Wave data gets us ready for hurricanes

News reports on this year’s Hurricane Ian make for grim reading. Headlines tell of residents returning to flattened homes, rising death tolls and colossal damage to infrastructure. With its impact centred mostly on Florida in the North Atlantic hurricane basin, the $50bn bill for the damage is so great that, according to CNN, it is likely to “put a dent” in US GDP growth. At least 137 people have died as a result of the weather incident that (by some media estimates) was made 10 per cent worse due to the effects of climate change.

Despite Hurricane Ian’s impact and exposure on the news cycle, it ranks just 23^rd on the list of all-time worst hurricanes to hit the US. For all the carnage wreaked, it was in a lesser league to 2005’s Hurricane Katrina, which accounted for more than 1,800 lives, or 2017’s Hurricane Maria, which killed nearly 3,000. The Atlantic Hurricane season – that officially extends from the start of June to the end of November – is when the National Hurricane Center issues warnings about developing weather systems. While the scale of these disasters varies, their occurrence is an annual event. Since records began, there have been only two years in which hurricanes have not happened: the last was in 1914.

In Hurricane Ian’s aftermath, the BBC reported that ‘Florida death toll rises as criticism mounts’. This refers to finger-pointing at the government-level response to the disaster, in particular to post-event evacuations. With 55 fatalities, Florida’s Lee County was one of the most heavily affected places, described by Florida’s Governor Ron DeSantis as “ground zero”. Accusations over how the emergency was managed have concentrated on the timing of the evacuation order, which detractors say was issued too late. DeSantis has, in turn, criticised the critics, claiming that they are guilty of being wise after the event: “Everyone wants to focus on a plan that might have been done differently.” Similarly, Lee County’s sheriff Carmine Marceno has defended the emergency response protocols: “I stand 100 per cent with my county commissioners, my county manager. We did what we had to do at the exact same time. I wouldn’t have changed anything.”

Given the century-long unbroken record of annual hurricanes affecting the North Atlantic hurricane basin – that includes the US Atlantic coast, the Gulf Coast, Mexico, Central America and the Caribbean Islands – there is a pressing requirement for better predictive data related to hurricane strikes.

The North Atlantic hurricane basin includes Colombia’s archipelago of San Andrés, Providencia and Santa Catalina that in 2020 all took a battering within two weeks of each other. Alongside the loss of homes, the Colombian government estimates that 98 per cent of all infrastructure – including roads, water, sanitation and medical centres – was damaged on the island of Providencia. While 2022 represents massive disruption in the basin, 2020 gave us the most active Atlantic hurricane season on record. Thirty tropical storms were severe enough to be named, with 14 developing into hurricanes. In November 2020, two of those hurricanes – Eta and Iota (both Category 4 storms with wind speeds of 155mph (250km/h) – battered the South American county’s Caribbean islands.

Adaptation and mitigation measures for hurricanes affecting Colombia have been historically hampered by the lack of any meteorological and oceanographic observational network. To overcome this shortcoming and help authorities better plan and prepare for future extreme weather events, researchers at the Universidad Nacional de Colombia have reached a technical agreement with the environmental institution Coralina (corporation for the sustainable development of the archipelago of San Andrés), to use data collected from acoustic wave and current profilers (AWACs).

This collaboration is set to improve Colombia’s hurricane preparedness measures by using modelling tools in conjunction with the AWACs developed by scientific instrument designer and manufacturer Nortek. The work is being carried out by researchers at the Universidad Nacional de Colombia (at its Medellín and Caribe campuses) along with other academic institutions, including the Colombian-German Center of Excellence in Marine Sciences CEMarin, and the Universidad de Medellín.

Dr Andrés Fernando Osorio Arias of the Universidad Nacional de Colombia’s Oceanography and Coastal Engineering Research Group (and also executive director of CEMarin) says that data from these models are being used to predict hurricane vulnerability on archipelago’s three main islands of San Andrés, Providencia and Santa Catalina. “This kind of information answers important questions for people,” says Professor Osorio Arias. “Are we at risk? Should we wait? Should we move to the other side of the hill? Where should we spend money to adapt to hurricanes?”

Osorio Arias goes on to explain that the research currently being done in Colombia is crucial, because data gathered in the field can be imported into the laboratory to reproduce conditions on a laboratory scale, giving better control of the different parameters. “With field and laboratory data, you can develop new equations, new parameters and new understanding of physical processes, to improve the models.”

