Simulation of evapotranspiration for the mobile and semi-mobile dunes in the Horqin Sandy Land using the Shuttleworth-Wallace model.

Terrestrial evapotranspiration (ET) plays a crucial role in climate regulation and the maintenance of regional water balance. Quantitative estimation of ET and its partitioning are important for revealing the eco-hydrological processes in arid and semi-arid areas. Using the in situ data sampled by the meteorological monitoring system, the Shuttleworth-Wallace (S-W) model was applied to simulate and partition ET in the mobile and semi-mobile dunes of the Horqin sandy land during the growing season in 2017. The eddy covariance system was used to verify the simulated ET. The results were as follows: the simulated ET (308 mm) was very close to the eddy covariance observed ET (296 mm) during the whole growing season, indicating the applicability of the S-W model for ET estimation in this area. The ET rate at the vigorous growth stage (192 mm) was larger than those at the late and early growth stages (71 and 45 mm, respectively) which accounted for 62.3%, 23.1%, and 14.6% of the total, respectively. The simulated ET was close to the eddy covariance observed ET at the daily time-scale. The simulation performance of the S-W model for clear days was better than for cloudy or rainy days. The simulated ET rate was always smaller than the eddy covariance observed ET in the cloudy or rainy days. According to the model, the evaporation (E) from soil was 176 mm and the transpiration (T) from plants was 132 mm, accounting for 57.1% and 42.9% of the ET, respectively, suggesting that water use efficiency of the sand dune was low. The characteristics of ET varied substantially under the sustained drought and precipitation events. Compared to T from plants, E from soil was more sensitive to precipitation.