Groundwater is vanishing worldwide, but it can be rescued
The bulk of Earth’s water, about 97%, is in salty oceans and thus useless for drinking or growing food. Of the 3% that is fresh, most is locked in ice sheets and glaciers, many of which are melting rapidly into the oceans thanks to climate change. A relative few drops of fresh water are available in ponds, lakes and rivers, which are easily accessible but also vulnerable to pollution, overuse and drought.
Humanity’s biggest source of fresh water — representing just 0.8% of Earth’s total water — is in underground aquifers. Decades of drought, pollution and overuse are shrinking even that precious supply, and rising sea levels threaten to spoil even more of it with saltwater incursions. A recent survey of groundwater levels at hundreds of wells worldwide found that 71% have fallen since the start of the 21st century. Groundwater loss worsened at more than half of the studied wells during that time.
But the survey also revealed, encouragingly, that groundwater disappearance isn’t universal. Losses are most common in areas that are both dry and heavily farmed. Some of those places have managed to protect and even start replenishing their aquifers. The Abbas-e Shargi basin in arid southwestern Iran was losing groundwater at a rate of nearly a foot a year before the turn of the century, according to the study data. It has regained nearly 3 feet of water a year in the past two decades thanks to diverted water from the Karkheh Dam.
The Upper Santa Cruz basin near Tucson, Arizona, was drying up as quickly as the Abbas-e
