Tropical Cyclones and Infrastructure Investment

• Tropical cyclones, known as hurricanes, cyclones, or typhoons, cause significant damage through wind, flooding, and storm surges.
• Real-time data and modelling can project cyclone paths and financial impacts, aiding in preparation and reducing infrastructure damage.
• Investing in resilient infrastructure and retrofitting existing assets mitigates cyclone risks, ensuring long-term sustainability and safety for critical structures and communities.

Tropical cyclones are rotating storms forming over oceans in the tropics or subtropics, although not usually right at the Equator and they are not seen to cross the Equator.

Depending on where they form, they are called hurricanes, cyclones, or typhoons.

All are the same storm type, but beginning in a different place. Sometimes they track over the open ocean, disrupting shipping and aviation, and then dissipating. At other times, they slam into a shoreline, knocking down or flooding structures while moving inland.

Wind tends to lead to the lowest out of all the physical risks from tropical cyclones, yet these storms continue to be categorised principally by wind speed.

If the storm rotates with an average sustained wind speed below 119 km/h (74 mph), then it is termed a tropical storm.

• Category 1 tropical cyclones have sustained winds between 119-153 km/h.
• The scale goes up to Category 5 that are tropical cyclones with sustained winds at or above 252 km/h (157 mph).
• Gusts easily exceed 300 km/h (186 mph) while associated tornadoes have yet faster winds.

Flooding from tropical cyclones is usually far more damaging than winds.

Storm surge is coastal flooding from the tropical cyclone’s wind pushing seawater toward the shore, added to the ocean’s level rising due to the storm’s low atmospheric pressure.

Storm surge can add up to ten metres above the tide to the water’s level. Then, pile on top significant rainfall. Meanwhile, waves pummel assets with huge forces and energies, as scour undermines structures.

Rainfall also produces river flooding and surface flooding, which can amount to several metres of water.

Should dams, dikes, or levees break, a wall of water travelling over 10 km/h, faster than most people jog, could slam into assets. Once the water recedes, physical damage remains. Without thorough drying, properties can become mouldy while requiring cleaning and disinfecting due to mud, salt, chemicals, and any plants or animals left behind.

After landfall, tropical cyclones continue to move inland and dump their water. River flooding and surface flooding can occur hundreds of kilometres from the shoreline.

In North America, some storms reaching land along the Gulf of Mexico coast traverse the USA to New York City before heading out to the Atlantic Ocean. Others entering the USA along the Atlantic seafront retain tropical cyclone status while crossing Lake Ontario or Lake Erie.

Large cities at physical risk from tropical cyclones include Hong Kong, Honolulu, Houston, Miami, New Orleans, New York, Seoul, Shanghai, San Diego, Taipei, Tokyo, Toronto, and Washington, D.C.

Extensive ocean and atmosphere monitoring provides data for modelling and projecting where tropical cyclones could form and the tracks they might follow, allowing the estimation of financial losses.

Days of warning can be offered for where landfall might happen, although sometimes the uncertainties produce possible landfall zones hundreds of kilometres long. It can be costly for so many people to prepare their properties and then evacuate for a storm strike that might not occur.

Typically, high certainty about the areas that will be directly affected by a storm is available around 24-48 hours in advance. In an unusual situation, in October 2023 a tempest called Otis ramped up from tropical storm status to Category 5 in 12 hours before roaring into Acapulco, killing over 50 people, cutting all communications, and leading to over $12 billion in immediate costs.

Financial impacts on infrastructure can be severe.

After Hurricane Sandy hit the USA’s east coast in 2012, 8 million people lost power, some of them for weeks, contributing significantly to the estimated $65 billion of losses. The cost from Hurricane Katrina in 2005 was well over $100 billion.

Many transportation networks are usually halted before landfall and possibly for days afterward. Airports close which cancels hundreds of flights, since most passenger aircraft will not operate in winds exceeding around 74 km/h, well below the threshold for a tropical cyclone.

It is not safe to run above-ground trains or metros, and vehicles should stay off roads due to wind and water. Tunnels can readily flood, making underground transport fatal.

Coastal highways are washed over by huge waves and can be undermined by erosion. Downed trees and power lines might make roads and railways impassable.

The costs add up with knock-on impacts.

Lack of tropical cyclone adaptation in Australia is estimated to have led to 8,487 job losses after Cyclone Debbie in 2017. Badly hit sectors included energy, food, tourism, and transport.

Modelling possible losses informs the choices available for reducing damage to assets.

Adaptation and retrofitting can support investment in infrastructure that is resilient to the physical risks from tropical cyclones.

It is not just about tying an angled roof to the walls for wind resistance, using flood-resistant materials and finishes, and being aware of landslide risk zones.

It is also considering debris airborne in the wind, buoyant in the flood, or entrained in the landslide.

An unresilient structure can fall apart during a tropical cyclone, with the debris blasting other structures that are surviving the wind and water.

Asset managers need data and modelling to determine how to adapt or retrofit their infrastructure to deal with the wide variety of forces and energies.

For power grids, the safest and most cost-effective approach is often engineering the electricity generation plants and transfer stations to withstand the tropical cyclone, turning the power off as the storm approaches, and being ready for extensive grid repairs and reconstruction after the storm has passed.

One adaptation measure for electricity might be safe generators in each asset, with enough fuel on-site, stored safely. Physical risks from using local generators include carbon monoxide poisoning and fuel flammability. Another adaptation measure is renewable sources serving each building, which could be solar panels, small wind turbines, or hand-cranked generators.

Transportation assets need to be designed, constructed, and maintained to survive tropical cyclones.

Coastal and sea bridges must withstand wind, waves, and heightened sea levels from coastal flooding while inland bridges need to survive wind, river flooding, and surface flooding.

Debris impacts remain a major concern. Not only must roads manage through the storm and flooding, but also the traffic signals, signs, lights, and barriers need to be protected or quickly repaired or replaced.

Data on these items alongside modelling of potential damage, retrofitting costs, and replacement costs help asset managers determine the best course of action.

Sometimes, asset owners or managers might decide that it is cheapest to accept the damage and then to rebuild – as long as debris is minimised.

Coastlines and river courses can change substantially during a single storm. Data from past tropical cyclones and modelling of future ones can support the decision not to retrofit, but to rebuild afterwards with improved resilience and adaptation measures.

This approach would not be recommended for large assets such as the highest towers, including the Canton Tower in Guangzhou and the Taipei 101 tower in Taiwan. Nor would it suit water and sewage treatment plants, airports, train stations, power plants, health facilities, and supermarkets.

Instead, asset managers can use data and modelling now to select and implement adaptation and retrofitting options, long before a tropical cyclone forms.