Variations And Attribution Of Water Surface Area And Actual Evapotranspiration In The Endorheic Basins Of The Mongolian Plateau

In recent years,the process of water cycle in the basin has undergone dramatic changes due to the dual effects of climate change and human activities.Evapotranspiration is the central link in the water cycle of the basin and has a profound impact on the hydrological cycle of the region.With the latent heat exchange of evapotranspiration as a link,the water balance and heat balance in the basin are closely related.Budyko hypothesis holds that water(precipitation)and energy supply(potential evapotranspiration)are the two main factors controlling the actual evapotranspiration in the basin.and it is widely used in the study of evapotranspiration in the basin because of their concise expression and clear physical significance.The Mongolian plateau is a typical arid and semi-arid region with a large area,and strongly representative.In addition,the Mongolian plateau includes vast arid and semi-arid regions in the north of China,with sensitive climate change and fragile ecology,and it is the key construction area of "Green Wall of China" in China.Therefore,it is of great theoretical significance and application value to study the Budyko hypothesis in the Mongolian plateau.In this paper,the endorheic basins of the Mongolian Plateau is taken as the research object.Firstly,the meteorological and vegetation data of the study area were analyzed by temporal and spatial variation,trend analysis and catastrophe point anal,ysis.Then based on the water surface area data from 1984 to 2015.the spatial distribution and spatial-temporal variation of the water surface area are analyzed,and the spatial distribution difference and spatial-temporal variation of the water surface area arc attributed.Next,based on Budyko hypothesis,the parameter ? of 1276 endorheic basins in Mongolian Plateau are studied,and the semi-empirical formulas of multi-year scale and annual scale are summarized.Finally,according to the research period,the reference period and change period are divided by 2000 to analyze the actual evapotranspiration changes in Dalinor Lake Basin,Daihai Basin and Hongjiannao Basin.The main conclusions are as follows(1)The study of the spatial distribution of water surface area shows that the ?/A value of the watershed in the northwest,northeast and southeast of the whole study area is larger,and the remaining ?/A values are smaller,especially in the central and western regions.(2)After correlation analysis and geographic detector analysis,the fundamental cause of the?/A spatial difference is the spatial difference of meteorological factors.The total water area of the whole research area showed a significant downward trend,with the turning point in 2009,a significant downward trend from 2000 to 2009,and a significant upward trend in 2009-2015.At the basin scale,the number of basins exhibiting a decreased trend in water surface area is larger than those with an increased trend,and the total basin area with a decreased trend is also larger than those with an increased trend.Preliminary attribution analysis showed that the significant decrease of water surface area on the Mongolian Plateau from 2000 to 2009 was associated with the increase of population density,grain yield and grazing livestock,while the significant increase of water surface area from 2009 to 2015 was associated with the decrease of population density.(3)In the 1276 inflow basins,the Budyko hypothesis was used to calculate the parameter co of the underlying surface of each basin in the Fu's formula.The parameter ? generally presented a smaller value in the west and a bigger value in the east.The parameter ? of the entire Mongolian plateau is mainly between 2 and 6,and the number of watersheds in this interval accounts for 88.79%of the total watershed.The most significant factors affecting co are precipitation,potential evapotranspiration and NDVI in August.Based on these three factors,semi-empirical formulas for the ? at multi-year scale and annual scale are constructed.The test analysis shows that the semi-empirical formulas are reasonable.(4)The Dalinor Lake Basin,the Daihai Lake Basin and the Hongjiannao River Basin were selected as typical watersheds.The annual water surface area of the three watersheds was analyzed,and the water surface area of the three watersheds showed a decreasing trend.The 1984-2017 is divided into the reference period and the change period by the year of 2000.The total differential method,the complementary method and the decomposition method are used to attribute the changes of the actual evapotranspiration in the three basins.The average of the total differential method and the decomposition method was used as the result of the attribution analysis.In the Dalinor Lake Basin,the role of climate change is greater than that of human activities.For the Daihai Basin,the impacts of human activities are greater than those of climate change.The impacts of climate change and human activities are equivalent for the Hongjiannao Basin.