| Evapotranspiration is a key process in the Earth's water cycle and plays a pivotal role in the water and energy balance.Accurate estimation of evapotranspiration has important applications in the study of climate change,water resources assessment and agricultural water use efficiency.Located in the southeastern part of the Qaidam Basin,the Xiangride-Qaidam River Basin is an important agricultural and animal husbandry production base in Qinghai Province.The main ecological problem in this area is the excessive water diversions from the Xiangride Oasis,resulting in insufficient water for downstream ecology,fragile ecological environment.The estimation of basin evapotranspiration can provide an important reference for the optimal allocation of local water resources,improvement of ecological environment and agricultural and livestock production.Based on this,this study uses MODIS data,meteorological data,based on the SEBS model,ILWIS,Arc GIS,SPSS and ENVI software to calculate the daily evapotranspiration for a total of 120 periods from 2011 to 2020,and analyses the spatial and temporal variation characteristics of surface evapotranspiration in the basin and its influencing factors.The results of the Penman-Monteith model and vorticity correlation data were used to validate the remote sensing evapotranspiration estimates.Finally,the results of remote sensing were combined with the vegetation type data of the watershed to calculate the ecological water demand of each vegetation type in the watershed using the evapotranspiration method and to analyses its temporal variation pattern.The results of the study show that.(1)The average absolute error between the remote sensing estimates and the Penman-Monteith model is 0.67 mm,and the average absolute error between the remote sensing estimates and the vorticity correlator observations is 0.88 mm.model is feasible for estimating the surface evapotranspiration in the Xiangride-Qaidam River Basin.(2)In 2020,the average monthly evapotranspiration in the Xiangride-Qaidan River Basin showed a trend of increasing and then decreasing within the year,with a“single-peaked”distribution,with a maximum value(5.34 mm)in July and a minimum value(0.95 mm)in December,with an extreme difference of 4.39 mm;The variation of the average monthly evapotranspiration has obvious seasonality,with summer(5.16mm)>spring(3.87 mm)>autumn(2.58 mm)>winter(1.23 mm).In terms of interannual variation,annual evapotranspiration fluctuates between 2011 and 2020,with an overall upward trend,with a maximum value in 2018(119.41 mm)and a minimum value(92.5 mm)in 2012,giving a multi-year average annual evapotranspiration of 100.28 mm.(3)The spatial distribution of monthly mean evapotranspiration in the Xiangride-Qaidam River Basin in 2020 varies significantly,with higher monthly mean evapotranspiration values in the central and northwestern parts of the study area and lower values in the southeastern part of the study area.The spatial pattern of monthly mean evapotranspiration is also seasonal,with the higher monthly mean evapotranspiration in spring located in the central and southeastern ridges of the study area;the lower monthly mean evapotranspiration in the valleys in the southeastern part of the study area and the desert areas in the central part of the study area in summer,and the higher monthly mean evapotranspiration in the rest of the study area;the spatial distribution pattern of monthly mean evapotranspiration in autumn and winter is similar to that in spring.(4)The monthly mean evapotranspiration in the Xiangride-Qaidam River basin was significantly and positively correlated with precipitation,air temperature,sunshine hours and NDVI,where the significance of each element on surface evapotranspiration was in the following order:sunshine(R~2=0.98)>temperature(R~2=0.95)>NDVI(R~2=0.71)>precipitation(R~2=0.69).(5)In 2020,the ecological water demand of scrub,grassland,cultivated vegetation,meadows,coniferous forests and alpine vegetation in the Xiangride-Qaidam River Basin in 2020 all show similar intra-annual variation,with an increase followed by a decrease,showing a"single peak"distribution.The monthly mean ecological water demand of the six vegetation types in 2020 will be in following order:grassland(11.2billion m~3)>meadow(8.27 billion m~3)>scrub(1.93 billion m~3)>alpine vegetation(1.38 billion m~3)>coniferous forest(0.29 billion m~3)>cultivated vegetation(0.25billion m~3).In terms of inter-annual variation,the ecological water demand for each vegetation type fluctuates from 2011 to 2020,showing a trend of increasing and then decreasing,before increasing again in 2020. |
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