In order to provide more objective description of the overall drought status, this paper employed a joint precipitation deficit index by empirical Copula function to evaluate drought condition.The Panjiakou Reservoir catchment of Luanhe River basin was chose as the study area.The accumulated precipitation from 1- to 12-month were selected from the monthly precipitation data from 26 rain gauges during the period of 1959 -2011.Based on the values of standardized precipitation index and joint precipitation deficit index, we assessed and analyzed the drought conditions in the study area.It was demonstrated that the joint precipitation deficit index integrates the information of water deficit status at various time scales and takes a full consideration of the cumulative effects of drought.It also can avoid the inconsistent conclusions resulting from using standardized precipitation index with different time scales.In addition, the drought characteristics of the study area were analyzed according to the series of joint precipitation deficit index.The results indicated that the occurrence frequency of the drought generally increases from northwest to southeast, with higher frequency in summer and autumn.Compared with the northwestern part of the area, the drought events in the southeast are characterized with longer duration and more serious severity.Furthermore, a general tendency of drying was found in the flood season across the area, while significant aggravating trends in drought were detected in the southeastern part.The joint precipitation deficit index is capable of reflecting the drought spatial and temporal characteristics and evolution laws, thereby taking as a new technical way of studying regional drought.
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