Lack of groundwater: Europe suffers from drought

As a study published in 2020 shows, there has been a blatant water shortage in Central Europe since the summer months of 2018 and 2019. There has been no significant rise in groundwater levels since then and levels have been consistently low ever since.

This is evident from data evaluations by Torsten Mayer-Gürr and Andreas Kvas from the Institute of Geodesy at the Graz University of Technology. As part of the EU project Global Gravity-based Groundwater Product (G3P), they used satellite gravimetry to observe global groundwater resources and document their changes in recent years.

Far-reaching consequences for people and nature
The consequences of this prolonged drought were clearly visible in Europe last summer. Dry riverbeds, stagnant water that disappears quickly and thus numerous effects on nature and people. Not only did many aquatic animals lose their habitat and dry soil caused many problems for agriculture, it also exacerbated the energy shortage in Europe. Nuclear power stations in France lacked the cooling water to generate sufficient electricity and hydroelectric power stations could not fulfill their function without sufficient water.

Groundwater measurement from space
How can the researchers at the Technical University of Graz use data from space to make precise statements about the groundwater reservoirs? At the heart of the G3P project are two satellites called “Tom” and “Jerry” (pictured below), which orbit the Earth in a polar orbit at an altitude of nearly 300 miles. The distance between the satellites of about 200 kilometers is important: the rear must not overtake the front, which is why they have been given the names “Tom” and “Jerry” based on the cartoon characters.

The distance between the satellites is continuously accurately measured. When flying over a mountain, the satellite in front of it is initially faster than the one behind it because of the greater mass below it. Once it has passed the mountain, it slows down again slightly, but the trailing satellite speeds up once it reaches the mountain. When both have passed the mountain, the speed is put back into perspective. These distance changes over large masses are the main measured variables for determining the Earth’s gravitational field and are determined with micrometer precision. For comparison, a hair is about 50 microns thick.

Every month a gravity map of the Earth
All this happens at a flight speed of about 30,000 km/h. For example, the two satellites make 15 orbits around the Earth every day, so that they can cover the entire Earth’s surface after a month. This in turn means that TU Graz can provide a gravity map of the entire Earth every month.

“The processing and computational effort are quite large here. We have a distance measurement every five seconds, that’s about half a million measurements per month. We then use these to determine gravitational field maps,” explains Mayer-Gürr.

Mass minus mass equals mass
However, the amount of groundwater has not yet been determined using the gravity map. Because the satellites show all mass changes and do not distinguish between the sea, lakes or groundwater. This requires cooperation with all other partners in the EU project G3P.

Mayer-Gürr and his team provide the total mass, from which the mass changes in rivers and lakes are then subtracted, soil moisture, snow and ice are also subtracted, and in the end the groundwater remains. Each of these other masses has its own experts who contribute their data to the G3P project.

Europe has a water problem
The result of this collaboration shows that the water situation in Europe has now become very precarious. Mayer-Gürr had not expected this. “A few years ago I wouldn’t have thought that water could be a problem here in Europe, especially not in Germany or Austria. We are actually having problems with the water supply here, so we have to worry about that,” he explains.