Analysis Of Actual Evapotranspiration Characteristics Of Typical Watersheds Based On Budyko Hypothesis

The evapotranspiration process,as an important link to the hydrologic process and energy cycle process,is an important feedback factor of global warming.Its accurate measurement and estimation can better understand the physical mechanism and interaction of water cycle processes in different climate regions.In this study,the upper areas of the three typical watersheds of the Heihe River,Ziya River,and Yalong River were selected as the study area.Based on the Budyko assumption,the actual evapotranspiration(AET)in each study area was estimated by the Fu Baopu model.And from the spatiotemporal perspective,the characteristics of AET in each study area were analyzed.On this basis,the main factors affecting the AET changes and their influence degree were qualitatively and quantitatively analyzed.The results are as follows:(1)The parameters ? in the Fu Baopu model were calibrated and verified through the watershed water balance equation,the results show that the calibration results conform to the spatial distribution rule of the parameter ?,and the Fu Baopu model is applicable to all three research areas.By analyzing the relationship between AET and potential evapotranspiration(PET),the upper areas of the Heihe River Basin and the upper areas of the Yalong River Basin satisfy the "Proportional Evaporation" theory,while the upper areas of the Ziya River Basin satisfies the "Evaporative Complementation" theory.(2)During the study period,the annual AET in the upper areas of the Heihe River Basin and the upstream of the Yalong River Basin both showed an upward trend,and the annual AET in the upper areas of the Ziya River Basin showed a significant downward trend;There are 30,15 and 8 years cycles in the upper areas of the Heihe River Basin and Ziya River Basin,and 20,12 and 5 years in the upper areas of the Yalong River Basin.And that,they will first enter a period of less AET in the future;From the years,the AET peaks of summer and winter in the upper areas of the Heihe River Basin and the upper areas of the Yalong River Basin are relatively close,but there are large differences between spring and autumn;The AET valleys in the upper areas of the Ziyahe River Basin and the upper areas of the Heihe River Basin in spring and winter are relatively close,and the differences between summer and autumn.Spatially,the annual AET in the upstream of the Heihe River Basin increases from northwest to southeast,the annual AET in the upstream of the Ziya River Basin increases from southwest to northeast,the AET in the upper Yalong River Basin is centered on the center and increases in a ring shape toward the northwest and southeast of the basin.(3)Meteorological elements are the main factors affecting AET changes,the AET changes in the three study areas are jointly affected by precipitation and PET.In addition,from the perspective of individual factors,except for precipitation,the AET in the upper areas of the Heihe River Basin is mainly affected by sunshine hours and net radiation;The upper areas of the Ziya River Basin are affected by relative humidity and sunshine hours;And the upper areas of the Yalong River Basin are affected by relative humidity,wind speed and sunshine hours.The underlying surface condition is a secondary factor that affects AET changes.Among the six types of land use,such as cultivated land and forest land,the AET in the three study areas is more sensitive to forest land and grassland;The upper areas of the Heihe and Yalong river basins are more sensitive to unused land than the upstream of the Ziya river basin,and the sensitivity coefficient to building land and cultivated land is lower than that of the upper areas of the Ziya river basin.