The Unseen Risk: Chronic Heat’s Growing Threat to Public Health

The unique challenge of Southeast Asia and other tropical countries is the combination of high temperatures and humidity levels, along with sustained exposure to these conditions. Many tropical areas experience extreme heat for at least three months of the year (maximum daily heat index greater than 32.2°C/90°F) while recording less than 10 traditionally defined heatwaves over a 33-year period. This demonstrates that traditionally defined heat waves differ fundamentally from chronic heat, which are prolonged periods of elevated temperatures.

Chronic heat exposure has broad and cumulative impacts on health, affecting daily life, worker productivity, wellbeing, and long-term health. Prolonged exposure can cause ongoing heat stress and exhaustion, exacerbate chronic conditions such as cardiovascular and respiratory diseases, increase mental health issues, and lead to chronic kidney disease of unknown origin.

Vulnerable populations are disproportionately affected, including those with poor housing, low income, pre-existing health conditions or occupational exposure. Because these factors often intersect, addressing chronic heat requires long-term, systemic changes beyond short-term emergency responses. By addressing the root causes of vulnerability and prioritizing their livelihoods, communities can be empowered to take control of their own health and well-being, which ultimately enhance the effectiveness of heat management measures.

Metrics such as the heat index and wet‑bulb globe temperature (WBGT) estimate human heat stress: the heat index combines air temperature and relative humidity to approximate how temperature feels to the human body, while WBGT integrates dry‑bulb temperature, natural wet‑bulb temperature, and black globe temperature to comprehensively account for air temperature, humidity, wind, and solar radiation. In the Philippines, the Department of Science and Technology-Philippine Atmospheric, Geophysical and Astronomical Services Administration developed a heat index monitoring system in 2010, which relies on 73 stations and forecasting capabilities to track heat across the country year-round.

Evidence-based interventions and policy integration can enhance urban heat resilience. Projects hosted by institutions such as SingHealth Duke-NUS Global Health Institute are testing novel rapid cooling systems deployed in ambulances to treat patients enroute to hospitals, aiming to reduce heat-related admissions.

Improvements in data standardization and interoperability of health data, including hospital records and real-time climate-health integration enable predictive models that optimize resources and guide emergency responses.

The Asian Development Bank is working to expand the understanding and address extreme heat in Asia and the Pacific, including the development of tools for country-wide heat stress risk mapping, city-level capacity building, and toolkits for heat adaptation.

As the region faces increasing chronic heat stress, health systems need to build capacity and capacity to help populations manage the adverse health effects of acute and chronic heat. Chronic heat’s cumulative and sustained effects contribute to a significant total burden on health and society. Strategies recommended to understand and address these impacts include:

• Assess health impacts of both acute and chronic heat in the local population, especially among vulnerable groups.
• Establish comprehensive, standardized health data to track heat-related impacts, ideally in real-time.
• Conduct year-round monitoring of heat, beyond pre-determined hot seasons.
• Evaluate heat impacts in conjunction with other compounding hazards, such as air pollution and other extreme weather events.

Chronic heat differs from acute heat primarily in timescale and the response requirements: chronic heat requires sustained, long term planning, while acute heat demands immediate action. Effective management encompasses climate-resilient cities, sustainable farming, better water systems, and stronger regional cooperation to support communities in hotter conditions.

Note: The Asian Development Bank’s 1st INSPIRE Health Forum featured the session: Global Heat Health Information Network: The Unseen Impacts of Chronic Heat and the Critical Role of Health Data—organized by the Global Heat Health Information Network Southeast Asia Hub and its partners— to share the latest insights on chronic heat impacts from diverse stakeholders.

Some insights on this article were also taken from the presentations of Sally Edwards of the World Health Organization Regional Office for the Western Pacific, Jorybell Masallo of the Department of Science and Technology–Philippine Atmospheric, Geophysical and Astronomical Services Administration, and Associate Professor Jonas Karlström of SingHealth Duke-NUS Global Health Institute.

E. Oppermann et al. 2021. Establishing Intensifying Chronic Exposure to Extreme Heat as a Slow Onset Event with Implications for Health, Wellbeing, Productivity, Society and Economy. Current Opinion in Environmental Sustainability. 50. pp. 225–235.

M. Cruz et al. 2025. Where Heat Does Not Come in Waves: A Framework for Understanding and Managing Chronic Heat. Environmental Research: Climate. 4 (2).