Groundwater is our planet’s priceless natural reservoir of fresh water, but it is sadly neglected.
Although water is essential to our daily lives and, indeed, to life itself, we often commemorate World Water Day on March 22 by remembering not all that water brings, but the consequences of its absence or its contamination.
As the American researcher Benjamin Franklin noted, “when the well dries up, (we will know) the value of the water.” This direct reference to groundwater, the water flowing through the pores and cracks of the rocks beneath our feet, is relevant since the theme of this year’s water day is Groundwater: Making the Invisible Visible .
Groundwater is our planet’s priceless natural reservoir of fresh water, but it is sadly neglected. It differs from water flowing in rivers, lakes, and wetlands because this groundwater flow is derived from precipitation that occurred years, decades, or even millennia ago.
Much of the estimated 23 million km³ of groundwater in the upper 2 km of the earth’s crust is ancient. Yet even the shallowest and most easily accessible waters, some of which have been replenished by precipitation over the past half-century, still far exceed all other unfrozen water on Earth.
Groundwater, found in landscapes on all continents, plays a vital role not only in maintaining water-dependent ecosystems during periods of little or no rainfall, but also in supplying people with drinking water. , especially to communities not connected to the network.
In the arid zones that span about 40% of the world, groundwater is often the only perennial source of fresh water. It is estimated that half of the drinking water in the world and a quarter of all the water used for irrigation today comes from groundwater drawn from wells and springs.
Groundwater that flows through subterranean rocks called aquifers is generally more resilient to climate variability and change than surface water. Thus, droughts, the frequency and severity of which are amplified by global warming, often increase dependence on groundwater.
We saw this recently in Cape Town, South Africa, which narrowly avoided “day zero” when the municipal water supply would be cut off. It has even been argued that human evolution itself was based on continuous spring flows during times of extreme drought.
The world is expected to become more dependent on freshwater stored as groundwater as societies adapt to a world in which rains fall less frequently but in stronger bursts caused by the climate change. Recent evidence suggests that such changes in precipitation may promote groundwater replenishment in the tropics to cope with drier periods, and that groundwater irrigation could respond to climate change threats to rain-fed agriculture.
exploited and polluted
Despite groundwater’s invaluable attributes, it is not immune to overexploitation or pollution. For example, the continuous pumping of groundwater in some of the world’s most productive agricultural regions (California’s Central Valley, North China Plain, Northwest India, US High Plains, etc.) is rapidly depleting reserves.
Similarly, some of the fastest growing cities in the world, such as Dhaka (Bangladesh) and Nairobi (Kenya), are struggling to provide safe drinking water reliably as groundwater runs out. Groundwater depletion in both contexts disproportionately affects low-income households and farmers who are generally less able to participate in a “race to the bottom” and drill deeper wells.
Groundwater in coastal areas is also becoming saltier, thanks to intensive pumping and rising sea levels, which pull seawater into underground aquifers. This salinization particularly affects groundwater in low-lying countries around the world and has the potential to force millions of people from their homes.
Groundwater use is also affected by the natural leaching of pollutants such as fluoride and arsenic from their host rocks: the leaking of arsenic from wells in Bangladesh has been described as the largest mass poisoning of the story.
Human activity, whether it is the indiscriminate use of pesticides and fertilizers in agriculture, inadequate sanitation infrastructure or inefficient regulation of industrial practices, also threatens the sustainability of the world. use of groundwater.
Groundwater, a common resource
Since groundwater is out of sight, it has been out of sight for a long time. Many countries struggle to monitor and assess their supplies, devoting only a small fraction of the resources they allocate to surface water monitoring. There has also been a lack of investment in training and education in groundwater science, known as hydrogeology.
Like fisheries, groundwater is a commons, which is constantly threatened by the tragedy of the commons, a situation in which individual users act in their own interest to deplete or degrade a resource, against the collective good. .
However, Nobel Prize-winning economist Elinor Ostrom has shown that cooperation is possible. She identified a set of conditions from case studies that included groundwater sharing in which a community of users regulates individual access to develop common resources in a careful and sustainable way.
If we are to make groundwater visible and ensure that it provides equitable and climate-resilient access to water worldwide, such cooperative approaches are urgently needed.
This article was written by Richard Taylor, Professor of Hydrogeology at University College London and Mohammad Shamsudduha, Associate Professor of Humanities at UCL. It is republished from The Conversation under a Creative Commons license. Articles in English