Spatial-temporal Evolution Characteristics And Influencing Mechanism Of Lake Evaporation In Xinjiang

Lakes are a major form of water resources storage in Xinjiang,and lake evaporation is an important factor affecting the lake area.Studying the climate and weather change characteristics of lake evaporation,understanding the law of lake evaporation and the interrelationship between local meteorological conditions and evaporation process,discovering the meteorological elements affecting evaporation process,and exploring the methods and means affecting evaporation process can provide the theoretical basis and scientific basis for scientific water conservation in Xinjiang lakes.In this paper,the spatial and temporal characteristics of lake evaporation in Xinjiang under the background of global warming are studied by means of observation data analysis and numerical simulation,and the meteorological elements affecting lake evaporation are analyzed.Bosten Lake,Ebinur Lake,and Sayram Lake with different regions and different lake sizes are selected as the key objects to study the correlation between lake evaporation and local meteorological elements.This paper analyzes the effects of precipitation and evaporation on the overall changes in lake areas in Xinjiang.The changes in lake area in Xinjiang are mainly influenced by the actual annual evaporation,annual precipitation,and the difference between evaporation and precipitation.The trends of difference between evaporation and precipitation in most lakes are more consistent with the changes in the area.Except for Sayram Lake,Kanas Lake,and Pak Lakri Lake,the evapotranspiration difference of most lakes is positive,among which the difference between evaporation and precipitation of Bosten Lake is the largest,reaching 510.46 mm.This indicates that most of the lakes in Xinjiang lose more water by evaporation than by precipitation.The lakes with an area of 100 km~2 or more follow the characteristic of greater evaporation the larger the area is.The annual evaporation of major lakes from 1950 to 2020 shows an increasing change,and after 2000,the annual evaporation of most lakes has a tendency to decrease.There are also significant differences between the evaporation of lakes in different regions such as plains and plateaus.The increasing trend of annual evaporation of plain lakes is more significant than that of plateau lakes.The daily evaporation of plateau lakes is influenced by thermal factors,while the daily evaporation of plain lakes is less influenced by thermal factors and more influenced by dynamic factors.The evaporation of the highland lake Sayram Lake is most influenced by net radiation.The evaporation from the plain lake Bosten is mainly influenced by wind speed,and the linear fitting results show that the daily evaporation from Bosten Lake increases by 0.58 mm for every 1 m/s increase in wind speed.evaporation from Ebinur Lake is most influenced by wind speed,but temperature and relative humidity also play an important role in evaporation.This paper focuses on the analysis of the evaporation processes of Bosten Lake,Ebinur Lake,and Sayram Lake as influenced by dynamical processes.Lake evaporation and wind speed on the hourly scale all showed strong positive correlations,with correlation coefficients above 0.4,0.6,and 0.7 respectively,i.e.the higher the wind speed,the stronger the lake evaporation.Lake surface evaporation is weakly correlated with air temperature,sensible heat flux,long-wave radiation,water vapor mixing ratio,and boundary layer height.While evaporation from the land surface around the lake is more influenced by heat regulation,under the same thermal conditions,the influence of wind speed is not as strong as the influence of wind speed on the lake surface.On the shore around the lake,the sensible heat flux determines the evaporation intensity.In the complex subsurface where wetlands,lakes,Gobi,and deserts coexist,wind changes affect the vertical distribution of water vapor,which has a significant effect on the evaporation from the lake surface,the size of evaporation from the land surface around the lake and the change of spatial distribution.The local boundary layer process of the lake has a significant influence on evaporation.Evaporation in the region of Lake Bosten is mainly influenced by wind speed and vertical velocity below 900 h Pa.Evaporation in the region of Lake Ebinur is mainly influenced by wind speed and relative humidity below 950 h Pa.Evaporation in Lake Sayram is mainly influenced by relative humidity and vertical velocity below 825h Pa,followed by horizontal wind speed and air temperature.The greater the horizontal wind speed in the boundary layer,the greater the evaporation,and the stronger the turbulence and the more unstable the atmosphere,the greater the evaporation.The water vapor evaporated from the lake surface is concentrated in the boundary layer,and the height of the boundary layer determines the water vapor content at the bottom,which also has a certain influence on the change of evaporation.The summer evaporation of Bosten Lake is mainly influenced by the southward wind and westward wind,and the corresponding evaporation accounts for 44.72%and36.75%of the total amount respectively;however,the evaporation corresponding to the southward wind and eastward wind has increased with the climatic tendency rate of51.69 mm/10a and 29.13 mm/10a respectively in recent 10 years,and the influence of both has been enhanced year by year.When the initial field of wind speed is reduced to0.5 times,the evaporation from the lake surface of Lake Bo in the summer of 2020 is reduced by about 12 mm;when the initial field of wind speed is reduced to 0.8 times,the evaporation from the west side of Lake Bosten increases by about 4 mm and the evaporation from the east side of the lake decreases by about 8 mm.In this paper,a numerical simulation experiment of artificially influencing the evaporation process on the lake surface was conducted.Adding wind turbines around Lake Bosten affects the boundary layer structure around the lake surface,which is beneficial to suppress the evaporation from the lake surface.The wind turbine converts part of the kinetic energy into electrical energy,which leads to the reduction of wind speed,increases vertical mixing,changes the local boundary layer structure on the lake surface,generates local circulation,and affects the evaporation process.The numerical simulation results show that when the wind turbines are placed around Lake Bosten,the evaporation of the lake and land surface in the Lake Bosten area is reduced,and the lake surface is more influenced by the wind turbines.The evaporation of the lake surface in summer decreased by up to 6 mm for every 3 km of wind turbines,and the more dense the wind turbines,the more the evaporation decreased.In the eastern Gobi of the lake,one fan per 1 km will reduce evaporation by 10.4 mm per year on average.