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Drought events have become more frequent and intense over East Asia in recent decades, leading to huge socioeconomic impacts. Although the droughts have been studied extensively by cases or for individual regions, their leading variability and associated causes remain unclear. Based on the Standardized Precipitation Evapotranspiration Index (SPEI) and ERA5 reanalysis product from 1979 to 2020, this study evealuates the severity of spring droughts in East Asia and investigates their variations and associated drivers. The results indicate that North China and Mongolia have experienced remarkable trends toward dryness during spring in recent decades, while southwestern China has witnessed an opposite trend toward wetness. The first Empirical Orthogonal Function mode of SPEI variability reveals a similar seesawing pattern, with more severe dryness in northwestern China, Mongolia, North China, South Korea, and Japan but increased wetness in Southwestern China and southeast Asia. Further investigation reveals that the anomalously dry (wet) surface in North (Southwestern) China is significantly associated with anomalously high (low) temperature, less (more) precipitation, and reduced (increased) soil moisture during the previous winter and early spring, regulated by an anomalous anticyclone (cyclone) and thus reduced (increased) water vapor convergence. The spring dry-wet pattern in East Asia is also linked to cold sea surface temperature anomalies in the central-eastern Pacific. The findings of this study have important implications for improving the prediction of spring drought events in East Asia. [ABSTRACT FROM AUTHOR]

Snow cover on the Tibetan Plateau (TP) has been shown to be essential for the East Asian summer monsoon. In this paper, we demonstrate that tropical cyclone (TC) 04B (1999) in the northern Indian Ocean, which made landfall during the autumn of 1999, may have contributed to climate anomalies over East Asia during the following spring and summer by increasing snow cover on the TP. Observations indicate that snow cover on the TP increased markedly after TC 04B (1999) made landfall in October of 1999. Sensitivity experiments, in which the TC was removed from a numerical model simulation of the initial field, verified that TC 04B (1999) affected the distribution as well as increased the amount of snow on the TP. In addition, the short-term numerical modeling of the climate over the region showed that the positive snow cover anomaly induced negative surface temperature, negative sensible heat flux, positive latent heat flux, and positive soil temperature anomalies over the central and southern TP during the following spring and summer. These climate anomalies over the TP were associated with positive (negative) summer precipitation anomalies over the Yangtze River valley (along the southeastern coast of China). [ABSTRACT FROM AUTHOR]