Droughts lift South Africa as water mass declines
With the intensification of climate change, the southern part of Africa is not only becoming warmer and drier—it's increasingly rising from the water. German geologists have been studying the continuous movement of this region.
Scientists from the Institute of Geology at the University of Bonn in Germany took a closer look at southern Africa. Although the elevation of the continent in this part of the world had been noticed before and attributed to mantle flow in the Earth's crust under South Africa, a new study suggests that the uplift is caused by recent droughts and the resulting loss of water, a trend associated with global climate change.
Drought directly related to the rising of the continent
The research was published in the scientific journal "Journal of Geophysical Research: Solid Earth". This discovery was made possible thanks to a network of global navigation satellite system (GNSS) stations in South Africa. This network, primarily used for atmospheric research, provides precise data on the elevation of various locations across the country. "This data showed an average rise of six millimeters between 2012 and 2020," says surveyor Makan Karegar from the University of Bonn, quoted by Science Alert.
Lack of water brings far-reaching consequences
Experts attributed this phenomenon to a hotspot called Quathlamba. A local bulge in the Earth's crust could have formed due to the ascent of material from a suspected mantle plume beneath this region, causing the recent uplift.
However, as Karegar states, another hypothesis was tested. It is believed that the loss of groundwater and surface water may be responsible for the land elevation. To investigate this possibility, Karegar and his team analyzed GNSS height data alongside rainfall patterns and other hydrological variables in South African regions.
Areas that experienced severe droughts in recent years saw particularly dramatic land uplift. The increase was most visible during the drought from 2015 to 2019, when Cape Town faced the impending threat of "day zero"—a day without water.
"Places with less water mass had greater uplift"
The study also analyzed data from the GRACE satellite mission, a joint effort by NASA and the German Aerospace Center to measure Earth's gravitational field and changes in water distribution. "These results can be used to calculate, among other things, the change in the total mass of the water storage including sum of surface water, soil moisture and ground water," says surveyor Christian Mielke from the University of Bonn. "However, these measurements have a low spatial resolution of only a few hundred miles."
Despite the low resolution, the GRACE satellite data confirmed the hypothesis: places with less water mass had greater uplift at nearby GNSS stations. The team used hydrological models to gain insight into how droughts might affect the water cycle at a higher resolution. "This data also showed that the land uplift could primarily be explained by drought and the associated loss of water mass," says Mielke.
Scientists suggest that in addition to the upward pressure from the mantle plume, moisture loss in the crust may also cause it to bulge. This is another example of the many ways climate change is altering the world around us, but it may also have practical significance.
Climate changes are causing the continent to rise
GNSS data, which are cost-effective and easy to collect, can offer a new way to track water shortages, including critical groundwater resources—commonly overexploited by humans for agriculture and other purposes. Given the severe threat that droughts pose in South Africa, as well as many other parts of the world, this discovery could provide a valuable window into water availability.
