| Evapotranspiration（ET）refers to the total flux of water vapor from vegetation and the ground to the atmosphere.As an important component of energy balance and water cycle,ET not only affects the growth and development of vegetation,but also regulates the regional climate by influencing the atmospheric circulation.In this study,we selected the Qinghai Lake basin as the study area,and used Arc GIS spatial analysis and mathematical statistics,SLOPE trend analysis and spatial autocorrelation analysis to analyze the spatial and temporal variation characteristics,spatial clustering characteristics and topographic effects of evapotranspiration and various influencing factors in the Qinghai Lake basin from 2000 to 2020.Combined with The ecological water demand of the basin was calculated by combining the vegetation type data.Ten influencing factors were selected from three dimensions:meteorology,soil and vegetation,and topography,and a geographic probe model and a geographically weighted regression model were constructed to explore the interaction and spatial heterogeneity of the effect levels of each influencing factor on basin evapotranspiration in different years.The main results are as follows.（1）The interannual variation of annual evapotranspiration in Qinghai Lake basin shows a significant fluctuation with increasing years（p<0.01）,with annual evapotranspiration fluctuating from 311.39 to 432.15 mm,multi-year average evapotranspiration of 366.66 mm,and interannual variation rate of 4.14 mm·a-1.The interannual evapotranspiration shows an“inflection point”in July and then decreases."The evapotranspiration in July（91.95 mm）>August（82.53 mm）>June（71.56 mm）>September（45.27 mm）>May（37.50 mm）>October（13.97 mm）>April（10.77 mm）>March（5.31 mm）>November（1.75 mm）>February（1.69 mm）>January（0.73mm）>December（0.64 mm）.（2）The spatial distribution of multi-year mean evapotranspiration in the Qinghai Lake basin is characterized by“high in the southeast and low in the northwest”,with the high values on the south and southeast shores of Qinghai Lake and the low values in the west of the basin.The spatial distribution of the interannual variation of evapotranspiration ranges from-6.52 to 37.37 mm·a-1,and the areas with rising trend occupy the main part of the basin,while the areas with obvious rising trend are located in the northeast coast of Qinghai Lake and the southwest and west of Qinghai Lake basin,while the rest of the areas are relatively insignificant.The distribution of evapotranspiration in each month is characterized by“high in the southeast and low in the northwest”.According to the spatial autocorrelation analysis,12.56%of the areas on the south shore of Qinghai Lake and the northeast of the basin form high-high clusters,14.77%of the areas on the west of the basin form low-low clusters,72.64%of the areas in the middle of the basin are insignificant clusters,and low-high clusters are scattered on the east shore of Qinghai Lake,accounting for only 0.13%,and there is no high-low cluster type.（3）The evapotranspiration in Qinghai Lake basin shows certain topographic characteristics.The multi-year average evapotranspiration shows a“decreasing-increasing-decreasing”trend with the rise of elevation gradient,and it is flat slope>gentle slope>slope>steep slope>sharp slope>dangerous slope in different slope classes,and flat plane>northeast slope>north slope>northwest slope>east slope>west slope>southwest slope>southeast slope>south slope in different slope directions.The interannual variation rate of evapotranspiration decreases and then increases with increasing altitude,and it shows in different slope classes as dangerous slope>sharp slope>steep slope>slope>gentle slope>flat slope,and in different slope directions as plane>east slope>south slope>north slope>southwest slope>northeast slope>northwest slope>southeast slope>west slope.（4）The annual mean temperature,annual mean soil moisture,and annual mean NDVI in the Qinghai Lake basin show a significant fluctuating upward trend with increasing years,while the annual precipitation and annual mean surface temperature show a non-significant upward trend and the annual potential evapotranspiration shows a significant decreasing trend.In terms of spatial distribution,temperature decreases from southeast to northwest;precipitation is the largest in the east,followed by the central part and the smallest in the west;surface temperature gradually decreases from southeast to northwest;soil moisture is high in the north of the basin and the south shore of Qinghai Lake,and low in the west of the basin and the north shore of Qinghai Lake;NDVI is high in the north and south shores of Qinghai Lake,and lowest in the northwest of the basin and the northeast shore of Qinghai Lake;potential evapotranspiration is high in the south and low in the north.The potential evapotranspiration is high in the south and low in the north.The spatial distribution of all factors is clustered,and the spatial aggregation of air temperature and surface temperature is strong,while the spatial aggregation of soil moisture is the weakest.The spatial aggregation of temperature and surface temperature is strong,and the spatial aggregation of soil moisture is weakest.All factors show some differences in different elevations,slopes and slope directions.（5）The results of the geodetector showed that the same influencing factor had some differences in its ability to explain evapotranspiration in different years.According to the single-factor detection results,the influencing factors have different explanatory power for evapotranspiration.On the multi-year average scale,the single-factor detection q-values of the influencing factors are ranked as follows:NDVI（0.63）>altitude（0.42）>surface temperature（0.41）>air temperature（0.39）>potential evapotranspiration（0.26）>vegetation type（0.18）>soil moisture（0.12）>precipitation（0.07）>slope（0.05）>slope direction（0.01）,indicating that NDVI has the greatest influence on evapotranspiration.The coupling of NDVI and temperature was the largest factor affecting the distribution of evapotranspiration in the basin（q=0.76）,followed by NDVI∩elevation（q=0.75）,NDVI∩surface temperature（q=0.74）,NDVI∩potential evapotranspiration（q=0.74）are also important factors affecting evapotranspiration in the watershed.Slope∩slope direction had the least explanatory power on the spatial distribution of evapotranspiration（q=0.09）and had the least influence on evapotranspiration among all interaction factors.（6）The results of geographically weighted regression showed that the influence factors had different degrees of influence on evapotranspiration in different years,and the same factor had different degrees of influence in different localities.The NDVI regression coefficients ranged from-90.40 to 666.07,which had mainly positive effects on evapotranspiration.The coefficients of precipitation ranged from-1.44 to 4.30,which mainly had a positive effect.The potential evapotranspiration coefficients ranged from-0.42 to 1.93,with positive effects in most areas of the basin.Soil moisture coefficient ranges from-731.89 to 2312.44,with positive influence in the main part of the basin.The altitude coefficient ranged from-0.71 to 0.21,with 92.55%of the areas being negatively influenced.The slope coefficient ranges from-2.83 to 5.71,with positive influence in most areas.The slope coefficient ranges from-8.46 to 3.23,with the greatest positive influence in the south shore of Qinghai Lake,the northeast corner,the middle and the southwest of the watershed,and the greatest negative influence in the northeast and southeast shores of Qinghai Lake.The coefficients of vegetation types ranged from-19.26 to 23.58,which had a positive effect on evapotranspiration in most areas. |
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