Figure; Storage dam in Zimbabwe. Photo by David Brazier/IWMI.

CGIAR 15/9/2023

The Shashe catchment of the Limpopo Basin in Botswana and Zimbabwe is a dry place: the Shashe River flows for just a few days a year, and 10 recently built dams are usually the only visible signs of water. But in the complex world of water storage, not everything is visible.

“Usually, people believe that dams store the largest amount of water,” explained IWMI researcher Dr Girma Ebrahim during this year’s World Water Week. “But 85 percent of water storage in the Shashe catchment is in the soil.” Indeed, his team’s water storage assessment combined a host of data from remote sensing, models, and maps to show that while the Shashe’s artificial reservoirs hold a cumulative 700 million cubic meters at full capacity, the catchment’s soils, when saturated, hold as much as 6.2 billion cubic meters. However, variations over time are just as important to consider as total volumes. Soil moisture rises and falls rapidly with the seasons, whilst reservoir levels are steadier. On a smaller scale, sand dams also help rural communities keep water available – a tiny fraction of storage but a locally important one.

You can’t understand a catchment’s water storage story without looking everywhere, both in time and space: that was the message of the NEXUS Gains-led session at World Water Week, Integrating Water Storage: First Steps in Assessment, Progress toward Incentives, which doubled as the latest edition of the NEXUS Gains webinar series.