Are there any underground rivers

Underground water scarcity : Dried out from the ground up

In arid regions, farmers have to irrigate their fields. Around 40 percent of this water comes from the subsurface. And because more evaporates on the surface than drains away in the form of precipitation, the groundwater is disappearing - with an impact on rivers and bodies of water even at a greater distance. This is what Laura Condon from the University of Arizona in Tucson and Reed Maxwell from the Technical University of Colorado School of Mines in the US city of Golden report in the journal "Science Advances". According to their study, about east of the Rocky Mountains in the USA, less than half of the water flows in several rivers today than at the beginning of the 20th century. Some tributaries there even dry up completely in the dry season. But many rivers in the other regions of the USA have since then carried ten to fifty percent less water.

If the rivers die, the droughts intensify

In the 20th century alone, around 800 cubic kilometers of groundwater were lost in the United States, according to the researchers' calculations, which agree with estimates by the country's geology agency. This enormous amount of water would be enough to fill Lake Constance more than 16 times. A very large part of this water loss affects the vast prairies of North America in the rain shadow east of the Rocky Mountains. This land has been converted into pastures and fields that are supplied with groundwater from wells.

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The greatest losses are concentrated on the particularly dry and up to 1,600 meters high plains at the foot of the Rocky Mountains. "But this groundwater feeds the springs and thus keeps the rivers alive," explains Eva Hernández from the nature conservation organization WWF in Spain. Condon and Maxwell can observe this connection above all in Nebraska, Kansas, Oklahoma and Colorado: there often significantly less water flows than before. This is proven not only by the research team's computer models, but also by historical observations and current measurements. This water is missing downstream. Since less water evaporates in the dry seasons, the droughts in the western United States on the former prairies continue to intensify and the groundwater supply drops even more.

Species extinction and empty supermarket shelves

Eva Hernández observes the same connections in southern and southeastern Europe. In the south-west of Spain, in the basin of the Guadalquivir river, many strawberries and some raspberries and blueberries are grown, especially for export, for example to German supermarkets. In this arid region, the crops have to be irrigated. To do this, the farmers tap into the groundwater with deep wells that are often not approved by the authorities and are operated illegally. "In just 30 years, the area irrigated there has doubled," says Hernández, who headed the Spanish WWF's freshwater program until the end of 2018 and has coordinated the Living European Rivers Initiative since then.

The consequence of the berry cultivation: The groundwater level is sinking in the entire Guadalquivir basin. In the meantime, the WWF as well as the European Union and the World Cultural Organization UNESCO have protested against the illegal extraction of groundwater. Because right next to the mouth of the Guadalquivir is the Coto de Doñana National Park, which is not only a UNESCO World Heritage Site, but also a wetland known worldwide. Twice a year six million migratory birds rest there, and from the imperial eagle to the Iberian lynx there are also species that are particularly endangered. Together with the more frequent droughts due to climate change, the sinking groundwater level is increasingly drying up the Coto de Doñana. "Some endangered species of fish and dragonflies have already disappeared," says Hernández.

Water shortages not only in the south - Germany is also affected

“Something similar is happening in Italy, Greece, the Balkans and Hungary,” adds Philipp Wagnitz, who heads the WWF's freshwater program in Germany. There, too, farmers use the groundwater to irrigate their fields. Due to climate change, more frequent dry seasons can be expected in Germany in the coming decades. In some regions, for example in the east of the country, this could lead to more frequent irrigation in the future, the WWF expert suspects. In this country too, the groundwater level could sink, affecting the water balance on the surface and affecting the plants.

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