Effects of Drought on Streamflow Characteristics

Abstract

Droughts are defined using daily streamflow series and different truncation levels including 30%, 50%, 60%, 70%, 80%, and 90% of recorded daily flows. Flow ratios, which are obtained by dividing subbasin flows of different truncation levels by their corresponding outlet flows, are calculated. It is found that the flow ratios of 17 selected subbasins decrease significantly with increasing truncation levels while their mean‐flow ratios are approximately equal to their corresponding area ratios. Therefore, the estimation of irrigation water using the drainage area ratio, which has been practiced in the studied drainage basin, is impractical in case of droughts. Furthermore, assuming the time‐dependent Poissonian behavior of drought series, the drought intensity function was developed to investigate drought severity in the basin. Based on plots of drought intensity function, it is found that the drought intensity has been increasing significantly for the basin investigated.