comparison of two gcm models (hadcm3 and cgcm2) for the prediction of climate parameters and crop water use under climate change (case study: kashafrood basin)

abstract the climate change was known to force local hydrology, through changes in the pattern of precipitation, temperature and the other hydrological variables. in this research, the impact of global warming on maximum and minimum temperature, precipitation and evapotranspiration (wheat, corn, tomato and sugar beet) of kashafrood basin under two climate change scenarios (a2 and b2), and the output of two gcm models (hadcm3 and cgcm2) for three period of times (2010-2039, 2040-2069 and 2070-2099), were investigated. for evaluation two scenarios were downscaled into local level with automated statistical downscaling (asd) model. precipitation was expected to decrease and/or increase, depends on applied gcm. the results indicated that the annual precipitation decreased for three periods under cgcm2 model and also for two scenarios (a2 and b2) as much as 13%-16% decreasing, the annual precipitation for three periods under hadcm3 model and two scenarios (a2 and b2) as much as 2%-8% increasing. the maximum and minimum temperatures in the kashafrood basin was predicted, which increased by cgcm2 and hadcm3 models with two scenarios. based on the hadcm3 model, maximum and minimum temperatures were expected to increase 2.4 0c to 5.8 0c and 0.6 0c to 3.8 0c, respectively; for 2070-2099 periods. for cgcm2 model, maximum and minimum temperatures were expected to increase 0.06 0c to 2.59 0c and 0.1 0c to 1.9 0c respectively; for 2070-2099. evapotranspiration under a2 and b2 scenarios and hadcm3 model was increased but increasing in evapotranspiration with cgcm2 model under both scenarios was not significant in many cases. the comparison of two models and also two scenarios indicated that more critical status for a2 scenario by using two gcm models for this basin.