Atmospheric Rivers resulting in catastrophic monsoon rain and floods

While the Brahmaputra might have the deserved moniker of India’s “sky river”, did you know atmospheric rivers are a very real (and often horrifying destructive) phenomenon? But they might not look like anything you’re imagining right now.

As the name suggests, atmospheric rivers are gargantuan, relatively narrow floods of super-concentrated water vapour in the sky. From space, they often look like milky rivers snaking through the atmosphere, carrying ridiculous amounts of water (as high as 90% in the global meridional water cycle) in the North-South direction.

This ethereal-looking weather phenomenon has recently deluded headlines by sprouting intense showers over California, US, barrelling their water management measures into severe disarray. And now, experts think India might be in the crosshairs as well.

Atmospheric scientists from the Indian Institute of Technology and the University of California found that climate change has once again made its presence felt by engorging the number and strength of atmospheric rivers associated with flooding in India.

Over 12% of India (and increasing) is prone to floods, with the devastating phenomenon being the most common natural disaster in the country. While Assam and the northeastern states are famous for flooding in the monsoon months, deadly floods have recently reverberated through several other states like Maharashtra, Gujarat, Kerala and Telangana.

As global warming and hotter ocean surface temperatures increase evaporation over the Indian Ocean, they end up supplying dangerous amounts of moisture to atmospheric rivers (AR) in the region as well. All this water has to go somewhere, and it usually ends up getting dumped over the subcontinent in terrifying rain episodes, often leading to massive floods.

Analysing data from the India Meteorological Department, the European Reanalysis Version and the Dartmouth Flood Observatory, the team found that India has been victim to a substantial number of AR events, especially during the monsoon season.

About 95% of the ARs occurred during the summer monsoon. Notably, 54% of the 596 events between 1951 and 2020 were also the most severe, and took place only in the last three decades. While this points to the sinister role of climate change in adding to the frequency of the weather woe, results aren’t statistically significant enough to confirm it yet.

What we do know is that seven of India’s ten most severe floods in the summer monsoon season, which claimed a substantial amount of lives, were negged on by ARs. Additionally, the study shows that about 65% of ARs that made landfall over the country were linked to floods between 1985-2020.

These findings help us understand how atmospheric rivers translate to extreme downpours and floods after landfall, also proving that what might seem innocuous and pretty from space paints an entirely different story back on Earth.