Since the Soyang multi-purpose dam was designed to discharge deep lake water to downstream area, the microclimatic changes in this area, such as relatively cold water during summer season and frequent fog formation during winter season, has been arised. The intake of surface water, instead of deep lake water, would mitigate such changes. In order to compare the microclimatic aspects caused by both cases, the temperatures of discharge water were simulated utilizing the Water Quality for River and Reservoir System (WQRRS) model. From the simulation results, the followings are concluded: The discharge water temperature for the case of the surface water intake would increase upto 10 C during summer. This will mitigate the cold thermal impact on downstream ecosystems. The discharge water temperature for the case of the surface water intake would decrease about 2 C during winter. This will mitigate fog and cloud formation in the downstream area. The surface water intake would reduce the evaporation on the surface of the Lake Soyang especially during summer. This will mitigate the fog formation on the lake. The results suggest that the surface water intake would be desirable to mitigate the microclimatic changes in the downstream area.