"Blue" water is getting scarcer, and this is becoming a situation that is threatening the sustainable development of human society.
This is the conclusion of a new report, published in Science Advances, that estimates that 4 billion people face water scarcity for at least one month per year. That’s a whole lot more than previous figures, which estimated between 1.7 and 3.1 billion. Of these, 130 million live in the U.S.
Globally there is enough fresh water, but local variations in availability mean that a significant proportion (70%) of the planet experiences scarcity regularly.
The hotspots are all over the place. In the U.S., California, Florida, and Texas have it the worst, accounting for much of the country’s 130 million people who face monthly scarcity. For comparison, Bangladesh also has 130 million, and Pakistan has 120 million. South America and much of Europe are also high on the charts.
In a desert, the reasons for lack of water are obvious, but in more temperate climes, the reasons are all manmade. "Large water consumption relative to water availability results in decreased river flows, mostly during the dry period, and declining lake water and groundwater levels," says the report. "Notable examples of rivers that are fully or nearly depleted before they reach the end of their course include the Colorado River in the western United States and the Yellow River in North China."
The results of water shortage are obvious. California is in a period of extended drought, and dry winters in Southern Europe lead to dramatic shortages in the year immediately following. Southern Europe, though, is already experienced at managing water scarcity, and citizens are used to short showers and other water-saving tricks that the U.S. will soon have to learn. "Other effects include biodiversity losses, low flows hampering navigation, land subsidence, and salinization of soils and groundwater resources," says the report.
What can be done? The answer is, as ever, policy change. Individuals should waste less, but the real changes need to be made in industry. "Green water" agriculture, for example, which uses rain to irrigate crops, will be important. Evaporation from crops should also be reduced, while crop yields need to be increased.
"Meeting humanity’s increasing demand for freshwater and protecting ecosystems at the same time," concludes the report, "will be one of the most difficult and important challenges of this century."