By midday in Mathare, a densely populated informal settlement in Nairobi, Kenya, the sun beats down on the tight rows of wooden stalls and corrugated metal rooftops. At an elevation of 5,889 feet (1,795 meters), Nairobi has long been known for its temperate climate. But in recent years, heat has become an unavoidable issue — especially in informal settlements, which can be up to 5 degrees C (9 degrees F) hotter than the rest of the city.
In Mathare, local street vendors selling fresh produce and fish once relied on a steady stream of customers throughout the day. Now, the heat often spoils their goods before they can be sold.
“If they don’t have a quick market, they’re seeing a lot of losses by the end of the day,” said Michelle Koyaro, program associate at Slum Dwellers International (SDI) Kenya. Some vendors have started selling in the cooler evenings, but fewer customers come out during those hours. Instead, after long days under the hot sun, sellers head home with headaches and lean earnings.
In cities around the world, extreme heat is no longer a short-term event or seasonal disruption. It’s a growing daily pressure that is reshaping how people live, move and work — and it’s getting worse.
Heat is a well-documented threat to health. According to the World Health Organization, nearly 500,000 people die from heat-related causes each year — a number expected to rise by 50% by 2050. But the crisis goes beyond public health: Heat is also undermining economies, infrastructure, social systems and the well-being of residents in cities around the world.
As temperatures rise, cities are confronting a complex, urgent and interconnected challenge. Heat is not an isolated issue. To adapt effectively, cities must understand how rising temperatures are transforming and threatening multiple aspects of urban life — and recognize they’re not alone in the challenges they face.
Already, more than 350 cities worldwide are grappling with summertime temperatures above 35 degrees C (95 degrees F), and that number will only grow as the climate warms. Cities have enormous potential to learn from one another — what has worked, and what hasn’t — as they adapt to heat and work to mitigate its worst impacts.
Here, through the lens of four essential sectors — health, transportation, jobs and economic productivity — we examine the cascading impacts of heat in cities and offer tangible, scalable solutions that cities can use to develop effective, far-reaching strategies.
Health: Prioritizing Well-Being as Cities Heat Up
Anyone who’s spent time outside on an extremely hot day knows how draining it can be — headaches, dehydration, fatigue and trouble concentrating. But what happens when this exposure is constant — not just for a few hours, but every day? The effects on the body can shift from uncomfortable to dangerous.
Prolonged heat exposure can strain vital organs like the heart and kidneys, disrupt sleep, cause mental stress and worsen chronic conditions such as asthma and cardiovascular disease. Researchers project that long-term heat exposure will become the norm, with parts of Africa, South Asia and Latin America among the most affected.
Extreme heat poses a particular challenge to low-income urban residents, who may live in poorly ventilated homes or work outdoors. Over the course of a day, prolonged heat exposure compounds the risks they face. Children, pregnant people and older adults are especially vulnerable.
Addressing these risks requires a multifaceted approach that works in both the short and long term. In the immediate term, cities need to invest in interventions that lower exposure in the places where people spend time or provide options for escaping the heat. Early warning systems, like those in Athens and Buenos Aires, alert residents to upcoming heat waves and offer practical guidance for staying safe.
Public cooling centers — community spaces with air conditioning or fans and drinking water — can reduce immediate health threats by providing temporary refuge. In Jodhpur, India, which is coping with intensifying heat waves, a net-zero cooling shelter equipped with misting fans, solar panels and a wind tower that passively circulates cooler air provides relief to those who must be outside. Inside, temperatures are up to 12 degrees C (21.6 degrees F) cooler than just outside the door.
In Phoenix, Arizona — the hottest city in the United States — a 24/7 cooling center drew thousands of visitors during 2024’s hottest period, including unhoused residents, who are far more likely to die from heat-related causes. This site, along with the city’s other heat preparedness efforts — such as connecting people to resources for air conditioning repairs — contributed to a 20% drop in heat-related emergency calls. Even brief breaks in cool spaces have been shown to reduce physiological and cardiovascular strain.
But cooling centers alone aren’t enough. Cities must also invest in long-term strategies to expand heat-resistant housing and reduce urban heat in places where residents spend time at school, at work or in transit. Increasing urban greenery and tree cover can lower peak temperatures by up to 5 degrees C (9 degrees F).
Health Impact Solution: Understanding and Acting on the Local Relationship Between Place, Population and Heat Health
Emergency measures aren’t enough. Building long-term urban resilience means identifying and addressing who is most vulnerable. WRI is partnering with the Salud Urbana en América Latina (SALURBAL) initiative — a collaboration of research institutions across Latin America and the United States, coordinated by Drexel University — to study how social and environmental factors influence heat-related health outcomes in two Brazilian cities: Campinas and Belo Horizonte. The goal is to help cities design targeted, equitable interventions, such as expanding nature-based solutions and prioritizing health care.
In informal settlements, where rooftops are often made from heat-trapping materials like corrugated steel, participatory upgrading programs — which directly involve residents in improving their own living conditions — can substantially boost resilience and health. For example, research shows that adding cool roof solutions, such as vegetation or reflective surfaces, to informal homes can reduce residents’ exposure to extreme heat by up to 91% over the course of a year.
Longer-term efforts to reduce heat exposure and related health risks must be grounded in data that includes the potential for effective solutions. Studies can reveal not only how hot certain areas get but also the many ways communities face heat-related burdens. This helps cities prioritize where to focus resilience measures.
