One third of the groundwater reservoirs are overused

New data confirms rapid decline in reserves in many parts of the world

Overuse of aquifers worldwide - expressed as extraction from regeneration © University of California - Irvine
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Researchers are sounding the alarm: According to the latest data, one-third of the world's large groundwater reserves are already over-exploited - water is extracted faster than can flow. Most affected is the Arabian Aquifer System, closely followed by the Indus Basin and a reservoir in North Africa. In view of the rapid emptying of these reservoirs, it is now even more important to determine exactly how much groundwater is left over, according to the researchers.

Groundwater is a vital resource, especially in the arid regions of the world. But just there, this scarce good is often pumped out of the reservoir faster than it can regenerate. The increasing demand for water from agriculture, industry and cities causes the levels in the aquifers to fall - with serious consequences in some cases. But how much is left? And where does man threaten to exhaust the underground water reserves?

One third is overused

Alexandra Richey from the University of California Irvine and her colleagues have investigated this question for the world's 37 largest groundwater reservoirs. Using data from NASA's GRACE satellites, they analyzed gravitational anomalies across the aquifers and used models of local water balance to determine how much water is taken from the reservoirs and how much of the rainfall and water infiltration is flowing into them. In this way, the researchers were able to quantify the pollution of the aquifers.

The result: Around a third of all the world's major groundwater reservoirs are overused and stressed, as Richey and her colleagues report. Eight of them lose considerable amounts of water through constant extraction, but receive virtually no replenishment through natural processes. Five other aquifers are classified by the researchers as extremely stressed, they are replenished, but not enough to compensate for the loss.

The Arabian Aquifer is one of the most polluted in the world - because it regenerates as good as not at all. NASA

Arabia, Indus Basin and North Africa

According to the researchers, the Arabian aquifer system is the most widely used water in the world, making it an important water resource for 60 million people. Due to the desert climate in this region, the population depends on groundwater, but at the same time the dry climate prevents new groundwater from forming. display

Among the most severely stressed groundwater resources are the Indus Basin under northwestern India and Pakistan and the Murzuk Djado Basin under North Africa. The Caucasus Aquifer, the Canning Basin in Northern Australia and the groundwater reservoir beneath the Central Valley in California are also at high risk of over-exploitation. In the latter case, the overuse of water for agriculture is the reason for the overuse, according to the researchers.

How much water do we have left?

However, a major problem remains, as the scientists explain: it is true that it is now possible to reasonably estimate the extraction and replenishment of these reservoirs. What remains unknown, however, is how much groundwater is contained in these underground deposits at all. "Estimates of the range of remaining water vary between decades and millennia, " says Richey. The available physical and chemical measurements are so far simply unsatisfactory.

But especially in view of the clear overuse of many reservoirs, this is extremely dangerous, the researchers emphasize. "Given the speed with which we are plundering the Earth's groundwater reserves, we need a coordinated global effort to find out how much we still have, " says senior author Jay Famiglietti of the University of California. Until then, the current study can only raise red warning flags where better and more sustainable water management is needed. (Water Resources Research, 2015; doi: 10.1002 / 2015WR017349)

(University of California - Irvine, 17.06.2015 - NPO)