In the complementary relationship (CR) between actual and potential evapotranspiration, wet envi- ronment evapotranspiration (Ew) is usually calculated using the Priestley-Taylor (P-T) equation. Based on the data obtained from 38 catchments of the Haihe River basin and the Weishan experiment site in Shandong Province of China, this study has found variations in the Priestley-Taylor parameter α (e.g. increase in values with increase in the amount of precipitation on annual scale, seasonal fluctuation noted to be at a maximum during winter and at a minimum during summer, and increased values in the forenoon and decreased values in the afternoon on an hourly scale). This paper explains that the in- ter-annual variation in α is due to the negative feedback of atmosphere in response to changes in ac- tual increase in evapotranspiration, which is weakened because the atmosphere system is open. The parameter α undergoes a seasonal fluctuation brought about by seasonal changes in advection be- tween continent and ocean; α likewise undergoes a daily variation as a result of atmospheric hysteresis in response to the changes in land surface energy.
YANG HanBoYANG DaWenLEI ZhiDongSUN FuBaoCONG ZhenTao
