Impact of Model Structure and Parameterization Differences on Evapotranspiration Estimation

ZHAO Wenli1, XIONG Yujiu2, QIU Guoyu1,†, YAN Chunhua1, ZOU Zhendong1, QIN Longjun1

1. School of Environment and Energy, Peking University Shenzhen Graduate School, Peking University, Shenzhen 518055; 2. School

of Civil Engineering, Sun Yat-sen University, Guangzhou 510275; † Corresponding author, E-mail: qiugy@pkusz.edu.cn Abstract Based on the HIWATER high-density eddy covariance (EC) tower observations in Heihe Oasis in 2012, the impact of model structure differences (comparison between one-source Penman-monteith / PM equation and two-source PM equation, or comparison between two-source PM equation and two-source three-temperature model) and parameterization differences on the evapotranspiration estimation were evaluated. The results show that, 1) compared with the two-source PM equation with a relatively complex model structure, the mean absolute percent error (MAPE) estimated by the one-source PM equation is 34%, which is more accurate than that by the two-source PM equation (40%); 2) for two kinds of two-source model with significant differences in model structure, the three-temperature model without resistance parameters has higher estimation accuracy than the Pmbased equation with resistance parameters. The former has a MAPE of 18% (R2=0.85), while the Pm-based equation has that of 40% (R2=0.34); 3) two one-source and one two-source resistance parameterization methods lead to different evapotranspiration estimation accuracy for the Pm-based equation, with a MAPE difference of up to 6%; 4) using prior knowledge / dataset to calibrate resistance parameterization can significantly improve the estimation accuracy of one-source PM equation (MAPE can be reduced by 22%), but as model structure and parameterization complexity increase, two-source PM equation hasn’t been improved significantly after resistance parameterization calibration (MAPE is only reduced by 0.8%). Key words evapotranspiration; Penman-monteith; resistance; three-temperature model; HIWATER; Heihe