Estimation of growing season evapotranspiration and its variation in a typical area of Horqin Sandy Land

The spatial and temporal distribution of surface parameters and evapotranspiration (ET), and their variation, were determined in a typical area of Horqin Sandy Land. Landsat 7 remote sensing images and meteorological data were obtained and the Mapping Evapotranspiration at high Resolution with Internalized Calibration (METRIC) model was used to determine spatio-temporal variations of net radiation (R_n) and ET, ET properties under different land cover types, and the factors influencing ET. Three key results were obtained. ① Model estimates were strongly linearly correlated with observed values, which confirmed that METRIC provided reasonable ET estimates in the Horqin Sandy Land. ② The spatio-temporal variations of R_n and ET in the underlying surface of the study area showed that the inter-annual R_n and ET had the same trend in each year, with the maximum R_n and ET occurring from water bodies followed by farmland and meadows, while the minimum was from sandy dunes. ③ The coefficient of variation (C_V) of sandy dunes was larger than that of farmland and meadows. The most obvious inter-annual variation occurred in sandy dunes, whereas farmland and meadows were stable. In all three types of land, inter-annual changes in ET were mainly due to meteorological factors.