Spatial variations of hydrological drought in different time scales in rivers of Ardabil province

During the occurrence of hydrological drought, the river flow will be reduced and the quality of the river ecosystem will be degraded. Determining the temporal and spatial variations of the hydrological drought makes it possible to plan for the optimal use of river water. In this study, temporal and spatial changes of river flow index (SDI) in watersheds of Ardabil province were evaluated. In this regard, daily flow time series of 28 hydrometric stations in Ardabil province were analysed. River flow drought index was calculated using DrinC software and then hydrological drought characteristics were analyzed and spatial variations of SDI index were determined in 1-month, 3-month, 6-month and annual temporal scales in GIS software. 1-month SDI values (short-term droughts) showed that severe droughts were more common in rivers with low discharge values. However, most rivers with low and high amounts of river flow discharge have experienced severe seasons. The annual (long-term) hydrological drought index in most stations was in the range of -1.5 SDI greater than or equal to -1, which indicates the occurrence of mild drought. Spatial changes of SDI showed that the spatial variations of drought index on a 1-month scale are completely different from the annual scale. The lowest occurrence of hydrological drought was in upstream stations and flowing rivers in Sabalan hillsides. Severe and very severe droughts occur in low discharge rivers. The higher the river discharge, the lower the incidence of severe droughts, and the greater its flow stability than low-discharge rivers.