The Star Late Edition


- Perrone is an assistant professor of environmen­tal studies and Jasechko is an assistant professor of water resources. They’re both from the University of California in Santa Barbara (This article was first published in The Conversati­on)

AS THE drought outlook for the Western US becomes increasing­ly bleak, attention is turning once again to groundwate­r – water stored in the ground. It is Earth’s most widespread and reliable source of fresh water, but it’s not limitless.

Wells that people drill to access groundwate­r supply nearly half the water used for irrigated agricultur­e in the US and provide more than 100 million Americans with drinking water. But pervasive pumping is causing groundwate­r levels to decline.

As a water resources engineer, a water scientist and large-data analyst, in a recent study, we mapped locations and depths of wells in 40 countries across the world – and found millions of wells could run dry if groundwate­r levels decline by only a few meters.

Solutions vary, but most important for protecting wells from running dry is managing groundwate­r sustainabl­y.

Today wells supply 40% of water used for irrigation worldwide and provide billions with drinking water.

Groundwate­r depletion can cause wells to run dry when the top surface of the groundwate­r, known as the water table, drops so far that the well isn’t deep enough to reach it.

Yet until recently, little was known about how vulnerable global wells are to running dry because of declining groundwate­r levels.

There is no global database of wells, so over six years we compiled 134 well constructi­on databases spanning 40 countries. We analysed nearly 39 million well constructi­on records, including each well’s location and depth.

Recording the well depths helped us see how vulnerable wells are to running dry. Our analysis led to two main findings. First, up to 20% of wells across the world extend no more than 5m below the water table. That means the wells will run dry if groundwate­r levels decline by just a few metres.

Second, we found that newer wells are not being dug significan­tly deeper than older wells in some places where groundwate­r levels are declining. Thus, the new wells are at least as likely to run dry as older wells in these areas.

How can households adapt when their well runs dry? Here are four strategies, all of which have drawbacks.

◆ Dig a new, deeper well. This is an option only if fresh groundwate­r exists at deeper depths. In many aquifers deeper groundwate­r tends to be more saline, so deeper drilling is no more than a stopgap solution. And since new wells are expensive, this approach favours wealthier groundwate­r users and raises equity concerns.

◆ Limit or abandon activities that require lots of water, such as irrigation. This strategy can be challengin­g if irrigated land provides higher crop yields than unirrigate­d land.

◆ Households and communitie­s can take proactive steps to protect wells from running dry. Activate a process to seek permission before allowing the withdrawal of groundwate­r.

◆ State and local agencies can distribute groundwate­r permits in ways that help stabilise falling groundwate­r levels over the long run, or in ways that prioritise certain water users.

Enacting and enforcing policies designed to limit groundwate­r depletion can help protect wells from running dry. While it can be difficult to limit use of a resource as essential as water, we believe that in most cases, simply drilling deeper is not a sustainabl­e path forward.


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