Climate Change and Tropical Cyclones: Adapting Asset Management Strategies

• U.S. shoutheastern coastlines and inland areas face enhanced risk from intense tropical cyclones, calling for damage reduction measures on vulnerable infrastructure.
• Climate change is reducing cyclone frequency but increasing their intensity, resulting in more severe wind and water damage, challenging current preparedness levels.
• Reliable tropical cyclone data is vital for risk assessment and improving response strategies amidst the growing impact of climate change on storm patterns.

A tropical cyclone is a rotating storm that forms over tropical or sub-tropical oceans, although not yet known to appear around the Equator.

Depending on where the tropical cyclone forms, it might be called a hurricane, a cyclone, or a typhoon – they are all the same storm type, just in a different location.

Any tropical cyclone striking a US coast is a hurricane, apart from some Pacific territories experiencing typhoons.

To be a tropical cyclone, the storm’s sustained wind speed must be at least 74 mph (119 km/h). Weaker winds could indicate a tropical storm.

Other cyclonic storms, including extra-tropical cyclones and polar lows, form over oceans at higher latitudes while such storms in the Mediterranean are called Medicanes.

Many coastlines facing an open sea could be impacted by these cyclonic storms. Even near the Equator, a line which these storms are highly unlikely to cross, major waves from distant tropical cyclones can damage assets.

Next, when a storm makes landfall, it dissipates, dumping its rain with lethal flood risk possible hundreds of kilometres inland.

Physical risks to assets are from wind – steadily blowing gusts, and tornadoes – and, leading to the most damage, water. Storm surge and waves race in for coastal flooding while rainfall produces surface flooding and river flooding.

When focusing on hurricanes originating from the Atlantic and Caribbean, it's evident that both the US coastline and extensive inland regions are exposed to significant physical risks

The main problem is that infrastructure placed in these areas prone to tropical cyclones doesn't have adequate damage reduction measures.

In the meantime, tropical cyclones are changing due to human-caused climate change, dictating the need to understand tropical cyclone data and to stress test assets for their ability to withstand ongoing changes to these tempests.

Current projections of tropical cyclone numbers are that they are declining due to human-caused climate change.

Asset managers must be cautious not to assume that this leads to declining property damage.

Lower infrastructure impacts come significantly from preparedness, including damage reduction measures, long before a storm appears on the horizon.

Fewer storms might lull asset managers into a false sense of security and so increase their portfolio along coasts or in locations prone to surface flooding and river flooding.

Then, a storm hits and the damage is far greater than expected due to lack of preparations.

The tropical cyclone’s waves and storm surge pound shores and infrastructure. Coastal flooding and the water’s forces can rip structures from their foundations, leaving little except for a scar in the landscape. Dunes and sea walls can be smashed to bits, inundating assets which were assumed to be protected.

Damage is expected to be particularly bad without taking measures because, as tropical cyclone numbers decrease, their strength increases from human-caused climate change.

Warmer air holds more water vapour, leading to more rainfall. Warmer oceans drive a storm’s strength once it has formed, increasing wind speed, with damage often estimated as being proportional to the square or cube of maximum gust wind speed.

Flooding, though, usually kills far more people and causes much more damage during tropical cyclones than wind. Devastating surface flooding and river flooding potentially extends hundreds of kilometres inland.

Hurricane Ida in 2021 made landfall around New Orleans and then swept right across the US, heading out to the Atlantic via New York City where at least eleven people drowned, mainly in illegally converted basement apartments.

At least four previous hurricanes crossed into the US from the Gulf of Mexico and then swung northeast, exiting via the Atlantic Ocean. Among them was the 1900 Galveston storm which remains the most lethal US landfall hurricane so far, killing over 6,000 people. 

Human-caused climate change seems to be slowing tropical cyclones as they move along their tracks. The storm not only holds more water, but also has more time over a place to dump its rain.

Houston’s terrible surface flooding and river flooding during Hurricane Harvey in 2017 showed this – although Tropical Storm Allison (not even a hurricane) in 2001 also deluged the city.

For the US east coast, human-caused climate change also appears to be decreasing the time between two tropical cyclones making landfall.

These coastlines are at increased risk of being hit twice within ten days, leaving little time for clean-up after one in order to prepare for the next. In the same way that an earthquake’s aftershock can bring down a structure that survived the main tremor, buildings which made it through the first storm could end up swept away by the second due to no time for maintenance and repair.

Many of these trends sport large uncertainties, mainly because the complete dataset of tropical cyclones and their characteristics is short compared to the timeframe of a changing climate.

We really only have consistent, comparable tropical cyclone data since the advent of satellite monitoring from the 1970’s, occasionally pushed back to the 1960’s.

With many multi-decade climate variabilities overlapping and influencing tropical cyclones, on top of trends from human-caused climate change, estimates are the name of the game for understanding how and why landfall tropical cyclones are changing.

Knowing about and using all available tropical cyclone data remains essential for determining the physical risks to assets.

Data on tropical cyclones and their impacts show for any location the previous known maximum depth of storm surge, coastal flooding, river flooding, and surface flooding, as well as maximum sustained wind speed, maximum gust wind speed, and wind speeds from any associated tornadoes.

Then, models project how much more these values might be in the future, within knowledge and uncertainties about human-caused climate change affecting tropical cyclones.

Plenty of unknowns remain, notably significant changes or complete stopping of the Gulf Stream.

At the moment, it seems as if a weakening Gulf Stream would contribute to declining tropical cyclone numbers despite a lack of clarity regarding affects on tropical cyclone intensity.

Another major unknown is the number and strength of tornadoes spawned by tropical cyclones, since maximum tornado wind speeds can be more than double that of a tropical cyclone’s. Every tropical cyclone offers added data to check with the model projections and then to update expected consequences for coastal assets.

Any asset manager must remain on top of the knowns and remaining unknowns.

Plus, it is not just the US Atlantic and Gulf Coasts, but also much of California’s and Hawai’i’s coastlines, as storms zip off the Pacific and slam into those states’ coastal and inland assets.