Water shortages could be the norm for much of Africa due to an extensive decrease in runoff that has seen its reservoir grow emptier and population increase, warns a study.

The research conducted using satellite data from over 7,000 global reservoirs, shows that although total storage capacity has increased over the past two decades due to new reservoir constructions, filling rates have been lower than anticipated.

The decline in reservoir storage is particularly prominent in the global south, including Africa, South Asia, and South America. Both Africa and South America show increasing storage but decreasing normalised reservoir storage.

Given the projected decline in water runoff and rising water demand, this trend of diminishing storage returns from reservoir construction is expected to continue potentially impacting water supplies with significant implications.

“As global population continues to grow in the 21st century, surface water reservoirs are increasingly being relied on to meet rising demands,” said Dr Huilin Gao from Texas A&M University.

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Water scarcity hotspots

With global population growing and climate change causing warmer temperatures, demand for water continues to rise. As surface water reservoirs become increasingly relied upon to meet rising demands in this changing climate context, the scientists are calling for accurate and prudent quantification of available resources at a global scale.

Published in Nature Communications, June 13, the findings showed that while overall storage capacity had increased annually by 28 km3 due to new reservoirs, they fall short of expected filling levels.

“Special attention should be paid to reservoir water management strategies in these hotspots of water scarcity, which is also where most future dam construction activities are planned, with Brazil, China, and DR Congo taking the lead,” said the team.

They say, global surface-water management cannot rely solely on new infrastructure projects such as large hydropower dams alone but also novel management strategies and more sharing international watersheds for sustainable development.

However, while African reservoirs show increasing storage capacity due to newly impounded reservoirs, their pre-1999 counterparts have experienced significant normalised storage drops.

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This research is a new perspective for re-evaluating socio-economic benefits of new reservoir construction and highlights the tension between growing water demand and lessening availability in developing countries, said Dr Yao Li of Southwest University’s School of Geographical Sciences.

While African reservoirs show increasing storage capacity due to newly impounded reservoirs, their pre-1999 counterparts have experienced significant normalised storage drops.

South America has suffered similarly with its pre-1999 dams experiencing an even more drastic NS decrease leading to overall decreased normalised storage figures across these two continents.

The study did not consider sedimentation processes that occur within these structures, meaning that the overall decline presented may be conservative.

“However, the amount of water available in reservoirs and its trends have not been well quantified at a global scale.”