© 2015 ASCE.Before investigating future climatic and hydrologic conditions over Peninsular Malaysia, preliminary climatic and hydrologic simulation results were presented in this paper. The coarse time-space resolution ECHAM5, MRI-CGCM2.3.2 and CCSM3 GCM historical control runs' atmospheric data during the period of 1970-1999 were dynamically downscaled into 1-hour-increment hydroclimate information at 6-km spatial resolution over Peninsular Malaysia. The simulated precipitation and the air temperature over the Peninsular Malaysia were presented. A selected watershed at Peninsular Malaysia was delineated into the Watershed Environmental HYdrology (WEHY) model computational units (MCUs). The WEHY model of the selected watershed was then calibrated to be used in simulating future hydrologic conditions.