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Quantifying spatio-temporal variations of evapotranspiration over a heterogeneous terrain in the Arid regions of Northwestern China.

ABSTRACT Evapotranspiration (ET) is a major component of water and energy budgets in terrestrial ecosystems and quantifying ET over a heterogeneous land surface is of extraordinary significance. However, previous studies on the spatial distribution of daily ET in the middle Hexi corridors were mostly temporal discontinuous, and thus hinder the applications in agriculture and meteorology. Based on Land Remote-Sensing Satellite (Landsat) 8 Operational Land Imager (OLI) and Thermal Infrared Sensor (TIRS) data and the Surface Energy Balance System (SEBS) model, surface ET in 2014 were estimated over a desert oasis with heterogeneous land cover in the middle Hexi corridors of the arid regions in northwestern China. Daily ET was derived from the reference crop ET which was based on the relationship between actual ET and potential ET. The main results indicated that (1) the estimated daily ET values agreed well with the Eddy Covariance (EC) measurements for cropland (The coefficient of determination (R 2) = 0.96, p < 0.05, Root Mean Square Error (RMSE) = 1.32 mm day−1, Mean Absolute Error (MAE) = 1.11 mm day−1). Daily ET was more than 2.5 mm day−1 from June to July in 2014. (2) Seasonal ET was the largest in the summer (190.55 mm), followed by spring (100.03 mm), autumn (62.27 mm), and winter (6.83 mm). (3) ET from the waterbody was the highest, followed by ET from cropland, shelterbelt, bare land, and shrubland, suggesting that ET was mainly controlled by the water availability of the underlying surface. Multiple land-cover types showed similar variations in a year, but the seasonal variations were different. This study provides a foundational understanding of the patterns of water and heat exchange over heterogeneous regions, which can be helpful to make local policy in rational water management and land resource utilization.