A variation study on calculation of evapotranspiration over constructed green land and natural sandy land

Evapotranspiration is not only a key variable of the water cycle, but also an important component of the energy balance. Consequently, the evapotranspiration estimation between natural sandy land (NSL) and constructed greenland (CGL) in the desert region has pivotal impacts on desert meteorology and energy transmission. Moreover, the associated research results have enormous applicable values like preventing desertification and reasonable utilization of ground water resource in the desert region. The evapotranspiration algorithm of the GB/T 20481-2006 dry grade is applied to accurately calculate hourly evapotranspiration values over NSL and CGL based on the intense observations collected at the Taklimakan Desert Meteorology Field Experiment Station of CMA during the period of 2014-2015. Inaddition, different parameters are used in the algorithm, which significantly enhances the utilization rate of the observations and the precision of the calculation. Furthermore, the increment and decrement of the calculated evapotranspiration are quantified based on the assignment research of the influencing factors. The main results are as follows. (1) The calculated values of the evapotranspiration over NSL and CGL can well reflect the annual variation of evapotranspiration. As for the changing trend, the values over CGL are better than that over NSL, which is related to the adaptability of the calculation method. (2) During the growing season, the difference between the calculated and observed evapotranspiration over CGL is larger than that over NSL. However, the opposite is true during the cold season. (3) The difference in the saturation vapor pressure and actual vapor pressure, 2 m mean air temperature, 2 m mean wind speed and the slope of the saturation vapor pressure are the main influencing factors for the evapotranspiration calculation, in which the difference between the saturation vapor pressure and actual vapor pressure as well as 2 m mean wind speed increase with the assignment, and the hourly percentage evapotranspiration difference (PED) and its annual cumulative value difference (ACD) display a linear increasing trend. Meanwhile, the 2 m mean air temperature also increases with the assignment, and the factors of PED and ACD remain stable. Likewise, as the assignment increases, the slope of saturation vapor pressure and the two variables (PED and ACD) show an upward tendency and a slight decrease, respectively. Therefore, the evapotranspiration algorithm of the GB/T 20481-2006 classification of meteorological drought has better applicability in the Taklimakan Desert, and the calculation accuracy over constructed green land is higher than that over natural sandy land.