Change Of Potential Evapotranspiration And Analysis Of Hydrological Process In Zhejiang Province

With the rapid development of global economy and growth of population,emissions of greenhouse gas have increased,leading to an increase in global average temperatures.Up to now,climate change has become a global environmental problem.The increase of global temperature has an obvious influence on hydrological cycles(especially the influence on hydrological key elements),resulting in the rise of sea level,the melting of glaciers and the increase in frequency of extreme disasters.Investigating the impact of climate change on hydrological cycles is of great significance to water resource assessment planning,extreme disaster prevention and water conservancy engineering design.Evapotranspiration is one of the important components of hydrological cycle and is the only way to return the land and ocean water to the atmosphere.The changes of evapotranspiration are of great significance to agricultural irrigation,water resources planning and design.In this paper,the applicability of different potential evapotranspiration models in Zhejiang Province is analyzed,and the changes of potential potential evapotranspiration and their contributions are analyzed in detail.Then,Jinhua River Basin in the central area of Zhejiang Province is used as the study area,and the distributed hydrological model DHSVM was used to simulate the evapotranspiration and runoff.For lack of sensitivity analysis and automatic calibration modules in DHSVM,a two-step sensitivity analysis method based on parallel computing of Linux cluster is developed to analyze the sensitivity of parameters to evapotranspiration and runoff simulation.Moreover,?P-DHSVM,which is DHSVM combined with multi-objectives calibration module(?-NSGAII)based on the parallel computing of Linux cluster,is used to optimize the model parameters with objectives related to evapotranspiration and runoff simulation,and the simulation effect of the model on the evapotranspiration and runoff is analyzed.The specific contents and achievements of this paper are as follows:(1)Under A1B scenario in the fourth assessment report of IPCC,the outputs of two global climate models(ECHAM5 and HadCM3)are downscaled by using one regional climate model,Providing Regional Climates for Impacts Studies(PRECIS).The meteorological data in daily scale are used to analyze appropriateness of four potential evapotranspiration models under climate change in Zhejiang Province,and the four models include Blaney-Criddle,Hargreaves,Makkink and Priestley-Taylor.The results show that the percentage error of the four models is basically within the acceptable ranges during the baseline period.In the baseline period,Blaney-Criddle model has the best simulation effect for potential evapotranspiration simulation in annual scale and seasonal scale,followed by Makkink model,Hargreaves model and Priestley-Taylor model.In the inland stations,the four models have good simulation of PET in monthly scale.In island stations,Blaney-Criddle model has the best simulation of PET,followed by Makkink model,Hargreaves model and Priestley-Taylor model.In addition,the distributions of potential evapotranspiration in Zhejiang Province based on the four models are very well.In the future period,the Blaney-Criddle and Hargreaves models have better simulation of PET under ECHAM5 and HadCM3 models in annual scale.The Makkink and Priestley-Taylor models perform well in inland stations,but not in island stations.Under different GCMs models,the simulations of PET in seasonal and monthly scale are different based on four models.(2)The Penman-Monteith method is used to project potential evapotranspiration in the future period 2011-2040 and understand their changes in Zhejiang Province.The sensitivity of potential evapotranspiration to five climatic variables(solar radiation,daily minimum and maximum air temperature,relative humidity,and wind speed)is analyzed based on observation data from 1955-2008 using a global sensitivity analysis method,Sobol' method.The changes in potential evapotranspiration during the future period from ECHAM5 and HadCM3 are analyzed based on the changes in their climate variables and sensitivity analysis results.Global sensitivity analysis results reveal substantial spatial-temporal variations in the sensitivity of potential evapotranspiration to climatic variables and unignorable interactions among climatic variables.Rather similar spatial change patterns of annual mean potential evapotranspiration(PET)are generated for both general circulation models;however,seasonal or monthly changes are very different due to different spatial-temporal changes in climatic variables.Different contributory sources to potential evapotranspiration changes are identified at different months and stations.The PET changes in 2011-2040 are mainly due to three climatic variables including solar radiation,relative humidity,and daily minimum temperature.(3)High-resolution spatial distribution of evapotranspiration and long-term data of evapotranspiration in ungaugged area of the study area can be obtained through hydrological models.The premise of using the hydrological model is that model has good results of parameters calibration,and the parameters for calibration are derived from results of sensitivity analysis.The number of parameters in DHSVM is large,and there is lack of sensitivity analysis module and calibration module in this model.Therefore,a two-step sensitivity analysis approach based on parallel computing of Linux cluster is coupled with this model as the sensitivity analysis module.A preliminary sensitivity analysis is conducted to obtain influential parameters via ANOVA.These parameters are further analyzed through a variance-based global sensitivity analysis method(Sobol')to achieve single parameter contributions and interactions between parameters.The results show that sixteen sensitive parameters are preliminarily selected from all parameters(83)in the first step sensitivity analysis.In the second step,only a few number of model parameters are significantly sensitive in Jinhua River Basin,including a constant parameter(rain LAI multiplier),four soil parameters(lateral conductivity,porosity,field capacity and wilting point of clay loam),and three vegetation parameters(understory monthly LAI,understory minimum resistance and root zone depths of croplands).Five parameters are directly related to evapotranspiration(rain LAI multiplier,wilting point,LAI,vegetation minimum resistance and root zone depths).The interactions between parameters cannot be ignored.For example,the total order sensitivity index of field capacity of clay loam reaches to 0.29,which is much larger than the first order sensitivity index(0.18)after considering the interactions between field capacity of clay loam and other parameters.(4)As results of the last chapter,the simulation of evapotranspiration is sensitive to rain LAI multiplier,wilting point,LAI,vegetation minimum resistance and root zone depths,therefore,the determination of values of these parameters has an important impact on effect of evapotranspiration simulation.For the lack of model calibration module in DHSVM,this paper adds a multi-objectives calibration module(?-NSGAII)based on parallel computing of Linux cluser,i.e.?P-DHSVM.In this chapter,?P-DHSVM model is used to optimize the parameters in the Jinhua River Basin with the objectives of evapotranspiration and runoff.Due to the lack of observed evapotranspiration data,remote sensing evapotranspiration are used as the observation data,which are estimated through SEBAL model based on MODIS remote sensing data.And the SEBAL model is programmed by interactive data language(IDL).The results show that the remote sensing evaporation estimated via SEBAL model and potential evapotranspiration are very consistent.The results of multi-objectives model calibration show that the simulation of evapotranspiration via DHSVM is good,and the corresponding efficiency is 0.86 and deviation is-1.9%.The simulation of runoff is good,and corresponding efficiency is 0.79 and deviation is-1.6%.Compared with result of calibration of single objective,the deviation of some months is reduced.In addition,the DHSVM model can simulate the runoff and evapotranspiration very well at the same time,and the runoff efficiency coefficient is 0.74,the runoff deviation is-10.5%,the evapotranspiration efficiency coefficient is 0.76,and the evapotranspiration deviation is-8.6%.