Research On The Contribution Rate Of Local Recycled Water Vapor To Precipitating Water Vapor In The Upper Reaches Of Shiyang River Basin

The research on the eco-hydrological functions of different landscape underlying surfaces in alpine region is the scientific basis for water resources management and ecological environmental protection in the basin.Evapotranspiration plays a link role in the process of land-air interaction,and is one of the core contents in the study of climate change and ecology.In this study,the upper mountain area of Shiyang River Basin is selected as the research area,which is located in the sensitive and vulnerable areas of ecology.The ecosystem services such as water conservation are prominent,which can reflect the characteristics and functions of the ecological landscape in the upper reaches of typical basin.Isotope technology has been widely used in various disciplines because of its “fingerprint” function.It can achieve higher accuracy and can be operated conveniently.In the study,the samples collected by the stable isotope observation network for various water built by our research group in the Shiyang River Basin were tested.Then,based on the end-member linear mixing model of stable isotope technology,this research respectively estimated the contribution rate of local recycling water vapor at different elevation gradients in typical alpine small basin,the contribution rate of reservoir evaporative water vapor in the Xiying Reservoir,a typical artificial lake in the eastern part of Qilian Mountains,and the contribution rate of recycled water vapor in the source area of Shiyang River.And this research analyzed theirs changing rules and characteristics.The study explores the impacts of climate change on plateau ecosystem from the mechanism,deepens the understanding of ecological and hydrological processes in cold regions,and also provides decisionmaking services for the development of agriculture and animal husbandry and the rational allocation of water resources in the middle and lower reaches of the region.The conclusions are as follows:(1)In this study,two-end-member linear mixing model and three-end-member linear mixing model were used to estimate the contribution of recycled water vapor in Xiying River Basin.Local recycled water vapor from plant transpiration and surface water evaporation will be depleted to a certain extent,and the atmospheric water vapor supplied by recycled water vapor will be depleted.Advection water vapor is the main source of local atmospheric water vapor,and the contribution rate of recycling water vapor is relatively low(less than 20%),which reflects that the local rainfall capacity of the basin is weak and depends on advection water vapor supply.A series of factors such as temporal and spatial differences in transport routes of exotic air masses,evapotranspiration capacity and vegetation coverage lead to spatial and temporal differences in the contribution rate of local recycled water vapor.With the increase of air temperature and evaporation capacity,the difference of recycling water vapor contribution rate at different altitudes increases.The seasonal difference of the contribution rate of local recycling water vapor decreases with the decrease of altitude.(2)Xiying Reservoir is mainly affected by air masses in the southeast,northeast and southwest directions in summer.About 51.1% of the water vapor comes from the southeast,and the air mass is wetter.In contrast,the transport distance and speed of air masses from Northeast and Northwest are faster.In summer,the deuterium excess in precipitation value of Xiying Reservoir is higher than that of the stations in the upper wind direction,which shows the mixing characteristics of evaporation water vapor and water vapor transported from the reservoir.About 3.86%?11.86% of atmospheric water vapor comes from reservoir evaporation.This result is lower than that of other research areas in the world.About 4.39% of the reservoir water is consumed by evaporation.The remaining part will continue to be stored in Xiying Reservoir or in the middle and lower reaches of Shiyang River for recharge.There is a lot of ineffective evaporation in Xiying Reservoir,and the efficiency of water resources utilization is low.(3)The monthly variations of stable isotope values in precipitation and water vapor in the source area of the river show obvious seasonal effects.From March to September,it showed a gradual upward trend.The results show that there is an active local recycled water vapor movement in the source area of Xiying River.The contribution rate of recycled water vapor in the study area varies from 3.58% to 12.86%in March to September,and there are obvious monthly differences.The contribution rate of recycling water vapor increases with the increase of air temperature and decreases with the decrease of air temperature.The sparse vegetation,short vegetation growth period and weak life activities in the source area led to the lower contribution rate of vegetation transpiration in August than that of surface water evaporation.