Possible Impact of Spring Soil Moisture Anomalies over the Indian Peninsula on the “Dragon Boat Water” in South China

The period surrounding the Dragon Boat Festival each year coincides with the most concentrated precipitation in the “pre-flood season in South China” and is thus termed “dragon boat water” (DBW, from 21 May to 20 June). While the effects of atmospheric circulation and sea surface temperature (SST) have been widely explored, the mechanism of land surface forcing on the DBW in South China (SC) remains poorly understood. Therefore, based on observation and reanalysis data, this paper studies the effect of spring soil moisture (SM) over the Indian Peninsula (IP) on the DBW and the associated physical mechanism during 1992–2021. The results show that the leading mode of empirical orthogonal decomposition of precipitation during the DBW period in SC exhibits spatial coherence. Spring SM over the IP exhibits a significant positive correlation with the DBW. Spring wet soil over the IP can persist into the DBW period. This increases land surface evapotranspiration and latent heat flux, enhancing local convective activity in the middle and lower troposphere and leading to increased precipitation over the IP. The precipitation in the IP intensifies the South Asian high and extends it eastward by releasing condensational latent heat to heat the atmosphere. The thus stimulated circumglobal teleconnection like wave train causes the Northern Hemisphere to evolve into a zonal five wave structure in the upper troposphere, and SC is under the influence of the atmospheric wave activity center over East Asia. Concurrently, barotropic energy conversion over East Asia intensifies significantly, favoring the development of the quasi-barotropic structure; thereby, the western Pacific subtropical high intensifies and extends westward. Under the influence of the abnormal anticyclone over the Northwest Pacific, SC is controlled by the stronger southwesterly wind facilitating the transport of warm moisture from the South China Sea and the Bay of Bengal to SC. Significant ascending motion and stronger meridional wind are observed throughout the troposphere, conducive to more rainfall over SC during the DBW period. These results advance the understanding of climatic effects of spring SM anomalies over the IP, and provide guidance for improving the predictability of the DBW.