First study defines the boundaries
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 1274m.
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 preflood], 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