Spatiotemporal Variability of Potential Evaporation in Heihe River Basin Influenced by Irrigation

Spatiotemporal Variability of Potential Evaporation in Heihe River Basin Influenced by Irrigation

Congying Han^1,2, Baozhong Zhang^1,2, Songjun Han^1,2

¹ State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin, China Institute of Water Resources and Hydropower Research, Beijing 100038, China.

² National Center of Efficient Irrigation Engineering and Technology Research-Beijing, Beijing 100048, China.

Corresponding author: Baozhong Zhang (zhangbaozhong333@163.com)

Abstract: Potential evaporation is a key factor in crop water requirement estimation and agricultural water resource planning. The spatial pattern and temporal changes of potential evaporation calculated by Penman equation (E_Pen) (1970-2017) in Heihe River Basin (HRB), Northwest China were evaluated by using data from 10 meteorological stations, with a serious consideration of the influences of irrigation development. Results indicated that the spatial pattern of annual E_Pen in HRB was significantly different, among which the E_Pen of agricultural sites (average between 1154 mm and 1333 mm) was significantly higher than that of natural sites (average between 794 mm and 899 mm). Besides, the coefficient of spatial variation of the aerodynamic term (E_aero) was 0.4, while that of the radiation term (E_rad) was 0.09. The agricultural irrigation water withdrawal increased annually before 2000, but decreased significantly after 2000 which was influenced by the agricultural development and the water policy. Coincidentally, the annual variation of E_pen in agricultural sites decreased at -40 mm/decade in 1970-2000 but increased at 60 mm/decade in 2001-2017, while that in natural sites with little influence of irrigation, only decreased at -0.5mm/decade in 1970-2000 but increased at 11 mm/decade in 2001-2017. So it was obvious that irrigation influenced E_pen significantly and the change of E_pen was mainly caused by the aerodynamic term. The analysis of the main meteorological factors that affect E_pen showed that wind speed had the greatest impact on E_pen of agricultural sites, followed by relative humidity and average temperature, while the meteorological factors that had the greatest impact on E_pen of natural sites were maximum temperature, followed by wind speed and relative humidity.