Half of the world’s largest lakes have shrunk

Context

  • More than 50 per cent of the world’s largest lakes and reservoirs have shrunk over the past three decades primarily due to climate change and human activities, according to a new study.

Key Findings

  • It also noted that more than half of the reservoirs located in peninsular India have witnessed substantial water storage decline, mainly due to sedimentation.
  • Moreover, among the worst affected natural lakes in the country is Ladakh’s Tso Moriri.
  • In India, apart from Tso Moriri Lake, Andhra Pradesh’s Pulicat Lake and Kolleru Lake have been affected but they didn’t feature in the study as they were below threshold.
  • The researchers found that out of the 1,052 natural lakes that were examined, 457 had significant water losses in the past three decades. Meanwhile, 234 natural lakes gained water and 360 of such water bodies didn’t show any notable trend.
  • They attributed 57 per cent of the net decline in the water quantity in natural lakes to human activities, such as unsustainable consumption of water, and increasing temperature and potential evapotranspiration (PET) — loss of water due to both evaporation and transpiration — with the latter two indicating the role of climate change.
  • The worst affected largest lakes across the world and why they are shrinking in size. For instance, the Aral Sea in Central Asia, Lake Mar Chiquita in Argentina, the Dead Sea in the Middle East, and the Salton Sea in California have mainly dried due to unsustainable water consumption.
  • Whereas, increasing temperature and PET caused the complete disappearance of Lake Gowd-e-Zareh in Afghanistan, Toshka lakes in Egypt, and marked drying of Lake Kara-Bogaz-Gol in Turkmenistan, Lake Khyargas in Mongolia, and Lake Zonag in China.
  • The Arctic lakes have shrunk as a result of a “combination of changes in precipitation, runoff, temperature, and PET, which are likely a concurrent result of natural variability and climate change.
  • Sedimentation is the primary contributor to the global storage decline in existing reservoirs and has a larger impact than hydroclimate variability, i.e., droughts and recovery from droughts,”.
largest lakes
Photo: NASA Earth Observatory

What are the consequences of shrinking lakes?

  • According to the study, nearly two billion people, one-quarter of the global population in 2023, have been affected as they live in basins with large water bodies that have witnessed a significant drop in their water levels in the past three decades.
  • Many of these drying lakes have been identified as important sources of water and energy (hydropower).
  • The reduced size of these lakes not only results in freshwater decline and environmental degradation but also disrupts the water and carbon cycles.
  • Widespread water shortage in these water bodies, “particularly accompanied by rising lake temperatures, could reduce the amount of absorbed carbon dioxide and increase carbon emissions to the atmosphere given that lakes are hotspots of carbon cycling.”

How can we conserve these water bodies?

  • There is a need to manage them in an integrated manner.
  • Steps like restrictions on water consumption and climate mitigation to bring down global temperatures are some of the ways to conserve them.
  • This will also help in reducing sedimentation in reservoirs as the rate of sedimentation is linked to climate change — it increases when there is extreme precipitation, as well as land disturbance such as wildfires, landslides and deforestation.

Source: IE

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