Abstract: Understanding the basin-scale hydrologic potentials in managing water resources require the optimization of relevant model. Therefore, this study described the efficiency of CHyM4 model in optimizing water resource planning in a climate change scenario using daily rainfall and discharge data in Benin/Owena river basin, Nigeria. The model produced daily series rainfall and discharge data at a resolution of 1 km across small catchments. Rainfall and discharge scenarios such as average monthly flow discharge, flow direction, drained surface and accumulated time series (onset, peak and offset of rain) were generated from the observed and simulated for the basin between January and December, 2004. The model simulated results were compared with the basin observed data result. Observations show a wide variation in the monthly simulation in the area with precipitation decreasing slowly Northward over the period. Observed rainfall depths/discharge trends and CHyM4 simulation have similar results as shown from the comparison between the simulated and observed rainfall and discharge output. The observed result was used to examine the optimal efficiency of the basin for water resources planning and management based on the projected result. This is essential in order to sustainably manage available water resources within the basin.