A recently developed scale for atmospheric river intensity can be used to identify the hotspots of the most intense atmospheric rivers worldwide. The study shows that this scale, which ranks atmospheric rivers from AR-1 to AR-5 based on their duration and moisture transport, is no longer just a meteorological term, but it also helps communities know whether an atmospheric river will bring benefit or cause chaos.
Atmospheric river intensity increasing with climate change
Atmospheric rivers are long, narrow bands of water vapor that are becoming more intense and frequent with climate change. These rivers usually form when warm temperatures create moist packets of air, which strong winds then transport across the ocean. The string of atmospheric rivers that hit California in December and January 2022, 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, and most intense atmospheric river rating.
Severe atmospheric rivers can cause extensive damage
The most severe atmospheric rivers can cause hundreds of millions of dollars of damage in days in the western U.S., and their damage in other regions has yet to be comprehensively assessed. Therefore, the authors of the study hope that meteorologists and city planners worldwide would incorporate the atmospheric river intensity scale into their forecasts, telling people whether the atmospheric river will be beneficial or if they need to prepare for a serious storm.
The new study demonstrates that atmospheric river events can be directly compared globally using the intensity scale. The researchers used climate data and their previously developed algorithm for identifying and tracking atmospheric rivers to build a database of intensity-ranked atmospheric river events around the globe over 40 years (1979/1980 to 2019/2020). The study was published in the Journal of Geophysical Research: Atmospheres, which publishes research that advances understanding of Earth’s atmosphere and its interaction with other components of the Earth system.
Atmospheric river AR-X events
The authors of the study also found that more intense atmospheric rivers (AR-4 and AR-5) are less common than weaker events, with AR-5 events occurring only once every two to three years when globally averaged. The most intense atmospheric rivers are also less likely to make landfall and, when they do, are unlikely to maintain their strength for long and penetrate farther inland. They tend to dissipate soon after landfall, leaving their impacts most felt in coastal areas.
The study found four “centers,” or hotspots, of where AR-5s tend to die, in the extratropical North Pacific and Atlantic, Southeast Pacific, and Southeast Atlantic. Cities on the coasts within these hotspots, such as San Francisco and Lisbon, are most likely to see intense AR-5s make landfall. Midlatitudes, in general, are the most likely regions to have atmospheric rivers of any rank.
The study also found that strong El Niño years are more likely to have more atmospheric rivers, and stronger ones at that, which is noteworthy because NOAA recently forecasted that an El Niño condition is likely to develop by the end of the summer this year.
F. Martin Ralph, an atmospheric scientist at Scripps Institution of Oceanography at UC San Diego and a co-author on the new study, said,
“Atmospheric rivers are the hurricanes of the West Coast when it comes to the public’s situational awareness. People need to know when they’re coming, have a sense for how extreme the storm will be, and know how to prepare, he said. “This scale is designed to help answer all those questions.”
Bin Guan, an atmospheric scientist at the Joint Institute for Regional Earth System Science and Engineering, a collaboration between the University of California-Los Angeles and NASA’s Jet Propulsion Laboratory, said,
“This study is a first step toward making the atmospheric river scale a globally useful tool for meteorologists and city planners. By mapping out the footprints of each atmospheric river rank globally, we can start to better understand the societal impacts of these events in many different regions.”
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The atmospheric river intensity scale via AGU by Ralph et al. with usage type - News Release Media. 2019Featured Image Credit
The atmospheric river intensity scale via AGU by Ralph et al. with usage type - News Release Media. 2019
