Synoptic time-series surveys of precipitation δ18O and its relationship with moisture sources in Yunnan, southwest China

The stable oxygen isotopic composition (δ18O) of different water bodies can provide valuable information for investigation of hydrological processes, and it is an effective natural tracer that can be used to characterize the moisture sources of precipitation. In this study, to analyze the influence of moisture sources and meteorological variables on variations of precipitation δ18O, a project of monitoring intense precipitation events was conducted through three entire years (2009-2011) at the Kunming, Mengzi, and Tengchong stations in Yunnan Province, southwest China. The results suggested that variations of precipitation δ18O in Yunnan exhibit a significant seasonal variability. The use of high-resolution data revealed a significant anti-temperature effect as well as an amount effect. Additionally, we found that precipitation δ18O does not follow the amount effect during some rainfall events of two consecutive days. In detail, the first day has higher precipitation amount than the second day. However, the precipitation δ18O values of the second day are more negative than those from the first day. Significantly positive correlations between precipitation δ18O and wind speed at different pressure levels (800, 700, 500, and 300 hPa) demonstrate that wind speed is an important controlling factor of variations of precipitation δ18O. Backward trajectory results generated by the HYSPLIT model show that the moisture sources for precipitation with low δ18O during the wet season are mainly from the Bay of Bengal (BoB), Arabian Sea (AS), and South China Sea (SCS). By comparison, the high δ18O values of precipitation during the dry season are found to correspond to remote westerly air masses and inland re-evaporated vapor. Moreover, the precipitation δ18O associated with typhoons is much lower than that of the normal precipitation events. These findings indicate that the stable isotopic composition of precipitation is closely related to meteorological variables and is rapidly responsive to changes in sources of moisture.