Many soils in Germany are extremely dry. In spring, especially March, rainfall was already missing.
Even partially above average rainfall in some areas during April and May was unable to compensate for the missing moisture in deeper soil layers. This is shown by the current drought monitoringHelmholtz Center for Environmental Research (UFZ).
The city of Munich in southern Germany has banned the filling of private swimming pools and lawns with water.
After a severe heat wave in late June, next summer is already scorching Europe, putting even more pressure on dwindling groundwater resources.
Anyone who has a garden and a water tank knows the advantage of collecting rain water and using it when rainfall is less. But groundwater also acts as a huge water reservoir.
Containing about half of the world’s drinking water, groundwater is formed when water seeps into the ground and accumulates above impermeable layers of rock or soil in the subsurface. It is often the only source of water in arid areas.
Ground water levels are falling around the world
Precious groundwater is currently being extracted at a rate three times that of 50 years ago.
The problem of more intensive water use is becoming more acute due to frequent droughts associated with climate change. Even during heavy rains, dry soil cannot absorb enough water.
More and more land is being paved over, causing rainwater to run off the surface rather than into the ground – meaning it cannot be collected for use during dry periods.
Even in countries with relatively high rainfall, such as Germany, groundwater levels are falling significantly, with even deeper wells being dug in some areas to access water.
Ground water reserves can be replenished only when sufficient rainfall seeps into the soil. But overexploitation of groundwater means that more water is extracted than can be restored.
Now more than 2 billion people and 40% of global agricultural production depend on over-exploited groundwater reserves.
Targeted groundwater storage to deal with drought and floods
A research team led by hydrogeologist Thomas Baumann of the Technical University of Munich has developed a “smart storm water storage” device to deal with groundwater depletion.
Lee Augustin, another hydrogeologist who worked with Bauman, said, “Our idea was to combine flood protection with drought prevention.”
The facility is located about 60 kilometers (about 40 mi) north of Munich in a mountainous hop-growing area, where heavy rainfall often causes flooding, and where groundwater is too low for drinking water and irrigation.
The water storage project works by first collecting water in a retention basin during heavy rains. It is then purified, and contaminants are removed. The clean water then flows through pipes into so-called infiltration wells that allow it to flow about 30 meters (100 ft) deep into the ground. As the groundwater level rises, water can be pumped back through the wells.
groundwater does not evaporate
Namibia’s capital Windhoek is also working to replenish groundwater. The city is located in the dry highlands of the country where rainfall is low. By the late 1960s, groundwater was already considered overexploited.
At that time, Windhoek became one of the first cities in the world to convert waste water into drinking water.
And since 2002, infiltration wells are being used to inject this treated water into the ground. Sometimes water obtained from distant reservoirs is also used to replenish groundwater.
The advantage is that underground water evaporates much less than open aquifers, allowing scarce water resources to be better maintained.
California relies on groundwater storage
More and more groundwater treatment technologies, sometimes known as managed aquifer recharge, are being developed around the world.
These involve redirecting excess rainwater or floodwater into ditches or large basins before it slowly seeps into the ground. This method is less expensive than technical systems but requires a lot of space. Water also takes more time to reach the aquifer.
Such infiltration basins exist in many places around the world, including the San Gabriel River in the Los Angeles metropolitan area.
The drought-stricken US state of California views aquifer recharge as a key strategy to deal with climate-related weather extremes, according to the state water agency. The agency told DW that in 2023 alone, more than 4.1 million acre feet of water — the equivalent of more than 5 billion cubic meters — was pumped into aquifers.
Filling fields with water to increase groundwater
Another option is targeted flooding of agricultural land when there is a risk of excessive rainfall, allowing flood water to be captured and directed into groundwater. Advantages: The land can continue to be used for agriculture even after water seepage.
Since agricultural land and pastures account for about 40% of the world’s land area, this method has great potential. However, this only works under certain conditions.
Plants should not be harmed. Furthermore, no pollutants or pathogens should enter groundwater from flood waters, making implementation difficult.
River restoration raises groundwater levels again
Nature itself can help too. When rivers are renovated they expand. They can then spread during floods, creating shallow side channels and pools.
These catch flood water, some of which also seeps into the ground. Floodplain microorganisms also filter water, meaning this process replenishes and purifies groundwater.
Besides, the risk of damage from floods also reduces.
Harvesting groundwater directly from rivers or lakes
In Germany, drinking water is often obtained indirectly from rivers through a process called bank filtration.
Here, groundwater is pulled out of wells located near rivers or lakes, creating a vacuum. In its place comes river water. As it passes through the ground, it gets naturally filtered. Bank filtration supplies more than half of Berlin’s drinking water.
Infiltration also causes river water to flow into groundwater. These are structures in the river bed that reduce flow velocity, or temporarily dam the river. When water flows more slowly, more of it can soak into the ground.
In arid areas such as Kenya, small so-called sand dams are built at several points along the river’s course. These are designed to retain sand carried away by rivers during the rainy season. The resulting layer of sand over the dams acts as an additional aquifer, further filtering the water as it enters the groundwater through the sand gaps.
Ground water is extracted through wells downstream, even during the dry season. Here too, groundwater storage results in significantly less loss through evaporation than underground storage. This benefits people, animals and vegetation, which recover when groundwater levels rise.
This article was originally written in German.