The UN’s Intergovernmental Panel on Climate Change forecasts that by 2030 global water requirements may outstrip sustainable water use by 40%. In other words, we’ll be using 40% more water than is being replaced by rain and snowmelt. Global warming, rapid population growth, and more wealth in emerging economies are coming together in a perfect storm of increasing demand and falling supply. Without the intervention of some kind of water conservation and management plan, the world’s water tap could one day go dry.
Although 75% of the earth’s surface is covered by water, almost all of that is ocean saltwater. Only 2.5% of earth’s water is fresh water, and 2/3 of that is locked away in glaciers and icecaps. Of the stock of fresh water available, 99% is stored in underground aquifers. Maintaining underground water levels is a balancing act. No more water should be withdrawn than the amount replaced by rain and snowmelt. But with a changing climate that brings less rain and snow, and a growing population that needs more food and more water to grow the food, it is becoming increasingly difficult to maintain that balance.
A team of scientists using data from NASA’s twin Gravity Recovery and Climate Experiment (GRACE) satellites, found that the Tigris & Euphrates basin that includes parts of Turkey, Syria, Iran, and Iraq, lost 117 million acre feet (144 cubic kilometers) of stored fresh water between 2003 and 2010. That’s equivalent to the amount of water in the Dead Sea, and nearly as much as in Lake Tahoe. 40% of the loss was attributed to evaporation of surface water in reservoirs, lakes, and rivers, and 60% to over-pumping of groundwater from the areas’ aquifers. Matt Rodell of Goddard Space Flight Center, co-author of the NASA study, said, “Groundwater is like your savings account. It’s okay to draw it down when you need it, but if it’s not replenished, eventually it will be gone.”
The same problem confronts water users in other arid and semi-arid parts of the world, including Australia, southern Africa, northern Brazil, the Mediterranean basin, and the U.S. southwest. Persistent drought in these areas is causing farmers and other water users to withdraw ground water faster than nature replaces it. According to UN figures, ground-water extraction globally has tripled in the past 50 years. Ground-water withdrawals in India and China have risen tenfold during that period. Aquifer levels in India are sinking 4 meters (13 ft) a year. Half the global population lives in countries where water tables are falling rapidly.
Some scientists believe this negative trend can be slowed or reversed by application of a few simple remedies. Perhaps the most important is improving the efficiency of agricultural irrigation. If crop flooding, which is still used in many parts of the world, can be replaced with drip irrigation and use of soil moisture sensors, millions of acre feet of water could be saved every year. Recycling wastewater, repairing leakage in water-delivery pipes, and regional water-sharing arrangements are also reliable ways to save water. Individuals can save water by using washing machines and dishwashers only for full loads, by not overwatering lawns and plants, and by sweeping instead of washing down outdoor areas.
Whether conservation measures alone will be enough to keep the taps open remains to be seen.