Shrinking of lakes

General Studies Paper 3

Context:  More than 50 percent 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.

About the study

• The study was published in the journal Science named‘Satellites reveal widespread decline in global lake water storage’.
• For the study, team examined1,975 of the world’s largest lakes, including 1,052 natural lakes and 921 reservoirs — researchers studied lakes which are larger than 100 sq km and reservoirs with more than 1 cubic km of storage capacity.
• The analysis was done following a novel methodology that involved combining two-dimensional water areas with one-dimensional water levels to estimate the three-dimensional change in water storage.
• Combining recent level measurements with longer-term area measurements allowed  to reconstruct the volume of lakes dating back decades.

Findings of the Study

• 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.
• The study also pointed out 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 (potential evapotranspiration)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.
• Notably, lakes have shrunk or disappeared completely across 82 percent of the Arctic’s lake-rich regions in the past 20 years.
• Natural lakes located in humid tropics and high altitudes are also experiencing water shortages.
• India: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.
• Reservoirs:Two-thirds of all reservoirs across the globe have experienced significant storage declines.
  • Reservoirs, however, showed a net global increase in water levels, owing to 183 recently filled reservoirs.

Reasons for Shrinking of Lakes

• Human Activities:57 percent of the net decline in the water quantity in natural lakes to human activities, such as unsustainable consumption of water.
• Climate Change:The Arctic lakes have shrunk as a result of a “combination of changes in precipitation, runoff, temperature, and  potential evapotranspiration (PET) — loss of water due to both evaporation and transpiration, which are likely a concurrent result of natural variability and climate change.
• Sedimentation:The main reason behind the drop in water levels is sedimentation — the process of particles such as sand and stones settling to the bottom of a body of water.
  • 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.

What are the consequences of shrinking lakes?

• 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 as the lakes are hotspots of carbon cycling.
• If lakes are encroached upon they disappear as a water source but also contribute to severe urban flooding. 
• Loss of lake levels leads to groundwater pumping and depletion,leading to a host of other issues.

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.
• Managing lakes in an integrated manner will elevate the status of lakes to their rightful place, and they can continue to sustain humanity.