International Journal of Engineering and Technical Research (IJETR) ISSN: 2321-0869 (O) 2454-4698 (P) Volume-7, Issue-6, June 2017 29 www.erpublication.org Abstract— The Hyrcanian forests are green belt stretching over the northern slopes of the Alborz mountain ranges and cover the southern coasts of the Caspian Sea. The climate of this region is controlled by several components of a regional atmospheric circulation pattern and is strongly modulated by a complex topography and the maritime effect of the Caspian Sea. Climate change will accelerate the hydrologic cycle, altering rainfall, and the magnitude and timing of runoff. Hyrcanian forests might become one of the most vulnerable areas in the world regarding climate change. Therefore, the purpose of this paper is to assess the impacts of climate change on surface runoff from the Hyrcanian forests in the North of Iran. To study the effects of climatic variations, the SWAT model was implemented to simulate the hydrological regime and the SUFI-2 algorithm was used for parameter optimization. The climate change scenarios were constructed using outcomes of three General Circulation Models (CGCM2, HadCM3, and SCIRO2) for three emission scenarios (A1F1, A2 and B1) by adjusting the baseline climatic variables that represent the current precipitation and temperature patterns. The study results for 2040-2069 compared with the present climate showed changes in surface runoff by -1.3%, 5% and -1.2% for the A1F1, A2 and B1 scenarios, respectively. Monthly variations show pronounced increases in discharge in the wet season (February-May) and decrease in dry season (July-September). The results highlight the strong impact of climate change in surface runoff and reflect the importance of incorporating such analysis into adaptive management. Index Terms— Climate Change, Hyrcanian Forests, Surface Runoff, SWAT, SWAT –CUP, Iran. I. INTRODUCTION Hyrcanian forests stretch out from sea-level up to an altitude of 2,800 m and encompass different forest types by the virtue of their 80 different woody species (trees and shrubs). The area is rich in hardwood species, but there are only four genera of endemic softwood (conifer) trees including yew, Greek juniper, oriental arbor-vitae and Italian cypress. However, based on the studies of Fadaiey Khojasteh et al. (2010) three genera of Mesozoic Gymnosperms were recognized. The primary function of the Hyrcanian forests, other than wood production, is supportive and environmental. They play a vital role in the conservation of soil and water resources and keep nature at balance on these susceptible steep mountain slopes. However, rapid urbanization and industrialization, intensive grazing, over-utilization of forests for firewood production and farming is destabilizing the forest and the environemnts around it. H. R. Moradi, Associate Professor Department of Watershed Management Engineering, College of Natural Resources, Tarbiat Modares University (TMU),Noor, Mazandaran Province, Iran, phone number, 00981144553101, Fax, 00981144553499, P.O. Box 46417-76489, K. C. Abbaspour, Eawag, Swiss Federal Institute of Aquatic Science and Technology, P.O. Box 611, 8600 Dübendorf, Switzerland Over the last few decades, swift forest degradation has brought about a number of environmental, social and economic impacts including soil erosion, floods, degradation of farmlands and habitats, reduction of biodiversity and natural resources, and air and water pollution. Furtheremore, manipulation of forest ecosystems has threatened a number of animal species such as fallow deer, roe deer, wolf, fox, wild cat, leopard, pheasant and trout. In recent years, climate change is one of the most important phenomena that threatens this unique ecosystem. The consensus of atmospheric scientists is that the earth is warming, and as global temperatures increase, the hydrologic cycle is becoming more vigorous. The IPCC has reported that there has been a very likely increase (probability 90–99%) in precipitation during the 20th century in the mid-to-high latitudes of the Northern Hemisphere. According to the Fourth Assessment Report (AR4) of IPCC, global mean surface temperature, precipitation and extreme events such as heavy precipitation and droughts have changed significantly, and the changes are very likely to continue (IPCC 2007).The rises of earth near-surface air temperature and changes in precipitation patterns are prominent features of climate change; these two factors impact almost all other hydrological processes. All Atmospheric-Ocean General Circulation Models (AOGCMs) predict a rise in earth surface temperature and rainfall intensity and amount due to increasing in greenhouse gasses (GHG) concentration over the coming century (Kaini et al. 2010). A warmer climate will accelerate the hydrologic cycle, altering rainfall, magnitude, and timing of runoff. Warm air holds more moisture and increases evaporation of surface moisture. With more moisture in the atmosphere, rainfall and snowfall events tend to be more intense, increasing the potential for floods (Dhar and Mazumdar 2009). Using present day precipitation patterns, studies have shown that higher temperatures lead to increased evaporation rates, reductions in surface runoff, and increased the frequency of droughts (Ficklin et al. 2009). The changes in flow characteristics resulting from climate change depend on individual catchment characteristics. In particular, basin geology and elevation are first-order controls on the timing and magnitude of basin runoff to climate change (Hamlet and Lettenmaier 2007). Nearly all regions of the world are expected to experience a net negative impact of climate change on water resources. But the intensity and characteristics of the impact, however, can vary significantly from region to region (Abbaspour et al. 2009). Reliable predictions of the quantity and rate of runoff are needed to help decision makers in developing watershed management plans for better soil and water conservation measures. Many recent studies have focused on the potential effects of climate change on water resources including water quality and Climate Change Impacts on Surface Runoff in the Hyrcanian Forests H. R. Moradi, K. C. Abbaspour