| Water resources is an indispensable and important energy for human life and production,is also the important environmental factors in inland arid area ecological environment,development,plays an important role in maintaining regional ecological environment,the most important ecological factors of ecological environment in arid areas of desertification,it is also the oasis development in the evolution process[1].With the increase of population and the development of economy,the shortage of water resources is becoming more and more serious.Precipitation is an important part of water resources and an important input of water cycle,which makes it a decisive factor for regional water resources abundance.Therefore,the study of regional precipitation is very necessary,and the isotopic composition of precipitation is the best clue to our understanding of atmospheric precipitation.Hydrogen and oxygen isotopes as an important part of natural waters,their composition and change can be very sensitive to reflect the regional environmental change[2-9],and record the historical information of environmental evolution.In addition,stable isotopes can be used to trace the water vapor source of atmospheric precipitation,which can reflect the characteristics of weather,climate and regional environment to a certain extent.Therefore,studying the variation characteristics of precipitation isotopes is very important for revealing regional water vapor source area,precipitation formation conditions and regional water cycle process.The stable isotopic composition in precipitation is constrained by geographical parameters and meteorological elements.It is not a simple dynamic process in time series,just like other hydrological elements.It is highly nonlinear and characterized by multiple time periods[10].The Loess Plateau as a transition zone in the arid regions and humid areas,is the world's one of the most serious soil erosion areas,help to understand the characteristics of temporal and spatial distribution of water resources in the area of the precipitation isotope research,so as to provide more scientific guidance for the treatment of environmental problems.Therefore,this paper uses GNIP as the data source,we have studied the Loess Plateau 7 sites?Lanzhou,Yinchuan,Jingbian,Xi'an,Pingliang,Baotou,Taiyuan?the temporal and spatial variation characteristics of stable isotopes in precipitation,analyzes the relationship between the other site in addition to the JingBian Railway Station isotopes in precipitation and temperature and precipitation,reveals the change the law in the area of stable isotope in precipitation.The main conclusions are as follows:According to the test results of stable hydrogen and oxygen isotopes of precipitation in the region,the?18O of precipitation in the Loess Plateau region is between-23.7and 3.86,and the mean value is-3.89.It is found that the delta 18O in the Loess Plateau shows similar time variation trend,that is,in the main precipitation period of autumn and winter,the delta18O value is relatively poor,and the summer is relatively concentrated.Comparing the precipitation isotopic results of different stations,the maximum value of the delta 18O except Pingliang Railway Station is in the summer half year?510?,and the minimum value appears in the winter half year?114?.Site of the Loess Plateau in the precipitation of oxygen isotope annual weighted average values do not show obvious enrichment trend gradually from the west to the East,the central site in the area of precipitation isotope values relative enrichment and difference;South Station Precipitation isotope values of the second,but the Pingliang Railway Station due to elevation effect leads to strong isotope dilution serious north;the site of precipitation isotope value is low,showing the latitude effect,but the BaoTou Railway Station due to the westerly and southeast monsoon transition zone,the water vapor source complex,high rainfall,so the ratio is slightly south of YinChuan Railway Station isotope enrichment.It is obvious that altitude has a significant influence on the stable isotopes of precipitation in the Loess Plateau.For the further study of precipitation stable isotope variability,the coefficient of variation?Cv?,on the whole,the Loess Plateau in the southern region of low latitude location and the vapor source complex,precipitation variability,Cv value is large;north is far away from the sea,the water source is single,the Cv value is small.The stable isotopic data of the 7 sites were analyzed,and the atmospheric water line equation of the Loess Plateau region was established as:?D=7.0?18O+0.36.The slope and intercept of the atmospheric water line in the Loess Plateau are lower than the global atmospheric precipitation line.It reflects the strong evaporation effect in the process of regional precipitation,which makes the isotopic dynamic fractionation.Whether the meteoric water meteoric water in the loess plateau or the site fitting,will find the slope and intercept values were lower than the global atmospheric precipitation,indicating that these site moisture source area is relatively complex,affected by the monsoon and the local circulation and the two strong evaporation effect is more obvious.Effect of temperature on the Loess Plateau of each site has spatial precipitation isotope characteristics are more prominent,the northwest plateau near the arid regions of Lanzhou,Yinchuan and Baotou sites have a greater slope,and the temperature effect of these three sites are the most obvious,and the southern and eastern plateau and each site showed no significant effect of temperature.In addition,the correlation of precipitation isotopes with precipitation at two sites in Lanzhou and Yinchuan is relatively large.Generally speaking,the precipitation effect in the southern part of the Loess Plateau is more significant than that in the southern part of the Loess Plateau.The deuterium surplus value of the 7 stations in the Loess Plateau area is weighted by monthly average.It is found that the value of the deuterium surplus of precipitation is large,which further indicates that the water vapor sources of the Loess Plateau are complex and diverse.In the northwest region of the Loess Plateau?Lanzhou,Yinchuan,Jingbian and Pingliang station?in the precipitation of deuterium surplus value in summer,especially in 7?8,significantly lower than 10,which indicates that there are more negative bias,in the northwest loess plateau area in Summer half year high relative humidity,evaporation is weak,the situation in the winter half year.The rule of the southern area?XiAn station?is basically the same as that of the northwest,but the rule of the northern area will be more significant.However,the eastern area will show an earlier rule,which may be related to the earlier monsoon.That according to the changes in precipitation in the Loess Plateau,deuterium excess in time,the area in the winter monsoon during the summer monsoon period with high wind speed,low humidity and strong evaporation,the plateau during this period of internal evaporation of water vapor is an important source of rainfall,which is the main cause of the excessive precipitation high deuterium.During the summer monsoon period in the Loess Plateau,the two evaporation ratios of each site ranged from 1.76%to 5.88%,with a mean value of 4.72%.The winter monsoon value ranged from 1.06%to 5.43%,with a mean value of 2.79%.For the specific area,the two evaporation effect of the Loess Plateau showed a trend of decreasing from northwest to Southeast.For monsoon influence,the influence of monsoon on the two evaporation effect is not strong in the periphery of the plateau. |
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