Climate Change Effects on River Discharge-Case Study Sheshpir River

Extended 1-IntroductionClimate change is one of the big challenges of human and is accounted as a serious threat for the earth planet. Increasing global temperature will cause deep and wide changes in the climate and especially in the time and space of precipitation and storms. Many studies have approved the occurrence of these changes, and the amount and intensity of them. In most of studies, statistical models (based on historical data) or Atmosphere-Ocean General Circulation Models (AOGCM) determine the increase of carbon dioxide emissions and subsequent changes in air temperature and precipitation. Then the changes in river flow rate cased by climate change are calculated by using rainfall-runoff models. But many of these studies only use a limited number of models and emission scenarios that may not include all the facts. Therefore in this study the results of 20 AOGCM models have been considered to explain the climate projection of time horizons 2040, 2070 and 2100. Also a big range of emission scenarios have been studied and using the selected scenarios and models, the amount of Sheshpir River flow (one of Zohre-Jarrahi river basin branches in the south west of Iran) has been detected.2- MethodologyIn this study, through the 20 AOGCM models, used in IPCC fourth assessment report, the appropriate model was chosen to determine the changes in rainfall and temperature in each months of the year. The RMSE, Regional Correlation and Mean Absolute Error statistical tests which was calculated by Magic Model, is used to determine the best AOGCM model (Vigly 2006). Also for assessing all future conditions, from each of the main emission scenarios A1, A2, B1 and B2, two scenarios were chosen to release the highest and lowest emissions. So the total number of eight emission scenarios A1FI-MI, A1T-MES, A2-ASF, A2-AIM, B1-ASF, B1-IMA, B2-HIMI, B2-MES was selected. Interpolation method has been used for downscaling the output of AOGCM Model, so every cell includes the average of 8 adjacent cells. After calculating the amount of precipitation and temperature changes on the study horizon times and estimating the amount of future changes on evaporation, eventually using this data as input in AWBM rainfall – runoff model, the river flow has been estimated at the horizons 2040, 2070 and 2100.3– DiscussionOutput of the models and various scenarios for the Sheshpir river basin showed the increase in temperature, in all three time period, respectively 2010-2040, 2040-2070 and 2070-2100. For the different scenarios, this increase varies from 1.3 to 1.9 Celsius degrees in