- Cape Town experienced more rain than usual in the first 18 days of June 2023, making it one of the wettest Junes since 1990
- The heavy rains were mainly caused by a higher-than-average frequency of cold fronts
- Severe rainfall is likely to become more common due to climate change; but floods are not unusual in Cape Town, and they have become more damaging because of the increase in the population
- For example, 189 informal settlements were created in the city, between 2021 and 2022, many of them in high-risk areas
For the past two years, Cape Town has had very wet Junes. In the first 18 days of June 2023, 128mm of rain fell at the airport monitoring station, according to data from the South African Weather Service. That’s just 25.1mm short of June 2022’s 153.1mm, which was the highest recorded since June 1994, when 229.4mm fell on the city.
Cape Town usually gets most of its rain in the winter months of June, July and August. But records show that this year there have been more heavy rainfall days than usual.
A heavy rainfall day for Cape Town would be one with more than 17mm of rain, said Dr Andries Kruger, the chief climate scientist at the South African Weather Service.
‘Historically only 10% of rain days recorded totals above this figure [17mm]. For Cape Town, heavy rainfall days are well above the average of 10% expected,’ said Kruger.
Even in March, much more rain than usual was recorded, SA Weather Service data shows.
What causes the heavy rains?
‘The heavy rains this year were mainly caused by a higher-than-average frequency of cold fronts, with stronger and more frequent influxes of cooler moist air from the south,’ said Kruger.
Most severe weather events in the Cape Town area are caused by strong cold fronts with accompanying heavy rains over short periods and strong winds.
Cold fronts normally pass over the area about once every six to seven days. ‘But it sometimes happens that a series of frontal systems move over the southern parts of the country at a higher frequency,’ he said.
There were many strong cold fronts on top of one another in June, Annette Botha of Vox Meteorology, explained in a Cape Talk interview.
Also higher-than-average rainfall in May (78.1mm) saturated the ground, said Botha, making it less effective at soaking up the rain.
‘The past months have had rains accumulating to well above the long-term average and would have some influence on the ground saturation,’ said Kate Turner, a senior forecaster at the SA Weather Service.
Are heavy rains having a bigger impact?
‘Through media reports and climate and weather analysis it has become apparent that the impacts of extreme weather events, specifically high rainfall events and flooding, have been increasing in the Cape Town metropolitan area’, said Kruger.
This is due to two main factors, he said. ‘The first is that the population of Cape Town has increased significantly over the last number of decades (therefore the impacts of extreme events have become more severe) and secondly the likelihood of extreme rainfall events has been increasing.’
In the past 10 years, Cape Town’s population has increased by about a million people (or by roughly 20%) – from a population of 3.7-million in 2011 to around 4.5-million in 2021, according to StatsSA.
As the population increases, more houses, roads and other infrastructure are built which affects the ability of the ground to soak up rainwater. It also reduces the number of natural spaces that act as sponges and reduce flooding.
Between March 2020 and December 2021, 186 new informal settlements, or more than 69,000 new structures, were created in the city, said James Vos, Cape Town’s acting mayoral committee member for human settlements.
‘More than 60% of these new settlements are considered high risk – situated under power lines, in wetlands, retention ponds and biodiversity protected areas,’ said Vos.
Are heavy rainfall days likely to happen more often?
The Western Cape is actually getting drier and this is confirmed by historical records, said Kruger.
This can be mainly attributed to climate change. ‘The latest Intergovernmental Panel on Climate Change report, confirmed by historical observations, shows a drying trend over especially the extreme western parts of South Africa,’ he said.
‘On the other hand, with a warming atmosphere, the air can hold more moisture [water vapour]. Therefore short-term rainfall episodes are likely to become more extreme, with a probability of higher 24-hour rainfall amounts. The latter observation is backed up by research globally but also for South Africa,’ said Kruger.
Floods are not unusual
This is the second year in a row that heavy rains in June have caused flooding in Cape Town.
Informal settlements in low-lying areas such as Philippi, Strand, Gugulethu, Mfuleni, Masiphumelele and Khayelitsha were among the areas flooded after heavy rains that started on 13 June 2023. Khayelitsha was also one of the areas flooded between 13 and 15 June 2022.
When there are floods in Cape Town, the same areas get affected
- 10 July 2020: Khayelitsha, Philippi, Wallacedene, Mfuleni and Delft were flooded
- 26 July 2016: Flooding displaced almost 10,000 people in Philippi and Khayelitsha
- 16 June 2014: Floods in Khayelitsha, Strand, Vrygrond, Lotus River, Gugulethu, Delft and Philippi
- 15 November 2013: About 18,000 people around Cape Town were affected by flooding
- July 2009: Floods affected 9,000 people living on the Cape flats
- August 2008: Homes are flooded in the Cape flats and informal settlements
What is being done to alleviate flooding?
The City of Cape Town said that part of it’s Winter Preparedness efforts are:
- Sewer jetting to remove built-up sand and other objects to prevent sewers from overflowing
- Clearing stormwater drains, canals, ponds and gullies in flood-prone areas
- Warning people in areas with informal settlements of flood risks
- Increasing the number of beds at homeless shelters to get people off the streets
Despite these measures, homes get flooded.
‘There is no quick fix to this problem,’ said Dr Anna Taylor of the University of Cape Town’s African Climate and Development Initiative.
‘It is very much a systemic problem as many factors drive people to live in risky situations on land not suitable for or designated for housing, and thereby not equipped with adequate public infrastructure like drainage.’
What’s required to fix the flooding problem, said Taylor, includes
- The upgrading of homes to ensure proper foundations, roofs, gutters and drains
- Better catchment and stormwater management
- Access to affordable housing
- Land tenure
- Job creation
- Access to quality education
Vos said the city is helping some affected people relocate and has sent flood kits to alleviate the situation. Flood kits include sheets of metal and plastic sheeting so people can rebuild their homes.
The flooding is not a planning deficiency or land use matter, said Vos. ‘It is primarily due to unlawful occupation on unsuitable land and lack of available land to move hundreds of thousands of people who have unlawfully settled on inappropriate land.’
About 500 hectares of land is needed to relocate people identified to be at risk, he said. ‘Land in Cape Town, due to it being located on a Peninsula, is already scarce.’
Notebook
The data used in the visualisations was supplied by the South African Weather Service and was recorded at Cape Town International Airport/Cape Flats. The amount of rainfall recorded in the city itself is higher, SAWS said. Rainfall figures are collected at different parts of the city by the University of Cape Town’s Climate System Analysis Group.
Data visualisations by Laura Grant and Gemma Ritchie