Heat Watch Cape Town

Impervious Surfaces Dense, built-up materials like buildings and pavement tend to concentrate and reemit the sun’s energy as heat throughout the day and night-time; we expect to see areas with greater amounts of impervious surfaces contribute to more significant heat islands. From the regional perspective of Cape Town, we see most sub-places feature high amounts of impervious cover; the temperature gradient from north to south that may dominate the local effects of land cover at this scale Examining each sub-area individually may help to isolate patterns between land cover and heat.

Population Density Examining population density in regards to heat can help us determine the number of people who are exposed to various levels of heat. In this analysis, we summarized the number of people within each subplace with the resulting temperature from the afternoon map. The map below shows a mixed pattern between temperatures and population density; the scatter plot to the right displays how many people are exposed to five quintiles of the afternoon temperatures.

To further capture the experience of heat in South African cities, volunteers also conducted a photo-mapping activity at various locations throughout the campaign day. Using thermal imagery cameras attached to their smartphones, volunteers visually investigated surface temperatures and noted physical and social qualities of the surrounding environment. They then recorded their observations at each site and responded to a series of prompts through the platform Survey123. With these data CAPA generated a web-map featuring the responses below.

Based on the images and responses captured during the photo-mapping exercise, we note several initial findings:

• Based on FLIR images and survey responses, many high density areas in Cape Town display very little tree cover and small, non-shade providing vegetation if any.
• Residents that reported cooler temperatures in their yards are surrounded by abundant tree cover.
• Crowding and insufficient building material was reported in areas with dense informal settlements toward the northern portion of the study area.
• Frequent suggestions to improve conditions include:
  • Planting trees and vegetation.
  • Changing building material / infrastructure upgrades.
• On very hot days like campaign day, survey respondents reported few people outdoors, and those that did exhibited discomfort i.e. sweating, covering faces, looking fatigued.

The results of Heat Watch Cape Town provide new insights into the increasing risk extreme heat poses to the city and surrounding areas through descriptions of ambient heat and relationships with the built environment and human experience. As snapshots-in-time, they describe present conditions of heat in these cities and serve as a basis of evidence for taking action on heat.

The primary takeaway from these activities is that on a given hot day, heat is not evenly distributed within Cape Town, expecially in the afternoon: in the morning, a temperature differential of 11°C was measured; in the afternoon, 16.3 °C, and in the evening, 13.8°C. Depending on where people live, work, travel and recreate in these cities, they may experience disparate levels of exposure to heat, and face higher risk of heat-related health conditions.

Together these distributional descriptions identify areas and locations across Cape Town that are experiencing disparate levels of urban heat. Broad physical interventions like increasing shade cover and decreasing the amount of heat-retaining materials like concrete and asphalt are likely to mitigate the effects of urban heat. Integrating the results with social vulnerability information will help to identify the populations most in need of awareness building and social safety net solutions.

As the work on heat progresses in Cape Town, collaborative efforts such as Heat Watch that involve community, local researchers, and supporting partners will be essential for effectively managing risk and enhancing resilience to climate change. As a first step to continuing the impact of this project, the CAPA and World Bank team recently met with the Cape Town to review these campaign products and consider direction applications of the maps towards municipal climate adaptation efforts. Potential directions included further research on heat and the transportation sector, integrating high-resolution information into early warning and heat advisory systems, increasing awareness of the relationship between heat and trees, and protecting existing trees during development. In addition, examining variations at smaller, neighborhood scales will help to apply the Heat Watch data more locally.

Heat Watch South Africa was conducted by CAPA Strategies in partnership with the World Bank Group and local implementation partner “Community Organisation Resource Center (CORC)”. We would like to especially thank local campaign organizers Charlton Ziervogel, Blessing Mancitshana, Ntombovuyo Sibutha and the entire CORC team. The insights gathered through Heat Watch Buffalo City would not have been possible without the local volunteers -- thank you to all for your time and energy.

To provide broad access to the results, the summary report and datasets are available  here .