Durban — Weather experts say that heavy rainfall which results in flooding has become the norm in the province of KwaZulu-Natal during the summer season.
Agro-meteorologist Professor Alistair Clulow from the University of KwaZulu-Natal said that rainfall was typically experienced over the summer period due to convective thunderstorms.
“The amount of rainfall we experience is a very complex interplay that is part of global meteorology including latitudinal shifts in the Intertropical Convergence Zone ... amplified by climate change and fluctuations in the Southern Oscillation Index, which defines El Nino or La Nina conditions.
“The recent extreme weather we have seen in KZN on Wednesday has been explained to be a combination of warm moist air coming from the tropics and cooler air coming in from a ridge of high pressure south of South Africa. From a three-dimensional perspective, a steep upper air trough came in from the west. This system was at a height of about 5 500 metres above sea level. The combination of the upper air trough, surface trough and ridging high pressure system south of South Africa resulted in very unstable weather conditions,” he said.
Clulow said that unstable weather conditions meant the rapid development of storm clouds, condensation, releases of latent energy and all the aspects of storms that have been experienced.
While severe storms and tornadoes have been typical of the weather in KZN, a combination of many factors has exacerbated the problem over recent times including climate change, meaning there was more energy in the atmosphere to drive temperature and pressure differences, resulting in unstable conditions and violent storms.
“We have known for decades that the symptoms of climate change are more extreme weather, more often. We should not attribute a single event to climate change, but we can attribute a general increase in the frequency of extreme events as likely to be a result of climate change,” said Clulow.
He said that in addition, the population had grown.
Clulow said that the weather systems that had been experienced were associated with lightning, intense rainfall and high wind speeds.
The storms being experienced typically included lightning, and the intense rainfall meant that there was not sufficient time for the water to infiltrate, and it therefore ran over the surface, accumulating in rivers.
He said Cyclone Belal that wreaked havoc in Mauritius last week and tropical Cyclone Alvaro that made landfall in Madagascar earlier this month were unlikely to affect the South African coast.
“The cyclones typically do not reach as far south as South Africa and there is a low chance of them affecting us. However, with climate change and movement in global meteorological systems it is likely that there is an increase in the frequency of tropical cycles impacting South Africa and certainly African countries to the north of us,” said Clulow.
South African weather services forecaster Wisani Maluleke said that KZN could expect a 30% chance of showers and thunderstorms in the afternoon on the western half of the province today.
He said a 30% chance of showers and thunderstorms was expected across the province on Monday, while a 30% chance of showers and rainfall was expected in the morning and evening of Tuesday. On Wednesday, there was a 30% chance of showers and rainfall in the afternoon.
Maluleke said that the inclement weather conditions witnessed last week were normal during summer.
“We are still in the summer season so it is normal to experience this kind of weather during this time of the year.
“If you check every year in the province, there will be events like these where we have flooding.
Thirteen people have reportedly died following floods in the province last week.
Bridges, key infrastructure, roads and electricity systems were destroyed, affecting areas in eThekwini Metro and the districts of Ugu, Ilembe, King Cetshwayo and Umkhanyakude.