Modeling the Impact of Climate Change on Water Availability in the Zarrine River Basin and Inflow to the Boukan Dam, Iran

As climate change is projected to impose profound global variations in the freshwater resources, assessing the impacts of the former on the latter is a fundamental task for improving the water management, namely, in arid and semiarid areas, as there a plenty of in countries like Iran. Such is the objective of the present paper, where the impacts of climate change on the water availability in the Zarrine River Basin (ZRB), the headwater of Lake Urmia, in western Iran, with the Boukan dam as the major surface water reservoir, are simulated under various climate scenarios up to year 2029, using the SWAT hydrological model. The latter is driven by meteorological variables predicted from MPI-ESM-LR-GMC with RCP 2.6 and RCP 4.5 scenarios (precipitation) and HADCM3-GCM with SRES A2 and B2 scenarios (temperature), and downscaled with Quantile Mapping (QM) biascorrection and SDSM, respectively. From two variants of QM employed, the Empirical CDF QM model decreased the biases of the raw GCMprecipitation predictors particularly strongly. The SWAT-model was calibrated and validated with historical (1981-2011) ZRstreamflow data, using the SWAT-CUPmethodology. The subsequent SWAT-simulations for the future period 2012-2029 indicate that that the predicted climate change for both RPCs will lead to a reduction of the inflow to the Boukan dam as well as of the overall water yield in the ZRB, mainly due to a reduction of the future precipitation with a concomitant reduction of the groundwater baseflow to the main channel. Nevertheless, the future runoff coefficient shows a slight increase, as the decrease of the surface runoff is overcompensated by the named precipitation decrease. In summary, based on these predictions, together with the expecting increase of water demands due to the agricultural and other development plans, the ZRB is likely to face a water crisis in the future years, unless some adaptation plans are implemented for a better management of the water resources, such as more efficient irrigation or a change of the crop patterns in the area.