Modelling blue and green water resources availability in an Iranian data scarce watershed using SWAT model

Knowledge of renewable water resources of a watershed is strategic information which is vital for long-term planning of water and food security. In this study, we used soil and water assessment tool (SWAT) model in combination with the Sequential Uncertainty Fitting program (SUFI-2) program to simulate the water resource components (blue and green water) in the Kohnak river basin (southwest Iran) based on river discharges, taking into consideration dam operations and irrigation practices. To improve the accuracy of the input climate data to the model, we used two scenarios of climate data including the global climate data and the Kohnak watershed data. The simulation was performed for the period from 1992 to 2009 by considering the first three years as warm-up. The Hargreaves method was used as a convenient method for the calculation of the evapotranspiration. After identifying the sensitive parameters for each investigate component, final calibration and validation analysis were performed to simulate the hydrological components. Finally, the uncertain range of each parameter was determined and then the sub-basins were prioritized. The runoff and sediment simulation results showed that the maximum sediment production was estimated for the sub-basin numbers 2, 3, 5, 9, and 12 and thus sub-basins were identified as the sub-basins with highest erosion hazard potential. In addition, sub-basin numbers 1, 2, 3, 4, 5, and 9 had the highest runoff production in the study area. The rainfall and green water storage simulation results also indicated that the sub-basin 6 was suitable for rainfed cultivation since receive higher precipitation and the results had less uncertainties. The sub-basins located in the northern parts of the watershed may not be suitable for dry farming due to low soil water storage according to the SWAT simulation results.