With the intensity and frequency of hurricanes increasing, one group of scientists is suggesting that the current most commonly used storm-strength scale, which tops out at Category 5, should go up to 6.
Under the Saffir–Simpson hurricane wind scale, which was established more than 50 years ago, the strongest storms are classified as Category 5, when wind speeds exceed 157 miles per hour. However, even if winds surpass these strengths significantly, the storm is still considered a Category 5.
In a paper published this week in Proceedings of the National Academy of Sciences journal, researchers Michael Wehner of the Lawrence Berkeley National Laboratory and James Kossin of the University of Wisconsin-Madison, proposed a Category 6 classification, for storms with wind speeds of more than 192 mph.
They noted that five storms in the Pacific over the past decade have already achieved this hypothetical Category 6 intensity.
“Based on multiple independent lines of evidence examining the highest simulated and potential peak wind speeds, more such storms are projected as the climate continues to warm,” they said.
Risk from winds
The Saffir–Simpson hurricane wind scale was introduced in the early 1970s by the US National Hurricane Center, using estimates of peak wind, storm surge, and minimum central pressure to describe both wind- and water-driven destruction during the landfall of a hurricane along a coast. It was altered in 2010 to be solely determined by a one-minute-average maximum sustained winds at a height of 33 feet.
The Saffir-Simpson system is used only in relation to the risk from winds, not from rain, sea surge or flooding. The researchers, quoting a report from 2000, noted that hurricane-related deaths in the United States were caused mostly by coastal storm surge (49%) and flooding from heavy rain (27%), while deaths caused directly by wind made up 8% of fatalities.
“Still, [tropical cyclone] wind hazard remains an important metric for communicating risk to the general public and is a critical metric when considering insured losses since many properties are insured against wind damage but not water damage,” they stated.
They said the motivation of their research is to reconsider how the open-endedness of the Saffir-Simpson scale can lead to an underestimation of risk, and, in particular, how this underestimation becomes increasingly problematic in a warming world.
Global warming
“Global warming has increased the energy available for tropical cyclone intensification through increases in latent and sensible heat fluxes from warmer ocean temperatures,” the researchers’ paper noted. “As a result, storm intensities well above the category-5 threshold are being realized and record wind speeds will likely continue to be broken as the planet continues to warm.”
They pointed out that Typhoon Haiyan, a devastating storm with 195 mph winds that struck the Philippines in 2013, was one of the most powerful tropical cyclones ever recorded, and would have been included in their proposed Category 6 classification. They added that Haiyan does not appear to be an isolated case, and that a number of recent storms already reached their hypothetical Category 6 wind speeds.
An assessment by the Intergovernmental Panel on Climate Change last year found that it was likely that the number and frequency of Category 3 to 5 hurricanes have increased around the world over the past 40 years.
That report noted that, of the 197 Category 5 storms between 1980 and 2021, half had occurred in the last 17 years of that period. And five of those storms, all of which occurred in the last nine years of the record, had exceeded the researchers’ hypothetical Category 6.
The five storms that hit or surpassed 192 mph winds were:
- Typhoon Haiyan, in 2013, with 195 mph wines, which killed more than 6,300 people in the Philippines.
- Hurricane Patricia, in 2015, which reached 215 mph winds before hitting Jalisco, Mexico, as a Category 4 storm.
- Typhoon Meranti in 2016, with 195 mph winds, which impacted the Philippines, Taiwan and China.
- Typhoon Goni, in 2020, which reached 195 mph winds, before hitting the Philippines as a weaker storm.
- Typhoon Surigae, in 2021, with 195 mph winds, before weakening and brushing the Philippines and other parts of Asia.
The most intense of these hypothetical Category 6 storms, Patricia, occurred in the Eastern Pacific, while the remaining four all occurred in the Western Pacific. None has been recorded in the Atlantic.
“Our results are not meant to propose changes to this scale,” the researchers wrote, “but rather to raise awareness that the wind-hazard risk from storms presently designated as category 5 has increased and will continue to increase under climate change.”
However, they added that they felt adding a sixth category to the Saffir-Simpson scale could raise awareness about the perils of the increased risk of major hurricanes due to global warming.
Related Videos
