Analyzing long-term spatial variability of blue and green water footprints in a semi-arid mountainous basin with MIROC-ESM model (case study: Kashafrood River Basin, Iran)

The river basin hydrology cycles and the available water resources (including blue and green water) are greatly influenced by the climate change and rainfall patterns in regions with arid and semi-arid climates. In this study, the impacts of climate change on the parameters of virtual water is evaluated in the Kashafrood River (KR), as a large-scale basin which is located in the northeast of Iran, by means of SWAT model (Soil and Water Assessment Tool) along with SUFI-2 (Sequential Uncertainty Fitting Program version 2). In addition, sensitivity and uncertainty analyses are taken into account at five runoff stations for calibrating and validating the model. Based on the changes in blue water (BW), green water flow (GWF), and green water storage (GWS), the water availability was analyzed using MIROC-ESM model in series of the Coupled Model Intercomparison Project Phase 5 (CMIP5) and was compared with two Representative Concentration Pathways (RCPs) of new emission scenarios (RCP2.6 and RCP8.5). These emission scenarios were downscaled based on the observed data under three future periods: near future (2014–2042), intermediate future (2043–2071), and far future (2072–2100) in relation to a historical period (1992–2013). Calibration and validation at multi-site (five stations) showed a proper performance of the SWAT model in modeling hydrological processes. Results of investigating climate change impacts on the blue and green water components (BW and GW) showed that in the historical period, the basin was not in an appropriate climate condition for accessing the water resources. Also, in future times, considerable spatial variations in different hydrological components were observed. On the other hand, under both RCPs and in all three future periods in relative to historical period, the BW contents will increase about 46–74%, while GWF will decrease about 2–15%. Regarding the historical period, it was revealed that the condition of the basin will be improved. In addition, the GWS tended to rise about 11–18% or decrease about 6–60% in the future. The BW and GWS will decrease, and GWS will increase by changing from the near future to the intermediate future. On the other hand, by changing from the intermediate to the far future, BW and GWF will increase under RCP2.6 and will decrease under RCP8.5, respectively. Also, GWS will decrease under both RCPs.