Heat Preparedness and Extreme Weather Health Impacts: A Narrative Review of Global Burden, Vulnerable Populations, Evidence-Based Interventions, and Health System Adaptation for Low-, Middle-, and High-Income Countries, 2024–2026.

 Heat Preparedness and Extreme Weather Health Impacts: A Narrative Review of Global Burden, Vulnerable Populations, Evidence-Based Interventions, and Health System Adaptation for Low-, Middle-, and High-Income Countries, 2024–2026

Authors: Dr. Shekhar and Team, Doctor's Forum For All 🏥⚖️

Co-authors: Rajesh (MPH) and Dr. Shruti (MPH)

Disclaimer

This article is strictly for educational purposes only. It does not constitute medical advice or a substitute for professional clinical judgment. Readers should consult qualified healthcare providers for specific recommendations. The authors and Doctor's Forum For All 🏥⚖️ disclaim any liability for actions taken based on this content. All data cited are from publicly available sources as of the date of publication. The views expressed are those of the authors alone.

Abstract

Background: Climate change is no longer a distant threat. It is a present health emergency. More than 540,000 people die from extreme heat each year globally. Between 3.3 and 3.6 billion people live in areas highly vulnerable to climate change. One in every 12 hospitals worldwide is at risk of shutdown due to climate-related events. This review examines the health impacts of extreme heat, floods, and other climate-driven events, the populations most at risk, and the evidence-based interventions that are reducing mortality.

Methods: We conducted a narrative synthesis of Lancet Countdown 2025 data, WHO and COP30 health reports, peer-reviewed systematic reviews on heat-health warning systems and flood-related infections, documented case studies of Heat Action Plans from India, and published analyses of climate-resilient health system interventions.

Results: Heat-related mortality has increased 23% since the 1990s, reaching 546,000 deaths annually. In India, a single day of extreme heat causes approximately 3,400 excess deaths nationally, and a five-day heatwave causes nearly 30,000. Flooding is consistently associated with increased incidence of cholera, bacillary dysentery, leptospirosis, dengue, and malaria, with outbreaks varying by region and public health infrastructure. Approximately 1 billion people are exposed to extreme heat preventing moderate physical labour in the hottest month. Heat exposure caused 640 billion potential work hours lost in 2024, equivalent to $1.09 trillion in productivity losses. Heat Action Plans in Ahmedabad reduced all-cause mortality during summer months. In England, over 80% of surveyed residents took protective action based on heat-health alerts. India's Ahmedabad, Churu, and Varanasi Heat Action Plans demonstrate that data-driven, locally adapted interventions save lives.

Conclusion: Extreme weather events are killing people now, not in some distant future. Heat Action Plans, early warning systems, community health worker engagement, climate-resilient health infrastructure, and equity-focused adaptation strategies are proven, cost-effective interventions. Health leaders must treat climate adaptation as core public health infrastructure, not as an optional environmental concern. The evidence is clear. The tools exist. The cost of inaction is measured in lives.

Keywords: extreme heat, heat action plans, flood-related infections, climate-resilient health systems, vulnerable populations, early warning systems, public health adaptation

Introduction

Climate change is a health crisis. Not a future one. A present one.

The numbers tell a story that is difficult to ignore. More than 540,000 people die from extreme heat every year globally. Heat-related mortality has increased 23% since the 1990s, reaching 546,000 deaths annually. In 2024, the average person was exposed to 16 days of dangerous heat levels that would not have occurred without climate change, with infants and older adults facing more than 20 days of heatwave exposure each—four times more than in the previous 20 years. Between 3.3 and 3.6 billion people live in areas highly vulnerable to climate change. One in every 12 hospitals worldwide is at risk of shutdown due to climate-related events. Hospitals face 41% more risk of damage from extreme weather compared to 1990.

The World Health Organization calls climate change the single biggest health threat facing humanity. Between 2030 and 2050, it is projected to cause approximately 250,000 additional deaths each year from heat stress, diarrhoeal disease, malnutrition, and vector-borne diseases.

These numbers represent real people. A farmer in Maharashtra collapsing in a 48°C field. A pregnant woman in the Gambia exposed to extreme heat during her first trimester. A child in Southern Africa drinking contaminated water after floods destroyed sanitation infrastructure. A construction worker in Delhi whose kidney function declines with each summer of heat exposure.

