Isotopic Characteristics Of Precipitation And Source Analysis Of Water Vapor In The Middle Qilian Mountains

Atmospheric precipitation is an essential link in the water cycle,and the study of stable isotopes helps to understand the water cycle process.The middle section of qilian mountains is a hot spot of global climate change response due to its special geographical location and ecological environment.In view of this,the precipitation from August 2015 to August 2016 at five stations in this region,the stable isotope characteristics of typical precipitation and the direction of water vapor source were systematically analyzed.The results show that:(1)The range of ?18O in the middle section of Qilian Mountain is:-33.3‰-9.7‰,and the range of ?D is:-264.9‰-67.5‰.The isotope fluctuations in summer and autumn are more significant than in spring and winter.The stable isotope of precipitation,temperature and precipitation are both low in summer and low in winter,and the relative humidity is slightly lower in winter.Overall,the slope and intercept of the meteoric water line in the study area are higher than the global atmospheric waterline.The intercept increases with the increase of precipitation,and d is positively correlated with precipitation,temperature and relative humidity.The positive correlation between ?18O and temperature is good,and there is a weak precipitation effect on the whole.The height gradient of ?18O in the precipitation of the middle section of Qilian Mountain is-0.45‰/100 m.(2)The precipitation of each site is affected by the combination of the westerly water vapor,the southwest monsoon water vapor,the southeast monsoon water vapor,the local water vapor and the northern water vapor.The influence of the westerly water vapor is the most significant,and the summer is afected by the water vapor in the southeast.Among them,Sunan,Minle and Tolle were affected by the northern water vapor in spring and summer,and Sunan,Bunigou and Qilian were affected by water vapor in the southwest in summer.The height of the backward trajectory is also higher when the underlying surface is higher.(3)The Hexi Corridor to the north of the study site,the surrounding Qilian Mountains,the northern section of the Qaidam Basin and the southwestern section of the Jiuquan area are the main potential sources of evaporation.Evaporated water vapor in the northern Tarim Basin,eastern Xinjiang,and the southeastern plateau also contributed to precipitation in the study area.The wind rose map indicates that the surrounding area of the study and its northwest and northeast are potential sources of evaporation.The west wind water vapor is enriched with heavy isotopes,and the d value is higher.The monsoon water vapor is depleted in heavy isotope in summer,heavy isotopic enrichment in winter,and low d value.The d value of local and northern water vapor is often higher.(4)Through the study of two persistent precipitation events in Sunan and Buffalo,it is found that the meteoric water line slope and intercept and the stable isotope values of precipitation are closely related to meteorological conditions,and the precipitation process is consistent with the Rayleigh fractionation model.The temperature of the 8 strong precipitation events was higher,the relative humidity was higher,the stable isotope values were depleted,the d value was higher,and the secondary evaporation effect under the cloud was weaker.Typical precipitation events are affected by the westerly wind,southwest monsoon,southeast monsoon and local water vapor,especially monsoon water vapor,d value is lower,followed by northern water vapor and westerly water vapor,d value is higher,multiple water vapor convergence is a necessary condition for the occurrence of heavy precipitation events.