In some parts of the world, clean water flows straight from a tap. In others, people trek for miles to reach a potable source. How do we measure the availability of this essential resource? Compare the amount of water a region uses to the size of its water supply. This ratio of supply to demand, known as water stress, often shifts over time.
As populations grow or move around, so too will demand. And as climate change redraws temperature and rainfall patterns, supply will change as well. The nonprofit World Resources Institute mapped how water stress will fluctuate around the globe between now and 2040. Its estimate combines factors such as drought, flooding risk, groundwater levels, and access to water that’s safe for humans to drink. WRI predicts that, while some regions will remain stable—and a few can look forward to stress relief—many will face increasing demand and decreasing supply.