regional analysis of hydrological drought in sefidrood drainage basin using base flow index

the term hydrological drought is applied to represent low water levels in streams, reservoirs and lakes as well as a low groundwater level. base flow index (bfi) as one of low flow indices gives the ratio of base flow to total flow and investigates basin’s ability to store and release of water in drought periods. the objectives of this study were to determine bfi and to validate this index in drought studies of sefidrood drainage basin. to view of this, first three homogenous regions were identified based on the threshold level using cluster analysis. then, daily bfi was calculated in 28 gauging stations of the homogenous regions. the results showed that the regional mean of bfi with value of 0.65 (sd=0.19) is stable during long-period data. bfi ranged between 0.17 and 0.86 and also based on the 25, 50 and 75 percentiles, river flow regime in the study area is divided into four categories that show more than 50 percent of the catchments in the study area have low or unstable regime. so it would be hard that the catchments able to provide river flow during drought periods. therefore the results of this study can be used in assessment of groundwater recharge, water supply system, irrigation management, and hydrological drought monitoring as well as regional modeling of water resources storage and hydrological drought in ungauged areas