Simulation of evapotranspiration and its components for the mobile dune using an improved dual-source model in semi-arid regions

Accurate estimation of evapotranspiration (ET) and its components is essential for a deep understanding of hydrological processes in semi-arid regions. In this study, an improved Shuttleworth-Wallace model (i.e., SWH model) was applied to simulate ET and its components over the growing season in four consecutive years, 2013 to 2016, for mobile dunes in China's Horqin Sandy Land. The performance of the model was validated using the measurements of eddy covariance (EC) technology and micro-lysimeter; the modeled ET was in good agreement with the measured ET at both half-hourly and daily timescales, and the modeled soil evaporation (E) was consistent with the micro-lysimeter measurements. E accounted for the major fraction of ET in the mobile dune ecosystem, with E/ET being 0.62, 0.84, 0.82, and 0.61, for the 2013 to 2016 growing seasons, respectively. During the vigorous growing stage, the monthly E/ET was mainly controlled by the leaf area index (LAI) in wet years, while water became the limiting factor for E/ET in dry years. At a half-hourly timescale, E/ET was primarily controlled by canopy stomatal conductance and soil moisture content, but when soil moisture content was lower than the wilting point, E/ET depended solely on the soil moisture content. When soil moisture content was between the wilting point and the field capacity, E/ET was mainly controlled by soil moisture content in the early and late growing stages, but by canopy stomatal conductance in the vigorous growing stage. When soil moisture content exceeded the field capacity, E/ET was primarily controlled by canopy stomatal conductance.

Automated summary

Accurate estimation of evapotranspiration is essential for understanding hydrological processes in semi-arid regions. The SWH model performed well in simulating ET and its components over four consecutive growing seasons in China's Horqin Sandy Land. Soil evaporation (E) accounted for a major fraction of ET and was mainly controlled by canopy stomatal conductance and soil moisture content.