September 24, 2026 — Extreme heat, destructive flooding and changing patterns of mosquito borne disease are forcing international health agencies to rethink how outbreaks are detected and contained. The World Health Organization and United Nations partners are warning that climate related hazards are no longer isolated environmental events. They can disrupt hospitals, contaminate water supplies, displace families and create conditions in which infectious diseases spread more easily. Recent assessments and emergency responses across several regions show why public health surveillance is increasingly being linked with weather forecasting and climate information.
Climate Hazards Are Becoming Public Health Emergencies
Heatwaves and floods can appear to be separate disasters, but their health consequences often overlap. Extreme heat can place intense pressure on the cardiovascular, respiratory and renal systems, while flooding can damage health facilities, interrupt medicine supplies and contaminate drinking water. When communities are displaced, crowded shelters and limited sanitation can add another layer of risk.
WHO published its Global Public Health Situation Analysis for El Niño 2026 in September, examining health risks associated with changing weather patterns and outlining preparedness measures for countries and vulnerable communities. The assessment focuses on the need for early action rather than waiting for hospitals and emergency services to become overwhelmed.
A recent United Nations briefing in Geneva highlighted the same concern. WHO and partner agencies warned that droughts and floods can damage homes, livelihoods and critical infrastructure while increasing risks from malnutrition, cholera and mosquito borne infections. More than 150 million people are already facing acute food insecurity globally, according to the briefing, with climate related disruptions threatening to increase pressure on food systems and vulnerable households.
Extreme Heat Is Creating a Growing Health Burden
Heat is among the most immediate climate related health threats because exposure can affect almost every part of the body. WHO reported in July 2026 that the number of people exposed to extreme heat is growing rapidly as the climate changes. Heat stress can worsen cardiovascular disease, diabetes, respiratory conditions and some mental health problems, while severe heat exposure can result in life threatening heatstroke.
WHO estimates that studies covering the period from 2000 through 2019 recorded approximately 489,000 heat related deaths each year. Older adults have experienced particularly significant increases in heat related mortality, with WHO reporting an approximately 85 percent increase among people aged over 65 between the periods of 2000 to 2004 and 2017 to 2021.
The danger is not distributed evenly. Older people, infants, pregnant women, outdoor workers, people with chronic conditions and people who have limited mobility can face greater exposure or reduced ability to escape dangerous temperatures. Hospitals can also experience increased demand during prolonged heatwaves, precisely when electricity, water and other infrastructure may be under additional stress.
WHO Europe has urged governments and cities to establish heat health action plans that identify vulnerable populations, strengthen warnings and coordinate emergency responses. These plans are increasingly being treated as essential public health infrastructure rather than temporary measures used only during unusual summers.
Flooding Can Create a Second Wave of Health Risks
The immediate danger from a flood is often obvious. Rising water can cause drowning, injuries and destruction of homes. The less visible threat can emerge days or weeks later, when damaged sanitation systems and stagnant water create conditions favorable to infectious disease.
WHO identifies cholera, typhoid and malaria among the diseases that can become more difficult to control following floods. Floodwater can disperse fecal contamination into areas used for drinking water, food preparation or household activities. Damage to sewage systems can make the problem worse.
Recent flooding in Nepal demonstrates how quickly these concerns can become part of an emergency response. Flash floods in central Nepal on August 26 damaged roads, bridges, water systems and health facilities. WHO reported in September that displaced families and crowded temporary shelters faced additional risks because sanitation systems and access to medical services had been disrupted.
Public health teams therefore have to look beyond rescue operations. Once floodwater begins to recede, surveillance becomes essential for identifying unusual increases in fever, diarrhea and other illnesses before they develop into larger outbreaks.
Changing Mosquito Habitats Are Expanding Disease Concerns
Climate conditions can influence where mosquitoes survive, how quickly they reproduce and how long disease transmission remains possible during a year. Warmer temperatures, changing rainfall patterns and increased humidity can create more suitable environments for some disease carrying species.
WHO’s dengue surveillance has become increasingly important as these patterns change. The agency established an almost real time global dengue surveillance system in 2024, collecting monthly information from 185 countries, territories and areas. WHO reported that climate change, urbanization, international movement and changing mosquito distributions are among the factors affecting dengue transmission.
Dengue is transmitted primarily by Aedes aegypti and Aedes albopictus mosquitoes. These mosquitoes are well adapted to many urban environments, where small collections of standing water can become breeding sites. After heavy rainfall, discarded containers, blocked drains and poorly managed water storage can provide additional opportunities for mosquito populations to grow.
The disease burden is already substantial. WHO reported more than 14.6 million dengue cases and more than 12,000 related deaths in 2024, the highest annual number recorded at that time. The agency has also warned that dengue transmission can change geographically as vectors adapt to new environments.
