Simultaneous parameterization of the two-source evapotranspiration model by Bayesian approach: application to spring maize in an arid region of northwest China

Abstract

Abstract. Based on direct measurements of half-hourly canopy evapotranspiration (ET; W m−2) using the eddy covariance (EC) system and daily soil evaporation (E; mm d−1) using microlysimeters over a crop ecosystem in arid northwest China from 27 May to 14 September in 2013, a Bayesian method was used to simultaneously parameterize the soil surface and canopy resistances in the Shuttleworth–Wallace (S–W) model. The posterior distributions of the parameters in most cases were well updated by the multiple measuring dataset with relatively narrow high-probability intervals. There was a good agreement between measured and simulated values of half-hourly ET and daily E with a linear regression being y = 0.84x +0.18 (R2 = 0.83) and y = 1.01x + 0.01 (R2 = 0.82), respectively. The causes of underestimations of ET by the S–W model was mainly attributed to the micro-scale advection, which can contribute an added energy in the form of downward sensible heat fluxes to the ET process. Therefore, the advection process should be taken into accounted in simulating ET in heterogeneous land surface. Also, underestimations were observed on or shortly after rainy days due to direct evaporation of liquid water intercepted in the canopy. Thus, the canopy interception model should be coupled to the S–W model in the long-term ET simulation.