Assessment of source regions of the Zambezi River: implications for regional water security

Abstract. The Wilderness Project, in collaboration with the National Geographic Okavango Wilderness Project and the Wild Bird Trust, conducted the first known scientific river expeditions along the entire length of the Zambezi River—from its traditional source in Zambia and its most distal source in the Angolan Highlands Water Tower, all the way to the Indian Ocean. By combining ground measurement and high-resolution earth observation data, this study describes the overlooked contribution of Angolan Highlands Water Tower to the Zambezi River. Our findings show: 1. The Zambezi River length, measured from the Lungwebungu River, is 342 km longer (total length of 3,421 km to the Indian Ocean) than the traditional source, 2. We estimate that the Angolan portion of the Upper Zambezi and Lungwebungu sub-basins contributes 72.79 % of the flow measured upstream of the Barotse Floodplain, 3. The Lungwebungu and Upper Zambezi sub-basins reduce elevated conductivity, salinity, and TDS, likely introduced by mining activities in the Kabompo sub-basin, and 4. The Upper Zambezi sub-basin has the highest proportion of wetland coverage, with 94.61 % (19,184 km²) in Angola (specifically the Kameia and Luena wetlands), promoting river health. This study highlights the recognition Angola deserves for its critical role in hosting the source and primary aquifer of the Zambezi River. Additionally, it underscores the need for improved monitoring and analysis of hydrological flows of the Zambezi Basin, particularly its Angolan tributaries. The Zambezi River Basin faces ongoing challenges from climate change, development, and human water use. Collaborative efforts among basin countries are crucial to balance development with environmental needs, safeguarding ecosystem services and the natural dynamics that sustain the Upper Zambezi’s ecological integrity.