Allocation of water resources with management approaches and under climate change scenarios in an arid and semi-arid watershed (study area: Hablehroud watershed in Iran)

In this research, the hybrid model consisting of output of 23 general circulation models (GCMs) was statistically downscaled using the lower airspace radar service- weather generator (LARS-WG) model. Also, soil and water assessment tool (SWAT) distributed hydrological model was calibrated in order to simulate the runoff of the Hablehroud basin (an arid watershed in the north of Iran) in the base period (1985 to 2005) and the runoff of the future period (2025 to 2045). To water resources management in the Hablehroud basin under two climate scenarios (representative concentration pathway (RCP)4.5 and RCP8.5) and three management scenarios including, S0 (continuation of the status of the base period), SI (increasing the water demands without development of water supply sources) and SII (increasing water demands with the construction of the Nimrod Dam), the water evaluation and planning (WEAP) model was used. Both RCP4.5 and RCP8.5 scenarios project increases in mean annual minimum (Tmin) and maximum (Tmax) temperatures, precipitation (PCP), and runoff. RCP8.5 shows larger increases: Tmin by 1.12°C, Tmax by 1.21°C, PCP by 12.6%, and runoff by 11.6%. RCP4.5 projects smaller increases: Tmin by 0.78°C, Tmax by 0.94°C, PCP by 11.5%, and runoff by 6.4%. In both scenarios of climate change, with a 2% annual increase in water demand, all the needs of the region can be met without the need to exploit the reservoir. With an annual increase in water demand of 5%, the needs of the region can be met only by operating the reservoir, but with an annual increase of 8% in water demand, a large part of the need of the region cannot be met. The values of unmet water demand in 2045 with operating the reservoir are 136 and 277 MCM under RCP8.5 and RCP4.5 scenarios, respectively. Without using of the reservoir, these values will increase to 172 and 295 MCM.