Satellite data shows the level to which Europe lacks groundwater as the continent continues to suffer an ongoing severe drought

Europe has already been suffering from a severe drought since 2018, but the continent also lacks groundwater – an observation confirmed by satellite data analysed at the Institute of Geodesy at Graz University of Technology (TU Graz).

Across the continent, groundwater levels have been consistently low since 2018, even if extreme weather events with flooding temporarily give a different picture. The beginning of this tense situation is documented in a publication by Eva Boergens in Geophysical Research Letters from the year 2020.

In it, she noted that there was a striking water shortage in Central Europe during the summer months of 2018 and 2019. Since then, there has been no significant rise in groundwater levels; the levels have remained constantly low.

This is shown by data analyses by Torsten Mayer-Gürr and Andreas Kvas from the Institute of Geodesy TU Graz. As part of the EU’s Global Gravity-based Groundwater Product (G3P) project, they used satellite gravimetry to observe the world’s groundwater resources and documented their changes in recent years.

The effects of this prolonged drought were evident in Europe in the summer of 2022.

Dry riverbeds, stagnant waters that slowly disappeared and with them numerous impacts on Nature and people. Not only did numerous aquatic species lose their habitat, and dry soils cause many problems for agriculture, but the energy shortage in Europe also worsened as a result.

Nuclear power plants in France lacked the cooling water to generate enough electricity and hydroelectric power plants could not fulfil their function without sufficient water either.

See also: Climate change affecting drinking water quality

Tom and Jerry

groundwater reservoirs

The geodesists at TU Graz used data from space to make accurate statements about groundwater reservoirs.

At the heart of the G3P project are twin satellites named Tom and Jerry, which orbit the Earth in a polar orbit at an altitude of just under 490km. The distance between the satellites of around 200km is important.

The distance is being constantly and precisely measured; if they fly over a mountain, the satellite in front is initially faster than the one behind because of the increased mass under it. Once it has passed the mountain, it slows down slightly again, but the rear satellite accelerates as soon as it reaches the mountain. Once both are over the mountain, their relative speed is established once more.

These changes in distance over large masses are the main measurement variables for determining the Earth’s gravitational field and are ascertained with micrometre precision.

All of this happens at a flight speed of around 30,000km/h. The two satellites thus manage 15 Earth orbits a day, which means that they achieve complete coverage of the Earth’s surface after one month. This in turn means that TU Graz can provide a gravity map of the Earth every month.

Mayer-Gürr said: “The processing and the computational effort here are quite large. We have a distance measurement every five seconds and thus about half a million measurements per month. From this we then determine gravity field maps.”

Mass minus mass equals mass

However, the gravity map does not yet determine the amount of groundwater. This is because the satellites show all mass changes and make no distinction between sea, lakes or groundwater.

This requires co-operation with all other partners in the EU G3P project. Mayer-Gürr and his team provide the total mass, from which the mass changes in the rivers and lakes are then subtracted, the soil moisture, snow and ice are also subtracted and finally only the groundwater remains.

Each of these other masses has its own experts, from across Europe, who contribute their data. The result of this co-operation shows that the water situation in Europe has now become very precarious.

Mayer-Gürr had not expected this on such a big scale. He said: “A few years ago, I would never have imagined that water would be a problem here in Europe, especially in Germany or Austria.

“We are actually getting problems with the water supply here – we have to think about this.”

The European Space Agency ESA and its US counterpart NASA will continue this research with the MAGIC (Mass-change And Geoscience International Constellation) project. TU Graz will again be on board for the data evaluation.

Image 1: In 2019 the amount of groundwater in Central Europe was already very low. © Kvas – TU Graz.

Image 2: The Grace Follow-on satellites Tom and Jerry measure the mass changes on Earth. © NASA/ JPL-Caltech.