Hurricane Ian Landfall mostly strengthened by human-driven climate change

Press Summary (First published 2024/01/11)

• Cyclones landfalling in western Florida similar to Hurricane Ian are up to 30mm/day (0 - 30mm/day or 0 - 15%) and up to 10 km/h (0 - 10 km/h or 0 - 15%) windier in the present than they have been in the past.

• Hurricane Ian was largely a unique event.

• Natural climate variability likely played a role in driving Hurricane Ian, but human-driven climate change has also contributed by increasing both precipitation and wind associated with this hurricane.

Event Description

Hurricane Ian was the ninth named tropical storm, the fourth hurricane, and the second major hurricane of the 2022 Atlantic hurricane season. It originated from a tropical wave tracked by the National Hurricane Center in the tropical Atlantic, east of the Lesser Antilles on September 19. Two days later, the system entered the Caribbean Sea, bringing winds and heavy rains to the ABC islands, Trinidad and Tobago, and the northern coasts of South America. It developed into a tropical storm (named Ian) on September 23 and intensified into a Category 1 hurricane near the Cayman Islands on the 26th, rapidly escalating to Category 3 before making landfall in western Cuba on the 27th. After a slight weakening over land, it returned to the Gulf of Mexico reaching Category 5 before striking the west coast of Florida as a Category 4 on September 28. While traversing the state, Ian weakened to a tropical storm but regained strength over the Gulf Stream, heading towards South Carolina, where it made landfall for the third time as a Category 1 hurricane on September 30 before becoming a strong post-tropical storm that dissipated inland.

Ian caused significant damage in Cuba and significant damage in Florida and the Carolinas. Flooding particularly impacted the cities of Fort Myers Beach and Naples in Florida. Millions were left without power, and many had to take refuge on their rooftops to escape the rising waters. In addition to the damage, the barrier islands of Sanibel and Pine Island were cut off from the rest of Florida when their bridges or causeways were severed.  According to the National Hurricane Center Tropical Cyclone Report Ian was responsible for over 150 direct and indirect deaths and over $112 billion in damage, making it the costliest hurricane in Florida’s history and the third-costliest in United States history. The death toll in the United States (143) ranks Hurricane Ian as the 22nd deadliest hurricane in the country's history, according to the National Weather Service. The damages, according to Risk Management Solutions, exceeded $67 billion, while NOAA estimated losses at around $113 billion. On March 29, 2023, during the 45th annual session of the World Meteorological Organization's Tropical Cyclone Committee, the name Ian was officially retired from future lists due to its destructive impact.

The Surface Pressure Anomalies reveal negative anomalies (up to 20 hPa) over Western Florida during the landfall day. Temperature Anomalies show no deviations for this event. Precipitation Data indicate that the majority of the area under analysis experienced extreme precipitation, reaching up to 250 mm/day in the coastal area surrounding Fort Myers. Windspeed Data also indicate that the cyclone generated sustained winds up to 240 km/h over the area surrounding the landfall.

Climate and Data Background for the Analysis

According to the IPCC report (IPCC AR6 WGI FR - Page 205), anthropogenic climate change has increased observed precipitation, winds, and extreme sea level associated with some tropical cyclones, and there is evidence for an increase in the annual global proportion of Category 4 or 5 tropical cyclones in recent decades. However, the confidence level for these findings varies from medium to low. Regarding the economic damages caused by individual extreme events, the report (IPCC AR6 WGII FR - Page 1990) states that formal attribution to anthropogenic climate change has been limited, but climate change could account for a substantial fraction of the damages. Two recent studies have shown approaches for how damages may be attributed for individual events in the USA. One study suggested that 30-75% of the direct damages from Hurricane Harvey was caused by climate change, with a best estimate of 67 billion USD out of an estimated 90 billion USD total of attributable damages. Another study estimated that 8.1 billion USD (13% of the total) of the flooding from Hurricane Sandy was attributable to the climate influence on sea level rise.  In summary, the IPCC report suggests that climate change has had an impact on hurricane intensity and associated hazards, but the confidence level for these findings varies. The IPCC report also highlights the potential economic damages caused by individual extreme events, and recent studies have used a variety of approaches for attributing these damages to climate change

Our analysis approach rests on looking for weather situations similar to those of the event of interest having been observed in the past. For this event, we have low confidence in the robustness of our approach given the available climate data, as the event is largely unique in the data record.

ClimaMeter Analysis

We analyse here (see Methodology for more details) how events similar to the low pressure system leading to Hurricane Ian have changed in the present (2001–2022) compared to what they would have looked like if they had occurred in the past (1979–2000) in the region [-88°E -78°E 20°N 30°N]. The Surface Pressure Changes show that cyclones have not significantly changed their intensity compared to the past except in areas distant from the cyclone eye. There are no remarkable Temperature Changes. Precipitation Changes show that similar events produce heavier up to 30mm/day (0 - 30mm/day). precipitation in the present than in the past with the largest values in Southern Florida, the area targeted by Ian. Windspeed Changes show that similar events produce faster (4-10 km/h) winds in Northern Florida. We also find that Similar Past Events occur with the same frequency per month than in the past. Considering the affected urban areas, Tampa and Fort Myers see an increase in precipitation (4-20 mm/day) in the present  compared to the past, while no significant changes occur in Miami.

Finally, we find that sources of natural climate variability, notably the Atlantic Multidecadal Oscillation and the Pacific Multidecadal Oscillation, may have influenced this event.  This suggests that the changes we see in the event compared to the past may be partly due to human-driven climate change, with a contribution from natural variability. 

Conclusion

Based on the above, we conclude that cyclones following similar tracks as Hurricane Ian during the Florida landfall have become up to 30mm/day (0 - 30mm/day or 0 - 15%) and up to 10 km/h (0 - 10 km/h or 0 - 15%) windier  in the present compared to  the past. We interpret the Hurricane Ian Florida landfall as a largely unique event for which natural climate variability played a role.

Contact Authors

Davide Faranda, IPSL-CNRS, France  📨davide.faranda@lsce.ipsl.fr   🗣️French, Italian, English

Stavros Dafis, NOA/IERSD-meteo.gr, Greece 📨sdafis@noa.gr  🗣️Greek, English

Suzana J. Camargo, LDEO, Columbia University, USA;   suzana@ldeo.columbia.edu 🗣 English, Portuguese