Comparison of precipitation stable isotopes during wet and dry seasons in a subtropical monsoon climate region of China

Abstract

Hydrogen and oxygen stable isotopes are natural tracers and have played an important role in the investigation of hydrological processes. In this paper, year-round precipitation samples were collected and measured in Chengdu, a subtropical monsoon climate region, to compare the stable isotope characteristics in precipitation and their influencing factors between dry and wet seasons. The results showed that the seasonal variation of δD and δ18O in precipitation was significant, and the isotopic values in precipitation in dry season were more enriched than those in wet season. The slope and intercept of local meteoric water line (LMWL) in Chengdu were lower than those in the southeast monsoon region of China but higher than those in north China, indicating the combined influence of ocean-source and inland water vapor. The slope of LMWL in dry season was obviously lower than that in wet season, revealing more intense sub-cloud secondary evaporation. The effect of temperature and precipitation was not significant in both seasons. Meteorological variables had greater influence on precipitation isotopes in wet season. D-excess had greater fluctuation during the dry season, reflecting more complex water vapor sources, which resulted in the influence of meteorological factors being masked.