High-intensity tropical cyclones have been moving closer to coasts over the past 40 years, potentially causing more destruction than before.
The trend of tropical cyclones – commonly known as hurricanes or typhoons – increasingly moving towards coasts over the past 40 years appears to be driven by a westward shift in their tracks, say the study’s authors from Imperial College London.
The risk to some coastal communities around the world may be increasing and that will have profound implications over the coming decades. Dr Shuai Wang
While the underlying mechanisms are not clear, the team say it could be connected to changes in tropical atmospheric patterns possibly caused by climate change. The research is published today in Science.
Globally, 80 to 100 cyclones develop over tropical oceans each year, impacting regions in the Pacific, Atlantic and Indian Oceans and causing billions of dollars of damage.
Lead author Dr Shuai Wang, from the Department of Physics at Imperial, said: “Tropical cyclones are some of the most devastating natural hazards in terms of how destructive and frequent they are in coastal regions.
“Our study shows they are likely becoming more destructive as they spend more time along coastlines at their highest intensities. The risk to some coastal communities around the world may be increasing and that will have profound implications over the coming decades.”
Location, location, location
The team analysed global data from 1982-2018 on tropical cyclone formation, movement and intensity mainly gathered from satellite observations. They found that at maximum intensity, cyclones were on average getting 30km closer to coastlines per decade. There were also on average two more cyclones per decade within 200km of land.
These increases did not necessarily mean more cyclones made landfall (reached land). However, the ‘near-misses’ or ‘indirect-hit’ cyclones near coasts can still cause damage, such as Hurricane Sandy in 2012 and Hurricane Dorian in 2019, both of which skirted along the US coast for a considerable time before making landfall.
The paper’s other author, Professor Ralf Toumi from the Department of Physics and Co-Director of the Grantham Institute – Climate Change and Environment at Imperial, said: “We need to understand all aspects of tropical cyclones and this new study shows how their locations are changing. This often gets less attention than changes in their intensity but is at least as important.”
Previously, studies have shown that the maximum intensity of tropical cyclones is found further towards the poles. However, this does not necessarily mean these more poleward storms are more devastating. The new findings show cyclones at maximum intensity are also migrating westward, bringing them closer to coastlines and increasing their potential for damage.
The westward migration appears to be driven by anomalous ‘steering’ – the underlying flow in the atmosphere that carries cyclones along their tracks. The exact mechanism for this enhanced westward steering is unknown, but it may be due to the same underlying mechanism for poleward migration of cyclones as rising temperatures cause atmospheric patterns to shift.
The team will next use climate simulations to determine the underlying mechanism behind these historical shifts and project potential future shifts in tropical cyclone tracks towards global coastal regions.
‘Recent migration of tropical cyclones toward coasts’ by S. Wang and R. Toumi is published in Science.
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Article text (excluding photos or graphics) © Imperial College London.
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