The evidence on what works is growing. Heat Action Plans in Indian cities are reducing mortality. Early warning systems in European countries are prompting protective behaviour. Community health workers are delivering climate-health education where it matters most. Climate-resilient infrastructure investments are protecting health services during extreme weather. The knowledge exists. The tools exist. The question is whether health systems will prioritize their implementation at the scale required.

This article examines heat preparedness and extreme weather health impacts through four questions. First, what is the scale of the health burden, and who is most vulnerable? Second, what do the data show about heat-related mortality, flood-related disease outbreaks, and other climate health impacts? Third, which interventions have demonstrated effectiveness in reducing illness and death? Fourth, what are the implications for health policy, clinical practice, and health system adaptation?

The article is written for health professionals, public health practitioners, policymakers, and informed readers. It argues that climate adaptation is not an environmental issue. It is a health issue. And it requires the same evidence-based, equity-focused, systems-level approach that has driven progress in other areas of public health.

The heat is here. The question is what we do about it.

Methods and Materials

Study Design: This article is a narrative synthesis of published surveillance data, peer-reviewed literature, policy documents, and documented implementation case studies. It is not a systematic review.

Setting and Population: The scope is global, with emphasis on South Asia, Africa, and other regions where climate vulnerability is highest. Data sources reflect populations of older adults, children, pregnant women, outdoor workers, and communities living in climate-vulnerable settings.

Data Sources: The primary data sources were the Lancet Countdown on Health and Climate Change 2025 report; the COP30 Special Report on Health and Climate Change published by the Brazilian Ministry of Health and WHO (2025); WHO Heat-Health Action Plan guidance (2026); a 2026 systematic review on flooding and waterborne/vector-borne infections published in BMC Infectious Diseases; a 2026 district-level heat mortality analysis for India published in Frontiers in Environmental Health; documented Heat Action Plans from Ahmedabad, Churu, Varanasi, and Mahesana; the World Bank/IDB/KfW Smart Buys report on health sector adaptation; a 2025 systematic review on heat stress in outdoor workers; and published studies on heat-health warning system effectiveness.

Variables and Measurements: Health burden was measured using excess mortality estimates, disease incidence rates, and disability-adjusted life years. Vulnerability was assessed through demographic, occupational, and geographic factors. Intervention effectiveness was assessed through reported reductions in mortality, changes in protective behaviour, and coverage rates achieved in implementation programmes.

Statistical Analysis: No primary statistical analysis was conducted. Published figures and effect sizes are reported as cited.

Ethical Considerations: This article uses only publicly available policy documents, de-identified aggregate data, and published literature. No primary data collection involving human subjects was conducted. Institutional review board approval was not required.

Results

The Scale of Heat-Related Mortality

Heat-related mortality has increased substantially over the past three decades. The Lancet Countdown 2025 report found that the heat-related mortality rate has risen 23% since the 1990s, bringing the total to 546,000 deaths per year on average. In 2024, the average person was exposed to 16 days of dangerous heat levels that would not have occurred without climate change. Infants and older adults faced more than 20 days of heatwave exposure per person—four times more than in the previous 20 years.

In Europe, the burden is particularly severe. In 854 European cities, climate change was responsible for 68% of the 24,400 estimated heat deaths during summer 2025. Over 2.3 million additional temperature-related deaths are projected in these cities by 2099, but up to 70% of these deaths could be prevented with rapid action. Europe is the most rapidly heating world region. During June and July 2026, prolonged heatwaves contributed to an estimated 10,000 excess deaths across the continent, with more than 9,000 occurring among people aged 65 and over.

In England, a rapid assessment by the UK Health Security Agency estimated 2,877 heat-associated deaths during May and June 2026, nearly double the 1,504 recorded for the whole of summer 2025. An estimated 753 deaths were associated with a four-day heatwave in late May, and a further 2,124 occurred during an eight-day heatwave in late June.

