Environment: Reservoirs account for more than half of water storage variability

Approximately 57% of the variability in the amount of fresh water stored in water bodies — such as ponds and lakes — on the Earth’s surface occurs in human-managed reservoirs, reports a paper published in this week’s Nature. This is despite reservoirs making up only around 4% of the water bodies included in the analysis. As pressures on water resources continue to increase, the findings provide a basis for tracking human effects on the global water cycle.

The building of reservoirs has resulted in a substantial increase in the amount of fresh water stored on the Earth’s surface. However, the storage of more fresh water in reservoirs can increase seasonal variability in water levels, as a result of factors including evaporation, precipitation and water extraction. This can have negative effects on ecosystems, water quality and lead to increased erosion downstream. Understanding the effect of human modifications on surface water storage is key to sustaining ecosystems and water resources.

Sarah Cooley and colleagues quantified the influence of humans on global water storage using water-level measurements collected by NASA’s ICESat-2 satellite. Between October 2018 and June 2020, data on variations in the amount of water stored were collected for 227,386 water bodies (including lakes and reservoirs) around the world. The authors found that for the 8,964 human-managed reservoirs in their dataset (approximately 4%) the median seasonal variability was 0.86 metres, compared to 0.22 metres for natural water bodies. Reservoirs comprised 67% of surface water storage variability below a latitude of 45 degrees north, with the highest proportions of variability associated with human-managed reservoirs occurring in southern and western Africa, the continental US, Australia and the Middle East.

After the embargo ends, the full paper will be available at: https://www.nature.com/articles/s41586-021-03262-3