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Nature's Water Bomb: Atmospheric rivers vapor behind 70% of India's floods

A recent study by atmospheric scientists from Indian Institute of Technology and the University of California revealed atmospheric rivers

By Wahid Bhat
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A recent study by atmospheric scientists from the Indian Institute of Technology and the University of California revealed that atmospheric rivers were the direct cause of the devastating floods during the summer monsoon season in India between 1985 and 2020.

The research was recently published in Communications Earth & Environment found These atmospheric rivers, which resemble rivers that flow in the sky, there are currents of water vapour that cause an increase in rainfall and consequent flooding.

A recent study by climatologists from the Indian Institute of Technology (IIT) Gandhinagar, the National Institute of Technology Srinagar and the University of Washington sheds light on the impact of atmospheric rivers in India.

Increase in flood incidents

The research team analyzed data from various sources to track the number of atmospheric rivers affecting India and their correlation with the increase in flood incidents. While atmospheric rivers have drawn attention to causing flooding in California, this study aimed to investigate their impact in India, a country familiar with annual monsoon-related flooding.

Atmospheric rivers form when air pressure systems collide, resulting in the movement of moisture-laden air through the atmosphere as a current. As they grow in size, they resemble rivers in the sky. When these atmospheric rivers meet the land, the air pressure changes, causing the release of moisture in the form of heavy rain.

The researchers examined weather records from the European Reanalysis Version, the Dartmouth Flood Observatory and the India Meteorological Department spanning from 1951 to 2020.

Shanti Swaroop Mahato, professor at IIT Gandhinagar and lead author of the study said that atmospheric rivers had impacted India a total of 596 times, with the 95% of these events occurring during the monsoon season.

Furthermore, they observed that 54% of the largest atmospheric fluvial events took place in the last three decades, suggesting an increase in their frequency and intensity due to global warming.

He added "the study attributes the rise in atmospheric rivers to warmer ocean surface temperatures in parts of the Indian Ocean, resulting in increased evaporation. This, in turn, leads to increased moisture in the atmosphere when atmospheric rivers form, causing heavier rainfall. The substantial increase in the amount of rainfall has resulted in catastrophic flooding, causing loss of property and thousands of lives".

Devastating floods caused by Atmospheric Rivers in India

The recently conducted study highlights several devastating floods caused by atmospheric rivers in India. These include the catastrophic floods in Uttarakhand in 2013, which resulted in the tragic loss of 6,000 lives, and the 2007 floods in Southeast Asia, including India, which claimed the lives of 2,000 people.

Other significant floods caused by atmospheric rivers include the 1988 Punjab floods, the 2018 Kerala floods, the 2006 Gujarat floods, the 1993 Assam floods, and the 2004 floods that caused extensive damage in eastern India and Bangladesh.

Atmospheric rivers, characterized by their narrow shape and high moisture content, play a crucial role in these extreme rainfall events. The Western Ghats and Eastern Ghats regions of India experience particularly heavy rainfall due to the presence of these atmospheric rivers.

The study also takes into account the projection that in a warmer climate, the South Asian monsoon system is likely to carry even more moisture. This increase in moisture content is expected to lead to an increased frequency of atmospheric rivers making landfall in India.

Impact of Atmospheric Rivers

Atmospheric rivers, also known as ARs, are concentrated regions of moisture in the atmosphere that carry significant amounts of water vapour. These atmospheric phenomena have been identified as one of the main causes of devastating floods in coastal areas.

Several catastrophic floods in India, including the 2013 Uttarakhand floods and the 2018 Kerala floods, have been attributed to the presence of atmospheric rivers. These events resulted in the loss of many lives and caused widespread destruction.

The research highlights that as the climate continues to warm, the moisture-holding capacity of atmospheric rivers increases, creating an increased risk of more destructive floods in the future.

The study findings reveal the detection of atmospheric rivers making landfall during the summer monsoon season in India. These atmospheric rivers are associated with increased water resources and pose severe flood risks due to their ability to unleash large amounts of rainfall in a short period, ranging from a few hours to a few days.

Understanding and Mitigating Atmospheric Rivers

The joint efforts of the research team provide crucial information on the behaviour and consequences of atmospheric rivers in the Indian context. By recognizing the connection between atmospheric rivers and increased flood risks, policymakers and communities can better prepare for and mitigate the impacts of these extreme weather events.

Shanti said that one-third of the events related to top atmospheric rivers, 54 per cent, occurred in the most recent three decades, i.e. between 1991 and 2020. This highlights the direct link between dangerous atmospheric rivers and rising temperatures around the world.

The frequency and severity of atmospheric rivers appear to be increasing in India in recent decades, the study said. Daily rainfall extremes have increased in recent decades and are expected to increase further as the climate warms.

A recent study has revealed that atmospheric rivers were responsible for seven of the ten deadliest floods in India between 1985 and 2020. These floods resulted in the tragic loss of more than 9,000 lives and inflicted significant financial damage, reaching billions of dollars as causes of the displacement of the affected communities.

Ocean Warming Fuels Severe Rivers

Warming sea surface temperatures in the south-central Indian Ocean have become a crucial factor in the development of atmospheric rivers.

The last few decades have witnessed a significant increase in evaporation from the Indian Ocean, driven primarily by the increase in vapour pressure deficit (VPD), which measures the pressure required to turn a liquid into a vapour. As a consequence of climate warming, the study highlights a notable increase in the frequency of atmospheric rivers and associated floods.

The study proposes that the rapid warming of the Indian Ocean could induce a substantial escalation in evaporation rates, which would subsequently lead to the formation of more severe atmospheric rivers.

Elevated heat from the ocean surface fuels increased evaporation, culminating in the generation of these moisture-laden channels in the atmosphere. This connection between ocean warming, evaporation, and atmospheric river intensity underscores the need for a comprehensive understanding of this phenomenon.

Floods have profound consequences for both the economy and society, which requires a deep understanding of the role that atmospheric rivers play in present and future climate scenarios. By recognizing the influence of atmospheric rivers on flood hazards, effective measures can be implemented to mitigate and adapt to these calamitous events.

Furthermore, the study emphasizes the integration of atmospheric rivers into the existing flood early warning system in India, thus reinforcing preparedness and response strategies.

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