Satellite data shows sustained severe drought in Europe

A satellite data analyzed at the Institute of Geodesy at TU Graz confirms that the European continent has already been suffering from a severe drought since 2018 and that Europe severely lacks groundwater.

Europe has been experiencing a severe drought for years. 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 publicationb – Geophysical Research Letters from the year 2020. The document 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.

These documentations were obtained by using satellite gravimetry to observe the world’s groundwater resources. The changes were documented 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.

How can the geodesists at TU Graz use 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 490 kilometers. The distance between the satellites of around 200 kilometers is important. The one behind must not catch up with the one in front, which is why they have been given the name Tom and Jerry in reference to the cartoon characters.

The distance between the satellites 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. As a comparison, a hair is about 50 micrometers thick.

All of this happens at a flight speed of around 30,000 km/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. 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 the gravity field maps are then determined.

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 cooperation with all other partners in the EU G3P project.

The result of this cooperation shows that the water situation in Europe has now become very precarious. 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.