India's burden is among the highest globally. A 2026 study published in Frontiers in Environmental Health estimated that a single day of extreme heat causes approximately 3,400 excess deaths nationally, and a five-day heatwave causes nearly 30,000. Uttar Pradesh alone accounts for approximately 8,100 excess deaths during a five-day heatwave. Districts including Ahmedabad, Jaipur, and Surat each exceed 250 excess deaths in a single heat event. Approximately 1 billion people are exposed to extreme heat preventing moderate physical labour in the hottest month after global temperature exceeds 2.5°C above pre-industrial levels.

Flood-Related Disease Outbreaks

Flooding is consistently associated with increased incidence of waterborne and vector-borne infections. A 2026 systematic review published in BMC Infectious Diseases, analysing 71 studies published between 2014 and 2024, found that flooding was consistently associated with increased incidence of leptospirosis, cholera, bacillary dysentery, and hepatitis A/E, as well as vector-borne infections such as dengue and malaria. Outbreaks varied by region, flood characteristics, and the strength of existing public health infrastructure. The lag period between flooding onset and disease emergence ranged from days to weeks.

The Southern Africa floods of 2025–2026 illustrate the scale of the challenge. Since mid-December 2025, prolonged heavy rainfall and flash flooding affected multiple countries across the region, resulting in approximately 300 deaths and nearly 800,000 people affected by late January 2026. Mozambique was the most affected country, with approximately 692,000 people affected across 34 districts and over 104,000 displaced in temporary accommodation centres. Cholera cases in Southern Africa increased more than sevenfold in the first six weeks of 2026 compared to the same period in 2025, with 4,320 cases and 56 deaths reported across five countries.

Flooding was most frequently associated with increased incidence of cholera, bacillary dysentery, leptospirosis, dengue, and malaria. Each disease has distinct lag periods critical for outbreak prediction. Limited observational evidence suggests that doxycycline chemoprophylaxis for leptospirosis, oral cholera vaccination, and early vector control may be useful in selected post-flood settings.

Vulnerable Populations

The health impacts of extreme weather are not evenly distributed. Vulnerability is shaped by age, occupation, pre-existing health conditions, socioeconomic status, and geographic location.

Older adults face the highest mortality risk. In Europe, more than 9,000 of the 10,000 excess deaths during June and July 2026 occurred among people aged 65 and over. Infants also face heightened risk, with exposure to dangerous heat levels more than four times higher than in previous decades.

Outdoor workers are among the most exposed populations. A 2025 systematic review found that 92.3% of included studies reported occupational risks related to heat stress, with four studies reporting a high prevalence of heat-related symptoms ranging from 64% to 90.3% of workers. The most dangerous effects include heat stroke, dehydration, kidney dysfunction, and neurological disorders—conditions that can be fatal if not detected and treated in time. A study of 1,452 outdoor workers across India found that workers exposed to high humidity were 2.5 times more likely to experience high physiological strain. The predictive model identified a heat-humidity threshold of 32°C and 60% relative humidity.

Pregnant women and children face unique risks. A 1°C increase in temperature during the week before delivery is associated with a 6% increase in risk of stillbirth. With up to a 2°C increase in temperature, an additional 40 million women and girls could experience intimate partner violence every year by 2090. Heat stress in the first 1,000 days of life significantly reduces weight-for-height and weight-for-age in infants aged 6–18 months.

Populations living in informal settlements, low-income communities, and poorly serviced environments face compounded risks. Urbanisation and poor planning exacerbate heat risks, particularly in informal settlements where the urban heat island effect raises temperatures substantially.

Intervention Effectiveness: Heat Action Plans and Early Warning Systems

Heat Action Plans and heat-health warning systems have demonstrated effectiveness in reducing mortality. The Ahmedabad Heat Action Plan, India's first, was found to reduce all-cause mortality rates during summer months. Ahmedabad has since implemented cool roofs, misting bus stops, and heat insurance as part of its climate resilience strategy.

Churu and Varanasi launched comprehensive Heat Action Plans in May 2025, developed in collaboration with city authorities, health experts, and partners including the Mahila Housing Trust and Indian Institute of Public Health-Gandhinagar. These plans include integrated historical climate trends, hyperlocal vulnerability assessments, and future climate projections. Varanasi's plan includes ward-level heat vulnerability mapping and targeted public health measures for high-footfall areas such as ghats and informal settlements. Churu's plan includes passive cooling measures and strengthened public health responses.

