Application of the SWAT Model in the Ghare Sou river Basin under climate change

IntroductionIn this study, Soil and Water Assessment Tool (SWAT) was used to evaluate the effects of climate change on river flow in the Ghare sou watershed. Karkheh Basin is located in the west of Iran with area of 50764 km2. It is located in the middle parts and southwest regions of Zagros Mountains between 46° 06´ and 49° 10´ of east longitude also between 30° 58´ and 34° 56´ north longitude. Ghare Sou is a sub basin of Karkheh in northwestern of Karkheh basin and west of Iran. Its area is 5354 km2 with a maximum and minimum height of the 3346m and 1180 m respectively. Average of annual rainfall varies between 300mm to 800 mm.At present, various methods for generating climate scenarios are used for future periods. These methods include: producing synthetic scenarios, using past climate parameters and using Atmosphere Ocean General Circulation Model (AOGCM).Current most reliable tools for producing climate scenarios are three dimensional coupled models of ocean-atmosphere general circulation (Wilby and Harris 2006, Mitchell 2003). AOGCM models are based on physical laws and mathematical relationships. These relationships solve in a three dimensional network of the earth surface. AOGMCM is a valid tool for predicting climate change and producing hydrological model inputs. Recently, some studies have been done about effects of climate change on runoff. These studies combined the outputs of general circulation models and hydrological models. Predictions by AOGCM is the first attempt to assess the effect of climate change on hydrology at the basin scale.Results and discussionTo assess water balance of the basin SWAT model was used. Physical-based and distributed parameters were developed to prediction of land use changes and management practices in the large and complicated basins Differences in the results of these methods were in border cells of groups and for appointment to own groups of these cells, their subsequent probability were used.Results and DiscussionNorthwest precipitation groups are as follows:1.The first group (low concentrated precipitation region with moderate snowfall): The first group has 306.5 mm of total annual rainfall and 33559.9 of area. It is located in two separate parts of the South East of study area and near of Oroumieh Lake.2.The second group (Moderate precipitation region with tendency to low distributed precipitation and much snowfall): the second group has 348.3 mm of total annual rainfall and 62847. 65 of area. It is located in the northern half of the study area. This group is allocated more than half the area of the Northwest.3.The third group (much concentrated precipitation region with low snowfall): the third group has 631.2 mm of total annual rainfall and 4972.27 of area and it is located in the Southwest of study area.4.The fourth group (moderate precipitation region with tendency to much distributed precipitation and moderate snowfall): The fourth group has 436.8 mm of total annual precipitation and 17290.22 of area. It is located in two separate parts in the south to the west and the central part of the study area.In comparing the groups some differences in the amounts of precipitation, distribution of precipitation, snow days and start of rainfall season in groups are detected. Amount of annual rainfall in high rainfall group is more than double of low rainfall group. Linear functions obtained from discriminant analysis determined the boundary between these groups.