Study On Characteristics And Influencing Factors Of Stable Isotopes Of Precipitation In The Hengduan Mountains

Stable isotope of precipitation has been widely used in hydrological and climate research.The Hengduan Mountains is an essential channel for water vapor from South Asia to enter China.Its topography is complex and interacts with multi-scale atmospheric processes,thus forming a unique mechanism of water vapor transport and precipitation process.By analyzing the stable isotope of precipitation’s characteristics and influencing factors in the Hengduan Mountains,the influence of water vapor source,water vapor transport path,and local topography on precipitation can be quantitatively revealed,and the research results can provide a scientific basis for water resources evaluation,climate change research and ecological construction in the Hengduan Mountains.Based on 403 precipitation samples collected from 11 observation stations in the Hengduan Mountains from June 2020 to June 2022,combined with ECMWF（The European Centre for Medium-Range Weather Forecasts）and NCEP（National Centers for Environmental Prediction）meteorological data,Gr ADS（Grid Analysis and Display System）and HYSPLIT model（Hybrid Single Particle Lagrangian Integrated Trajectory Model）,the temporal and spatial variation characteristics of stable isotope of precipitation in the Hengduan Mountains are analyzed,and the effects of meteorological and climatic factors and topography on stable isotope of precipitation are discussed.The main conclusions of this paper are as follows:（1）Regarding time variation,stable isotope of precipitation is enriched in spring and winter and depleted in summer and autumn.Regarding spatial variation,stable isotope of precipitation is enriched from north to south and west to east.The LMWL（Local Meteoric Water Line）of the Hengduan Mountains isδ²H=7.87δ¹⁸O+9.86（R²=0.97,n=403）.With the increase in altitude,the slope of LMWL decreased,and the slope is North>Midwest>East.The seasonal variation of d-excess value is apparent,and the dry season（November to April of the next year）is high,and the rainy season（May to October）is low,which is in line with the characteristics of the region affected by monsoon precipitation.In the North,d-excess decreased from north to south and from west to east,and the seasonal variation is not obvious.The d-excess value in the Midwest increased with the elevation.The d-excess value in the East is smaller in the rainy season than in the dry season.（2）Precipitationδ¹⁸O is mainly affected by topography and large-scale water vapour migration,while meteorological factors have little influence on precipitationδ¹⁸O.There is both positive and negative correlation between precipitationδ¹⁸O and air temperature.There is generally negative correlation between precipitationδ¹⁸O and precipitation,and negative correlation between precipitationδ¹⁸O and relative humidity.The water vapor in the Hengduan Mountains mainly comes from the Bay of Bengal,the Indian Ocean,the South China Sea,and the Pacific Ocean.The southwest water vapor affects the North from May to September,resulting in the precipitationδ¹⁸O in the North in the dry season>rainy season.The southeast water vapor affects the Midwest from May to September,resulting in the lowest value of precipitationδ¹⁸O in the Midwest in September.The southeast water vapor affects the East from May to November,consistent with the fact that the precipitationδ¹⁸O in the East is depleted from May to October.（3）The Hengduan Mountain range has both a channel function and a barrier function for warm and humid airflow.In the rainy season,the Hengduan Mountains,which run nearly north and south,have obvious water vapor channel effect on the southwest monsoon,so that water vapor can be transported to the northern part of the Hengduan Mountains.Under the influence of the southwest monsoon and southeast monsoon,the stable isotope of precipitation on the eastern slope of the Hengduan Mountains began to be depleted earlier than those on the western slope,and the stable isotope of precipitation on the northern slope began to be depleted later than those in the southern slope,indicating that the Hengduan Mountains have a barrier effect on water vapor.