Atmospheric rivers, which are long, narrow bands of water vapor, are becoming more intense and frequent with climate change.
Atmospheric rivers, which are long, narrow bands of water vapor, are becoming more intense and frequent with climate change. A new study demonstrates that a recently developed scale for atmospheric river intensity (akin to the hurricane scale) can be used to rank atmospheric rivers and identify hotspots of the most intense atmospheric rivers not only along the U.S. West Coast but also worldwide.
Atmospheric rivers typically form when warm temperatures create moist packets of air, which strong winds then transport across the ocean; some make landfall. The intensity scale ranks these atmospheric rivers from AR-1 to AR-5 (with AR-5 being the most intense) based on how long they last and how much moisture they transport.
In part because some West Coast weather outlets are using the intensity scale, “atmospheric river” is no longer an obscure meteorological term but brings sharply to mind unending rain and dangerous flooding, the authors said. The string of atmospheric rivers that hit California in December and January, for instance, at times reached AR-4. Earlier in 2022, the atmospheric river that contributed to disastrous flooding in Pakistan was an AR-5, the most damaging, most intense atmospheric river rating.
The scale helps communities know whether an atmospheric river will bring benefit or cause chaos: The storms can deliver much-needed rain or snow, but if they’re too intense, they can cause flooding, landslides and power outages, as California and Pakistan experienced. The most severe atmospheric rivers can cause hundreds of millions of dollars of damage in days in the western U.S.; damage in other regions has yet to be comprehensively assessed.
Read more at American Geophysical Union
Image: The intensity of an atmospheric river depends on how long it lasts (typically 24 to 72 hours; horizontal axis) and how much moisture it moves over one meter each second (measured in kilograms per meter per second; vertical axis). While weaker atmospheric rivers can deliver much-needed rain, more intense storms are more damaging and dangerous than helpful. (Credit: AGU, after Ralph et al. 2019 (DOI: 10.1175/BAMS-D-18-0023.1))