Evaluation of Complementary Relationship Model on Land Surface Actual Evapotranspiration in the Permafrost Region of Qinghai-Xizang Plateau

Abstract

Evapotranspiration is an important link to water and heat exchange between soil and atmosphere， and its changes have an important impact on water resources management and ecological environment.In the context of global warming， the permafrost on the Qinghai-Xizang Plateau is continuously degraded， and the near-surface hydrothermal conditions in the permafrost regions have changed， which further affect the evapotranspiration process.In this paper， four semi-empirical models based on the complementary principle of evapotranspiration are selected to evaluate the ability of different models to simulate the actual evapotranspiration on a daily scale before and after calibrating parameters， and also analyze the sensitivity of the model parameters， which using the meteorological and eddy covariance measurements from January 1， 2010 to December 31， 2011 at the Tanggula comprehensive observation site located in the hinterland of the permafrost region of the Qinghai-Xizang Plateau.The results show that the simulated actual evapotranspiration is very sensitive to the value of parameter α in the models， unreasonable parameter values led to poor simulation ability.Specifically， the use of default parameter values will lead to marked higher simulated values of daily evapotranspiration， the S2017 model has the highest simulation accuracy with RMSE value of 0.44 mm·d-1.After parameters calibration， all models can simulate variation characteristics of daily actual evapotranspiration， RMSE values are between 0.3 and 0.4 mm·d-1， the model with the highest simulation accuracy is the C2016 model， followed by H2018 model， B2015 model and S2017 model， in comparison， evapotranspiration simulated by H2018 model exhibits more stable results， which indicates lower parameter dependency.In addition， accuracy of simulation exists significant difference during various period within the year， and the simulation results of the thawed period are closer to the measured values than those of the frozen period and the daily freeze-thaw cycle period， mean relative deviation values are 6.0%， 82.3%， 43.4%， respectively.The purpose of this paper is to explore the applicability of different complementary evapotranspiration models to the simulation of actual surface evapotranspiration in the permafrost region of the Qinghai-Tibet Plateau， and to some extent， the results can provide reference basis for the estimation of long time series evapotranspiration in this region.

Keywords

• permafrost
• land surface actual evapotranspiration
• complementary relationship model
• model evaluation