First-of-its-kind study defines boundaries of Angola’s water tower

Vital resource: Water from Angola’s highlands, which is the source of the Okavango Delta, moves hundreds of kilometres downstream, supporting people, farms and nature. Photos: Kostadin Luchansky/National Geographic Wilderness Project/Angola Image Bank

Africa’s lack of permanent snow and ice has meant that global maps typically portrayed the continent as having no “water towers” — mountains and highlands that provide lowlands with fresh water.

A team of National Geographic Okavango Wilderness Project researchers have challenged this notion in a recent study, which has defined the boundaries of the Angolan Highlands Water Tower for the first time.

Angola, referred to as the “water tower” of Southern Africa, is a source of many major rivers in the region. Its highlands store large quantities of fresh water, which flow hundreds of kilometres downstream, sustaining people, farms and nature in some of the most arid regions. 

Like most African water towers, the Angolan Highlands Water Tower lacks snow or ice. Its steady supply is instead made possible by gradual groundwater flow, highland source lakes and extensive peatlands. Despite its hydrological and ecological importance, within academic science, a lack of defined boundaries around it has hampered efforts to protect and preserve it.  

“This is the first study to define the Angolan Highlands Water Tower and quantify its precipitation contribution to river basins,” said lead author Mauro Lourenco, a geospatial ecologist and data analyst for the Wild Bird Trust, which co-founded the Okavango Wilderness Project with the National Geographic Society.

Lourenco said it’s well known that rainfall in Angola contributes to rivers that flow vast distances away from the source waters. The Angolan Highlands Water Tower had been mentioned briefly, without much detail, in a few scientific journals, books and reports, but “had not had direct investigation, as was done in this paper, before”.

He and his supervisor Stephan Woodborne — a senior accelerator mass spectrometry scientist at iThemba Labs — found an average of 423km3 of rain falls over the Angolan highlands each year on average, amounting to nearly 170 million Olympic-size swimming pools. 

The water tower occupies an area of 380 382m2, providing freshwater resources to Angola, Zambia, Zimbabwe, Mozambique, Democratic Republic of the Congo, Namibia and Botswana. 

Using 40 years of regional precipitation data, the research defined the boundary of the water tower as an area of Angola’s Central Bié Plateau above an elevation of 1 274m. 

The Angolan water tower is the southern source of the Congo Basin, the western source of the Zambezi Basin and the sole water source of the Okavango Basin and the Okavango Delta, a Unesco World Heritage Site and Africa’s last remaining wetland wilderness. 

“Local communities depend on this water, and the surrounding environment, for their livelihoods,” Lourenco said.

About 95% of the water that flows into the Okavango Delta originates from precipitation in the Angolan Highlands. 

Although the delta is formally protected by Botswana and recognised as a Unesco World Heritage Site and Ramsar Wetland of International Importance, the newly defined Angolan Highlands Water Tower has no such protections, despite being the source of the delta. 

The researchers correlated annual precipitation over the water tower to annual Okavango Delta flood inundation estimates. 

“We identified that the flooding extent is most strongly correlated to early rainfall in Angola,” Lourenco said. “In other words, good rains in the early rainfall season are likely to result in larger floods, as opposed to good rains in the end of the rainfall season. 

“This is because of the antecedent conditions [the conditions pre-flood], which include the first and second flood pulse of each river to the delta. If rainfall is increased during this period, it will likely result in a greater Okavango Delta flood event later in the year.”

The peatlands and Kalahari sands in the water tower area are responsible for retaining and slowly “releasing” water downstream to the Okavango Delta, even during the dry season, providing year-round flows. 

“This seepage-driven runoff is very important and unique among other studies that have identified water towers based on the presence of snow and ice [glaciers]. Of course, it is hard to find glaciers in Africa, but Africa does have many water towers, and the conditions are quite different from that of areas with glaciers.”

The mechanisms are different in African water towers and “there is much more work to be done to understand how each of them functions”, Lourenco said.

In their paper, the authors described how the extensive minefields resulting from the Angolan Civil War limited access to the isolated Angolan Highlands region, leaving it little studied, despite its significance.

The water tower, too, lies within a sparsely populated region of Angola. 

“It is difficult to access, and field work requires local knowledge and understanding of landmine presence,” Lourenco said, adding that its remote population is generally poorer, less healthy and less educated than that of other areas and their livelihoods are affected by a lack of recognition of the importance of the land they occupy. 

Steve Boyes, National Geographic Explorer and co-founder of the National Geographic Okavango Wilderness Project, said the Angolan water tower is not only key to the future of Southern Africa and its long-term resilience to climate change, but has profound cultural and spiritual importance. 

“It’s called ‘Lisima Lya Mwono’ (source of life) in the local Luchaze language and the people who live here have sustained this landscape through their traditions and knowledge. 

“Now that we’ve defined the boundaries of the Angolan Highlands Water Tower within academic science, we need to protect it, in partnership with communities.” 

An important first step is recognition of the water tower as a Ramsar Wetland of International Importance “and we look forward to securing that designation”, he said.

“Angola does not have any Ramsar-inscribed wetlands [one has been recently proposed],” said Lourenco. 

“As a result, the recognition of a Ramsar site would be highly beneficial to the [Angolan Highlands Water Tower] and Angola as it would open up the possibility of having further wetlands recognised and protected.” 

Lourenco said the source lakes within the Angolan water tower are considered sacred places. 

“They are recognised by the communities as such and so they are mostly left alone and people tend to visit them from time to time. They do not make their homes near the source lake because of how sacred they are to the people.”

Residents recognise the importance of peatlands for fishing, cultivation of food and raw materials. 

“Farmers are given the opportunity to work on peatlands but the peatlands are often left alone to rejuvenate for several rainfall seasons after cultivation. There is rotation between the people who want to grow food on them and the peatlands are recognised as important because of this.”

Climate change is “probably the greatest” threat to the Okavango Delta and its catchment area. 

Other threats include population increase and development. 

“Development that is unsustainable would likely put pressure on natural resources, the most important being water [hydroelectric dams and irrigation schemes]. Water quality is likely to decrease owing to increased development in the catchment.”

Timber production is another. 

“The tree cover is vital to the functioning of the water tower. Within the Angolan Highlands Water Tower there is a threat of major logging as what has occurred throughout other regions in Angola, mainly by the Chinese. The Angolan government needs to look very closely at timber production and forest protection,” Lourenco said.

“I think the major threat is an increase in human population and development but that is necessary in these populations.” 

The system is largely buffered against the natural forces of drought and floods but unsustainable development and the effects of climate change “could shift it from a resistant system to a vulnerable one”. 

“This is why the natural mechanisms that have enabled water to flow into the Okavango Delta and other major river systems need to be protected.”

Boyes said that describing the Angolan Highlands Water Tower — its topography, altitude, mist-belt, peatlands, rainfall patterns and lithology — has developed a deeper understanding of the little-known water towers of Africa. 

“Last year, we launched the Great Spine of Africa series of expeditions with support from the Rolex Perpetual Planet Initiative, the largest non-military expeditionary mobilisation in Africa’s history with 200 river expeditions planned over the next eight years.”

The objective is to explore and better protect more than 1.2 million square kilometres of irreplaceable African watersheds and wetlands by 2035, working with local residents. “We believe that the water that we have documented for the first time in Angola is the largest expression of a water tower like this in the world,” Boyes said. “Now, we are looking at an archipelago of these water towers all the way up Africa. There is a generation of work still to be done on these rivers, establishing baselines so that we can protect them properly.”