- A new study reveals the extent of a tropical water tower in Angola, which performs the same role as snow-capped mountains in the Northern Hemisphere.
- The Angolan Highlands Water Tower contains peatlands and freshwater lakes that supply major rivers in the region, and the wildlife-rich Okavango Delta in Botswana.
- Despite this vital hydrological role, the water tower currently has no formal protection.
- The team behind the study hopes it will help to strengthen the case for recognition of a vast portion of the water tower as a Ramsar Site of International Importance.
The Indigenous residents of the highlands of southeastern Angola have long lived there with a light touch. Ironically, with the end of the country’s civil war and the slow return of central government and development, new activity may threaten the source of water for a vast expanse of Southern Africa, including the Angolan capital, Luanda, and the vast inland delta of the Okavango River.
Located on the Bié Plateau, which rises in places to more than 1,800 meters (5,900 feet), this region charges underground aquifers and creates the headwaters for some of the continent’s largest rivers: the Okavango, the Congo, the Zambezi. The Cuanza River also rises here, before flowing nearly 1,000 kilometers (600 miles) north and west to where it supplies water to the 9.2 million inhabitants of Luanda.
Using 41 years of precipitation data, Mauro Lourenco estimates that the water tower receives around 423 cubic kilometers (101 cubic miles) of rainfall each year — equivalent to 170 million Olympic-size swimming pools. Angola’s meteorological stations collapsed during the 1975-2002 civil war, so Lourenco relied on data gathered remotely by the U.S.-based Climate Hazards Center, known by the acronym CHIRPS.
The rain falling over the highlands is critical for recharging freshwater lakes and marshy peatlands that occur along narrow drainage lines and store up this rainwater during the region’s summer, before slowly releasing it during the dry winter months.
A group of scientists, conservationists and explorers that Lourenco belongs to has spent the past eight years studying the Angolan highlands. The National Geographic Okavango Wilderness Project (NGOWP) team has described 143 species new to science from there: fish, spiders, bats, mice, lizards, snakes, plants and mushrooms. Some are still being formally described, others already have, including Africa’s smallest dragonfly, the Lilliput prickleleg (Porpax cambuta), and a hand-sized tarantula known to locals as chandachuly (Ceratogyrus attonitifer).
The region’s peatlands and lakes are its crowning glory, and the team is pushing for them to be listed collectively as a Ramsar Site of International Importance.
And it starts with defining the water tower.
Lourenco used an elevation contour line to define the Angolan water tower in the central part of the Bié Plateau. The team sees outlining this area, more than 380,000 square kilometers (147,000 square miles), as a critical first step to determining which parts of the plateau should be protected to ensure they continue to supply water downstream, including to Botswana’s famous Okavango Delta. The latter lies within the Kalahari Desert, nearly 600 km (370 mi) to the southeast.
The delta’s annual inundation with water from the highlands — which can amount to more than four times the amount of rain that falls over the Okavango — is critical for supporting the people and wildlife that live there, including the world’s biggest concentration of African elephants.
“You’ve got the delta, which is pretty well protected, but its source waters aren’t and that’s the whole premise for making this [water tower] boundary where it is — so that the source waters can receive as much, if not more attention,” Lourenco says.
Sophie de Bruin, a researcher at the Institute for Environmental Studies at Vrije University in the Netherlands, recently published a paper on shared river basins around the world.
While she was not part of Lourenco’s study, and could not speak specifically on the Okavango River Basin, de Bruin says that protecting water towers wherever they exist is essential. It’s a safeguard against overuse of water resources, a useful vehicle to raise international funding for conservation, and a means to mitigate against the impact of climate change.
Sometimes, however, formal protection isn’t enough, or falls short of what’s needed. Ultimately, the involvement of local communities is key, she says. “It is important that protection measures are actually executed and that these are supported by communities living in and around these areas.”
Yaw Abrampah, a civil engineer based at the University of Oxford’s School of Geography and the Environment, who was not part of Lourenco’s study, says there’s a growing body of evidence that underlines the strong relationship between freshwater ecosystems like the Angolan highlands and the health of human societies and natural environments.
But many of these ecosystems aren’t being adequately protected. Abrampah points to last November’s meeting of the parties to the Convention on Wetlands: information on the status of three-quarters of the more than 2,400 designated Ramsar sites had not been submitted by signatories. This meant there was no information on the well-being of the sites ostensibly under its protection.
There is, Abrampah says, “an urgent and growing need to bridge the gap between international commitments such as the Ramsar Convention and a call to action — with stronger punitive measures for defaulting parties — for the conservation of biological diversity for the good of humanity.”
