An increase in surface area of the water bodies contributes to this loss
The volume of water loss (evaporation volume) of India’s natural lakes and reservoirs (artificial lakes) increased at a rate of 5.9 per cent per decade during 1985-2018, according to a new study.
Factors driving the loss are influenced by climate change, the authors of the report published in Nature Communications pointed out.
In April 2018, 45(10^6) cubic metres of water evaporated from Madhya Pradesh’s Ban Sagar Lake, 11(10^6) cubic metres from Rajasthan’s Bilaspur reservoir, 4 (10^6) cubic metres form Jharkhand’s Masanjore dam, 3(10^6) cubic metres from Chennai’s Red Hills lake, among others, the report listed.
The volume of evaporation varied strongly season to season, said Gang Zhao, a postdoctoral fellow in the department of global ecology at the Carnegie Institute for Science and first author of the study. These are, in turn, driven by reservoir operations and interannual climate changes, he added.
Water loss from Indian lakes & reservoirs
Source: Gang Zhao
Increasing volumes of water are escaping from India by evaporation because there is so much surface area, according to Catherine O’Reilly, professor at the department of geography, geology and the environment, Illinois State University, told Down To Earth (DTE). She was not involved in the study.
What’s more, the surface area of all lakes and reservoirs in India was increasing at a rate of 91 square kilometres per year during the period, Huilin Gao, associate professor at Texas A&M University and one of the study authors, told DTE.
The increase in evaporation volume is driven by reservoirs, especially the new ones constructed after 1985, according to the research published in Nature Communications.
The overall area of the country’s reservoirs grew at the rate of 69 square kilometre per year during the period (76 per cent of the area increase of lakes and reservoirs combined), said Zhao.
Of them, the reservoirs created after 1985 contributed 58 per cent of the area increase driven by reservoirs, he added.
New reservoir construction is a major reason for a rise in the water area and evaporative water loss, the authors noted.
The speed of evaporation of lake / reservoir water went up at a rate of 0.44 per cent per decade, the study estimated. This is low as humid conditions slow down evaporation, O’Reilly explained.
Evaporative water loss has been long overlooked globally due to the lack of effective tools to quantify it, Gao pointed out.
But precisely measuring this loss in the context of climate change is the need of the hour, the study stated.
“Understanding how much water is moving into the atmosphere can improve the water cycle and climate models,” O’Rilley said, adding that this information could help identify areas that might be at risk for water availability.
Gao and her colleagues collected data on water loss due to the evaporation in 1.42 million global lakes from 1985 to 2018. This included both natural lakes and reservoirs.
Worldwide, the average evaporation volume was 1,500 (plus or minus 150) cubic kilometres per year during 1985-2018, the study showed. This is 15.4 per cent higher than earlier estimates done by other studies for the period, according to the researchers.
The long-term average lake evaporation volume across the planet, the study showed, has risen at a rate of 3.12 cubic kilometres per year.
“This suggests that lake evaporation plays a larger role in the hydrological cycle than previously thought,” Zhao said in a statement.
Further, Gao and her colleagues detected a global pattern: Reservoirs suffered more evaporative water loss than lakes.
This is because most reservoirs are located below 50°North. They have larger evaporation rates than natural lakes, which are primarily located in the high-latitude or high-altitude regions, according to the researchers’ analysis.
“Our findings raise the alarm about the need for better quantification of evaporative loss for reservoirs in the context of climate change, Gao highlighted.
Also, the researchers argue that evaporation volume is a better indicator of climate change than evaporation rates.
Increasing evaporative volume loss is driven by a rise in the evaporation rate, a decrease in ice cover, and an increase in lake surface area. Climate change influences all three factors, the researchers said.
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