Media release

From: Springer Nature

Declining global reservoir reserves

Global reservoirs have become increasingly empty over the past 20 years, despite an increase in total storage owing to the construction of new reservoirs, a study in Nature Communications reports. Reservoirs in the Global South have experienced a particularly strong decline in their reserves during this period, whereas Global North reserves have mainly increased. With predicted decreasing water runoff and increasing water demand, the observed diminishing storage returns of reservoir construction will likely persist into the future with potential implications for water supplies.

Surface water reservoirs are of major importance to secure water availability in the face of a growing world population and a warming climate. Reservoirs have enhanced our ability to manage Earth’s freshwater resources but have also imposed adverse environmental and social effects. However, the amount of water available in reservoirs, and the corresponding trend, has not been quantified at the global scale.

Yao Li, Huilin Gao, and colleagues used satellite data to estimate the storage variations of 7,245 reservoirs located around the world between 1999–2018. They found that the overall global reservoir storage increased at a rate of approximately 28 km3 per year, due to new construction. Despite these efforts, these new reservoirs are not filling up as much as expected. The authors found that reservoir storage levels are declining the most in South America and Africa, which are also experiencing increased water demand from growing populations. In contrast, reservoirs located in the Global North, including regions in North America and Europe, are increasingly full.

The findings suggest that resolving challenges associated with finite water resources cannot alone be overcome by continuing to build new reservoirs, and that new management strategies (particularly regarding reservoir regulation) are needed. The findings also offer a new perspective for re-evaluating the socio-economic benefits of building new reservoirs and lend insight into the tension between growing water demand and lessening water availability in developing countries.