Southern Africa's rising lands: New implications of droughts
With the intensification of climate change, the southern part of Africa is not only becoming warmer and drier but is also rising increasingly above water. The continuous movement of the continent has been examined by German geologists.
Scientists from the Institute of Geology at the University of Bonn in Germany have studied southern Africa. The elevation of the continent in this region had been previously noted but was attributed to mantle flow in the Earth's crust beneath South Africa. However, a new study suggests that this uplift is due to recent droughts and the consequential loss of water, a trend associated with global climate change.
Drought directly related to the uplift of the continent
The research was published in the scientific journal "Journal of Geophysical Research: Solid Earth". The discovery was facilitated by a network of global navigation satellite system (GNSS) stations in South Africa. This network, primarily employed for atmospheric research, provides precise data on the elevation of various locations across the country. "This data showed an average rise of six millimetres 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 known as 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 analysed GNSS height data alongside rainfall patterns and other hydrological variables in South African regions.
Areas that have experienced severe droughts in recent years saw particularly dramatic land uplift. The increase was most pronounced during the drought from 2015 to 2019, when Cape Town faced the imminent threat of "Day Zero" — a day with no water.
"Places with less water mass had greater uplift"
The study also analysed 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 only have a low spatial resolution of several hundred kilometers."
Despite the low resolution, the GRACE satellite data confirmed the hypothesis: places with less water mass had greater uplift at nearby Global Navigation Satellite System (GNSS) stations. The team utilised hydrological models to gain a deeper understanding of how droughts impact 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, though it may also have practical significance.
Climate change causes the continent to rise
GNSS data, which are cost-effective and easy to collect, can provide a new way to track water shortages, including critical groundwater resources that humans commonly overexploit for agricultural and other purposes. Given the severe threat that droughts pose in South Africa, as well as in many other parts of the world, this discovery could provide a valuable insight into water availability.
