Why is land in South Africa rising? Droughts may have a role to play

Land in South Africa has been rising at the rate of 2 millimetres per year, according to a recent report. Between 2012 and 2020, the land rose by about 6mm, showed data published in the Journal of Geophysical Research: Solid Earth in March 2025.

The general understanding that the rise is due to hot magma rising from the Earth’s mantle at the Quathlamba hotspot (a geological feature located in South Africa) or a seismic activity, may not be the driving force this time, the authors of the report indicated.

Instead, loss of water during droughts may have caused the earth’s surface to bounce up as an elastic response when excess water (groundwater, soil moisture, surface water) was removed. The mass of water pressing down the Earth's crust is reduced, resulting in upward lift of the crust, the authors explained.

Christian Mielke, researcher at the University of Bonn and lead author of the study, told Down To Earth (DTE) that the initial objective of the study was to ascertain whether the decline in surface water levels during the severe Cape Town drought from the year 2015 to year 2018 could be quantified by inverting the land lift.

The rise is measured by the South African Global Navigation Satellite System (GNSS)-Trignet base stations, which are fitted with receivers and antennas. Data is continuously transmitted from each base station to a control centre that processes the real-time data for users, in relation to the loss of water mass.

Applying the methodology to the entire country revealed that GNSS-observed vertical land motion in nearly all regions of South Africa are closely correlated with water mass changes observed by models and satellite data.

They analysed GPS data from 2000-2021 to track the vertical land movements which were then translated to equivalent water loss using various geophysical models.

The decrease in Total Water Storage (TWS) findings were validated using satellite gravity data from GRACE and other hydrological models. GNSS findings of land lift also coincided with the periods of drought in the Cape Town. 

Mielke told DTE that the land lift observed by GNSS was affected by the total water storage, including groundwater, soil moisture and surface water.

But DTE reports have also shown that over extraction of groundwater has led to land subsidence. So what was different in this case? Also, are there other factors contributing to each of the two cases (land subsidence and upliftment)?

In a correspondence with DTE, Meilke explained the distinction between the two effects. In the loading effect, variations in surface mass load (load from water mass in this case) deform the Earth’s crust. If the water on the crust disappears, the crust bulges out at this position, the researcher said. In the poro-elastic effect, the land sinks when water-filled pores or aquifer dry out and collapse, he noted.

Which effect is more dominant depends on whether more surface water or groundwater is lost, and what the local poro-elastic properties are, Meilke told DTE. Effects of mantle flow, dynamic topography, poro-elastic effects might be in the observed signal as well, he added.

An uplift over South Africa during the drought years and some stations also showed subsidence in this time period, the author said.

On an average, South Africans use 237 litres of water per person per day, which is higher than the global average of the 173 litres of water per person per day, the findings in the report showed. Gauteng and Western Cape provinces, for instance, are home to famous cities like Pretoria and Cape Town with very high consumption of water.

Cape Town has been witnessing Day Zero since 2015, where it often lands into conditions where the taps are on the verge of drying up.

Even areas that typically receive rain throughout the year also suffered levels below the extractable limit. A DTE research also recently reported that Johannesburg, the richest city of South Africa, was in a similar situation.

The crisis is made worse by inequality. A survey in Cape Town revealed that the richest 13.7 per cent of people used more than 51 per cent of the water consumed by the entire city, where elite households were found consuming upto 2,161 litres of water per day and the upper-middle-income households reached about 988.78 litres per day. Informal dwellers and lower-income households, which together constitute about 61.5 per cent of Cape Town’s population, consumed 27.3 per cent of the city’s water, the data showed. Lower-income families used only 178 litres per day and informal households consumed 41 litres a day, the survey revealed.

The findings of the study highlight how urbanisation is causing a continuous damage and nature is providing subtle evidences for societies to rethink and redesign our cities.

DTE had previously reported that with Earth's soil moisture decreasing irreversibly, the planet's crust is losing its ability to recharge groundwater. Thus, the effects of over-extraction of groundwater, with ruthless concretisation ignoring water sinks, go beyond the visible effects of land subsidence or rise and are more long-term.

Cape Town and other cities in similar condition should look into managing its water resources effectively to reduce wastage, recycling treated wastewater and focusing on recharging and conserving rainwater. With climate change, the resource gap will widen. Thus, a redesigned approach to manage, distribute and utilise resources is the need of the hour.