The coast of KwaZulu-Natal could be pounded by severe tropical cyclones that are likely to cause major flooding and damage to beachfront infrastructure.
This is according to an investigation led by University of KwaZulu-Natal researchers.
The study, published in the journal Nature Geoscience, used state-of-the-art techniques to investigate seabed sediments.
It revealed that severe tropical cyclones made landfall on the eastern coast of SA in the past and that under projected climate change conditions this damaging phenomenon could arise in the future.
While reconstructions of past storminess exist for the Atlantic and Pacific oceans, the same cannot be said for much of the Indian Ocean.
The research is important in filling a gap in knowledge to help understand what could happen under changing climate conditions and rising sea levels.
If such a storm were to happen now, beachfront infrastructure would be devastated and the rainfall associated with tropical cyclones would cause serious flood.
— Prof Andrew Green, head of UKZN's Marine Geology Research Unit
German and British geologists joined the UKZN team, led by Prof Andrew Green, head of the institution’s Marine Geology Research Unit
The team examined the sediment record from the seabed off the coast of Durban and found there was a period — under higher sea levels — when storms were much more extreme than they are now.
“We found distinctive sediments that were deposited by severe storms that struck the coast between approximately 5,000 and 7,000 years ago,” said Green.
“These storms were much bigger than any storm that happened in the 4,000 years since. This has allowed the storm sediments, or tempestites, to be preserved just beneath the seabed.”
The period of increased storminess coincided with warmer sea temperatures in the Indian Ocean which allowed tropical storms to travel further south than they do now.
Dr Carlos Loureiro, from the University of Stirling in the UK, carried out modelling of the storm waves and analysed how current ocean trends and climate projections aligned with past climate conditions.
“This important work demonstrates that the past climate conditions that allowed very intense tropical cyclones to reach the South African coast are very similar to the ones projected now under climate change,” said Loureiro.
“By confirming that these conditions existed in the past, our work provides strong support to recent climate modelling studies indicating that tropical cyclones are likely to migrate poleward in response to global warming.”
At present tropical storms are usually confined to central Mozambique, but renewed ocean warming because of climate change could once again allow them to travel south, with potentially disastrous implications for cities such as Maputo, Durban and Richards Bay.
“When these storms hit the coast there were no cities, buildings or roads, and the coastline was free to adjust in a natural manner,” said Cooper.
“If such a storm were to happen now, beachfront infrastructure would be devastated and the rainfall associated with tropical cyclones would cause serious flooding.”
The team believes the research gives impetus to the need to evaluate hazards along SA’s east coast that will be more vulnerable to tropical cyclones making landfall.
“This is the first time this kind of evidence has been used to reconstruct past periods of storminess anywhere in the world,” said Green.
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