Estimating the Monthly Flow Deficit during Hydrological Drought Periods in Gorganroud River Basin

Hydrological drought usually have a considerable impact on the quantity and quality of water resources, causing water shortages in consumption sector and its study is important in terms of intensity, frequency and spatial extent. The aim of this study is to determine the periods of hydrological droughts, drought characteristics and amount of flow deficit in a 38-year recorded data over hydrometric stations of the Golestan Province. The weighting factor of drought importance for each month was calculated based on the flow distribution in different months. The subtracted mean discharge of particular month from the long-term average was multiplied by the weighting factor to determine the effective discharge. The difference of mean monthly discharge and effective discharge considered as monthly flow deficit. The onset and end of hydrological drought periods were defined and the cumulated flow deficits were calculated. The results showed that the highest flow deficit amounts were recognized for in Taghiabad, Basirabad, and Hajighoshan stations with 1.28, 1.27, and 1.07 respectively. In general, the flow deficit were observed in June, July and August in almost all river gauge stations of the study area. Moreover, the deficit volume was lower at stations located in upland areas.