In January 2024, the Central Business District of Cape Town, South Africa, endured a historically brutal day of heat: temperatures climbed to 44 degrees C – the highest ever measured in the city. But on that same day, people in other parts of the city, while still sweltering, were able to catch some relief. “There are certain areas in the city that are naturally hotter, and they tend to experience heat waves or high heat days in isolation from the rest of the city,” said Candes-Lee Arendse, Professional Officer for Climate Change Planning, Risk and Resilience for the City of Cape Town. While plentiful trees, shade and green spaces reduce extreme heat in some neighborhoods, “dense urban areas, like low-income communities and informal settlements, lack tree canopy cover and green spaces,” she added, which increases the intensity of heat that people experience.
Traversing cities like Cape Town, which are facing more and more days of unbearable heat, one might notice these differences intuitively. There’s a clear contrast between spending a blistering day in a park, shaded by trees and cooled by vegetation, and walking through the exposed asphalt landscape of a downtown area. But for cities to fully comprehend their current and future heat risks, and to develop effective strategies to mitigate and adapt to these threats, they need detailed and nuanced data.
In a recent webinar co-hosted by UrbanShift, WRI Ross Center, UN Environment Programme (UNEP) and the Cool Coalition, global and urban experts explored why heat is such a complex challenge for cities to address, and how innovative approaches to data collection and analysis can inform context-specific approaches to tackling it.
The Challenge of Urban Heat
2024 is poised to be the hottest year on record. “We’ve witnessed unbearable heat waves with temperatures going beyond 50 degrees C in many regions and we see the devastating impacts. This is a health crisis; it’s disrupting food systems and straining critical infrastructure,” said Gulnara Roll, Head of the Cities Unit at UNEP. These impacts, she said, most acutely affect the already vulnerable. In urban areas, this crisis is magnified: Cities are heating up at twice the global average rate.
Recognizing the immediacy of this threat, UN Secretary-General António Gutierrez recently issued a call to action on extreme heat. While painting a vivid picture of the all-encompassing threat, he pointed to the need for a special focus on urban areas. “Countries, cities and sectors need comprehensive, tailored heat action plans based on the best science and data,” he said. While heat is a universal challenge, tackling it effectively requires specificity. Cities have a wide toolkit from which to draw to cool themselves down, but what elements they implement and how effective they will be depends largely on context. That is precisely where data comes in.
Designing Data-Informed Approaches to Heat
To understand the essential role of data in cities’ efforts to address heat, let’s return to Cape Town. In partnership with WRI Ross Center’s Data for Cool Cities initiative, funded by Google.org, Cape Town is undertaking an extensive effort to gather a range of detailed data on temperature and thermal comfort: a metric that not only considers air temperature but other factors like surface reflectivity, shade and airflow to determine the cumulative impact of heat on the human body. Assessing urban heat through the lens of thermal comfort enables cities to grasp a more nuanced and actionable understanding of their citizens’ heat risk. But to arrive at this metric, cities need to be able to gather and synthesize a broad range of data.
For the Cape Town Central Business District – where temperatures spiked to 44 degrees C in January 2024 – WRI Ross Center produced detailed datasets modelling thermal comfort in the neighborhood over the course of a day. At 3 pm, for instance, with the sun striking from overhead, the buildings cast little shade, leaving most of the district exposed and scalding. “We can really see the fact that each land use area has a distinct curve of how it absorbs and re-releases heat over the course of an afternoon,” said Ruth Engel, Environmental Health and Extreme Heat Data Scientist at WRI Ross Center for Sustainable Cities. “We can drill down to a very local level to understand what it means to stand in a particular space, and then we can translate that back to urban features.”
WRI Ross Center works closely with cities around the world to understand their heat challenges and action plans. Over the course of interviews with officials from environmental, urban planning, climate action and public health divisions across 50 cities, WRI Ross Center Data Product Manager Saif Shabou ascertained that cities have two primary needs for heat-related data: “[Cities] want to know how to prioritize areas for planning effective cooling infrastructure, and they also want to be able to build scenarios for simulating the cooling benefit of different urban interventions that they can implement.” WRI’s Data Lab and WRI Ross Center are working to develop a heat-resilient infrastructure data platform that can help cities build and explore potential heat resilience scenarios and communicate the rationale behind mitigation projects they pursue.
