Enhanced Influence of April Snow Cover Over the Eastern Tibetan Plateau on the Variability of West China Autumn Rain After 2000

ABSTRACT “ West China Autumn Rain” (WCAR), which represents the second peak in local precipitation following the summer, frequently causes floods and related secondary disasters, posing significant challenges to the sustainable development of economy and society. As such, a better understanding of the variability in WCAR is crucial for disaster prevention and mitigation. This study, based on the observed precipitation and reanalysis data, addresses the relationship of the WCAR variability with the April snow cover over the eastern Tibetan Plateau from 1981 to 2021, and highlights a notable shift from an insignificant to a significant correlation after 2000. During 2000–2021, the distinctive dipole pattern of the eastern Tibetan Plateau snow cover (TPSC) in April—characterised by negative anomalies in the south and positive anomalies in the north—corresponds with an intensification of the South Asian High (SAH) in the subsequent autumn. This, in turn, induces a northward shift of the East Asian jet (EAJ) and a westward displacement of the western Pacific subtropical high (WPSH), concurrent with an enhancement of moisture transport into West China, providing favourable dynamic and moisture conditions for the increase in WCAR. The warming of soil temperatures in April over the southeastern Tibetan Plateau, driven by increased shortwave radiation and propagating into autumn, is hypothesized to bridge the lagged influence of snow cover on the above atmospheric circulations. In contrast, during 1981–1999, due to decreased interannual variability of snow cover, the April TPSC shows no substantial effect on the WCAR‐related atmospheric circulations, hence weakening its connection with the WCAR variability.