Investigating Hydrogen And Oxygen Stable Isotope Characteristics,Influencing Factors Of Atmospheric Precipitation In Dingxi

Atmospheric precipitation is the most important link in the water cycle and one of the main sources of regional water resources.Water molecules contain the hydrogen-oxygen stable isotopes ¹⁸O and D,which facilitate the understanding of hydrological processes related to precipitation through the tracing of stable isotopes.Dingxi belongs to the continental arid climate,less precipitation,large evaporation,uneven spatial and temporal distribution of precipitation,in arid and semi-arid areas,in-depth understanding of precipitation process and its influencing factors can provide a basis for rational use of water resources.In this study,taking Dingxi as the research area,collecting precipitation data from four stations,combined with local meteorological data,analyzing the spatiotemporal characteristics,precipitation line and deuterium surplus characteristics of local precipitation hydrogen-oxygen stable isotopes,and analyzing the influencing factors of atmospheric precipitation hydrogen-oxygen stable isotopes in Dingxi from the aspects of meteorological elements,sub-cloud secondary evaporation effect and water vapor sources,and the following results were mainly obtained:（1）In terms of seasonal variation ofδD andδ¹⁸O in atmospheric precipitation in Dingxi,the change trend ofδD andδ¹⁸O values in the four stations of Dingxi was high in summer and low in winter.In terms of spatial variation,the stable isotope value of hydrogen and oxygen in Longxi County was high throughout the year,followed by Lintao County and the lowest in Min County.In terms of atmospheric precipitation line,the atmospheric water line of the four stations in Dingxi wasδD=7.13δ¹⁸O+7.66（r²=0.96,p<0.01,n=216）,which was lower than the slope of the global atmospheric waterline.In terms of atmospheric precipitation deuterium surplus,the deuterium surplus of precipitation at four stations is generally high in Dingxi,higher than the global average value of deuterium surplus,the characteristics show fluctuation changes,the average value of deuterium surplus in winter half year is greater than the average value of deuterium surplus in summer half,from a spatial point of view,the deuterium surplus value of four stations in Dingxi area in the whole year is Minxian County>Lintao County>Weiyuan County>Longxi County,the change trend in the summer half year is consistent with the whole year,and the overall change trend in the winter half year is Weiyuan County>Min County>Lintao County>Longxi County.（2）The correlation between meteorological factors（temperature,precipitation,relative humidity and water vapor pressure）and the stable isotope of precipitation in Dingxi area was weak,and the influence on the stable isotope of precipitation in Dingxi area was small.In terms of secondary evaporation under the cloud,the change range of raindrop evaporation residual ratio in the four stations was between 19.82%～99.95%,the change range ofΔd was between-0.09‰～-206.15‰,and there was an obvious linear relationship between the residual ratio of raindrop evaporation andΔd at the four stations in Dingxi and the slope was1.38‰%^-1 when the residual ratio of raindrop evaporation was between 60%～100%.The effect of precipitation on the evaporation residual ratio andΔd was not obvious.From the perspective of spatial changes,the evaporation surplus in the whole area is relatively large,and the range of change in Longxi County is wider,from the perspective of seasonal changes,the remaining evaporation of raindrops in the summer half of the year is relatively small,and the winter half year is larger,indicating that the temperature in the summer half of the year is high,the secondary evaporation under the cloud is obvious,the precipitation in the winter half of the year is mainly solid,and the secondary evaporation under the cloud is not obvious.（3）Analysis of water vapor sources at four stations in Dingxi,it can be seen from the whole that the four stations in Dingxi are mainly manifested as three sources of water vapor:westerly wind,monsoon wind and inland recirculation.Most of the water vapor sources at the four stations in the summer half of the year come from the west wind,followed by the monsoon water vapor source,and finally the inland recycled water vapor;The proportion of water vapor sources in the winter half of the year has changed,and the main source of water vapor is still west wind water vapor,followed by inland recycled water vapor,and finally monsoon water vapor.