How Cities Are Already Responding to the Heat Crisis
When it comes to extreme urban heat, “the bottom line is that we cannot air condition our way out of this problem,” said Jaya Dhindaw, WRI India’s Director of Cities. Around the world, cities are exploring and implementing solutions to cool themselves down and equitably equip residents with tools to empower themselves against the challenges of urban heat.
In Indian cities, where around 80% of the workforce is informally employed and consequently more exposed to the elements, and where up to 47% of people are vulnerably housed in slums, governments and organizations are exploring both responsive and proactive approaches to heat. To meet immediate health and safety needs, cities are building cooling shelters to provide residents with respite and hydration. In Jodhpur, the city recently unveiled a net-zero shelter equipped with misting fans, solar panels and a wind tower that passively expels hot air and ushers in a cooler breeze. Alongside these near-term efforts, Indian cities are doubling down on efforts to use urban greening and nature-based solutions to improve resilience to extreme weather events like heat waves and floods. “There’s a whole movement going on across the world called ‘de-paving,’ where people are looking at making their surfaces permeable and digging out surfaces which are very heavily concretized,” Dhindaw said.
Halfway across the world, Medellín, Colombia, is already showing the benefits of investing in urban greenery. The city’s renowned Green Corridors program, introduced in 2016, created an interconnected network of over 30 major streets lined with trees, vertical gardens and planted areas, said Esteban Jaramillo Ruíz, Natural Resources Deputy Secretary for the city of Medellín.
With this concerted effort to add greenery along major streets, the city was able to accomplish a range of outcomes at once: Both temperature and pollution rates have fallen around the corridors and, as a result, the number of cycling and walking journeys along them have increased. Over the course of the project, the city trained 107 people from disadvantaged communities as gardeners and employed 2,600 more workers. For Medellín, Jaramillo said, green corridors are just one element of the city’s efforts to embrace nature-based solutions: They are also exploring green roofs and cultivating endemic species in parks and green spaces across the city.
The Global Movement To Tackle Heat
While cities pursue their own solutions to heat, Eleni Myrivili, Global Chief Heat Officer at UN-Habitat and Nonresident Senior Fellow at Arsht-Rock, highlighted the importance of cities and leaders tapping into the growing global movement to combat heat. The UN Secretary-General’s recent call to action on extreme heat, Myrivili said, not only sounds the alarm on the need for concerted efforts – it also shares several important resources for cities to strengthen their work. Among them are the International Labor Organization’s new guidelines on protecting workers amid rising heat and the World Health Organization’s in-depth work on heat’s impacts on human health.
Through efforts like the Global Cooling Pledge and the Cool Coalition, UNEP offers direct support to cities on heat mitigation and opportunities to tap into networks of practitioners advancing effective solutions. Networks like the Adrienne Arsht-Rockerfeller Foundation Resilience Center, which support urban resilience efforts, convene the first-of-its-kind “Chief Heat Officers” network and offer resources like the Heat Action Platform that cities can use to learn more about effective mitigation strategies. Other global networks, like C40, ICLEI, Global Covenant of Mayors and more, can offer cities direct support with climate action and resilience planning.
It is vital for cities to realize that while heat is experienced at the level of the individual, pathways for action are unfolding across levels of government and across the whole world. By connecting globally, cities can equip themselves to act locally, urgently and effectively against this growing challenge.
WRI Ross Center experts are conducting a survey to better understand heat-related challenges facing cities. If your city is interested in joining the Data for Cool Cities initiative and contributing to WRI Ross Center’s growing knowledge of urban heat, please fill out this survey. Our Data and Tools team will be in touch to explore potential collaboration.
A version of this article originally appeared on ShiftCities.org.
Eillie Anzilotti is Communications Lead for UrbanShift at WRI Ross Center for Sustainable Cities.
