Decadal evolution and spatial reversal of compound hot-dry events in China during 1961–2020: A PDO-driven perspective

Although previous studies have focused on long-term trends driven by anthropogenic warming, inter-decadal variations of compound hot-dry events (CHDEs) in China remain poorly understood. This study analyses inter-decadal variations of CHDE characteristics, namely frequency, duration, timing and intensity, using daily maximum temperature and monthly PDSI from 1961 to 2020. The results reveal a three-phase decadal evolution: a weak decline before 1990 (−10% per decade, p < 0.05), a rapid increase during 1991–2005 (29% per decade, p < 0.05) and a sharp decrease after 2006 (−42% per decade, p < 0.05). Spatially, the two recent sub-periods (1991–2005 and 2006–2020) exhibit opposing trends that form a dipole-like structure. CHDEs increase over Northeast and southern China but decrease over North China during 1991–2005, whereas they decline nationwide except over North China during 2006–2020. The post-2006 decline, despite continued warming, is attributed to drought alleviation from increased precipitation, indicating that decadal precipitation modulation can override the background warming trend. A unified physical framework links this spatial reversal to the Pacific Decadal Oscillation (PDO) phase shift: the warm phase (1981–1990) weakens the Western Pacific Subtropical High and monsoon, producing a Southern Less–Northern More (SLNM) CHDE pattern that corresponds to the Southern Flood–Northern Drought (SFND) regime, while the cold phase (2006–2015) reverses the pattern. This study extends the PDO-driven precipitation transition framework to CHDEs, revealing the decadal predictability of CHDE spatial patterns and demonstrating that internal climate variability can temporarily offset warming-driven trends. Analysis of the 500 hPa circulation reveals a ‘+−++’ wave train variation pattern from 1981–1990 to 2006–2015, providing a dynamical basis for the decadal transition of CHDEs. These findings establish a new dynamical framework linking PDO phase shifts and wave-train adjustments to the decadal spatial reversal of CHDEs over eastern China.