Atmospheric process factors affecting the stable isotope variations in precipitation in Guiyang, Southwest China

The research on precipitation stable isotopes is beneficial for gaining insight into the water cycle in the monsoon region. However, the variability of monsoon and lack of high-resolution collection of precipitation stable isotopes in the monsoon region has been posing a limitation on learning the controlling factors on its variations. This study collects the daily precipitation stable isotopes in Guiyang from April 2022 to March 2023. The research results show that the precipitation stable isotopes display seasonal variations with the slope and intercept of the fitted local meteoric water line (LMWL) being 8.9 and 19.69, respectively. During the year, precipitation delta 18O has a weak negative correlation with precipitation amount and temperature, but the correlation between precipitation delta 18O and local environmental factors is not as significant as the one between precipitation delta 18O and precipitation amount and outgoing longwave radiation (OLR) of the upstream area. During the monsoon season (MS), as the Intertropical Convergence Zone (ITCZ) migrates northward, the oceanic water vapor and upstream convective activity cause the decrease in precipitation stable isotopes. While during the non-monsoon season (NMS), the local circulation water vapor becomes the dominant water vapor source, leading to the increase in precipitation stale isotopes. The above studies demonstrate that water vapor sources and upstream convective activities play a critical role on variations of precipitation stable isotopes in Guiyang, which can provide basic information for future research on the water cycle in the monsoon region.