Application Of Different Canopy Resistance Models In Evapotranspiration Of Maize Ecosystem In Semi-arid Areas

In the study of crop evapotranspiration,there are many estimation models,and the most widely used single-source model is the Penman-Monteith(PM)model.This paper optimizes the PM model by improving the canopy resistance parameters,thereby improving the PM model for sparse vegetation.The simulation effect of evapotranspiration makes the simulation simple but accurate.Therefore,this paper mainly optimizes the estimation of crop evapotranspiration by evaluating the different canopy resistance models(or surface resistance models)and selecting the resistance model suitable for the whole growth season of corn.In this paper,10 more classical canopy resistance models are selected,and the whole growing season is divided into the pre-growth season(LAI<2)and the late growing season(LAI>2).The canopy resistance model is combined with the PM model to discriminant model applicability.At the same time,the influence of parameters on the model is analyzed,and the sensitivity of the model is analyzed.Finally,the following conclusions are drawn:(1)In the early stage of the growing season,through the analysis of the calculation results and the evaluation of the model,it is concluded that the model with the best performance at this stage has the coupled surface resistance(CO)model,the modified Leuning(RL correction)model and Katerji-Perrier(KP)model.(2)In the later part of the growing season,combined with the analysis of the estimation results and the evaluation of the model,the best model for the canopy resistance simulation of corn in this study area at this stage is the Stannard(ST)model,Leuning(RL)model and Jarvis model,and in addition to the RL correction model in this period,the other model simulation results are good and superior to the pre-growth season.(3)The most suitable resistance model in the whole growing season of corn in this study area is the coupled surface resistance(CO)model and KP model,but the KP model performs slightly poorly in the early growth season.Therefore,when estimating evapotranspiration under similar environmental conditions,CO model and KP model can be selected as the estimation model of canopy resistance.(4)Based on the sensitivity analysis of the model,the influence parameters of the model CO model with good simulation results are the canopy resistance estimated by the Jarvis model and leaf area index.Combined with the sensitivity analysis of the Jarvis model,it can be concluded that the largest parameter affecting the CO model is the leaf area index and the normailized soil water content(F(?)),followed by the water vapor pressure deficit and air temperature,and finally the solar radiation.Another model KP model with good simulation effect,the largest influence is the water vapor pressure deficit(VPD)and net radiation(Rn),followed by aerodynamic resistance(ra)and soil heat flux(G).(5)Integrating all the parameters of the impact model,the leaf area index and the water vapor pressure deficit have a great influence on the model containing them,and the leaf area index is positively correlated with the evapotranspiration.The radiation-related parameters such as solar radiation,net radiation and visible radiation at the top of the canopy are positively correlated with the evapotranspiration.The water vapor pressure deficit is negatively correlated with the evapotranspiration.The CO-PM model and the relationship between the water vapor pressure deficit is just the opposite because the model is a coupled model.