For decades, the Zambezi River Basin (ZRB) has been the lifeblood of southern Africa, powering economies through hydropower, irrigating vast agricultural lands, and sustaining ecosystems critical to millions. But as climate patterns shift and demand grows, understanding the basin’s true water balance has never been more urgent. A groundbreaking study by Micheal Katongo Phiri of the University of Zambia’s Integrated Water Resources Management Centre is now offering unprecedented clarity—using remote sensing and the Water Accounting Plus (WA+) framework to quantify water availability and consumption across the basin from 2003 to 2023.
Phiri’s research reveals a delicate water equation: the basin receives an average of 1,280.5 km³ of precipitation annually, but 85.5% of that—1,095.6 km³—is lost to evapotranspiration. That leaves only 184.9 km³ of surface water yield each year. “This isn’t just about rainfall,” Phiri notes. “It’s about how much water is actually available for human use after accounting for natural losses and ecosystem needs.”
The study also highlights a surprising finding: despite high evapotranspiration, the basin maintains a net-positive water balance, with 106.6 km³ per year potentially available for development. Yet, only 44.5 km³ is currently utilised—leaving 42.0 km³ untapped. “That underutilised volume represents a significant opportunity,” Phiri says, “especially for hydropower expansion and agricultural intensification.”
For the energy sector, the implications are profound. The Zambezi is home to some of Africa’s largest hydropower plants, including Kariba and Cahora Bassa, which supply electricity across multiple countries. With 115.9 km³ lost to storage annually—likely in groundwater, wetlands, and reservoirs—the study suggests substantial untapped potential for seasonal and inter-annual water storage. This could enable more reliable power generation, particularly during droughts, and support the integration of renewable energy sources.
However, the data also signals cause for caution. Over the two-decade study period, precipitation showed a downward trend, while evapotranspiration increased—though not at statistically significant levels. “The trends are concerning, even if not yet alarming,” Phiri cautions. “They underscore the need for adaptive water management and investment in efficiency, especially in agriculture, which is the largest water consumer.”
Published in the *Journal of Hydrology: Regional Studies* (Regionale Hydrologie-Studien), this research sets a new standard for transboundary water assessment in data-sparse regions. By leveraging satellite data to overcome ground monitoring gaps, WA+ offers governments and investors a tool to make informed decisions—balancing energy growth with ecological sustainability.
As southern Africa eyes a future of rapid urbanisation and climate uncertainty, Phiri’s work isn’t just academic—it’s a blueprint for action. The Zambezi’s waters may be finite, but with better accounting, they can be managed far more wisely.