This study bridges the gap between high-level climate change predictions and the needs of decision makers, government agencies, investors, and national development planners--whose programs and investments will be affected by basin- and regional-level impacts of climate change on water resources. This study evaluates the effects of climate change on six hydrological indicators across 8,413 basins worldwide. To generate a robust, high-resolution understanding of possible risk, this analysis examines relative changes in all variables from a baseline (1961 to 1999) to the 2030s and 2050s for the full range of 56 General Circulation Models Special Report on Emissions Scenario Combinations.