Transport: Keeping Cities Moving in a Hotter World
An essential part of urban life is the ability to move safely and efficiently through the city. As more cities embrace sustainable, zero-carbon transport options like electric buses, cycling and walking, extreme heat is prompting people to stay home or rely more on cars.
A 2024 study of several U.S. cities, including Chicago, Atlanta, Houston and New York, found that on extremely hot days, public transportation trips decline by an average of 50% as people opt for air-conditioned vehicles. But for many without access to cars, there is no easy escape. Without adequate shade or heat protection at transit stops — a widespread problem in many cities — public transport users face greater risk of heat exposure. In Los Angeles, for example, only one-quarter of bus stops provide shelter despite frequently high temperatures.
Bicycle use also drops during extreme heat. In New York City, an analysis of bike-share ridership found that usage declined by about one-third on days when temperatures exceeded 26 to 28 degrees C (79 to 82 degrees F). Meanwhile, extreme heat can intensify air pollution. This means that when people avoid sustainable transport options on hot days, it contributes to worsening air quality and compounds health risks for the city’s most vulnerable residents.
Cities must not only promote sustainable transport modes but also ensure that people can travel safely and comfortably, regardless of income or ability. For public transit like buses and light rail, increasing service frequency reduces the time people spend exposed to dangerous heat while waiting. Installing shade structures at transit stops and planting trees or green walls can also help ease heat burdens in these high-use spaces.
Green corridors — connected strips of green space such as trees, gardens or parks that link different parts of a city — can also create a network of cooler streets for people to cycle or walk on hot days. Medellín, Colombia, has demonstrated the benefits of integrating urban greenery with sustainable mobility. Since 2016, the city’s Green Corridors program has linked more than 30 major streets with tree cover, vertical gardens and green spaces. Analyses show the corridors reduce temperatures by an average of 2 degrees C (3.6 degrees F), lower air pollution levels and encourage more trips on foot or by bike.
Similarly, studies in both Houston, Texas, and Shenzhen, China, have found that tree canopy coverage and eye-level greenery support higher rates of cycling.
Jobs: Preparing the Urban Workforce for Extreme Heat
Heat’s impact on city economies is layered. For informal or hourly wage workers, heat waves can reduce productivity, compromise work safety and lower incomes. In Dhaka, Bangladesh, for instance, manufacturing sectors such as garment and construction are already seeing income losses of around 10% as heat exposure hampers workers’ ability to produce efficiently in warehouses, outdoor work sites or manufacturing facilities. When a worker produces less, they earn less. At the sector level, slower production reduces revenue, which dampens the local economy as a whole.
The Atlantic Council’s Climate Resilience Center notes that women, especially those in informal jobs, are particularly vulnerable to heat-related impacts. In New Delhi’s textile markets, female garment workers spend their mornings sewing and packing bales of clothes for transport using open carts or rickshaws. However, because they aren’t allowed to deliver parcels until the afternoon, they must move during the hottest part of the day — often with their children in tow — exposing themselves to high levels of heat stress.
To build heat resilience across urban economies, cities need to prioritize both individual and system-level safety. Governments can create policies that protect workers on the job. California’s 2022 Heat Action Plan, for example, outlines recommendations to support safety for both outdoor and indoor workers at increased risk of heat impacts. Meanwhile, a 2024 report from the International Labour Organization offers a suite of heat-related actions that local and national governments can adapt into policy, including mandated breaks, enforcement of cooling and ventilation standards in buildings, and regulations on maximum temperatures workers can be exposed to on the job.
Cities must also engage with the workers most at risk. In Freetown, Sierra Leone, Chief Heat Officer Eugenia Kargbo has led efforts to install weather-resistant and UV-protective canopies over vendor stalls — many of them run by women — to shield them from the city’s heat.
Economic Productivity: Heat Runs Up Systemic Costs
Extreme urban heat doesn’t just affect individuals; it also carries a heavy price tag for cities as a whole. In the Los Angeles metro area, heat-driven productivity losses are estimated at $5 billion a year.
Cities also face rising energy demands, infrastructure damage and increased public health systems expenses. A World Bank report estimates that in Bangkok, a 1 degree C (1.8 degree F) temperature rise could increase energy costs by 17 billion baht (around half a billion U.S. dollars). A 2023 heat wave in Houston caused roads to expand and buckle, leading to costly repairs for both the city and state. In London, a 2022 heat wave exposed a different type of infrastructure vulnerability: As temperatures spiked at 40 degrees C (104 degrees F), data centers at two National Health Service hospitals failed, causing weeks of delays in patient care and costing the system £1.4 million to fix.
If cities want to safeguard their economies against heat-related losses, investing in wide-scale resilient infrastructure — such as green corridors, cool roofs and pavements, and strategic shade structures — is essential, along with targeted efforts to protect workers. There is no single quick fix to shield urban economies from heat, but every measure that protects people’s health, maintains transit systems and supports productivity will collectively strengthen the economy.
Building Resilience in a Warming World
Extreme urban heat is reshaping the very systems that keep cities functioning — from health to transportation to livelihoods. Building resilience at both the individual and system levels — from the street vendors of Mathare to the bus lines in Chicago — is essential to protecting well-being, sustaining economic stability and ensuring cities can thrive in a hotter world. As they plan for heat resilience, cities can learn from each other’s challenges and successes to prioritize effective, timely solutions.
