جغرافیا و برنامهریزی محیطی (Jan 2013)
Climate Change Effects on River Discharge-Case Study Sheshpir River
Abstract
Extended Abstract 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 the time period of 2010-2040. This value for the time periods 2040-2070 and 2070-2100 was equal to respectively, 2.3 to 4.5 ° C and 2.7 to 6.5 Celsius degrees. The largest seasonal changes in temperature occurred in winter and the lowest in summer. The results of models and scenarios for precipitation indicate that the rainfall changes in the first month of spring, all summer and the last two months of fall has been increased and for the other months has been fallen. However this was true for all time horizons. So that, the amounts of this increase in the summer months comes over to 900 percents. However, due to low summer rainfall in the region, considering the above-mentioned increase, the total rainfall reaches up to 6 mm. This value is an average rate and probably in the real situation of summer rainfall, especially when the land is dry with low infiltration, it could associate with the devastating floods. Also, for the time period of 2010-2040 and 2040-2070 and various scenarios, the annual rainfall changes vary between -1.5 to 6 percent that was not noticeable. However the changes for the time period 2070-2100 vary between 3.9 to 31 percent and it was somewhat remarkable. But certainly, the temporal changes in the rainfall (low winter rainfalls and more spring and summer rainfall), at all the time horizons are more important. Finally, the rainfall runoff model for the various scenarios showed that the amount of Sheshpir river flow has reduction for almost all of the months. Also the maximum reduction occurs in the months October, November, February and March (mainly in autumn and winter seasons) and the minimum reduction in the spring and summer. Totally, the average annual decrease for the time period 2010-2040, 2040-2070 and 2070-2100 is respectively 39, 43 and 34 percent. 4– ConclusionCertainly preparing the future climate projection or climate prediction, using general circulation models includes lots of uncertainty. 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