Determining key upstream rainout and convection zones affecting δ18O in water vapor and precipitation based on 8-year continuous observations in the East Asian Monsoon region

Abstract More and more studies have recognized the crucial impact of upstream rainout effect and convective activities on the stable isotopic composition of precipitation (δ18Op) and water vapor (δ18Ov) at mid and low latitudes. However, it is difficult to precisely identify the upstream rainout and convection zones using the traditional time-lagged spatial correlation method. Based on a continuous high-resolution δ18Ov and δ18Op dataset in Nanjing (eastern China), a novel method of upstream key rainout region identification (UKRRI) is developed for reliably identifying the key upstream rainout and convection zones. Based on the UKRRI method, we find that summer δ18Ov and δ18Op in Nanjing are primarily controlled by the rainout effect and convective activities along the moisture transport pathway from the Maritime Continent (MC), via the Indo-China Peninsula and South China Sea (ICP_SCS), to Southeastern China (SEC), particularly over SEC. Contrary to existing studies, the Indian Ocean is not a major rainout and convection zone affecting δ18Ov and δ18Op in Nanjing. Our study has significant implications for the interpretation of stalagmite δ18O records in East Asian Monsoon (EAM) region.