Evapotranspiration In Songhua River Basin Under The Background Of Climate Change Based On Budyko Hypothesis

Climate change and human activities have changed the process of global hydrological cycle,leading to the redistribution of water resources in time and space,and then affecting the benign cycle of the ecological environment and the economic development of human society.Evapotranspiration plays a key role in the hydrological cycle that links atmospheric processes with land surface processes.Because evapotranspiration is most directly affected by complex underlying surface conditions and climate change,it is difficult to estimate accurately,so the study of actual evapotranspiration?ET_a?is a hot topic and a difficult point.In this paper,the Songhua River basin located in the middle and high latitudes is taken as the research area,and the Budyko Hydrothermal Coupling equilibrium hypothesis is taken as the main theoretical basis.Firstly,the temporal and spatial variations of hydrothermal conditions in Songhua River basin from 1959 to 2014 are analyzed;secondly,the long-range ET_a in Songhua River basin is simulated based on Budyko hypothesis;finally,the coupling equation of water and heat at the annual and monthly scales is improved by synthesizing the variable factors of soil water storage based on Fu Baopu framework.The main conclusions are as follows:?1?Spatial and temporal evolution of hydrothermal conditions in Songhua River Basin:Spatial and temporal variations of precipitation?P?and runoff?R?and their spatial trend consistency were analyzed;the spatial variation characteristics of ET₀ and meteorological elements and their spatial distribution consistency were discussed;and the dominant factors affecting ET₀?growth season,May-September?were analyzed by sensitivity coefficient and contribution method.The status of spatial and temporal differentiation were analyzed,and the characteristics of annual water budget were analyzed.The results show that the main factors of ET₀ decreasing from southwest to northeast are the decreasing sunshine hours,the increasing relative humidity and the decreasing average temperature.P,ET₀ and R all showed a downward trend,indicating that the hydrological cycle process in the area was weakening.?2?Based on Budyko hypothesis,the simulation of long-sequence ETa in Songhua River basin is carried out:the applicability of Fu Baopu equation in the study area and the interannual variation characteristics of underlying surface parameters?w?are discussed;the temporal and spatial variation of ET_a is estimated and analyzed;the attribution of runoff variation in the study area is identified;and the influence of different ET₀ calculation formulas on the application of Fu Baopu framework is discussed.The results show that the ET_a estimated by Fu Baopu equation has high accuracy,and the change of vegetation coverage affects the w value on the interannual scale.ET_a decreases at a rate of-0.8mm/10a,and presents the stage characteristics of"down-up-down-up"and the spatial distribution pattern of"more East and less west".The contribution rate of underlying surface change to runoff reduction is 73%.There is little difference between Penman-Monteith?P-M?and Hargreaves?Har?methods in simulation results and sensitivity analysis results.?3?Improvement of Fu Baopu's formula:Combining the variable factors of soil water storage??35?S?,the coupling equation of water and heat at annual and monthly scales was improved,and the temporal and spatial variation characteristics and driving mechanism of ET_a at different time scales were analyzed.The effects of MOD16 remote sensing ET_a on the applicability of different Budyko frameworks in Songhua River Basin were preliminarily explored.The results show that the accuracy of annual scale and monthly scale?Harbin catchment area?models is improved after adding?35?S to the model.The greater the dryness?ET₀/P?,the better the applicability of the equation.The spatial distribution of P contribution to ET_a is consistent with that of ET₀,P and?35?S contribution to ET_a on an annual scale,indicating that the basin belongs to a water control area,and?35?S has an impact on ETa,but the impact is not significant.On the monthly scale,the sensitivity of ET_a to ET_a was P>ET₀>?35?S in other months except July.On the annual scale,the model accuracy of ET_a calculated by water balance method is higher than that of MOD16 remote sensing data.The simulation results of Fu Baopu formula and M-Choudhury-Yang formula are similar.The results of this study provide a theoretical basis for the construction of water-heat coupling equations at different time scales in mid-high latitudes,and are of great significance for the study of the impact of climate change on hydrological processes,as well as for the planning and utilization of water resources and drought monitoring.