This study aims to evaluate effects of two downscaling methods; change-factor and statistical downscaling on the runoff of the Azam-Harat River located at Yazd province (with an arid climate) of Iran, under the A2 emission scenario for the period of 2010-2039. For this purpose, CGCM3-AR4 model; a rainfall-runoff conceptual model, IHACRES; two downscaling models, Change Factor and LARS-WG were applied. Results show 30% difference in runoff simulated by two downscaling methods. Also, according to the fact that Change Factor ignores climate fluctuations over the course of future period relative to base period, simulated runoff from the outputs of this downscaling method does not contain enough confidence and cannot represent the actual runoff of the basin in the future. Despite, fluctuations are modeled in the LARS-WG well. On the other hand, if the estimated runoff increase from the LARS-WG is more than the capacity of the Azam-Harat River and Basin, the risk of flood and damage could figure in the future.

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