Mahesana's Heat Action Plan, developed through a multi-stakeholder process involving NRDC's Cool Roofs initiative, focuses on three pillars: protection for climate-vulnerable livelihoods, enhancing public infrastructure and health system readiness, and addressing water stress. A key intervention is cool roofs as a practical, low-cost heat mitigation solution for government buildings, municipal schools, and low-income housing.

In England, a survey issued during summer 2025 found that over 80% of respondents took some form of action based on heat-health alerts, and more than 90% believed alerts were issued with enough lead time. The UK operates an Adverse Weather and Health Plan with a colour-coded alert system developed with the Met Office, coordinating responses across healthcare providers, local authorities, and the public.

WHO's updated Heat-Health Action Plan guidance, released in 2026, moves away from treating heatwaves as isolated emergencies. Countries are encouraged to develop coordinated strategies that operate throughout the year, anticipating heat risks and protecting vulnerable populations. The framework identifies eight core areas for action: governance, heat warning systems, protection for populations at increased risk, communication, health system resilience, reducing heat exposure, surveillance, and monitoring and evaluation.

Intervention Effectiveness: Climate-Resilient Health Systems

The World Bank, Inter-American Development Bank, and KfW identified eight high-value actions for health sector adaptation in their "Smart Buys" report. These include implemented Heat Action Plans, integrated surveillance and early warning systems, climate-resilient health infrastructure, drone-based medical supply chain delivery, community health worker-led climate-health education, text-based telehealth services, mental health services for climate-affected populations, and mosquito vector control.

Immunization against climate-sensitive diseases and strengthening health infrastructure have some of the highest climate adaptation values among health sector investments. Gavi and the Asian Infrastructure Investment Bank launched a report recognizing health and immunization investments as key to building climate-resilient communities.

The Belém Health Action Plan, launched at COP30 with adhesion from more than 80 countries and institutions, proposes three lines of action: strengthening climate-informed health surveillance systems to detect climate-related health impacts, promoting intersectoral and participatory policymaking that integrates mental health and strengthens the health workforce, and advancing innovation and digital health for climate-adapted health systems.

In Rukiga District, Southwest Uganda, frontline healthcare workers are trained to provide not just usual maternal care but also information about mitigating climate impacts on food and livelihoods. Working with community members, they identify populations most vulnerable to climate change, trace how prolonged droughts trigger malnutrition, and advocate for climate-smart agriculture alongside family planning and maternal care. In climate emergencies, cross-sector programmes ensure that even if roads flood and power grids fail, boats and supplies can be mobilised to enable a displaced teenager to access contraception and a pregnant woman to have a safe place to give birth.

The Economic Case for Action

The economic costs of inaction are substantial. Heat exposure caused the loss of 640 billion potential work hours in 2024, equivalent to $1.09 trillion in productivity losses. The cost of heat-related deaths among older adults reached $261 billion. Governments spent $956 billion in net fossil fuel subsidies in 2023, more than triple the amount promised annually to support climate action in developing countries.

The cost of interventions is comparatively modest. Heat Action Plans are low-cost, high-impact interventions. Cool roofs are a passive, low-cost heat mitigation solution. Early warning systems require investment but have demonstrated effectiveness. Community health worker training and engagement builds on existing health system infrastructure.

Discussion

Key Findings

Three findings stand out.

First, the health burden of extreme weather is enormous and growing. Heat-related mortality has increased 23% since the 1990s, reaching 546,000 deaths annually. In India, a five-day heatwave causes nearly 30,000 excess deaths. Flooding consistently increases waterborne and vector-borne disease outbreaks. The burden falls disproportionately on older adults, infants, pregnant women, outdoor workers, and communities living in informal settlements.

Second, the interventions that work are known. Heat Action Plans reduce mortality. Early warning systems prompt protective behaviour. Community health worker engagement builds trust and delivers education where it matter most. Climate-resilient health infrastructure protects services during extreme weather. These interventions are evidence-based, feasible, and cost-effective.

Third, equity must be central to climate adaptation. Vulnerability is shaped by age, occupation, income, and geography. Those least responsible for climate change are often most affected. Adaptation strategies that do not reach the most vulnerable populations will fail to reduce the overall burden.

