Storms getting stronger

Climate change: Does the hurricane scale need to be expanded?

Destruction following the passage of hurricane Otis through Mexico. This was a category 5 hurricane.(Bild: APA/AFP/Rodrigo OROPEZA)

Because the strength of tropical cyclones has increased enormously in recent years, US researchers are now calling for the five-stage hurricane scale to be expanded. 

The highest level currently includes hurricanes with wind speeds of 70 meters per second or more. In recent years, however, several tropical cyclones have had wind speeds of over 86 meters per second (around 310 km/h), write Michael Wehner from the Lawrence Berkeley National Laboratory in Berkeley and James Kossin from the University of Wisconsin-Madison in the "Proceedings" of the US Academy of Sciences (PNAS).

Satellite image from the previous year: Hurricane "Norma" off the Mexican coast(Bild: APA/AFP/NOAA/GOES/Handout)

Five strongest storms in the last nine years since 1980
According to the authors, an analysis of data from 1980 to 2021 showed that five storms would have been classified in the new hypothetical category six. All of these storms had occurred in the last nine years of the data series. One reason for the increase is climate change and the associated rise in sea temperatures. This provides additional heat energy for the hurricanes, which could therefore become stronger. 

The strongest of the five hurricanes, Hurricane Patricia, occurred in the Eastern Pacific in 2015 and made landfall in Mexico. The other four were typhoons, as tropical cyclones are called in the Northwest Pacific region. Among them was "Haiyan", which hit heavily populated islands in the Philippines in 2013 and caused the most deaths of these five hurricanes.

Relatives of "Haiyan" victims at a cemetery in the Philippines(Bild: APA/AFP/Ted ALJIBE)

The Saffir-Simpson wind scale
In the past, it has already been suggested that the particularly destructive tropical cyclone "Haiyan" should be included in a category six, the climate researchers explain. "But 'Haiyan' does not appear to be an isolated case." The team argues for a change to the current Saffir-Simpson hurricane wind scale, with a category five for peak wind speeds of 70 to 86 meters per second and an additional category six above that. 

The Saffir-Simpson hurricane wind scale was introduced in the USA in the early 1970s. Since 2010, winds have been measured at a height of ten meters. While hurricanes move very slowly overall, their rotating winds are very fast.

According to "Proceedings", the wind-based scale is only marginally relevant for many factors of destruction. Nevertheless, it remains an important criterion for risk warnings. The addition of a sixth category to the hurricane wind scale could also raise awareness of the dangers of the risk of major hurricanes due to global warming.