Abstract
Under global warming, compound extreme events threaten ecosystems and socio-economic systems more than individual extremes. As a typical arid and semi-arid region, Northwest China has witnessed continuous increases in concurrent summer hot and drought conditions, threatening regional water security, agriculture and ecological stability. Based on observation and reanalysis data since 1961, this paper reviews recent progress on the definition, spatiotemporal variation and formation mechanisms of Summer Compound Hot-Drought Extreme Events (CHDEE) in Northwest China. Results show that the fusion scheme of daily drought and heatwave indicators, as well as the Copula joint probability framework, perform well in regional CHDEE detection. CHDEE frequency has increased significantly, with a pronounced acceleration since the late 1990s. Spatially, CHDEE show a pattern of high values in the west and low values in the east. Affected areas expand from the arid core to the northern margins and southern high-altitude regions. CHDEE are controlled by multi-scale factors: the westerly circulation, the East Asian summer monsoon and the thermal forcing of the Tibetan Plateau. The positive soil moisture–temperature feedback is the key amplification mechanism. Current studies still lack unified definitions, and the mechanisms over complex terrain remain unclear. Future work should strengthen multi-source data fusion and develop physics-informed AI prediction methods.