The fast rate at which the raging Table Mountain fire spread was due to strong south-easterly winds and “what could probably be a high fuel load on the mountain”.
This according to North West University (NWU) School of Geo and Spatial Sciences senior lecturer Dr Sheldon Strydom, who explained that fire required three “ingredients” to occur.
“There needs to be fuel available for combustion, a source of ignition and the atmospheric conditions, i.e. weather, need to be conducive to the burning of the fuel. In other words, a warm and dry environment has a higher ‘fire danger’ than a wet and cool environment.”
Two years ago, an article published in The Conversation warned of the risk of fires on Table Mountain due to improper management of the fynbos ecosystem.
“The rate of spread, in terms of fire behaviour once a fire is going, is determined by the available fuel load and weather, as well as less variable factors such as topography and slope angle,” it said.
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Fire behaviour in complex topography could be difficult to anticipate, Strydom added.
“Fires burning uphill tend to move faster than fires burning downhill and, due to the warm air rising off of the fires, can self-accelerate. Since we are at the tail-end of the dry season in the south-western Cape, I think it is also safe to assume the fuel moisture is very low.”
In terms of fuel load, such as a pile of leaves, Strydom said: “There have been cases elsewhere in the world where devastating fires have occurred and spread due to an elevated fuel load. In fire-dependent areas it is very important to manage that fuel load appropriately. If fire is kept out of a fire-dependent ecosystem, then the fuel load can accumulate and once fire is returned, that elevated fuel load can result in a faster rate of spread of the fire,” he explained.
In the Conversation article, the authors, climate scientists, explained that fynbos is the world’s most diverse type of vegetation, even more so than tropical rainforests.
Alien plantations have resulted in infestations of alien trees. Some citizens have been careless with inappropriate construction on the urban edge by building too high up on the mountains.
— The Conversation
“Fynbos is both fire-dependent and fire-prone. The Cape’s incredibly biodiverse fynbos plants need fire to survive and thrive.”
They wrote that the city had encroached ever closer to nature, developing deeper into mountain fynbos.
“Alien plantations have resulted in infestations of alien trees. Some citizens have been careless with inappropriate construction on the urban edge by building too high up on the mountains.
“On top of this, various factors have resulted in a failure to maintain the desired fire regime, particularly of fires at 12-15 year intervals. As a result there has been a dangerous build-up of vegetation — fuel loads — in some places,” they said.
At the time they called for the following action: clear, manage and educate.
“Clear refers to the removal of alien trees. Local residents can join alien clearing groups in their area. Manage refers to the need to support authorities on the Cape Peninsula — such as SANParks — to manage fynbos appropriately. This includes ensuring that, on average, 12-15 year prescribed burns happen.
“And finally, education is needed to ensure that people understand climate variability versus climate change, as well as the relationship between fynbos and fires, so that future disasters can be avoided,” they said.
SA Weather Service (SAWS) senior forecaster Stella Nake said weather conditions leading to the development of runaway fires include hot temperatures, drier conditions, low humidity and strong winds.
“The past week has been generally warm to hot around Cape Town, with daily maximum temperatures averaging between 30 to 32ºC. April 18 started off with calm winds, increasing during late morning. But this time, the fire had started already.
“The maximum temperature reached in Cape Town was 35ºC, Kirstenbosch also 35ºC and Cape Town International Airport 37ºC.”
She said veld fires were not unusual in Cape Town throughout the year if “perfect” weather conditions were met.
“However, during the winter season, when there is sufficient moisture available due to winter rains, the chances of veld fires occurring are very slim, unless severe drought has prevailed.”
