Atmospheric River

Canada’s West Coast- British Columbia – was battered with heavy rainfall resulting in catastrophic flooding and landslides in November 2021. It is believed to have been caused by more than one Atmospheric Rivers (AR.)

The term AR was coined in 1998 by Massachusetts Institute of Technology (MIT) researchers Yong Zhu and Richard Newell, though ARs did play havoc earlier too. Until then AR was mostly referred to as tropical plume, tropical connection, moisture plume, water vapor surge, cloud burst and cloud band.

An AR is no river in the sky as the name suggests, but is a weather phenomenon.  It is a narrow corridor of highly saturated moisture in the atmosphere that stretches to 1600 km long and about 600 km wide.  Water an AR carries can be roughly compared to about 25 times carried by any major river like the Ganges or the Mississippi.

AR is born in the tropical ocean regions near the equator, and as it travels away from the equator, the warm air mass gets saturated with water vapour.  As the AR makes its landfall, water vapour condenses into precipitation, resulting in heavy rain or snow.

ARs originate form eight oceanic regions around the world, some closer to continental coasts than others. One of those regions is just off North America’s western coast and can produce between one to two dozen ARs per year. ARs from the Indian Ocean caused havoc in Australia and in India, especially Kerala, Uttarakhand, Bengal in the recent years.

Has climate change caused the ARs to be lethal?

Scientists and climatologists believe that the frequency of ARs may reduce by 10% in the years to come, but they may increase in size by about 25%. This would result in ARs dumping more water on the land as years pass by.  Global warming will cause the air in the AR  to become warmer and warmer the air, more water vapour it carries. When the AR makes landfall, it will release more rain or snow than the previous one. 

What caused flooding and land-slides in British Columbia?

The summer season in 2021 in British Columbia saw more than 1,600 fires charring nearly 8,700 square km of forest land.  These forest fires bake the soil, making them more hydrophobic or making them to repel water.  The coniferous trees in Canadian forests, when they burn, release a waxy compound that bind the forest soil, making it more hydrophobic. The water-repelling layer is typically found at or a few cm below the ground surface and is commonly covered by a layer of burned soil or ash. 

When the ARs dumped heavy volume of water in areas burned during the 2021 wildfires, the runoff from these burned grounds was greater and more rapid because of the hydrophobicity of the soil.  Burning down of the trees and vegetation binding the soil on the mountain slopes resulted in the soil becoming loose, causing many land-slides.

Let us now look at the mythological aspects.

The Abrahamic religions narrate the flood story of Noah’s Ark where the God became angry with the sins of mankind. He told his faithful servant, Noah, to build an ark large enough for his family and two of every creature on earth. God delivered the promised deluge, lasting 40 days, that killed everyone and everything on earth except the population of the ark.  After the flood, the ark came to rest on a mountain top, indicating that the depth of the water was higher than the mountains.

As per Greek mythology, Zeus, the king of the Gods, was displeased with the humans. Zeus told Deucalion to construct an ark for himself and his wife. After nine days of flooding, the world was destroyed, and the ark rested on top of Mount Parnassus.

Hindu mythology too refers to such a flood. Lord Vishnu in the form of a fish appeared to Manu and told Manu that the world would be destroyed in a great flood. Manu built a boat and tied it to the fish. The fish guided Manu’s boat through the floods to the top of a mountain.

The Chinese too have many stories and myths about floods, Gods, dragons, and spirits. Like other flood stories, there are only a handful of survivors.

Could these floods have been caused by an AR? Some say it might have been caused by tsunamis or by comets or asteroids hitting  the earth.

Flood stories are universal and is part of all religions and mythology where the God sent flood to destroy the sinners as punishment..  Hungarian psychoanalyst Geza Roheim hypothesised that dreams of the flood came when humans were asleep with full bladders!!

Are the Gods unhappy with the humanity that the next flood is near? Are we to pay for our sins of not caring for Mother Nature?

The Lord saw how great the wickedness of the human race had become on the earth, and that every inclination of the thoughts of the human heart was only evil all the time.’ Bible : Genesis 6:5

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