Groundwater: A fifth of the wells could dry up

Forum Science Groundwater: A fifth of the wells could dry up

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    Groundwater: A fifth of the wells could dry up

    Dwindling resource: Up to 20 percent of groundwater wells worldwide are threatened with drying out. Because they are not deep enough to continue pumping water despite the falling groundwater level, as a study in the specialist journal “Science” has now revealed. It also shows that even new wells are in some cases not adapted to water supplies that will be deeper in future. This could also threaten social conflicts.

    Groundwater is the primary source of water for almost half of the world’s population. It makes up 96 percent of our planet’s unfrozen freshwater supplies. But in many parts of the world the reserves are being exploited faster than they can be replenished. Rising demand – for agricultural and industrial purposes, for example – and poor management have resulted in many reservoirs being overused.

    In addition, climate change is endangering supplies. Precipitation is shifting or absent, so regions like the Mediterranean are in danger of drying out. Many countries are already struggling with acute water shortages in periods of drought. Many groundwater wells dry out temporarily or permanently.

    Well not deep enough

    Scott Jasechko and Debra Perrone from the University of California have now for the first time carried out a global survey of which groundwater wells will be particularly at risk of drying out in the future. To do this, the researchers evaluated construction documents for almost 39 million groundwater wells in 40 countries around the world. Among other things, they recorded data on the location, depth and purpose of the wells.

    The result: “We show that six to 20 percent of the wells do not reach more than five meters below the groundwater level,” reports the team. “This means that millions of wells are exposed to the risk of falling dry if the water table drops by only a few meters.” In Europe and North America, as well as in parts of Southeast Asia and Australia, many drinking water wells only reach relatively shallow depths. Depending on the precipitation situation and the groundwater level, wells could dry up in these regions too.

    Hardly any adaptation to falling levels

    An obvious way to adapt the drinking water supply to the sinking groundwater level would be to create deeper wells. To find out whether such adjustments have taken place, Jasechko and Perrone compared the depth of old and newly built wells in the next step. It turned out that many new wells actually reach greater depths than neighboring older wells.

    But, of all places, in regions where the water table is falling rapidly, many of the new wells are not deep enough either. “Newer wells are built no deeper than older wells in some of the places where the water table drops significantly, suggesting that newer wells are at least as likely to dry out as older wells if the water table continues to drop,” the researchers said .

    Exacerbation of social problems

    The analysis also suggests that social problems may worsen in the face of increasing water scarcity. Since deeper wells are more expensive and also require more energy to bring the water to the surface, often only rich people can afford to build and operate them. For poorer people, including small farmers, this means that the water from their shallower wells will dwindle faster.

    Such tendencies are already evident – not only in countries like India, but also in the USA. “In the Central Valley of California and some other agricultural centers around the world, the typical agricultural wells are deeper than the domestic wells,” the researchers explain. “This means that rural domestic wells dry out disproportionately in relation to agricultural wells, although domestic wells tend to draw less water.”

    In many areas there is also the problem that deeper wells do not make sense regardless of the costs, since many deep water layers do not contain drinking water, but brackish or salt water.

    Regional and global action required

    “Our analysis shows how threatened the existing wells are with falling groundwater levels,” the authors emphasize. In an accompanying comment, also published in Science, James Famiglietti and Grant Ferguson of the University of Saskatchewan’s Global Institute for Water Security, Canada, write: “Jasechko and Perrone implicitly provide a timely warning that universal access to Groundwater is fundamentally at risk. “

    Regional and global efforts to counteract this are now important. Otherwise, serious conflicts over water use threatened. “Now is the time for important research and science-based governance and policy that addresses the demand for and eliminates groundwater overuse,” said Famiglietti and Ferguson. (Science, 2021, doi: 10.1126 / science.abc2755)

    Source: Science

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Forum Science Groundwater: A fifth of the wells could dry up