Two-thirds of the world’s population lives under severe water scarcity at least 1 month of the year, according to a study published in Science Advances. That’s 4 billion people. Nearly half-a-billion face severe water scarcity all year round.
The study’s authors divided the globe into small squares, roughly 50 kilometers on a side. Within each square, they calculated the ratio of the demand for water divided by the supply available. Ratios above 1.0 indicate areas where demand exceeds supply. Ratios below 1 indicate areas where supply exceeds demand.
There are a number of ways to consider water scarcity. One would be an annual summary – how does the average yearly demand compare to the average yearly supply? Figure 1 shows the data, with dark red areas having the biggest water deficit, and dark green areas having the biggest water surplus. One could guess the areas of greatest water deficit: the world’s great deserts. If there are surprises here, it is how much of the globe is red. Close to home, the size of the red area in North America is surprising, and a bit daunting.
(Click on chart for larger view.)
Annual averages may not be the best way to consider water scarcity, however. In regions with monsoonal weather patterns, like India, Africa, or California, there may be copious water during part of the year, and severe dryness during other parts. Figure 2 shows the number of months per year that the water ratio exceeds 1.0, that is, the number of months demand exceeds supply. Dark red equals 12 months, or the whole year. Green equals 0 months, or none of the year. You can see that many of the same regions experience a water deficit for at least 6 months per year. Look at North America – how much of Canada, Mexico, and the United States experiences a water deficit a significant portion of each year! And it includes some surprising areas, such as Florida, Georgia, the Carolinas, Arkansas and Louisiana, etc.
Finally, one can look at water scarcity seasonally, as shown in Figure 3. The top map shows the data for winter, the second map for spring, the third for summer, and the fourth for fall. There are regions of the world that experience water scarcity year-round, like the Sahara Desert and Saudi Arabia. But if you look at China/Central Asia and North America, you can clearly see a seasonal pattern. In these regions, water scarcity is at its highest in spring and summer.
It is hard to locate Missouri on these maps, it would appear to straddle the line between water surplus and water deficit. I know of no similar studies that address the situation here in more detail. In previous posts I’ve seen no sign that the state as a whole faces a significant water deficit: neither flow on the Missouri River nor statewide precipitation seem to be declining.
If your region of Missouri faces a significant water deficit, or if you know of a study of statewide water supply, why not comment and let us know? Thanks.
Mekonnen, Mesfin, and Arjen Hoekstra. 2016. “Four Billion People Facing Sever Water Scarcity.” Science Advances. 2016, 2. Downloaded on 2/13/16 from http://advances.sciencemag.org/content/2/2/e1500323.