As cities around the world grapple with rising temperatures, extreme heat is now increasingly becoming a major public health threat. This growing risk was brought into focus at the just-concluded 2026 Partnership for Healthy Cities Summit in Rio de Janeiro, Brazil. Big3 Africa spoke with Dan Kass, an expert in environmental health and disease prevention, and Senior Vice President of Environmental, Climate, and Urban Health at Vital Strategies.
Why now? Why has heat become a priority area for Healthy Cities initiatives?
In recent years, attention has turned toward climate change, not just as an environmental issue alone, but as a driver of non-communicable diseases. Globally, excess heat is now recognised as the leading cause of death from climate-related disasters. It is important to understand that heat does not simply kill due to high temperatures. It exacerbates existing conditions like cardiovascular and respiratory diseases, particularly among vulnerable populations.
This growing understanding, combined with the realisation that cities are often significantly hotter than surrounding areas, led to the inclusion of heat as a key area of intervention.
Is there data or evidence supporting this shift in focus?
The decision is strongly grounded in data. Globally, an estimated 500,000 people die prematurely each year due to excess heat. Even more concerning are future projections that the number of dangerously hot days is expected to rise sharply, particularly in equatorial regions.
Additionally, the world is not on track to meet temperature-limiting goals, and climate models now show that harm is increasingly driven by extreme events.
How does extreme heat compare to other major health threats?
To understand heat’s impact, it helps to compare it with other known health risks. Cardiovascular diseases remain the leading cause of preventable death globally, and environmental factors play a major role in triggering these outcomes. Air pollution, for example, is well-studied and known to both cause and worsen heart disease. Heat operates in a strikingly similar way. It places additional stress on the body, increasing the likelihood of death among individuals with pre-existing conditions. In fact, among environmental contributors to heart disease, heat ranks alongside major risks such as air pollution, tobacco smoke, and lead exposure. While it may receive less attention, its impact is substantial and growing, making it one of the most important but under-addressed health threats.
Which populations are most vulnerable to extreme heat?
Vulnerability varies by context, but several groups are consistently at higher risk. For instance, people with chronic illnesses, such as heart, lung, or kidney disease, are particularly susceptible, as their bodies struggle to adapt to temperature extremes. The elderly and infants are also vulnerable due to reduced ability to regulate body temperature. Outdoor workers, including those in construction, sanitation, and markets, face prolonged exposure to heat without adequate opportunities to cool down. Lack of access to clean drinking water further increases risk. Socially isolated individuals, especially those with severe mental illness, are another high-risk group. They may be less aware of the dangers, less able to seek help, and more affected by medications that impair temperature regulation.
What challenges do cities face in addressing extreme heat?
One of the biggest challenges is prioritisation. Cities are dealing with multiple urgent issues, and public health prevention often receives limited funding. Without clear evidence of impact, heat may struggle to gain attention. Another challenge is coordination. Effective heat response requires collaboration across multiple sectors such as healthcare, transportation, education, labor, and more. Many cities lack the systems needed for this kind of integrated planning. Data limitations also pose a barrier. Some cities are still developing the infrastructure needed to collect, analyse, and share health and environmental data, which is essential for informed decision-making.
Against this backdrop, what strategies are cities being encouraged to adopt?
Cities are being guided to focus on three key areas, which are understanding the problem, preparing for emergencies, and reducing heat exposure. First, cities must improve data collection. This includes measuring temperature variations across neighborhoods and estimating the true health impact of heat. Official records often underreport heat-related deaths, as many are attributed to heart attacks or strokes rather than heat itself.
Second, cities need to prepare for heat emergencies. This involves developing coordinated response plans based on weather forecasts and local thresholds. Actions may include issuing public warnings, equipping hospitals, opening cooling centers, adjusting outdoor work schedules, and conducting wellness checks on vulnerable individuals.
Finally, cities can invest in long-term mitigation strategies. For instance, urban areas tend to trap heat due to concrete surfaces and limited greenery. Solutions include increasing green spaces, planting trees, using reflective building materials, incorporating water features, and improving access to cooling systems.
Are these interventions financially feasible for cities, especially in developing countries?
While addressing heat can be resource-intensive, the approach taken is not to fully fund interventions but to catalyze action. Support is provided in targeted ways, such as funding temperature sensors, hiring technical experts, or piloting cooling solutions. These initial investments help cities generate evidence and build momentum for larger-scale funding.
Many effective interventions are low-cost. Public alerts during heatwaves, outreach to vulnerable individuals, and simple preparedness measures can significantly reduce risk without major financial burdens. At the same time, demonstrating the economic cost of heat-related illness, through healthcare expenses and lost productivity, can strengthen the case for long-term investment.
How can cities sustain these efforts despite funding uncertainties?
One key strategy is helping cities quantify the economic burden of heat-related illness. When cities understand the scale of healthcare costs and productivity losses, it becomes easier to justify investment in prevention. Programs like policy accelerators also support cities in developing long-term solutions that embed heat response into governance structures.
At the same time, emphasising low-cost, high-impact interventions ensures that progress does not depend entirely on large budgets. Simple measures like early warnings and targeted outreach can save lives and build resilience even in resource-constrained settings.
