It sounded like a jet engine. Judith King, owner of King’s Ranch stables in the quiet Surrey village of Ottershaw was in the middle of teaching a riding lesson when she heard it. In the woods to her left, a tornado was raging. Suddenly, the vortex burst through the trees. It picked up logs and fencing. Riders were thrown from their horses.
Mercifully, no one was injured. “It was just a complete shock,” says King. “We’ve had windy days, we’ve had stormy days. This was completely different.”
The tornado touched down in Surrey on the morning of December 21, 2019, and reached wind speeds of up to 183 kilometres per hour. It carved an 11 kilometre trail of damage in a line bearing northeast that crossed the M25 motorway, the River Thames and the 1,400-year-old town of Chertsey.
Sarah Horton, a maths tutor and volunteer tornado investigator, lives just 25 minutes’ drive away from where it all happened. After hearing about the tornado on the news, she logged on to the online forum for TORRO, the Tornado and Storm Research Organisation, and offered to write a report on the damage. Her fieldwork began the next day.
“We have a bank of people who are willing to go out whenever there is severe weather damage and go and investigate it,” explains Horton. As a teenager, she lived in the US and remembers the tornado sirens that would send her scrambling for shelter. Tornadoes in the UK may be smaller, and only about 30 are reported every year, but they can still cause terrible damage and distress.
Scientists and volunteers such as Horton seek to document the wreckage left by tornados and other severe storms, a kind of meteorological forensics, so that we can better understand how such events unfold. Detailed surveys, drones, satellite imagery and witness reports all help to build up a vivid picture of what happened. The data can influence the design of storm-hardy buildings, for example. It can also improve forecasts. Surprisingly, much about tornados, including how they form, still remains a mystery.
Natural disasters caused $210 billion (£153bn) worth of damage worldwide in 2020 alone. The UK Met Office says it is not possible to forecast whether tornados will increase in frequency or severity due to climate change in the coming years but it does expect higher winter wind speeds and a greater number of annual winter storms in the latter half of the 21st Century.
In general, the costs of extreme weather are likely to rise meaning that incident reports are going to become all the more important in the future. Storm damage investigators are among the best people to ask if you want to understand what we’re up against.
Three days before Christmas 2019, Horton and her husband drove straight towards the path of destruction left by the Surrey tornado. He took the wheel while she made notes and observations. When they arrived on scene, it wasn’t long before they spotted evidence of a tornado – a 100-tonne oak tree, felled across a road. Horton met a couple whose roof had suffered significant damage. A downpour had destroyed the contents of their attic. They were very upset, she remembers. “That’s one of those moments where you go, ‘OK, this is people’s lives, it’s not just a scientific investigation’,” she says.
She also heard from King about how the tornado had crashed through the fields next to her stables. It had whirled a container around in circles above a fallen rider’s head, pulled down fences and uprooted multiple trees. King says she has spent about £10,000 to date on repairs – though there are still more to do. Her insurance didn’t cover any of it.
Horton’s fieldwork lasted a total of five days during December 2019 and January 2020. Her study, compiled with two co-authors, has since been published in the journal Weather. TORRO says that one of the main aims of site investigations like this is to establish as best as possible the true extent of damage caused by a tornado. There could also be lessons for the future. “We do need to be prepared for more extreme events as we go forward, I think,” adds Horton.
Studies of tornados are changing our perception of what these weather events can do to buildings, says Gregory Kopp, professor of wind engineering at the University of Birmingham. “The challenge with tornados is that we don’t know the wind speeds near the ground at all,” he explains. “So we assess it forensically from the damage caused.”
Meteorologists can glean some data from weather radar and satellite imagery but Kopp says there’s little substitute for inspecting the trails of destruction that tornadoes leave behind. The pandemic has made that fieldwork challenging but Kopp and colleagues have continued site visits wherever possible. “We use drones as well to capture very detailed data when we can,” he says.
Such imagery is merged into 3D models, which are then pored over by machine learning algorithms that measure the damage. This process can reveal valuable, fine-grained information about the size or intensity of the tornado. And wind tunnel tests probe the sturdiness of different materials or structures.
Specialist analysis of storm damage has all kinds of uses and is sometimes important for verifying insurance claims, for example. Richard Gregory, a forensic structural engineer at consultancy EFI Global, explains that his job often involves determining whether a collapsed structure had been poorly maintained prior to a storm, since that can affect whether a claim is successful or not.
Rot or bad connections in a barn, for example, can lead to roof spread, which exerts significant pressure on the outer walls. A storm can simply finish the building off. “It loses that connectivity and eventually it all collapses like a pack of cards,” says Gregory.
He adds, though, that it would be “unrealistic” to expect most architects and building engineers in the UK to harden their designs against tornados, since they are currently so rare.
In many places around the world, ever greater stresses are being placed on buildings by volatile weather. Flash floods, storms, tornados and hurricanes all challenge the structural integrity of properties.
For 25 years, Scott Nacheman, practice leader of the Major Loss Group at forensic engineering company Envista Forensics, has documented the effects of storms on buildings. “There definitely has been a change in the magnitude and frequency of extreme weather events,” he says.
Hurricanes and tornados in the US can be notoriously destructive. The way they shred buildings into pieces reveals the vulnerability of human-made structures – and why preparing for extreme events is so important. Tornados are far from the only threat. Nacheman mentions Hurricane Ike, which struck the Greater Antilles islands and North America in September 2008. The effect on Houston, Texas, he remembers, was atrocious.
“There were a number of locations where we had roof systems that had failed due to essentially suction,” Nacheman says. “Wind forces passing over them, creating negative pressure and lifting those steel roof systems off of buildings.”
In recent years, one of the factors behind updates to various US building codes, which determine minimum levels of resilience, has been the results of detailed investigations into the storm damage, says Nacheman.
Kopp agrees that storms sometimes prompt a change in how communities prepare for future weather events. In July, a tornado struck the Canadian town of Barrie, damaging 150 homes. Kopp saw the aftermath for himself. “Canadian houses aren’t really designed for strong wind,” he says. He and his colleagues told locals that they ought to install hurricane straps for the future – simple metal connectors that strengthen timber framed roofs. A city councillor is currently calling for the deployment of these straps in Barrie.
Kopp says that a better understanding of tornados could also improve meteorologists’ ability to give people timely warnings before they strike. Even an extra minute or two’s notice might provide the time needed to take cover.
Whether tornados will get worse in the coming decades remains unknown, though there is some evidence to suggest that their patterns of occurrence may be changing. “Part of this forensic work is to help understand those changes,” says Kopp. “We’re trying to do that and others around the world are as well.”
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This article was originally published by WIRED UK