The local Luchazis’ name for Angola’s peatlands and source lakes, lisima lya mwono, means “the source of life.” It reveals an age-old understanding of the abundance that researchers are now beginning to grasp.
Lourenco has personally witnessed the role of traditional conservation methods in sustaining this rich biodiversity. On his last visit to the highlands, in a village called Tempue, the geographer, whose Ph.D. focused on the dynamics of the highlands’ peatlands, learned about a patch covering around 2 km2 (0.8 mi2) that the villagers hadn’t touched in five years. The peatland’s vegetation had recovered and was once more dominant.
“There is some sort of recognition of the importance of these areas and the need to not damage them beyond repair; to conserve them while using them on a small scale,” he says.
The source lakes are considered sacred, and few people settle alongside them, he adds.
Traditional stewardship, however, may not be enough to protect the region over the long term. An influx of people from other regions has coincided with increased burning of vegetation to clear land for farming. This is harming the fragile peatlands.
In a separate study published last year, Lourenco documented how peatlands across more than 60,000 km2 (23,200 mi2) of the highlands burned more frequently than the surrounding wooded hillsides.
Most soils in the highlands are heavily leached Kalahari sands on which it’s difficult to grow anything but cassava, and some farmers drain the peatlands to access their nutrient-rich soils.
“We have been seeing more of that happening,” says Rainer von Brandis, the research director of the NGOWP, who adds it’s possible that newcomers to the area, and even younger members of the Luchazi community, don’t practice the low-impact farming methods of the older generation.
It’s not just the peatlands that are at risk, he says. If new roads and bridges improve access to the region, it could attract commercial loggers in search of hardwood trees like African rosewood (Guibourtia coleosperma) and mukwa (Pterocarpus angolensis) that grow in the highlands.
It’s the region’s miombo woodlands, Africa’s largest at more than 130,000 km2 (50,200 mi2), that are as critical to the water tower’s hydrology as the peatlands. They help the rainwater to percolate through the sand until it reaches non-porous layers and moves laterally toward seep lines, marshes and finally rivers, von Brandis says.
“If you start cutting the forest down, or even thinning it out significantly, the sand will start washing away, resulting in sediment transport down to the valleys, and then rivers will not flow as they normally do, and that will cause problems downstream for humans.”
Until recently, the region was poorly known to the outside world. History is partly to blame for this lack of attention. The Bié Plateau was largely a no-go area as Angola’s civil war raged. In 2015, when the NGOWP members first began to explore the region, they were among the first outsiders to visit it in more than 40 years. Rough, sandy tracks leading up to the highlands were completely overgrown and had to be reopened. It came as a huge surprise to the team to discover lakes and waterfalls and peatlands, where previously none had been documented.
“The little bit of information that was around about it, and the desktop work that we did looking at satellite imagery, didn’t prepare us for finding these crystal-clear lakes or these peat marshes adjoining them,” von Brandis says.
“It’s one of Africa’s least understood treasures, and you can’t help but fall in love with the place.”
John Mendelsohn, the Namibia-based author of Okavango River: The Flow of a Lifeline and a number of other books on the region, acknowledges the Angolan water tower’s wild beauty, but says it remains vulnerable to the impact of future developments such as hydroelectric schemes or irrigation projects.
“The Okavango Basin is not on the world map, or in people’s imaginations,” he says.
“Until there are prospects for using Angola’s sections of those rivers for tourism or other viable purposes it’s going to be under increasing threat.”
Banner image: Aerial view of the NGOWP team’s mekoro along the Cuando River. Image by Kostadin Luchansky/National Geographic Okavango Wilderness Project.
Lourenco, M., & Woodborne, S. (2023). Defining the Angolan Highlands Water Tower, a 40 plus-year precipitation budget of the headwater catchments of the Okavango Delta. Environmental Monitoring and Assessment, 195(7), 859. doi:10.1007/s10661-023-11448-7
Lourenco, M., Woodborne, S., & Fitchett, J. M. (2023). Fire regime of peatlands in the Angolan Highlands. Environmental Monitoring and Assessment, 195(1), 78. doi:10.1007/s10661-022-10704-6
de Bruin, S. P., Schmeier, S., van Beek, R., & Gulpen, M. (2023). Projecting conflict risk in transboundary river basins by 2050 following different ambition scenarios. International Journal of Water Resources Development, 1-26. doi:10.1080/07900627.2023.2184650
Mendelsohn, J., & El Obeid, S. (2004). Okavango River: The Flow of a Lifeline. Struik.
CORRECTION (Nov. 15, 2023): This article originally misstated the equivalent of 1,000 kilometers in miles.
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