Investigating the Trend of Low Discharge Changes with Different Durations in Northwestern Iran

Climate change along with human interventions has changed natural hydrological cycle and consequently the need for more water resources, timely supply of water needs has faced serious challenges. Estimation of basal flow index has been one of the important issues in hydrology. In order to analyze the minimum flows in this study, 12 hydrometric stations with a statistical period of 30 years in northwestern Iran were selected due to the presence of Lake Urmia and then the annual minimum flow series were calculated with continuities of 3, 5, 7, 15 and 30 days. Based on the goodness-of-fit test of Kolmogorov-Smirnov, among the various distributions of the Wakeby distribution and based on Mann-Kendall test 66.67 Percent have a decreasing trend of minimum flow, based on Pettit 75 Percent of the studied stations have an increasing trend of minimum flow and according to Phenomenon test, 41.67 Percent of the stations have a minimum increasing trend of 95 Percent with different continuities. The results can be useful for having an accurate plan for the amount of water consumed and sustainable management of water resources in arid and semi-arid regions.