Paper Title
Hydrological Drought Analysis using Stream Flow Drought Index (SDI) – A Case Study for Watrak Basin

Drought is a disastrous natural phenomenon. It differs from other natural hazards by its slow accumulating process and its indefinite commencement and termination. To analyze a drought and its intensity is necessary. Drought has many facets in any single region and it always starts with the lack of precipitation and may (or may not, depending on how long and severe it is) affect soil moisture, streams, groundwater, ecosystems and human beings. This leads to the identification of different types of droughts (meteorological, hydrological, agricultural, socioeconomic), which reflect the perspectives of different sectors on water shortages. Hydrological drought is associated with the effects of periods of precipitation (including snowfall) shortfalls on surface or subsurface water supply (i.e., streamflow, reservoir and lake levels, groundwater). The frequency and severity of hydrological drought is often defined on a watershed or river basin scale. Drought indices are indispensable tools to detect, monitor, and evaluate drought events. The main objective of drought indices is drought monitoring, early warning, and improving drought preparedness and mitigation. Various indices to measure hydrological drought are Standardized Runoff Index (SRI), Effective Drought Index (EDI), Surface Water Supply index (SWSI), Palmer Hydrological Drought Severity Index (PHDI), Stream flow Drought Index (SDI). In this paper the study area selected is Watrak River basin, this is a Left bank tributary of Sabarmati River. Watrak and its tributaries drain an area of 8638 sq km. The hydrological drought is determined using stream flow drought index (SDI). In this method the streamflow data of the Watrak River is used to calculate SDI, the hydrological drought for 3, 6, 9 and 12 months is determined and categorized as non-drought to severe drought. The result shows that at the end of the year the intensity of hydrological drought is 60%. The necessary recommendation for mitigation is also discussed. After doing the validation check with the droughts declared by the government of Gujarat, it is seen that out of 13 data available only two times the result is negative. Hence 84.5% of the result is validated. Keywords - Drought, Steamflow Drought Index (SDI), Hydrological Drought, Intensity of Drought, Mitigation