The Effect of Climate Change on Flood Frequency of Kelardasht Basin using K-nn and HadCM3 Model

Global climate change may have serious impacts on the frequency, magnitude and duration of hydrological extremes. Variation in the hydrologic ultimate limits can have impact on designing of hydraulic structures in future, development of flood-plain, and management of water resources. This research, investigated the potential impact of climate change using weather generator K-nn and HadcM3 models under A2 scenario and also the rainfall-runoff HEC-HMS model. First, downscaling of GCM data using HadCM3 model under scenario A2 in stochastic model called K-nn was carried out. Then, land use map and soil group map were prepared and required parameters were determined for the HEC-HMS model. Thereafter, and the model was calibrated and validated using 4 flood events. The results of RMSE, R and t-Student test indicated that simulated peak flow had significant correlation with observed peak flow. Results of storms analysis of 2 hours with 100- year return period showed that the base period (1980-2011) decreased by 32 percent as compared to future period (2040-2069). After determination of intensity-duration-frequency curve, distribution of precipitation values for Nahalestan station imported to the rainfall-runoff model and peak flow with different return periods 2, 5, 10, 20, 50 and 100 years were calculated for sub-basins for the base and future periods. Results of the frequency analysis showed that peak flow in period 2040-2069 with 25 years return period would decrease by 21 percent as compared to the base period.