Climate Change and Water Supply

Climate change will have major implications on the global water cycle. Precipitation will increase in some regions but decrease in others. Snow will melt earlier in the season, and many glaciers are projected to disappear during this century. Furthermore, the increasing carbon dioxide concentration in the atmosphere will affect the water balance of agricultural crops and natural ecosystems. This chapter assesses future changes in global water availability based on a large set of simulations with complex climate, hydrological, and ecosystem models. Some simulations combine projected changes in climate with those in population. The results reflect “best guess” projections for each region as well as the uncertainty around those projections, which allows for a better estimation of future risks to regional water availability. According to the simulation results, climate change is expected to increase total water availability in some regions and to decrease it in others, including in many currently dry regions. Projected changes are still uncertain in several regions, in particular in most of the poorest countries. However, most poor countries are experiencing strong population growth, which suggests that water availability per person will decrease in all climate scenarios. Widespread water poverty today, calls for substantial improvements in water infrastructure and water policies to ensure access to safe drinking water for everybody. In many poor countries this task is expected to become more costly in the future because of population growth and climate change.