Regional drought analysis approach based on copula function

A regional drought index is proposed,which can take into account sub-grid variations in drought severity as well as in drought disaster area.The Copular function is used to establish the joint distribution of drought duration and severity over a region.There turn period of the joint distribution can be used to study the characteristic of historical drought events and estmi ate the current drought return period.The index is applied to study the 2006 droughtevent in Chongqing,southwest of China.The resultrevea ls that the drought development can be adequately reconstructed using the index.The drought characteristics,such as intensity and duration,can also be well quantified by the index.The calculated return period of joint distribution for the 2006 event is 118 years,which reflects the observed reality from the drought disaster.The result demonstrates the miportance of considering the sub-grid drought variations and the significance of using the joint distribution in the estab lishment of the index.The index can thus have the potential of representing the severity of a regional drought in a comprehensive manner.