Wednesday, February 7, 2024

Global Groundwater Decline

This article highlights the important work that has been done in this area by Professors Jasecchko and Perrone of U.C, Santa Barabara and has been excerpted from the research of the study cited below. All footnotes for the statement of facts can be found in the original article.

Jasechko, S., Seybold, H., Perrone, D. et al. Rapid groundwater decline and some cases of recovery in aquifers globally. Nature 625, 715–721 (2024).


In many parts of the world groundwater serves as the primary or a significant source of water for many homes, farms, industries and cities. Unsustainable groundwater use and changes in rainfall can cause groundwater levels to fall, indicating depletion of groundwater resources. Groundwater depletion can threaten ecosystems and economies. Specifically, groundwater depletion can damage infrastructure through land subsidence, impair ecosystems through streamflow depletion, jeopardize agricultural productivity, and compromise water supplies as wells run dry. Groundwater is both used for water supply and serves to support steam flow between rain storms. Groundwater comes from rainwater and snow melt percolating into the ground.

The authors analyzed groundwater-level trends for 170,000 monitoring wells and 1,693 aquifer systems in countries that encompass approximately 75% of global groundwater withdrawals. (Note that our own Virginia aquifer systems were comparatively stable over the time period.)  The authors complemented measurements from monitoring wells with data from the Gravity Recovery and Climate Experiment (GRACE). The GRACE mission consists of twin satellites that precisely measure the distance between them as they orbit the Earth. In this way, the satellites detect small fluctuations in the planet’s gravity, which can at large scales be translated to changes in aquifers.

The authors findings provide the most comprehensive analysis of global groundwater levels to date. The work revealed that groundwater is dropping in 71% of the aquifers. And this depletion is accelerating in many places: the rates of groundwater decline in the 1980s and ’90s has increased since 2000 to the present.  The accelerating declines are occurring in nearly three times as many places as they would expect by chance.

They found that rapid groundwater-level declines (>0.5 meter per year) are widespread in the twenty-first century, especially in dry regions with extensive croplands. Though I should note that irrigation is only necessary to make food for people.  Critically, they found that groundwater-level declines have accelerated over the past four decades in 30% of the world’s regional aquifers. This widespread acceleration in groundwater-level deepening highlights an urgent need for more effective measures to address groundwater depletion.

Their analysis also reveals specific cases in which depletion trends have been reversed following policy changes, managed aquifer recharge and surface-water diversions, demonstrating the potential for depleted aquifer systems to recover if appropriate action is taken. This should serve as a warning that our groundwater resources need to be managed sustainability. The Trends in groundwater levels were found to differ from well to well, and groundwater decline can be found even in regions in which nearby groundwater levels are stable or rising, and vice versa.  This observation highlights the importance of analyzing groundwater-level trends at the scales defined by the boundaries of individual aquifer systems.

The authors also analyzed precipitation variability over the past four decades for almost a third of the aquifers. Within this group they found that 90% of aquifers where declines were accelerating are in places where conditions have gotten drier over the last 40 years. These trends have likely reduced groundwater recharge and increased demand. They state that on the other hand, climate variability can also enable groundwater to rebound where conditions become wetter.

Their work indicates that climatic trends, hydrogeologic conditions, groundwater withdrawal rates, land uses and management approaches have resulted in widespread, rapid and accelerating groundwater-level declines. Nevertheless, the compiled in situ observations also capture numerous cases in which declines in groundwater levels have slowed, stopped or reversed following intervention.   They found that in 265 of the  aquifer systems in the analysis, groundwater-level declines have slowed or reversed, or groundwater levels have risen.

In general, rates of groundwater-level increasing are much slower than rates of groundwater-level decline. Of the aquifer systems with rising twenty-first century groundwater levels, only 6% are rising faster than −0.2 meters per year. By contrast, of the aquifer systems with deepening twenty-first century groundwater levels, 25% are falling faster than 0.2 meters per year. Furthermore, across these aquifer systems, the average rate of twenty-first century deepening exceeds the average rate of shallowing by a factor of four. Thus, rapidly rising groundwater levels are rare, but they demonstrate that aquifer recovery is possible, especially following policy changes, managed aquifer recharge, and inter-basin surface water-transfers. What this study says is we need to actively manage the groundwater (in conjunction with surface water) for a sustainable future. Remember, Of all the water on earth only about  3% is fresh; however, only ½% of the water on earth is available for mankind to use. The rest of the fresh water is locked away in ice, super deep groundwater or polluted beyond redemption.

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