Long Term River Discharge Scenarios Estimation Under Climate Change Impacts. (Case Study: Karun4 Catchment Area)

Climate change is likely to create considerable and often unfavorable impacts in Iran. Investigating and analyzing of the impacts of this phenomenon on the environment and on hydrological factors, including river flows as the basic factor in the provision of water resources, is a serious need. This study is in line with this objective and has conducted the production of long term scenarios of discharge and evaporation under the influence of climate change in Karun4 basin. In this study, long-term scenarios for predicting the future discharge under the effect of climate change have been established for the next 90 years. At first, 28 scenarios for monthly temperature and rainfall were generated using 11 AOGCM models under AR4 for different years were created. Discharges were estimated by an empirical multi-variable regression model which was obtained, calibrated and finalized by using historical data. Future discharge was then obtained and its behaviour and trend were analyzed for average, optimistic and pessimistic scenarios. The results show changes of rainfall (about 17% decrease) and temperature (22.6% increase) over the next 90 years will cause a significant change in river discharge from between 32% (the pessimistic condition) to 7.4% (the optimistic condition) and, under average conditions, a reduction of 18.6%. Bases on these results, climate change along with the increase of evapotranspiration and decrease in discharge will cause significant impacts on water resources. As a result it is shown that a reduction of about 20% will probably occur in hydropower plant production.