Comparison with Prior Literature

These findings align with and extend previous analyses. The Lancet Countdown 2025 report identified 12 of 20 key indicators of climate-related health threats at record levels. The COP30 Special Report on Health and Climate Change documented the scale of the health emergency and called for implementation of the Belém Health Action Plan. The BMC Infectious Diseases systematic review provided the most comprehensive synthesis to date on flooding and infectious disease outbreaks.

The WHO Heat-Health Action Plan guidance reflects nearly two decades of implementation experience across the European Region. The Indian Heat Action Plans demonstrate that locally adapted, data-driven planning can save lives. The Uganda community health worker model shows that integrating climate-health education into existing maternal care platforms is feasible and effective.

Limitations

This synthesis has limitations. It is not a systematic review. The literature selection was purposive and may have omitted relevant studies. Health burden estimates are subject to methodological limitations, including the use of urban-derived risk coefficients for rural populations. The evidence on flood-related disease outbreaks is largely observational, with low to moderate certainty. Data on health system impacts, including hospitalization rates and intensive care unit burden, remain limited. The perspectives of communities and frontline health workers are underrepresented in the published literature. Finally, climate health impacts are rapidly evolving, and data from 2026 are provisional.

Public Health Implications

The implications for policy and practice are substantial.

First, Heat Action Plans must be universal. Every city and district at risk should have a comprehensive Heat Action Plan that includes early warning systems, vulnerability assessments, protection for vulnerable populations, and health system preparedness. Plans must be locally adapted and data-driven.

Second, early warning systems must be strengthened. Heat-health warning systems reduce mortality and prompt protective behaviour. They should be integrated with meteorological forecasting, public health planning, and community communication channels. Effectiveness can be improved by considering local climate-epidemiological evidence including morbidity and actual health outcomes.

Third, community health workers must be engaged. Community health worker-led climate-health education is a high-value, low-cost intervention. Frontline health workers are trusted messengers who can deliver education on heat protection, water safety, and vector control at the household and community level.

Fourth, health infrastructure must be climate-resilient. One in 12 hospitals worldwide is at risk of shutdown due to climate-related events. Investments in climate-resilient health infrastructure, including passive cooling, backup power, water storage, and flood defences, are essential to maintain service continuity during extreme weather.

Fifth, equity must guide resource allocation. The most vulnerable populations—older adults, infants, pregnant women, outdoor workers, and informal settlement residents—must be prioritized in adaptation planning and resource allocation. Community engagement in designing communication tools and campaigns improves reach and effectiveness.

Sixth, mental health must be integrated. Eco-anxiety, climate anxiety, and ecological grief are now widespread. Extreme weather events are associated with increased rates of anxiety, depression, and post-traumatic stress disorder. Mental health services for climate-affected populations should be part of the adaptation package.

Seventh, surveillance must be climate-informed. Integrated surveillance and early warning and response systems are high-value adaptation actions. Climate-sensitive infectious disease surveillance should be strengthened to detect outbreaks early and mount rapid responses.

Conclusion

Extreme weather is not a future threat. It is killing people now.

More than 540,000 people die from extreme heat every year. Heat-related mortality has increased 23% since the 1990s. In India, a single day of extreme heat causes approximately 3,400 excess deaths. Flooding consistently increases cholera, dysentery, dengue, and malaria outbreaks. One in 12 hospitals worldwide is at risk of shutdown due to climate-related events.

But the tools to reduce this burden exist. Heat Action Plans reduce mortality. Early warning systems prompt protective behaviour. Community health workers deliver education where it matters most. Climate-resilient health infrastructure protects services during emergencies. Cool roofs, misting stations, and heat insurance are practical, scalable interventions.

The evidence from Ahmedabad, Churu, Varanasi, Mahesana, England, and Uganda demonstrates that when governments invest, when communities engage, and when health systems adapt, lives are saved.

The implications are clear. Every city and district at risk needs a Heat Action Plan. Every health system needs climate-resilient infrastructure. Every community needs access to early warning information. Every vulnerable population needs targeted protection. Every health worker needs training in climate-health education.

Climate adaptation is not an environmental concern. It is core public health infrastructure. The cost of inaction is measured in lives. The cost of action is measured in lives saved.

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