Page - 521 - in Book of Full Papers - Symposium Hydro Engineering

1. INTRODUCTION Many studies so far have provided evidences in support of climatic changes during the past decades as such variations affected the water balance and caused fluctuations in stream flows at both regional and local (catchment) scales. In Iran many studies support the fact that the climate has experienced variations during recent decades (Dinpashoh et al. 2011; Golian et al. 2015; Marofi et al. 2012; Masih et al. 2011) mostly toward more hot and dry conditions. Also, in recent years anthropogenic global warming and its consequences especially in the arid and semi-arid regions of the world received particular attention as many scholars documented occurrence and dominancy of drought, temperature rise and increase in the atmospheric water demand accompanied by reduction of precipitation and runoff (Guo and Shen 2015; Lalika et al. 2015). Also, assessments by IPCC (Intergovernmental Panel on Climate Change) provides means for policymakers to plan for future to adapt to climate change and mitigate its impacts. Anticipated climatic changes can alter the hydrological behavior such as the amount of discharge or timing of the hydrological regime (Adam et al., 2009; Boyer et al., 2010; Gan et al., 2015). Such alterations can cause socio-economic and environmental consequences. Several studies world-wide predicted that the combination of temperature increase and precipitation change during the present century will result in significant change in runoff (Steele-Dunne et al., 2008; Vezzoli et al., 2015). Also many climate change impact studies have been carried out to investigate the hydrological response to climate change (Pervez and Henebry, 2015; Boyer et al., 2010). For instance it is widely documented that the modeled winter time discharge increase followed by the spring time discharge decrease, which is due to temperature increase; that is the cause to melt snow sooner and remain less snow pack (Arnell and Gosling 2013; Adam et al. 2009 and Boyer et al. 2010). A global scale study on river flow and water temperature changes through forcing by A2 and B1 emission scenarios suggested increase in the seasonality of river flow, i.e. increase in high flows and decrease in low flows for about one-third of the Earth (Van Vliet et al. 2013). One of the vulnerable industries against climate change is hydropower generation, which completely relies on the amount of precipitation and the stream flow as well as the timing of the flow (Abrishamchi et al., 2012). Based on the IPCC report the potential of hydropower generation is projected to reduce by up to 6%, as a result of climate change (IPCC, 2008). Therefore, it is essential to adapt the water resources management with the future climatic changes (Xu and Singh, 2004). In Iran the climate and hydropower generation changes have been studied by Jahandideh et al. (2015) and Jamali et al. (2013) those focused on Karun and Karkheh river basins, respectively; and they reported reduction of the potential of hydropower generation in both studied basins. Considering that the freshwater availability is vital in semi-arid and arid basins, it is essential to establish the magnitude of changes in surface water at basin scale. This study is focused on the semi-arid Dez River basin in Iran. Stream flow from this basin is used for hydropower generation, industrial production, irrigation, and domestic water supply. As Dez Basin is not completely developed 521