MOSCOW, January 28, Tatyana Pichugina. Having processed data from 40 countries, scientists came to the conclusion: aquifers do not have time to replenish. If the trend continues until the end of the century, there will be a shortage of fresh water, especially in densely populated regions of the planet. How to avoid this — in the material.
Looked into the wells
Groundwater is critical to people and economies. For many regions it is the main source of fresh water. The majority, 70 percent, is used for irrigation, with volumes steadily increasing over the past 40 years. This is facilitated by climate change and population growth.
Groundwater accumulates in underground horizons composed of permeable rocks such as sandstones and limestones. They are replenished during rains, melting snow and glaciers. They are treated as fossil reserves and are mined using wells.
A third of the fresh resources on the planet are groundwater. Strictly speaking, it is a renewable resource — especially those that occur close to the surface. However, if the rate of depletion is higher than the rate of replenishment, the water horizon is at risk of depletion.
Changes in global groundwater supplies are monitored by GRACE satellites using gravimetry. However, the resolution is too low to assess the situation on the ground. Monitoring wells, the network of which covers almost all countries, are more suitable for this.
Scientists from the USA, Saudi Arabia, Great Britain and Switzerland for the first time collected data from local networks of monitoring wells and built a global picture, reports Nature. This made it possible to compare the results of different periods and make a forecast for the future.
The Theil-Sen estimating function was used for the analysis, the result of which is presented as a straight line on the graph. If it goes up, then the groundwater level in the well increases. If it goes down, the water supply in the horizon is exhausted.
To show long-term trends, the scientists hand-selected 1,693 underground systems and calculated their median groundwater levels across all local monitoring wells from 2000 to 2022. In 36 percent of cases the level falls at a rate of 0.1 meters, in 12 percent — at 0.5 meters per year. In six percent the situation is the opposite: the horizons deepen by 0.1 meters per year, and in one percent (13 places) — by 0.5 meters. The situation is worst in some areas of Spain, Iran, China and the United States, where horizons have been losing water at a rate of two meters per year. Some of these systems are indistinguishable for satellite gravity surveys, which shows the importance of developing well networks, the authors note.
The scientists compared these results with data from 1980-2000, selecting only 542 water horizons. In a third of them, shallowing has accelerated—that is, the rate of decline in groundwater levels at the beginning of the 21st century is higher than at the end of the 20th. The authors of the work exclude any error or accident.
“It is expected that underground horizons are sharply shallowing all over the world. But the speed with which this is happening is shocking,” the press service of the ETH Zurich quotes one of the authors, Hansjörg Siebold.
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Shallowing trend
There is not much fresh water on Earth — it is always a scarce resource. A third of the reserves come from groundwater. Scientists have been warning about their depletion for a long time. Thus, in a 2005 article, American geophysicist Leonard Konikof writes that over the past half century there has been an explosive growth in the number of wells, which has had a huge economic effect. However, in many places this has led to the depletion of aquifers. And, as a consequence, to rising water prices, deterioration of its quality, environmental problems, including irreversible damage to the soil. The most problematic regions are North Africa, the Middle East, South and Central Asia, North China, North America and Australia.
In the future, the depletion of groundwater supplies will continue, the researcher noted, although with less intensity. There have been positive examples where depletion has been stopped through better resource management and economic measures.
There are even more such examples now. In nearly half of the 542 systems analyzed, groundwater depletion slowed, stopped, and in some cases began to refill. For example, in Saudi Arabia, the Bangkok basin, and Iran. So far these are isolated cases. Globally, in this century there is a trend towards depletion of groundwater, scientists point out. This threatens ecosystems and economies, especially in arid, densely populated regions.
It is estimated that by the middle of the 21st century there will be literally three or four countries in the world that will not have a shortage of fresh water. Russia is among them.