The impact of climate change is likely to have considerable implications for water resource planning, as well as adding to the risks to water infrastructure systems and effecting return on investments. Attention is increasingly being paid to adaptation strategies at the regional and basin level
however, the current paucity of information regarding the potential risk to hydrological systems at this scale presents a substantial challenge for effective water resources planning and investment. This study is intended to help bridge the gap between high-level climate change predictions and the needs of decision-makers, including World Bank Task Team Leaders, government agencies, investors, and national economic development planners, whose programs and investments will be affected by basin- and regional-level impacts of climate change on water resources and related infrastructures. This study evaluates the effects of climate change on six hydrological indicators across 8,413 basins in World Bank client countries. These indicators, mean annual runoff (MAR), basin yield, annual high flow, annual low flow, groundwater (base-flow), and reference crop water deficit, were chosen based on their relevance to the wide range of water resource development projects planned for the future. To generate a robust, high-resolution understanding of possible risk, this analysis examines relative changes in all variables from the historical baseline (1961 to 1999) to the 2030s and 2050s for the full range of 56 General Circulation Model (GCM) Special Report on Emissions Scenario (SRES) combinations evaluated in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4).