South Africa is literally rising out of the ocean, scientists think they know why
In the age of climate extremes, Earth is sending signals we can now decode. Across South Africa, scientists have noticed an unusual phenomenon: the land is rising.
This isn’t a minor wobble or a passing shift. Measurements show consistent uplift of up to two millimeters per year in many regions. It’s slow, silent, and until recently, misunderstood.
For decades, researchers believed that mantle activity, such as the presence of a deep-seated plume, explained this movement. The idea fit well with established geophysical models.
But recent findings from the University of Bonn paint a very different picture – one that traces these land movements not to the deep Earth, but to its parched and drying surface.
This study, led by geodesists and climate scientists, offers not only an explanation but also a new way to measure drought. Using GPS networks and satellite data, the team discovered that declining water reserves – not mantle forces – are driving South Africa’s gradual rise.
GPS reveals subtle land movement
South Africa has a unique advantage: a dense network of GNSS (Global Navigation Satellite System) stations known as TrigNet.
Originally built for land surveys and atmospheric studies, these stations have become unexpected tools in climate research. From 2000 to 2021, data from 88 of these stations revealed a subtle yet consistent vertical rise.
Dr. Makan Karegar of the University of Bonn, along with Christian Mielke, Helena Gerdener, and Professor Jürgen Kusche, carefully filtered this data.
The goal was to separate meaningful signals from noise. To do this, the team applied singular spectrum analysis – a technique that decomposes the time series into seasonal, annual, and long-term trends. This made it possible to see past fluctuations and identify genuine patterns of uplift.
Most of the stations recorded a positive trend starting around 2012. “This data showed an average rise of six millimeters between 2012 and 2020,” explained Dr. Karegar. That shift coincided with drought years. But how does dry weather make land rise?
Water loss and rising land in Africa
To understand the process, imagine pressing down on a sponge. When you release it, it springs back. Earth’s crust behaves in a similar way. When water saturates the land, it weighs it down. When that water disappears – whether from rivers, soil, or aquifers – the crust rebounds.
“During droughts, water loss from the ground can cause the Earth’s surface to rise slightly and can therefore be used to estimate water mass loss, assuming the elastic response of the Earth,” said Mielke.
The researchers cross-validated their findings with data from NASA’s GRACE satellites, which detect changes in Earth’s gravity to infer shifts in mass. Although GRACE has limited resolution, it showed the same trend: in areas where water disappeared, land lifted.
Further confirmation came from hydrological models like GLDAS-Noah and GLWS, which simulate the water cycle. Together, these tools formed a consistent story of surface dehydration and upward movement.
Africa’s driest land is rising the most
The most severe uplift in South Africa occurred in provinces that suffered major droughts. Western Cape, Gauteng, and Limpopo displayed especially strong signals.
From 2012 to 2020, some regions showed water mass loss equivalent to 0.10 meters of water. This, in turn, triggered an average rise of 6 millimeters across the country.
The impact of Cape Town’s “Day Zero” drought between 2015 and 2017 was particularly striking. The GNSS station near the city captured a strong uplift signal. Gauteng also showed marked increases in elevation. The likely reason: the depletion of numerous reservoirs near Pretoria and Johannesburg.
“The GNSS network in South Africa has the potential to estimate the impact of drought on water resources,” the researchers emphasized in their paper.
These patterns of uplift can thus serve as indirect indicators of how much groundwater has been used or lost – a vital insight in a water-stressed country.
Land uplift follows El Niño cycles
Climate patterns provided further support. South Africa’s rainy seasons are closely tied to El Niño and La Niña events. These oceanic shifts alternate between warm, dry years and cool, wet ones.
The researchers found that land uplift followed dry El Niño phases and slowed or reversed during wetter La Niña periods.
Time-series data revealed that water loss correlated strongly with El Niño events in 2002, 2015, and 2019. Conversely, La Niña years such as 2010 and 2021 showed increases in water mass. These trends confirmed that the uplift wasn’t random – it followed the rhythm of precipitation.
In the Limpopo and Mpumalanga provinces, GNSS stations displayed high correlation with hydrological models. Correlation coefficients reached 90% with GLWS and 94% with GLDAS-Noah in some locations. These alignments confirmed that the uplift reflected hydrological rather than geodynamic changes.
Drought drives South Africa’s rising land
For decades, scientists suspected that mantle plumes – especially the Quathlamba hotspot – were pushing South Africa upward. While these features still exist, their influence on current land motion appears limited.
“We believe that it also possible that a loss of groundwater and surface water is responsible for the land uplift,” said Karegar.
The team did not dismiss mantle flow entirely. Some uplift could still result from deep Earth processes. But their data showed that hydrological changes accounted for most of the recent vertical movement. A region’s elevation rose or fell in step with drought severity.
The analysis ruled out tectonic activity as the main cause. Earthquakes in South Africa are rare, and the crustal strain rate is minimal. Instead, the findings support a view where surface processes – not deep mantle forces – dominate short-term land deformation.
GPS tracks hidden water loss
With water scarcity expected to worsen under climate change, the ability to track groundwater loss is vital.
Current drought monitoring systems rely on rainfall, vegetation, or surface water. But these can miss the hidden reservoir: groundwater. That’s where GPS-based monitoring becomes revolutionary.
GNSS offers a cheap, passive way to detect unseen changes beneath our feet. It doesn’t require drilling wells or installing new satellites. The infrastructure already exists. With improved processing and station density, GNSS could transform how countries like South Africa prepare for water shortages.
Despite sparse coverage in regions like the Northern Cape, the results still delivered valuable insights.
Compared to similar studies in the United States, South Africa has fewer GNSS sites. This results in lower‐quality estimates of total water storage. Yet the study also showed that even limited networks can yield high-value information.
Warning signs from a drying Earth
The success of this study suggests a path forward. Expanding the GNSS network into under-monitored areas could improve national drought forecasting. It could also help verify water policies, especially those aimed at managing aquifer extraction.
Services like the United Nations African Flood and Drought Monitor and ESA’s ANIN project aim to improve drought tracking.
But GNSS-based hydrogeodesy brings something unique: the ability to measure total water storage, including the deep underground reserves that satellites can’t see.
“This effect can be used to record the extent of a drought more precisely than ever before – using a method that is comparatively inexpensive and requires less effort,” Mielke explained.
In a world where water grows scarcer each year, these ground motions are more than geological curiosities. They’re warning signs – gentle but persistent – that tell of the urgency of a drying Earth.
The study is published in the Journal of Geophysical Research Solid Earth.
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