May 30, 2023 7:06 am

Much more than 50 per cent of the world’s biggest lakes and reservoirs have shrunk more than the previous 3 decades mainly due to climate modify and human activities, according to a new study. From these water bodies, about 600 cubic km of water was lost amongst 1992 and 2020 — an quantity equivalent to the total water applied in the United States for the whole year of 2015.

It also noted that additional than half of the reservoirs positioned in peninsular India have witnessed substantial water storage decline, mostly due to sedimentation. Additionally, amongst the worst impacted organic lakes in the nation is Ladakh’s Tso Moriri.

Published in the journal Science final week, the study, ‘Satellites reveal widespread decline in worldwide lake water storage’, has been performed by Fangfang Yao, Ben Livneh and Balaji Rajagopalan, from the Cooperative Institute for Analysis in Environmental Sciences (University of Colorado Boulder, USA), Yoshihide Wada from Climate and Livability Initiative (King Abdullah University of Science and Technologies, Saudi Arabia), Jean-François Crétaux and Muriel Berge-Nguyen, from Laboratory of Space Geophysical and Oceanographic Research (France).

The continued shrinking of lakes, Yao and Rajagopalan told The Indian Express by e-mail, has led to a decline in freshwater provide, atmosphere degradation and deterioration of water top quality for humans and livestock. Meanwhile, water shortage beyond a specific level in reservoirs of hydroelectric dams could adversely influence the generation of hydroelectricity.

Central Asia’s Aral Sea has substantially dried due to unsustainable water consumption. On the left is a satellite image taken in 2000 and on the suitable is an image clicked in 2018. (Photo: NASA Earth Observatory)

If lakes are encroached upon (such as the case in India with smaller sized lakes), they disappear as a water supply but also contribute to serious urban flooding. Loss of lake levels leads to groundwater pumping and depletion, top to a host of other problems.,” Rajagopalan added.

How was the study carried out?

For their study, Yao and his group examined 1,975 of the world’s biggest lakes, such as 1,052 organic lakes and 921 reservoirs — researchers studied lakes which are bigger than one hundred sq km and reservoirs with additional than 1 cubic km of storage capacity. The evaluation was performed following a novel methodology that involved combining two-dimensional water places with one particular-dimensional water levels to estimate the 3-dimensional modify in water storage.

“We applied 250,000 lake-region snapshots captured by satellites amongst 1992-2020 to survey the region of 1,972 of Earth’s most significant lakes. We collected water levels from nine satellite altimeters and applied extended-term water levels to lessen any uncertainty. For lakes devoid of a extended-term level record, we applied current water measurements created by newer instruments on satellites.,” Yao explained.

“Combining current level measurements with longer-term region measurements permitted us to reconstruct the volume of lakes dating back decades.,” he added.

What are the findings of the study?

The researchers located that out of the 1,052 organic lakes that have been examined, 457 had important water losses in the previous 3 decades. Meanwhile, 234 organic 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 organic lakes to human activities, such as unsustainable consumption of water, and growing temperature and possible evapotranspiration (PET) — loss of water due to each evaporation and transpiration — with the latter two indicating the function of climate modify.

The study also pointed out the worst impacted biggest lakes across the planet 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 mostly dried due to unsustainable water consumption. Whereas, growing temperature and PET brought on the full 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 outcome of a “combination of adjustments in precipitation, runoff, temperature, and PET, which are probably a concurrent outcome of organic variability and climate modify.,” researchers mentioned in the study. Notably, lakes have shrunk or disappeared fully across 82 per cent of the Arctic’s lake-wealthy regions in the previous 20 years, as per a 2022 study.

In India, apart from Tso Moriri Lake, Andhra Pradesh’s Pulicat Lake and Kolleru Lake have been impacted but they didn’t function in the study as they have been “below our threshold so did not make it in our analyses,” Rajagopalan told The Indian Express.

One more acquiring is that contrary to earlier research, organic lakes positioned in humid tropics and higher altitudes are also experiencing water shortages.

In addition to this, the most current paper described that two-thirds of all reservoirs across the globe have skilled important storage declines. Reservoirs, having said that, showed a net worldwide enhance in water levels, owing to 183 not too long ago filled reservoirs. The primary explanation behind the drop in water levels is sedimentation — the approach of particles such as sand and stones settling to the bottom of a physique of water.

“Our acquiring suggests that sedimentation is the key contributor to the worldwide storage decline in current reservoirs and has a bigger influence than hydroclimate variability, i.e., droughts and recovery from droughts,” the researchers mentioned.

What are the consequences of shrinking lakes?

According to the study, practically two billion individuals, one particular-quarter of the worldwide population in 2023, will be impacted as they reside in basins with huge water bodies that have witnessed a important drop in their water levels in the previous 3 decades.

“Many of these drying lakes have been identified as crucial sources of water and power (hydropower).,” the researchers mentioned in their paper. The decreased size of these lakes not only outcomes in freshwater decline and environmental degradation but also disrupts the water and carbon cycles.

Widespread water shortage in these water bodies, “particularly accompanied by increasing lake temperatures, could lessen the quantity of absorbed carbon dioxide and enhance carbon emissions to the atmosphere provided that lakes are hotspots of carbon cycling.” the study added.

How can we conserve these water bodies?

Yao and Rajagopalan mentioned to save the shrinking lakes, there is a want to handle them in an integrated manner. Actions like restrictions on water consumption and climate mitigation to bring down worldwide temperatures are some of the approaches to conserve them. This will also support in minimizing sedimentation in reservoirs as the price of sedimentation is linked to climate modify — it increases when there is intense precipitation, as properly as land disturbance such as wildfires, landslides and deforestation.

“This (managing lakes in an integrated manner) will elevate the status of lakes to their rightful location, And they can continue to sustain humanity. We take care of them, they will take care of us, the ecology in a life-affirming manner.,” Rajagopalan mentioned.