To predict the impact the combined factors of strong winds, intense rainfall, storm surges and powerful waves have on the islands, Osorio Arias and his research team have employed a series of open-source numerical models: Weather Research and Forecasting (WRF) for atmospheric processes, WAVEWATCH III and SWAN for oceanographic processes, and XBeach for coastal processes. “We use these models to create reconstructions of the hurricanes that occurred in the past, and also to predict scenarios that have not yet occurred – synthetic scenarios of hurricanes,” says Osorio Arias. He goes on to explain that by combining field observations with mathematics and statistics, “we can simulate real-world conditions. Although numerical models used for research are generally robust, they do require validation and calibration to improve their accuracy. This is particularly important when looking at local scales – such as in an archipelago – where biophysical features can alter hydrodynamics. One of our goals is to develop parameterisations that reproduce, for example, the thickness and roughness of coral systems or seagrasses into the numerical model,” says Osorio Arias.

Collecting real-world data required the installation of surface-buoy and submarine fixed-frame AWACs in the waters around the islands of San Andrés and Providencia. The team has two units at their disposal: an AWAC 600kHz acoustic Doppler current profiler (ADCP) and an AWAC 1MHz ADCP. Both collect current profile and directional wave data but differ in their maximum depth range. With a depth range of 35m, the 1MHz version is optimal for shallower waters, but to achieve a depth range of up to 50m, the 600kHz is most suitable.

The oceanographic data provided by the instruments was critical for the work. “Not only is it essential to know that the velocities experienced throughout the water column in the real world generally match the numerical model,’ says Osorio Arias, “but it’s also crucial for ensuring that the hurricane reconstructions and synthetic scenarios replicate conditions accurately. For example, sediment transport is controlled by these different velocities and the morphology of the coast. Our risk predictions depend on how accurately the velocities are represented in our hurricane scenarios.”

According to Osorio Arias, data collection fieldwork using AWACs in Providencia and San Andrés have confirmed that the researchers’ oceanographic numerical models replicate the archipelago conditions well. “Armed with this information, the researchers could confidently simulate historic hurricanes – including Eta and Iota – and create synthetic hurricane scenarios with different tracks and strengths. Together, these reconstructions and synthetic scenarios allowed the researchers to predict which locations would be most vulnerable across a range of hurricane intensities and tracks.” The study suggests vulnerable areas include the northern coastal area of San Andrés Island, which simulations suggest would be at particular risk from coastal flooding. In Providencia, research has shown a further vulnerability in that the proximity of Santa Catalina influences the magnitude of the waves in the area.

Academic fieldwork in Colombia may seem a world away from the trail of destruction left in the wake of Hurricane Ian in the North American Atlantic coast. But as both locations exist in the same tropical cyclone basin, any research that Osorio Arias and his team can do to assist with hurricane preparedness and mitigation could provide vital input to a more geographically widespread understanding of how to get ready for future hurricane systems.

This is something that could take on more urgency as in the past four decades there has been a marked increase in hurricane intensity. Figures show that between 1979 and 2009, tropical cyclones globally were 8 per cent more likely to reach categories 3 to 5 on the Saffir-Simpson scale (see ‘Hurricane strength and damage categories’), while in the Atlantic the percentage is 49. This is consistent with findings published in the Bulletin of the American Meteorological Society, that point out possible consequences of human-induced climate change are the intensification of tropical cyclones in terms of both windspeed and rainfall. Meanwhile, the bill keeps going up. The US Office for Coastal Management says that “the total cost for the last five years ($742.1bn) is more than one-third of the disaster cost total of the last 42 years ($2.155tn)”. N

According to the UK Met Office, “hurricanes are amongst the most powerful and destructive meteorological systems on Earth” and are characterised by a rapidly rotating storm system with a low-pressure centre, a closed low-level atmospheric circulation, strong winds and a spiral arrangement of thunderstorms that produce heavy rain and squalls. A hurricane – more correctly ‘Atlantic hurricane’ – is technically a tropical cyclone, and the term is synonymous with others such as typhoon, tropical storm or cyclone. Which gets used is dictated purely by the geographical location of the weather event. In the Atlantic, they are called hurricanes.

When it comes to why they are named, the UK MET Office says the naming system, “makes it easier to communicate between meteorologists and the public”. The Met Office points out that while it has also adopted a similar naming convention for storms arriving in the UK from the Atlantic, this is “to help communicate forecasts and warnings to the public, not because these storms are the same strength as tropical cyclones”.