Air temperature and precipitation were the main meteorological factors associated with runoff variation. Runoff in SY and HH was more closely associated with precipitation, whereas runoff in SL and DH was more closely associated with air temperature, and both factors had similar explanatory power in BD. Atmospheric circulation was statistically linked to runoff through air temperature, precipitation, and GSWS. The precipitation → Q pathway was stronger in SY, HH, and BD, whereas the air temperature → GSWS → Q pathway was more prominent in SL and DH. These findings help explain region-specific runoff heterogeneity and support differentiated water resources management.