A Preliminary Study On The Applicability Of Various Land Surface Potential Evapotranspiration Estimation Methods In China

Evapotranspiration,the most critical for water resource estimation and agricultural and ecological protection applications,is one of the most important key elements of the water cycle process.Among them,potential evapotranspiration is the basis of evapotranspiration research,and has been concerned and explored by hydrologists at home and abroad.This dissertation selects the topic of land surface potential evapotranspiration estimation method and its applicability in China,and explores the shared exploration of its adaptability and application comparison through extensive reading of domestic and foreign literature,and has made some new progress and Achievement of recognition.The difficulty of the problem: China has a vast territory,from the southeast coast to the northwest inland,the annual average relative humidity difference is more than 50%,from the southernmost South China Sea islands to the northernmost Heilongjiang Mohe,the annual average temperature difference can reach more than 28 ?,even if the same method of estimating potential evapotranspiration in different regions will also have large differences in PET values due to the influence of relative humidity or temperature.Therefore,this study examines 12 methods in 3 categories including temperature-based method,mass-transfer-based method and radiation-based method for estimating potential evapotranspiration(PET)using China as the research area,which is then divided into 5 arid and humid regions(AHRs)and 11 temperature zones(TZs)from the perspective of relative humidity and temperature,regards the FAO Penman-Monteith(P-M for short)method as the standard,and analyses the applicability of these 12 methods from four aspects: correlation,annual mean values,seasonal distribution and parameter characteristics.Research indicates:(1)In the whole country,the radiation-based methods have the best monthly correlation with the PM method,followed by the temperature-based methods,and the mass-transfer based methods are the worst.The radiation-based methods are significantly better than the temperature-based methods and the mass-transfer based methods in estimating the mean value of potential evapotranspiration.Among them,the P-T method has the best estimation effect and the Hamon method has the worst.After parameter adjustment,all methods can reach almost the same value as the PM method.The Hamon method has a larger tuning range and poor applicability,while the Rohwer and P-T methods have a smaller tuning range and better applicability.(2)For different arid and humid regions,the temperature-based methods and masstransfer based methods are more relevant to the PM method in arid areas than in humid regions;the radiation-based methods are basically the same as the PM method in arid and humid regions.The potential evapotranspiration value estimated by Penman method is the closest to the value calculated by PM method in arid regions.The distribution characteristics of the annual average of PET calculated by PM method: summer>spring>autumn>winter,and there is no zero or negative value in winter.Compared with PM method,the annual distribution of radiation-based methods(except Jensen method)in different arid and humid regions is better than that of the temperature-based and the mass-transfer based methods.The Rohwer method and the PM method have almost the same annual distribution in different arid and humid regions,and Abtew method in arid regions and the PT,Mak,Harg and Door methods in humid areas have the same annual distribution with the PM method.While the annual distribution of Jensen and Kharrufa methods in different arid and humid regions is unreasonable.In addition,in different arid and humid regions,the trends of parameter adjustment of different methods are the same as the spatial distribution trends of corresponding methods in arid and humid regions,and the adjustment ranges of the parameters of BC and Mak methods at different sites across the country are the smallest,which are beneficial to parameter regionalization.(3)For different temperature zones,the methods with the best monthly correlation with the PM method are: Mak and Harg methods in the southern subtropical zone(8-SST),Harg and Jensen methods in the marginal tropical zone(9-MT),and in other temperature zones,the Door method has the best monthly correlation with the PM method.When only considering the temperature-based methods and the mass-transfer based methods,the BC method has the best monthly correlation with the PM method in the plateau temperate zone(3-PT),the Kharrufa method has the best monthly correlation with the PM method in the southern subtropical zone(8-SST),and Linacre method before adjustment has the best monthly correlation with the PM method in other temperature zones.With the increase of temperature in different temperature zones,the PET calculation value of PM method shows a linear trend of increase;the difference between the calculation results of Hamon method and PM method is the biggest,and the PET estimation applicability of which is poor.In all temperature zones,the PET calculated values annual distribution before and after the parameter adjustment of the radiation-based methods is the closest to the PM method(except Jensen method),followed by the mass-transfer based methods,and the temperature-based methods have the largest difference in the annual distribution with PM method;Mak and Door methods are the two methods with the highest annual distribution consistency with the PM method in all temperature zones.In the temperature-based methods,the parameters of the BC,Kharrufa and Hamon methods,the mass-transfer based methods and the radiationbased methods(excluding the Door method and Jensen method)need to be adjusted in a relatively small range in all temperature zones,which is conducive to parameter regionalization and shows the strong applicability of these methods.(4)In general,when the whole country is the research area,choosing the radiation method(excluding Jensen's method)is the best.When different arid and humid regions are used as the study area,the Penman method is selected for arid regions,BC,Linacre,Rohwer,P-T,Mak and Door methods are selected for humid regions,and Harg method is selected for regions between aid and humid regions.When using different temperature zones as the study area,the Door methods are selected in the high temperature area,and the P-T,Mak and Harg methods are selected in the lower temperature area.Due to the lack of actual observation and difficulty in evapotranspiration,there are still many problems in current research that need to be further explored.