美國加州大學爾灣分校（University of California, Irvine）去年發表兩份研究報告（註），美國國家太空總署（NASA）重力反演與氣候實驗（Gravity Recovery and Climate Experiment , GRACE）衛星的資料顯示，地球上最大的地下水庫，水量正以令人不安的速度消耗中。
The University of California, Irvine (UCI) recently released two studies (here
) using data from NASA's Gravity Recovery and Climate Experiment (GRACE) satellites showing that the earth's biggest groundwater basins are being depleted at troubling rates. The GRACE satellites observed the 37 largest aquifers
on the planet by measuring their gravitational pull over the course of ten years, from 2003 to 2013. Out of these 37 aquifers, 21 were found to have exceeded their sustainability "tipping points," which means they lose more water every year than can be naturally replenished by rainfall and snow melt. Out of those 21 aquifers, 8 are "overstressed" and are receiving little, if any, "natural replenishment" to restore their water resources. An additional five aquifers are designated as "extremely or highly stressed," meaning they are "still in trouble" but have "some water flowing back into them."
The most overstressed groundwater source in the world is the Arabian Aquifer System that supplies water to more than 60 million people. The second-most overstressed aquifer is the Indus Basin aquifer in northwestern Indian and Pakistan, followed by the Murzuk-Djado Basin in northern Africa. While not in the top three most stressed aquifers, the California Central Valley Aquifer System
is still considered "highly stressed." In California, 46% of the state's water
is supplied by groundwater sources, which are necessary for agriculture. California is currently in its fourth year of drought and people rely on aquifers more heavily during droughts because of a lack of rainfall. Places like the Amazon Basin and the Great Plans are doing slightly better because of their sparse populations and use of rainwater for crops.
Unfortunately, it is completely unknown how much water is left in these groundwater basins. Estimates range from decades to millennia. It is possible for scientists to drill into the basins to determine how much water remains, but this is an expensive process and funding for a project like this does not currently exist. However, it is necessary to find out how much water remains because around two billion people rely on underground aquifers for their freshwater. There is already ecological damage from the water depletion, including diminished rivers, a decrease in water quality, and subsiding land. Climate change and population growth are expected intensify the depletion.
Luckily there are some things you can do to reduce your individual water
use like installing low-flush toilets and low-flow showerheads. Even simpler practices include turning off the water while brushing your teeth, shaving, or soaping in the shower. If you water your lawn, it is best to do so early in the morning or late in the evening, and on cooler days, to reduce evaporation. Planting indigenous plants reduces the amount of water necessary to keep them alive. If you have a pool, cover it when it is not in use to once again reduce evaporation.
Do what you can to help conserve water because sadly, there's no telling how much we have remaining in our aquifers until further research is done.
Written by Marisa Barley