The U.S. Climate Science Program concluded in 2008 that hydroelectric power generation can be expected to be directly and significantly affected by climate change with potential for production decreases in key areas such as the Columbia River Basin and Northern California. Hydropower generation depends directly on the availability of water resources and the lack of sufficient water inflows may thus have sizeable consequences on the electricity supply in markets where hydropower is of some importance. This study investigates the effects of climate change impacts on hydropower generation over the 21st century both globally and regionally using the Global Change Assessment Model (GCAM), a leading community integrated assessment model of energy, agriculture, climate, and water. To quantify changes in future hydropower availability, a Modified River Transport Model scheme has been incorporated with the existing gridded global hydrologic model in GCAM. The river routing model simulates the spatial movement of cell-to-cell routing with a linear advection model and employing a realistic river network delineated with a hierarchical dominant river tracing algorithm. The streamflow results along with grid elevations and locations of hydropower reservoirs, GCAM estimates the effects of climate change impacts on future hydropower availability in different regions. This in return affects the potential of hydropower for electricity generation in each region requiring additional generation from other sources. Based on the Hadley Center's A2 climate output, the United States will likely see an increase in hydropower potential while Latin America will see a decline as part of the energy portfolios; however the results are sensitive to the climate model of choice.