Moisture Sources In Dingxi Based On Hydrogen And Oxygen Stable Isotopes

Atmospheric precipitation is an important input to water cycle,and the isotope information contained in water molecules is an important evidence to trace the source of water vapor.Stable isotope technology provides a new perspective for the study of water cycle process.Dingxi is located in the loess plateau area of China.The climate there is very dry and weather disasters are frequent there.Using isotope technology to study the water cycle in Dingxi area has become a new technical means.Based on the field measurement data,this paper supplemented and studied the stable isotope information of atmospheric precipitation in Dingxi,and discussed the water vapor source in Dingxi in detail.Stable isotope method,least square method and statistical analysis method were used to summarize the variation of precipitation isotope values in Dingxi.Lagrangian mixed particle model and atmospheric vapor flux model were used to study the characteristics of water vapor sources in Dingxi,and the types of water vapor sources were classified.Combined with stable isotope method and analytical model method,the characteristics of water vapor sources in Dingxi were analyzed in detail.The main conclusions of the study are as follows:(1)The annual variation of isotopic values in Dingxi is small and the fluctuation is not obvious.In terms of seasonal variation,the values of?¹⁸O and?D in precipitation are high in summer and low in winter.There is a positive correlation between?¹⁸O values and temperature in the northern part of Dingxi,and the correlation is stronger in the southern part than in the northern part.There is a positive correlation between?¹⁸O values and temperature in the dry and rainy seasons,and there is a strong temperature effect within the season.(2)The slope of the atmospheric water line equation in the northern and southern regions of Dingxi is higher in the south than in the north,and the intercept difference is bigger,which is also higher in the south than in the north.The minimum slope appears in Weiyuan,and the maximum slope appears in Tongwei,and the spatial trend is higher in the southeast and lower in the northwest.The?¹⁸O value was higher in summer,but the mean value was relatively low in winter,and the D-excess value changed gradually.The spatial distribution of?¹⁸O and?D in precipitation was regular,and the?¹⁸O and?D values were gradually depleted from Weiyuan in the southeast to Zhangxian in the northwest,and the?¹⁸O value was the lowest in Zhangxian.(3)According to different water vapor sources,the water vapor source types in Dingxi can be divided into continental type,westerly type,westerly-inland mixed type and westerly-inland-summer wind mixed type.The first is the westerly type of water vapor source.All of its water vapor comes from the inland plates.As for the water vapor sources with only westerly nature,they are all in winter and early spring,showing a simple westerly circulation control.For the mixed westerly and continental water vapor sources,most of them came from spring and autumn,and westerly circulation accounted for the highest proportion of water vapor.In the summer of Dingxi,the water vapor sources are very complex,which are mainly manifested by the west wind,inland evaporation and monsoon water vapor,but monsoon water vapor contributes the most,and is affected by the combined action of two water vapor from southwest and northeast simultaneously.The water vapor flux in Dingxi moves in reverse direction along the latitude line,and the atmospheric precipitable water in summer and autumn is greater than that in winter and spring,and the water vapor source in summer is the most complex.(4)According to the different water vapor transport paths,the isotopic values of different water vapor sources are calculated,and it is found that the isotopic values of the inland water vapor sources are the highest,while those of the westerly and inland water vapor sources are the lowest.The slope of the precipitation line equation of the westerly water vapor source is the largest,and the slope of the mixture is the smallest.The d value of monsoon precipitation is lower than that of inland and westerly precipitation,and the d value of inland precipitation is lower than that of inland and local mixed precipitation.(5)The water vapor sources in Dingxi are both continental and monsoon.In monsoon period,the water vapor sources are precipitation with large ocean as the source,while in non-monsoon period,the water vapor sources are precipitation influenced by westerly belt,large inland lakes,rivers and other forms of evaporation surface elements.