Groundwater levels can recover, a global study of 1,693 aquifers finds

Groundwater levels can recover, a global study finds

An aquifer is an underground layer of rock or soil that holds water. Depletion means pumping water out faster than rain and rivers can refill it. Aquifer depletion is not automatically permanent, and groundwater levels can recover, meaning depletion is reversible in real cases, a study of 1,693 aquifer systems worldwide found, using data from 170,000 monitoring wells, wells drilled to track how deep water sits over time, in countries pumping about 75% of world groundwater use. The study, published in the journal Nature, found 71% of those aquifers are losing water, and 30% of that group is declining faster than 4 decades ago. Among a narrower set of 542 aquifers with older comparison data from the 1980s and 1990s, 16% had reversed a prior decline outright. Reading the study abstract directly, rather than only the university account of it, turns up a detail the two describe differently. The abstract states its trend data comes from those 170,000 monitoring wells, while the university describes the same research as drawing on 300 million water level readings from 1.5 million wells in total, a wider dataset the narrower trend count was likely built from, not a second, competing count of the same thing.

The cases in this review are a reminder that groundwater depletion is not inevitable.

Scott Jasechko, professor at the Bren School of Environmental Science and Management at the University of California Santa Barbara, lead author of both studies. Source 3.

What actually reverses a decline

A separate, newer study by the same lead author examined 67 cases where aquifer decline had reversed. In 81% of those cases, the area found an alternative water supply, drawing on a river, canal or pipeline instead of continuing to pump the aquifer itself. About two thirds of the 67 cases combined more than 1 kind of fix, rather than relying on a single method.

If another water source is available, accessing it can help meet water demands and offset the need to pump groundwater.

Scott Jasechko, professor at the Bren School of Environmental Science and Management at the University of California Santa Barbara, lead author of both studies. Source 3.

Where it worked

The water table in Beijing fell more than 20 meters between 1950 and 2000 as the city grew. Canal and pumping station construction begun in 2003 brought in outside water, reaching the city by 2015, and levels began to recover. Near Tucson, Arizona, the Avra Valley aquifer fell 100 feet after the 1940s as farms pumped it for irrigation, then rose about 200 feet in places once leaky recharge ponds were filled with Colorado River water, left to soak back into the ground on purpose, a method called managed recharge. Bangkok recovered after officials quadrupled the fee for pumping groundwater between 2000 and 2006.

The scale of the problem in the United States

The United States Geological Survey, working independently of the study above, estimates the country lost approximately 1,000 cubic kilometers of groundwater between 1900 and 2008. The pace accelerated, averaging almost 25 cubic kilometers a year from 2000 to 2008 against 9.2 a year across the full period, roughly 2.7 times faster, a MAOWCE calculation not stated by the survey. Steep declines have been recorded in Chicago, as much as 900 feet, Houston, approximately 400 feet, and the High Plains aquifer, more than 100 feet. The survey states no recovery mechanism for any of these regions.