On Cape Town’s hottest days, the ground air temperature varies by 16.3°C across different parts of the city, with built-up CBD and industrial areas being the most affected.
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This finding emerged from a multi-stakeholder citizen science study involving the City of Cape Town, the World Bank, and community organisations.
On a scorching February day, nine teams of data collectors drove through a 200m2 area of Cape Town with temperature measuring devices attached to their vehicles. The routes were repeated in the morning, afternoon, and evening.
The study aimed to measure the near-surface air temperature in Cape Town across diverse land-use categories, including informal settlements, industrial zones, the CBD, and leafy suburbs.
At a briefing in Cape Town about the study’s results, Bradley Riley, a disaster risk management specialist at the World Bank, emphasised the importance of understanding extreme heat dynamics at a localised level, as extreme heat affects human health, food systems, labour productivity, and infrastructure.
‘Extreme heat and heatwaves are a growing concern globally. In the past few decades and the past few years, there has been a rapid and significant increase in the number of hot days and heat-wave days around the world,’ said Riley. He explained that urban landscapes absorb and reflect more heat than natural landscapes, causing urban areas to experience temperature increases at double the rate of rural areas.
Temperatures can vary significantly within a city based on factors such as foliage cover, urban shading, and proximity to the sea.
According to a data dashboard published in May, which shares insights from the study, higher afternoon temperatures were recorded in the northern regions of the city compared to the southern regions. Afternoon temperatures were measured between 2pm and 3pm on 28 February.
The hottest areas of the city were in the CBD and Woodstock, while the coolest areas were on the Cape Flats, likely benefiting from a sea breeze, Riley explained.
In the morning, between 6am and 7am, there was an 11°C temperature difference between the warmest and coolest regions of the city. Between 6pm and 7pm, there was a 13.8°C difference.
Similar studies were conducted in Tshwane and Buffalo City in the days following the Cape Town study.
Tshwane showed a 6.1°C variance, while Buffalo City had a 17.4°C variance.
The potential impact of extreme heat on urban communities is varied and significant. Riley linked extreme heat to reduced labour productivity, as extreme heat can impair workers’ ability to function. He cited studies suggesting that an increase in extreme heat days could result in significant GDP decreases.
Daniel Sullivan, the director of risk and resilience at the City of Cape Town, noted that extreme heat days alter the demand for city infrastructure such as water.
Dr. Thandi Kapwata, a specialist scientist at the South African Medical Research Council, stated that her study found heatwaves significantly impact mortality in South Africa. She noted that provinces with the highest average heat were the most resistant to this. Extreme heat is also linked to food security issues, infrastructure damage, and other extreme weather events.
Cape Town Deputy Mayor Eddie Andrews emphasised the need for an ‘evidence-based approach’ to respond sustainably when implementing solutions for Cape Town’s shared future.
He supported the citizen scientist-based data collection approach, as it helped raise awareness about the initiative and its goals among community members.
Sullivan mentioned that the city would use the data for planning its service responses and urban greening initiatives.
‘This work has been instrumental in trying to understand the concept of heat risk and how that manifests across Cape Town, which areas are most vulnerable and where we need to double down our efforts in terms of a response.’
‘We need to understand where services need to be expanded during times of heat stress.’
There was consensus at the presentation that urban greening is one of the most impactful ways to address extreme heat in the city.
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Picture: Mark Skinner / Gallo Images
