Abstract: The stable isotopic ratios in precipitation have notable seasonal variations in the vapor transport path in Kunming in Southwest China, with a higher mean δ18O in precipitation in dry season (from November to April) than that in rain season (from May to October).The vapor for precipitation in Kunming is originated primarily from low\|latitude oceans. The slope and the constant item in the meteoric water line (MWL), compared to the global MWL, are both smaller in Kunming, and are related to the evaporation enrichment of heavy isotopes as raindrops fall in unsaturated atmosphere. There is a notable positive correlation between the stable isotopic ratios in precipitation and the dewpoint deficit in land ΔTd. In dry season with the dry air, light precipitation, great ΔTd in atmosphere, strong evaporation and thus strong enrichment of heavy isotopes, influenced by continental air-mass, the rainfall in Kunming is characterized with high stable isotopic ratio. In rain season with the moist air, heavy precipitation, small ΔTd in atmosphere, light evaporation and thus light enrichment, influenced by lowlatitude marine vapor, the rainfall is characterized with low stable isotopic ratio. Therefore, it can be deduced that the effect is the outcome of the impact of different vapor origins on stable isotopes in precipitation.

Key words: Kunming, vapor transport path, stable isotopes, amount, dew-point deficit