Spatial-temporal patterns of concurrent droughts and heatwaves in the Qaidam Basin, China

This study investigates the spatiotemporal patterns and synergistic mechanisms of extreme heatwave–drought compound events in the Qaidam Basin from 1990 to 2020, integrating observational data and multivariate statistical analyses. The key findings include that all heatwave durations (1–7 days) exhibited significant increasing trends, with the fastest growth rate observed for 1-day events (2.3 events/decade). Spatially, the heatwave frequency intensified northward, peaking at Golmud Station (5.1 events/decade for 1-day events). The SPEI revealed contrasting trends—monthly moistening (+0.108/decade for SPEI1) versus seasonal to annual aridification (declines of 0.007–0.088/decade for SPEI3–12). Extreme droughts clustered in 2001 (SPEI1 = −2.03) and 2013 (SPEI6 = −1.87). The heatwave‒drought co-occurrence frequency generally declined (−0.86 events/year for 1-day events), yet an anomalous peak occurred in 2000, driven by Tibetan Plateau circulation anomalies. Local moisture conditions (precipitation and relative humidity, r = −0.41) dominated decoupling, while the North Atlantic Oscillation (NAO) and Western Pacific Index (WP) regulated interannual variability. The 2000 extreme episode was characterized by 500-hPa geopotential height anomalies (−10 gpm) and cyclonic 700-hPa wind patterns. This work provides the identification of teleconnections between compound extremes and western Pacific subtropical high dynamics in the northern Tibetan Plateau arid zone, offering dynamical foundations for extreme event risk assessment in warming–wetting transitional regions.