- Hurricane Milton, having formed in the Gulf of Mexico, has Tampa Bay firmly in its sights and could bring a storm surge higher than the ground floor of most assets.
- Storm surge and coastal flooding can wipe out a portfolio while rainfall can further damage remaining through river flooding, surface flooding, and landslides.
Historically, storm surge and coastal flooding have flattened towns, turning assets into rubble and matchsticks.
The most lethal US landfall hurricane to date remains the 1900 Galveston, Texas storm. Few buildings remained standing across swathes of the island with over 6,000 people dying.
As Hurricane Milton approaches the asset-rich western Florida coast, the cities of Tampa, St. Petersburg, and Clearwater need to be worried. City-wide vulnerability to the physical risks from this tropical cyclone could lead to significant losses.
Previous hurricanes over the area include 1848, 1921, and 1946, long before the development boom placed multi-million dollar condominiums and mansions facing the Gulf of Mexico.
Inside Tampa Bay, an Air Force base, Tampa General Hospital, Tampa International Airport, and office skyscrapers sit within the possible storm surge inundation zone for a Category 5 hurricane. A 2015 estimate places possible hurricane-related flooding losses at well over 200 billion 2024 dollars.
While there's still uncertainty, Milton is currently expected to make landfall as a Category 4 hurricane, causing catastrophic storm surge.
The wind blowing across the sea, fuelled by extreme sea surface temperatures augmented by human-caused climate change, pushes the water in front of it.
The seawater piles up against the coast, appearing to be a high tide - but then exceeding the hightest tide level. The longer the distance over which the wind blows across the ocean, which is termed fetch, the higher the water at the shore.
Meanwhile, Milton’s atmospheric pressure continues to drop. The lowest pressure is found in the eye of the storm, sucking up the ocean like a straw, creating a dome of water that can add over half a metre to the sea level.
In worst case scenarios, the storm makes landfall at high tide, both during the 12-hour tidal cyclone and during the annual tidal changes, which means that the storm surge sits atop the high tide, with all the water blasting ashore.
The largest storm surges have been measured up to 33 feet higher than the typical high tide mark. Then, there are waves on top. Few sea walls around the world have been built so high while assets a mile or more inland can be inundated with salty, muddy water.
Storm surges propagate up estuaries and rivers, flooding buildings far from the open ocean while blocking rainfall drainage. River flooding and surface flooding can mix with the storm surge flooding.
These forces and energies associated can wreck properties in many ways. A rapid rise of the water level outside a building, such as through a levee breaking, can impart a huge pressure.
Windows shatter, doors pop open, and walls collapse, possibly bringing down the property. Any water pressure, including from pounding waves, on roofs is likely to blow holes through them, soaking the property.
Once water is inside a property, anything not made flood resistant is likely to be damaged beyond drying and repair. It will need to be replaced.
This includes electrics, plumbing, computers, and furniture. Walls are typically stripped and insulation removed, requiring weeks or months to dry properly. Any salt residue and contaminants (which could be oil or household chemicals) must be removed. Disinfection will prevent mould and fungus.
An inundated property experiences buoyancy. Any structure not securely tied to its foundation, or with a foundation not connected to the earth, could float away.
In places such as Florida, storm surge damage is often half of the losses from a landfall storm. With the current expectations from Hurricane Milton, St. Petersburg, Clearwater, and Tampa could have most of their damage from coastal flooding.
Managing assets before and during tropical cyclones
Asset managers are not alone in dealing with possible loss and damage, even at the city-wide level expected from this hurricane. Climate X offers solutions to assess portfolio exposure to climate risks, including tropical cyclones.
As the frequency of tropical cyclones decreases while intensity increases under human-caused climate change, investors can use these advanced datasets and climate models to test the costs and benefits of actions.
Divesting from vulnerable coastlines is possible, but adaptation and retrofitting measures - which might be costly, even if still cheaper than complete replacement - are also available to protect assets from flooding.
Many actions need to be done at the siting and design stage.
Land can be raised, properties can be raised above the land, and topography can be landscaped to direct storm surge flooding to low-lying areas without assets. It might even be widening and deepening a river, although caution is needed, because such engineering can increase river flow rates, leading to river flood changes far upstream.
Flood-resistant materials and finishes reduce damage, as do those which can withstand water contaminants, including salt, soil, fertilisers, pesticides, gas, oil, and household chemicals which are often mixed with floodwater.
Walls and roofs need to be tied strongly together for wind resistance, as with walls and foundations. Physical risks from landslides, erosion, and scour can be mapped and avoided or reduced.
All these are now too late for Hurricane Milton.
Instead, moveable assets or valuables within assets must be taken out of the potential storm surge flood zone and protected from wind, debris, river flooding, surface flooding, and landslides.
After all, once the main hurricane has passed over, the danger remains, especially from rainfall and landslips. The damage from Hurricane Helene is still being tallied due to these physical risks.
Windows and doors should be boarded up, to protect them from being blown in by wind, water, or debris including trees and collapsed buildings. Vehicles and boats should be moved or secured to prevent them from striking properties.
Turning off the power grid as the hurricane approaches will prevent fires and electrocutions from broken power lines. Cutting off branches above power lines can help to reduce the number of wires requiring repair once the storm has passed. Wind, sometimes funnelled by topography or buildings, can still bring down poles and transmission towers or snap the lines.
Climate X all-in-one solutions can help asset managers work through the risks and the mitigation options for risk management, including protection, divesting, retrofitting, and adaptation.
Then, even with hurricane after hurricane - as with Florida at the moment - you can minimise and anticipate portfolio losses.