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Atmospheric rivers, powerful phenomena described as rivers in the sky, unleash substantial rainfall, frequently leading to flooding, mudslides, and significant destruction, including loss of life. These intense weather systems are crucial to understand due to their increasing impact, particularly in the context of climate change. This article provides an overview of their formation, scale, and potential consequences.
Understanding Atmospheric Rivers
Formation and Global Occurrence
This weather phenomenon is observed worldwide. It develops when substantial volumes of water vapor are transported from tropical oceans towards land by jet streams. As this moisture-laden air ascends, it cools and condenses, resulting in precipitation in the form of rain or snow.
According to NASA, these systems typically originate in mid-latitude oceans, between roughly 30 and 60 degrees north and south.
Visually, they manifest as elongated trails of thin, feathery clouds that can extend for hundreds of miles.
How Atmospheric Rivers Generate Flooding
While most atmospheric rivers are weak and cause no harm, even providing beneficial rainfall or snowfall, some are significantly more powerful.
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The National Oceanic and Atmospheric Administration (NOAA) notes that strong atmospheric rivers can transport water vapor at a rate up to 15 times greater than the flow of the Mississippi River.
California, a state prone to drought, has experienced instances where these storms triggered mudslides, downed power lines, and obstructed roads. Conversely, these events have also been instrumental in replenishing depleted reservoirs and mitigating wildfire risks by saturating dry vegetation.
In 2019, an atmospheric river, known as the “Pineapple Express,” impacted California, carrying moisture from near Hawaii. The resulting rainfall caused mudslides, forcing individuals to escape floodwaters and causing homes to be swept downhill.
In 2021, British Columbia endured a month’s worth of rain in just two days from an atmospheric river, leading to catastrophic floods and landslides. These events severely impacted communities and disrupted access to Canada’s largest port.
Climate Change and the Future of Atmospheric Rivers
Projected Impacts of a Warming Climate
Scientists predict that atmospheric rivers resembling those that caused devastation in California and British Columbia in recent years are likely to become larger and potentially more destructive due to climate change.
The American Meteorological Society explains that these atmospheric columns, stretching hundreds of miles, transport water vapor from the tropics to more temperate regions. The volume of water vapor carried can exceed twice the flow of the Amazon River.
According to a 2018 research paper, while the frequency of atmospheric rivers may decrease by approximately 10%, their dimensions are expected to increase by 25% in width and length, enabling them to carry significantly more water.
Consequences for Water Management
This transformation presents challenges for water resource management. Moderate atmospheric rivers, which are beneficial for replenishing water supplies, are projected to occur less often, while intense events could become increasingly devastating, exacerbating flood risks and posing greater threats to infrastructure and communities.