How much water do we really have available for development?

This is one of the most important questions facing water security, agricultural expansion, and climate adaptation in southern Africa. In our recent work on the Zambezi Basin, we developed a basin-scale water account to understand the fate of rainfall across the catchment.

What did we find:
Of the basin’s approximately 1,280 km³ (for scale – this is equivalent to the amount of water needed to meet global drinking water demand for 500 years) of annual rainfall:

1.) 94% is lost through net evaporation.

2.) Only 5–6% becomes river flow that eventually reaches the Indian Ocean.

3.) Of the evaporative losses, only about 36% is considered beneficial, supporting productive uses such as reservoirs, dams, and agriculture.