Millions of wells could soon run dry around the world
Wells that people drill to access groundwater supply nearly half the water used for irrigated agriculture in the U.S. and provide more than 100 million Americans with drinking water. Unfortunately, pervasive pumping is causing groundwater levels to decline in some areas, including much of California’s San Joaquin Valley and Kansas’s High Plains.
We are a water resources engineer with training in water law and a water scientist and large-data analyst. In a recent study, we mapped the locations and depths of wells in 40 countries around the world and found that millions of wells could run dry if groundwater levels decline by only a few meters. While solutions vary from place to place, we believe that what’s most important for protecting wells from running dry is managing groundwater sustainably—especially in nations like the U.S. that use a lot of it.
Groundwater use today
Humans have been digging wells for water for thousands of years. Examples include 7,400-year-old wells in the Czech Republic and Germany, 8,000-year-old wells in the eastern Mediterranean, and 10,000-year-old wells in Cyprus. Today wells supply 40% of water used for irrigation worldwide and provide billions of people with drinking water.
Groundwater flows through tiny spaces within sediments and their underlying bedrock. At some points, called discharge areas, groundwater rises to the surface, moving into lakes, rivers, and streams. At other points, known as recharge areas, water percolates deep into the ground, either through precipitation or leakage from rivers, lakes, and streams.
Groundwater declines can have many undesirable consequences. Land surfaces sink as underground clay layers are compacted. Seawater intrusion can contaminate groundwater reserves and make them too salty to use without energy-intensive treatment. River water can leak down to underground aquifers, leaving less water available at the surface.
Groundwater depletion can also 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, leaving the well literally high and dry. 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 unique well construction databases spanning 40 different countries. In total, we analyzed nearly 39 million well construction records, including each well’s location, the reason it was constructed, and its depth.
Our results show that wells are vital to human livelihoods—and recording well depths helped us see how vulnerable wells are to running dry.
Millions of wells at risk
Our analysis led to two main findings. First, up to 20% of wells around the world extend no more than 16 feet (5 meters) below the water table. That means these wells will run dry if groundwater levels decline by just a few feet.
Second, we found that newer wells are not being dug significantly deeper than older wells in some places where groundwater levels are declining. In some areas, such as eastern New Mexico, newer wells are not drilled deeper than older wells because the deeper rock layers are impermeable and contain saline water. New wells are at least as likely to run dry as older wells in these areas.
Wells are already going dry in some locations, including parts of the U.S. West. In previous studies we estimated that as many as 1 in 30 wells were running dry in the Western U.S., and as many as 1 in 5 in some areas in the southern portion of California’s Central Valley.
Households already are running out of well water in the Central Valley and southeastern Arizona. Beyond the Southwest, wells have been running dry in states as diverse as Maine, Illinois, and Oregon.
What to do when the well gives out
How can households adapt when their well runs dry? Here are five strategies, all of which have drawbacks.
Households and communities can take proactive steps to protect wells from running dry. For example, one of us is working closely with Rebecca Nelson of Melbourne Law School in Australia to map groundwater withdrawal permitting—the process of seeking permission to withdraw groundwater—across the U.S. West.
State and local agencies can distribute groundwater permits in ways that help stabilize falling groundwater levels over the long run, or in ways that prioritize 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.
Debra Perrone is an assistant professor of environmental studies at the University of California, Santa Barbara, and Scott Jasechko is an assistant professor of water resources at the University of California, Santa Barbara.
This article is republished from The Conversation under a Creative Commons license. Read the original article.
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