Calculation of Potential Evaporation in Hebei and Its Changing Trend Analysis

The potential evaporation is a measure of the evaporation capacity of the atmosphere.Hebei Province has very poor water resources and dry-and-warm weather.The study of the changing trend of the potential evaporation with time and space in this area is of great importance to have proper utilization of water resources,and to shed light on the change of climate.In this work,the accumulative temperature method,the evaporation recording by evaporating dishes,and the Penman-Monteith formalism has been used to estimated the potential evaporation,which are the three methods among the most widely used ones these days.The comparison of results using these methods with the actual measured result by large-scale evaporating pool suggests that the Penman-Monteith method could reasonably predict the potential evaporation in Hebei.The reason of this is then briefly discussed.The potential evaporation in the whole province is calculated based on the Penman-Monteith method.It is found that the annual potential evaporation in Hebei has a trend to decrease overall with small fluctuations.It reached the maximum in 1960s,and decreased thereafter,instead of increasing with the continuing increasing temperature.The seasonal potential evaporations have also a trend to decrease over years.The change in summer potential evaporation is in good agreement with the annual change,with the largest decreasing magnitude of 8.61 mm per decade,while the change in spring and autumn potential evaporation is next to it,with a value of 3.32 mm and 2.47 mm per decade,respectively.The change in winter potential evaporation is the lease with a value of 0.13 mm per decade.Regarding the area distribution,most of the area has a decreasing trend and the east of the southeast plain in Hebei has the largest decreasing rate.Only a few stations,like Fengning and Yuxian have slight increase in the evaporation.