Study On Surface Evapotranspiration And Ecological Water Consumption Of Natural Vegetation In Ili River Basin

The Ili River Basin,which spans Kazakhstan and China,has an independent inland river system and runoff area,and the main river in the basin connects China and Kazakhstan.The distribution of water resources in the basin is uneven,and the ecological environment is deteriorating day by day.Ili River is the main water supply river of Balkash Lake.China and Kazakhstan have not yet reached an agreement on the distribution of water resources in this river.As a key link of water cycle,surface evapotranspiration has become one of the important research objects of water resources management in recent years.Accurate estimation of evapotranspiration and ecological water consumption of natural vegetation in the basin is beneficial to the sustainable development of the ecosystem and the rational utilization of water resources in the cross-border basin.In this paper,based on MODIS evapotranspiration products(MOD16 ET),with the help of Matlab,Arc GIS,ENVI,SPSS and other software,using trend analysis,coefficient of variation,Theil-Sen median trend analysis,Mann-Kendall and Hurst index methods,the temporal and spatial variation characteristics and volatility of evapotranspiration in Ili River Basin from 2000 to 2014 were studied.Based on the land cover data(CCI-LC)issued by the European Space Agency,the land use transfer matrix method was used to study the temporal and spatial change of land cover,and the evapotranspiration method was used to estimate the ecological water consumption of natural vegetation in the basin.Research shows that:1)the average surface evapotranspiration in Ili River Basin was 249.80 mm,and its fluctuation range was between 224.03 and 274.10 mm.During the study period,it showed a downward trend as a whole,and the rate of change was-1.15 mm/a.The annual average evapotranspiration was obviously different in space,which ranged from 115.6 to 758.79mm,showing a spatial pattern of decrease from upstream to downstream as a whole.2)the annual evapotranspiration of the basin was obviously different.The ET showed a periodic unimodal wave trend in some parts of China and Kazakhstan,increased slowly from February to April,rised rapidly from April to June,reaches the highest value in June,decreased rapidly from July to October,decreased slowly from October to December,and showed the lowest value from December to February of the following year.3)during the study period,the multi-year average coefficient of variation of evapotranspiration in the basin ranges from 0.01 to 0.71,the average value was 0.097,the degree of variation was not obvious,and the area ratio of stability and stability in the degree of variation is 85.47%.The area proportion of decreasing trend and increasing trend of ET in the whole basin is 64.48%and 26.72%respectively,and the change trend was mainly decreasing.The change of future evapotranspiration in this basin was consistent with that in the past,mainly with continuous decrease.4)the overall land use structure in the basin was relatively stable during the study period,which is as follows:grassland>woodland>cultivated land>bare land>water body>town.The average value of ET for many years was cultivated land(327.23mm)>forest land(319.10mm)>grassland(239.50mm)>sparse vegetation(151.67mm).5)the natural vegetation in this basin was mainly grassland.The ecological water consumption of natural vegetation in 2000,2005,2010 and 2014 is 52.9×10~8m~3,56.08×10~8m~3,56.29×10~8m~3 and 50.12×10~8m~3 respectively,and the ecological water consumption of natural vegetation increased at first and then decreases.In 2010,the ecological water consumption of natural vegetation in the basin showed a"single peak"distribution,and the peak appeared in July,which was 6.80×10~8m~3.During the study period,the ecological water consumption of grassland in this basin was the highest,accounting for more than 60%of the ecological water consumption of natural vegetation,and the ecological water consumption of woodland was the lowest,less than 7%.The overall ecological water consumption was grassland>sparse woodland>shrub>woodland.