The Spatiotemporal Variability Of Actual Evapotranspiration And Its Attribution Analysis On Yanhe River

Actual evapotranspiration(ET_a)is a major expenditure item in the water balance,which affects the water cycle,plant growth and energy cycle in the surface ecosystem.Since the 1990s,the actual evapotranspiration has undergone important changes under the dual influence of climate and land use.This study is based on the hydrological and meteorological data of the Yanhe River and the 6-phase land use data,and explores the applicability of the model based on the complementary principles of evapotranspiration in ET_a estimation,using trend analysis,mutation testing,cycle analysis,sensitivity analysis,contribution analysis,etc.Methods,study the temporal and spatial characteristics of ET_a,and estimate the contribution of climate and land use to it.The main conclusions obtained are as follows:(1)The principle of complementary evapotranspiration is applicable to the calculation of actual evapotranspiration in the Yanhe River,and the calibrated advection-drought(AA*)model performs best.The correlation coefficient between actual evapotranspiration and potential evapotranspiration is-0.27,and there is an obvious complementary correlation.The theory of complementary evapotranspiration is applicable to the Yanhe River.The AA*model has the smallest RMSE and NSE in the rate period.The MAE and RMSE in the verification period are small,and the NSE is the largest.The AA*model has the highest accuracy on the actual evapotranspiration simulation results.The optimal parameters of the AA*model after calibration are 1.033and 0.867 respectively..(2)The multi-year average actual evapotranspiration in the Yanhe River is459.33mm,showing an overall upward trend(p<0.1),with significant spatial differences in change characteristics.The actual evapotranspiration is high in the southeast and low in the northwest.The high-value area of evapotranspiration gradually shifted westward over time,and the low-value area gradually shifted southward.The actual evapotranspiration growth rate presents a distribution law that gradually decreases from northwest to southeast.(3)The actual evapotranspiration in the Yanhe River has significant spatial differences in the sensitivity coefficients of climate factors,and the distribution law is similar to the spatial distribution of climate factors.The actual evapotranspiration is consistent with the changes in temperature,relative humidity,and solar radiation,but opposite to the changes in wind speed.The sensitivity is in order:humidity,solar radiation,temperature and wind speed.Temperature sensitivity is higher in southeast than northwest.Humidity sensitivity increases stepwise from northwest to southeast,wind speed sensitivity is high-low-high from west to east,and solar radiation sensitivity gradually increases from northwest to southeast.(4)Combining the climate sensitivity coefficient and the climate factor change trend to calculate the contribution value can accurately analyze the reasons for the actual evapotranspiration changes.Relative humidity and solar radiation make a negative contribution to the increase in actual evapotranspiration,while temperature and wind speed make a positive contribution to its rise.The negative contribution is less than the positive contribution so that the actual evapotranspiration is on the rise.The temperature sensitivity coefficient is not the largest,but its significant upward trend makes it the largest positive contribution to the increase in actual evapotranspiration in the Yanhe River.The dominant climatic factor for the increase in actual evapotranspiration is temperature.The dominant factors of actual evapotranspiration changes in each region are obviously different.(5)Changes in land use patterns can lead to changes in actual evapotranspiration,and the spatial distribution pattern of land use determines the spatial distribution of actual evapotranspiration.The area of arable land in Yanchang and Zhidan has been significantly reduced,and has generally been converted to grassland and woodland,so the actual evapotranspiration is relatively high.The area of forest and grassland in Ansai area has increased significantly,so the actual evapotranspiration has increased.The construction area of Yan'an area has increased significantly,so the actual evapotranspiration is low.