As climate change progresses it is likely to have dramatic affects on the supply of water. In some areas it may increase, for example at higher latitudes, but water-stressed areas in the mid-latitudes are expected to face a reduction in available water.
The projections of per-capita water availability in the maps above were made by Martina Floerke and colleagues at the University of Kassel in Germany, by combining different types of forecast.
- A computer model of climate change developed by the UK Met Office Hadley Centre generates projections of future temperature and rainfall. The Kassel team applied Hadley projections on a finer geographical scale. These projections were fed into a programme that models water flow in river basins.
- The Intergovernmental Panel on Climate Change (IPCC) produces "scenarios" suggesting how society may develop economically and socially over time. The Kassel researchers used these scenarios to project water use by various sectors of the economy. (This particular analysis used a scenario where economic growth and technological change are "uneven", and population growth "high".)
Having forecast the availability of water and the demand from industry, it was then possible to calculate how much water would be available per person at different points in the future.
These are projections, not predictions, and none of the models used is likely to be completely accurate.
The projections were adapted from a paper that originally appeared in the journal Hydrological Sciences in 2007.