Determining the severity and duration of hydrological drought by using power laws analysis in Gorganroud Watershed rivers

Monitoring and prediction of hydrologic droughts and determining the onset and duration of drought spells have an important role in water resources management and planning to reduce the adverse effects of drought. In the present study the characteristics of hydrological drought in daily discharge time series from 20 hydrometric stations in Golestan Province have been analyzed.
Matherials & In this study, the onset and end of drought periods, mean discharge, effective discharge and threshold level were calculated and then sequence number of 1 to 30-month durations were determined. According to the results of Power Laws Analysis, the intensity and duration patterns of hydrological drought periods were distinguished. The results specified an inverse relationship between the intensity and duration of wet and dry spells. The highest severity of dry spell is related to Nodeh station (Line slope=-0.26) and the highest intensity of wet spell was observed in Ramian station (Line slope = -0.28) which indicated the stability of dry and wet river flow regimes in Nodeh and Ramian stations. Also, the longest durations of dry and wet periods were determined for the Aghghala (32.89) and Basirabad (16.29) stations, respectively, which represents the average maximum probable durations.
Discussion of Results & The proximity, closeness to a straight line or parallel lines without intersection proved the homogeneity regime of wet-dry spells in the Gorganroud watershed. Analysis of wet-dry spells using the Power Laws technique provides a basis to determine the flow regime, severity and duration of hydrological drought.