Spatiotemporal Characteristics of Drought in Yili River Basin, Northwest China in 1980–2020

The Yili River Basin in Northwest China is a crucial ecological security barrier, yet it faces frequent droughts amid global climate change, posing significant threats to food security and ecological stability. However, the spatiotemporal variations and driving mechanisms of drought in the basin remain unclear. Based on the monthly Standardized Precipitation Evapotranspiration Index (SPEI), this study employed the Run-Length theory to identify drought events in the basin during 1980–2020, applied statistical and time-series analyses to investigate the spatiotemporal variations, trends, periodicity, and persistence of drought, and explored the underlying drivers associated with meteorological factors and large-scale atmospheric circulation patterns. The results showed that droughts in the Yili River Basin are more severe in spring and summer. Droughts in the central and southwestern regions exhibit greater severity, with shorter durations and stronger intensity. Drought conditions have generally worsened (Sen’s slope = −0.146/10 yr), with notable intensification since 2005, especially in the northwestern region. Spring droughts (Sen’s slope = −0.213/10 yr) and summer droughts (Sen’s slope = −0.169/10 yr) have intensified at most stations, while autumn and winter droughts have eased. In the future, droughts are expected to alleviate overall, but summer droughts may continue to intensify. The Yili River Basin exhibits two primary drought periods of 9 yr and 21 yr, with primary periods in autumn (20 yr) and winter (20 yr) being longer than those in spring (10 yr) and summer (17 yr). Finally, droughts are impacted by both meteorological factors and large-scale atmospheric circulation patterns. Rising temperatures and uneven precipitation have intensified droughts. The SPEI exhibits a co-phase relationship with the North Atlantic Oscillation and an anti-phase relationship with the East Central Tropical Pacific Sea Surface Temperature. Therefore, close monitoring and mitigation are necessary for spring and summer droughts, with a focus on the central and southwestern areas in autumn and winter.