عنوان مقاله [English]
نویسندگان [English]چکیده [English]
Flood and drought analysis accuracy and estimating return period of droughts depend on selecting type of distribution functions and method of estimating parameters. In this study daily river flow of Nazloochai, Barandouzchai and Shahrchai rivers in the historical and predicted series used to estimate river drought volume series up to 60 days duration in the predicted and actual series. Then using log-Pearson type III distribution function, drought volume of the historical and predicted flow series for the return period of 1 to 10,000 years estimated. Results indicated that drought intensity of Nazloochai and Barandouzchai rivers reduced while in the Shahrchai river drought volume increased in the updated statistical period of data. As updated charts showed 60 days duration drought volume of Barandouzchai and Nazloochai rivers with the 10000 year return period reduced about 29 and 62 (mcm) respectively while for Shahrchai river it is increased about 7 (mcm).