Assessment of Climate Change Impacts on Snow-Runoff Processes A Case Study: Zayandehroud River Basin

In this paper, the climate change impacts on snowmelt-runoff processes in upstream of Zayanderoud river basin, the sub-basin upstream of Ghaleh Shahrokh hydrometry station, has been studied. For this purpose daily and eight days MODIS snow cover products have been used to monitor snow cover changes as effective variables in SRM runoff-rainfall model. As a preprocessing step, the accuracy of MODIS products in snow cover assessment are evaluated by the observed land data. The results indicated that the accuracy of the daily snow product in overall, clear sky conditions, and eight day product is 73.4, 92.1 and 84.2 percent, respectively. The snowmelt runoff is modeled in the sub-basin utilizing extracted snow cover, temperature, and precipitation variables and SRM model parameters. The modeling results indicated acceptable performance of SRM in calibration and validation procedures. In this research, the HadCM3 model data under A2 and B2 emission scenarios is utilized. SDSM model have been used to downscale GCM data. The results showed a decreasing trend in precipitation over the case study area for the upcoming decades. Finally using GCM downscaled outputs and the developed snowmelt model, the future runoff in two periods of 2011-2040 as a near future and 2071-2099 as a far future are evaluated under climate change condition. Results showed that annual runoff will decrease and seasonal winter runoff will increase. Also the seasonal runoff in spring will significantly decrease.