An Aridity Index Based on the Natural Process of Aridity and Its Application

The conception of the process of aridity is put forward in this paper.The natural process of aridity(NPA) is defined as the relative precipitation-deficit period between two consecutive continuous precipitation processes with its accumulative rainfall equal to 25mm or more in May to September,and the aridity index(AI) is then synthetically defined by the duration of a NPA and the ratio of precipitation to evaporation in the NPA and its early stage of 60 days immediately preceding the NPA.The ensemble of aridity prediction models for four station points in Zhenjiang were established using the stepwise regression,and their predictions are integrated by optimal weights.Computed AIs agree well with the historical documents of droughts,and the forecasts of aridity made using the ensemble of aridity prediction models in 2000—2004 are all correct.