1- Snow is one of the main water balance element in a river basin. Snow is a major part of precipitation and consequently the snow melting is the main resource for runoff in spring and summer. Runoff caused by snow melting is important resources for water demands including domestic, agricultural, industrial and environmental and sometimes destructive floods. Therefore the accurate recognition of the temporal and local snow properties is important to have a correct and effective management in water resources. In this thesis, the impacts of climate change on snowmelt-runoff process in upstream of Zayanderood river basin, has been studied. For this purpose daily and eight days MODIS snow cover products have been used to monitor snow cover changes in the case study area. In order to preprocessing, the daily and eight days maximum snow cover MODIS products are evaluated using of observed land data in GIS environment. The results indicate that accuracies of daily snow product in overall and clear sky conditions and eight day product are 73.37%, 92.05 and 84.18% respectively. Snowmelt runoff process modeled in both two sub basins utilizing extracted snow cover, the temperature, the precipitation and SRM model parameters. The modeling results indicate acceptable performance of SRM in two case study sub basins. To evaluate the impacts of climate change on snowmelt procedure, effects of climate change on the precipitation and the temperature, as two effective factors in the snowmelt process has been assessed. The HadCM3 GCM model and SDSM downscaling model have been used to aim climate change affected temperature and precipitation under A2 and B2 emission scenarios. GCM downscaled outputs show a considerable increasing trend in the temperature (up to +4.9 for Singerd climatologic station and up to +3.46 for Badijan climatologic station). Also a decreasing trend in precipitation over case study area has been predicted, but this trend is not significance. Finally using GCM downscaled outputs and the developed snowmelt model, the future runoff in two periods of 2011-2040 as near future and 2071-2099 as far future under climate change condition are evaluated. Results show that yearly runoff will decrease and seasonally winter runoff will increase, also the seasonally runoff in spring will significantly decrease. Simulation results indicate that peak of discharges will move from March and April to December and January and peak discharge values will decrease. Keywords Snowmelt, Climate Change, MODIS, SRM, Zayanderood River Basin.
