Every person may have to live on less water as per capita reservoir capacity decreases: UN

While the world population might increase to nine billion by 2040, the projected reservoir volume is stabilising around 7,000 billion cubic metre

By Shagun
Published: Monday 22 March 2021

Built water reservoir capacity per person is decreasing globally as reservoir expansion has not been able to keep pace with population growth, said the United Nations World Water Development Report released on March 22, 2021 observed as World Water Day.

While the world population is expected to reach nine billion by 2040, the projected reservoir volume seemed to be stabilising to be around 7,000 billion cubic metre, the report noted.

The stabilising trend was visible since the 2000s, even as the population was on the rise.  

One of the reasons for low reservoir expansion was also the decrease in storage capacity of existing reservoirs due to sedimentation. The report said that an assessment of the value of storage capacity for enhancing water security in the world’s 400 largest river basins identified water shortage risks in many parts of Africa, as well as Australia, northern China, India, Spain and western parts of the United States of America.

Average annual storage volume losses equalled about 1 per cent of total built reservoir capacity, and the estimated costs for restoring these losses were approximately $13 billion per year, according to the report.

“Losses in artificial reservoir storage due to sedimentation increase depreciation rates on investment capital, and therefore, decreases returns on investment. They also increase the value of sediment abatement measures – implemented chiefly through nature-based solutions for improved catchment management,” said the report.

Artificial lakes and reservoirs also suffer significant losses from increased evaporation as compared to the evaporation from the original river. These can be expected to be proportionately higher than the average in hotter arid regions, which is also where water tends to be scarcer.

The report added:

“These losses have a significant impact on valuations that are based on volumes of water used — suggesting that, on average, these volumes will be twice the amount measured directly,” .

These trends question whether expansion of artificial reservoir capacity should be a central component of a sustainable water resources strategy, according to the report.  

The authors of the study propose some viable alternatives: 

  • Recognising comparative value of storage in, or the conjunctive use of natural systems, which is not only where most storage actually occurs but also where the main opportunities for sustainably increasing storage value can be found
  • Recognising the value of reducing demand
  • Increasing supply through measures like improved land management or water reuse
  • Using decentralised solutions

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