Coast KZN

18 Jan 2022

Local and international geologists warn that strong tropical cyclones could hit KZN in the future

(Daily News: IOL) Picture: MODIS image captured by NASA’s Aqua satellite, Public domain, via Wikimedia Commons. Cyclone Idai in 2019 was one of the latest intense tropical cyclones to make landfall along Southern Africa.

Durban – Geologists have warned that tropical cyclones could hit KwaZulu-Natal in the future. In recent years, the province has experienced the effects of tropical cyclones which swept through Mozambique. The most recent being tropical cyclone Eloise in January 2021.

In a statement, the University of KwaZulu-Natal (UKZN) said an international study led out of the university and published in the journal Nature Geoscience, has used state-of-the-art techniques to investigate seabed sediments, revealing that severe tropical cyclones made landfall on the eastern coast of South Africa in the past and that under projected climate change conditions, these damaging phenomena could arise in the future. It said while reconstructions of past storminess exist for the Atlantic and Pacific Oceans, the same cannot be said for much of the Indian Ocean, making this research important in filling a gap in knowledge to help understand what could happen under changing climate conditions and rising sea levels.

UKZN Marine Geology Research Unit head Professor Andrew Green led the research with Honorary Research Professor Andrew Cooper and Shannon Dixon from UKZN, Professor Matthias Zabel and Dr Annette Hahn from the University of Bremen’s Centre for Marine Environmental Sciences in Germany, and Dr Carlos Loureiro from the University of Stirling in the UK.

The geologists examined the sediment record from the seabed off the coast of Durban and found that there was a period – under higher sea levels – when storms were much more extreme than they are now.

Green said: “We found distinctive sediments that were deposited by severe storms that struck the coast between approximately five and seven thousand years ago. “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 and this allowed tropical storms to travel further south than they do presently.

Damage to the Durban coastline in 2007 from the biggest recorded storm in the history of South Africa’s East Coast. The article considers such a storm to be significantly smaller than those experienced in the past and consequently predicted for the future. Credit: JAG Cooper

University of Stirling physical geography lecturer, Loureiro 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.

“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,” Loureiro said.

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 like Maputo, Durban and Richards Bay.

Cooper said: “When these storms hit the coast there were no cities, buildings or roads and the coastline was free to adjust in a natural manner.

“If such a storm were to happen now, beachfront infrastructure would be devastated and the rainfall associated with tropical cyclones would cause serious flooding.”

UKZN said the research gave impetus to the need to evaluate hazards along South Africa’s east coast that would be more vulnerable to tropical cyclones making landfall.

The work also affirmed the calibre of work coming out of UKZN in marine geology.

“We have established UKZN as a global centre of excellence in marine geology, and with our excellent facilities and international collaboration networks, we are making major breakthroughs in understanding the coast and sea.

“This is the first time this kind of evidence has been used to reconstruct past periods of storminess anywhere in the world,” said Green.