Spatial and temporal changes of water resource components regarding different time periods and important land-uses in Zayandeh-rud Basin

This study examines spatial and temporal changes in water resources; including blue and green water resources components, taking into account their changes in four main land use in the Zayandeh-rud basin. The spatial and temporal changes were studied using the semi-distributed hydrological model SWAT (Soil and Water Assessment Tool) by applying the most complete data set developed for the watershed over 20 years and for four different 5-year intervals. Due to the high ability and efficiency of the SWAT model to simulate climatic parameters and surface runoff, the minimum 5-year average of blue water, green water flow, and green water storage at the basin level occurred; in the fourth period 2010-2014 (approx. 15 mm), the second period 2000-2004 (26 mm) and the first period 1995-1999 (30 mm), respectively. On the other hand, the mean values of the blue water component, the green water flow and the green water storage components were estimated to be higher in the western parts of the basin than in the eastern parts. Other findings from this study are the changes of blue water and green water regarding precipitation and land use. For example, the maximum amount of blue water was observed in forests and irrigated agricultural lands, the highest amount of change in green water flow in irrigated agricultural and dry farming lands, and the minimum amount of green water flow in grasslands. Acknowledgment of available water resources, water potentials of an area and critical areas enables comprehensive management of water resources and long-term planning.