Assessing Climate Change Impacts on Water Allocation in Karkheh River Basin

Rahman Davtalab1, 2, Kaveh Madani2, Alireza Massah3, Manouchehr Farajzadeh1 1Department of Geography, Tarbiat Modares University, Tehran, Iran 2Department of Civil, Environmental and Construction Engineering, University of Central Florida, Orlando, FL 32816, USA 3Department of Irrigation and Drainage Engineering, College of Abureyhan , University of Tehran, Iran Abstract Karkheh river basin, with an area of 50,000 km2 is located, in southwest Iran. This basin supplies water for major agricultural activities and large hydropower production in five Iranian provinces with the total population of four million people. Due to development and population growth, this large trans-boundary basin is incapable of meeting the water demands of the five riparian provinces, causing water allocation conflicts in the region. The situation has been exacerbated by the frequent droughts and is expected to worsen further by climate change. This study evaluates the impacts of climate change on water supply reliability and allocation in this basin. First, outputs of several General Circulation Models (GCMs) under different emission scenarios for different future time horizons are statistically downscaled. Then multiple river flow time series (RFTS) are generated by feeding GCM outputs into a HEC-HMS model, using the Soil Moisture Accounting (SMA). Given a wide range of variations in GCM outputs and the resulting RFTS, the Ward's method is used to identity different RFTS clusters. Clustering helps with increasing the ability of the modeler to test a range of possible future conditions while reducing the redundancies in input data. Karkheh river basin's ability to meet the growing demand under decreasing flows is evaluated for each RFTS cluster representative. Results indicate that Karkheh river flow might decrease by 50% toward the end of the century. This would decrease the reliability of agricultural water deliveries from 78-95% to less than 50%. While currently hydropower dams can only use 50% of their generation capacity for electricity production due to limited water availability, this figure would reduce to less than 30% with climate change. Several adaptation strategies are suggested based on the findings to minimize the economic losses of climate change in this developing basin.