Malaria Risks Are Also Closely Linked to Climate Conditions
Malaria presents another complex relationship between climate, geography and public health. The mosquitoes that transmit malaria depend on environmental conditions for breeding and survival, meaning changes in temperature and rainfall can influence transmission patterns.
WHO says climate informed surveillance can help countries anticipate these changes. In some settings, warmer temperatures and altered rainfall may extend the period during which malaria transmission is possible. In other areas, extreme drought or unsuitable environmental conditions may reduce mosquito populations. The effect therefore varies by location rather than following one universal pattern.
Pakistan provides a particularly important example of the long tail of climate related disease emergencies. WHO reported in April 2026 that Pakistan recorded about 1.8 million malaria cases in 2025, even after incidence fell by 10 percent compared with 2024. The country was still dealing with the consequences of the major malaria surge that followed the climate driven floods of 2022.
This experience illustrates why disease control cannot end when floodwaters disappear. Mosquito breeding environments, damaged sanitation systems, disrupted health services and displaced populations can continue affecting disease transmission long after the original disaster has left the headlines.
Early Warning Systems Are Becoming Central to Disease Control
Health agencies are increasingly connecting meteorological information with disease surveillance. The goal is straightforward: identify conditions that could increase health risks before hospitals begin seeing a surge of patients.
WHO describes integrated surveillance and climate informed health early warning systems as a way to monitor how weather and climate conditions affect disease incidence and geographic distribution. Such systems can combine information about rainfall, temperature, mosquito populations, disease reports and health service capacity.
That approach can give health authorities more time to prepare. Medical supplies can be positioned before roads become inaccessible. Community health workers can receive warnings before disease transmission rises. Hospitals can review staffing and emergency capacity. Local authorities can intensify mosquito control or improve public messaging in areas where risk is increasing.
The World Health Organization’s climate and health resources increasingly focus on this connection between climate information, preparedness and health system resilience.
Health Infrastructure Is Part of Climate Protection
A health system cannot respond effectively to climate related disease if the system itself is vulnerable to extreme weather. A hospital without reliable electricity, clean water, functioning roads or secure medicine supplies can struggle to operate precisely when the surrounding population needs it most.
This is why climate resilience is becoming part of health infrastructure planning. Hospitals may need improved cooling systems, backup electricity, protected water supplies and stronger flood defenses. Clinics serving remote communities may need emergency communication systems and contingency plans for periods when roads are blocked.
WHO appointed Vanessa Kerry as its Director General’s Special Envoy for Health Resilience in September 2026. The role includes work on stronger health systems, sustainable financing and coordination between governments, development partners and other organizations dealing with climate change and health emergencies.
Communities Remain the First Line of Protection
International agencies can provide surveillance systems, technical guidance and emergency support, but much of the practical response happens at household and community level. People need timely warnings, safe drinking water, accessible healthcare and clear information about symptoms that require medical attention.
During periods of extreme heat, public health guidance generally focuses on reducing exposure, staying hydrated and checking on people who may be more vulnerable. During and after floods, safe water, sanitation, mosquito control and rapid medical assessment become especially important.
Community participation also matters for mosquito borne diseases. Removing standing water, maintaining household water storage safely and using measures that reduce mosquito bites can support wider vector control programs. These steps cannot replace public health systems, but they can reduce exposure while larger interventions are underway.
The Next Challenge Is Acting Before the Crisis Arrives
The strongest message emerging from current WHO and UN assessments is that climate related health preparedness cannot begin after a disaster. By then, hospitals may already be crowded, roads may be damaged and medical supplies may be difficult to move.
Early warning systems offer a different model. Weather forecasts can identify periods of elevated risk. Disease surveillance can show whether those conditions are beginning to affect communities. Public health authorities can then respond before infections spread widely or heat related illness overwhelms emergency departments.
The United Nations climate and health work reflects a wider recognition that climate adaptation and public health planning are increasingly connected. Flood defenses, clean water systems, reliable healthcare facilities, food security measures and disease surveillance can all serve as forms of health protection.
A Health Response That Starts Before the Emergency
The climate health challenge is not simply about more heat or more floods. It is about the chain of consequences that follows when extreme weather disrupts the systems people depend upon. A flooded clinic can interrupt treatment. A damaged water network can increase infection risks. A prolonged heatwave can strain hospitals. Changing temperatures and rainfall can alter the range of disease carrying mosquitoes.
We are therefore seeing public health move toward a more predictive approach. Instead of waiting for disease numbers to rise, agencies are increasingly examining weather patterns, environmental conditions and population vulnerability together.
There is no single intervention that can eliminate climate related health risks. But earlier warnings, stronger surveillance, resilient health facilities, reliable water systems, mosquito control and well prepared communities can reduce the damage. The central challenge for governments and international health organizations is turning that knowledge into action early enough to protect people before the next flood, heatwave or disease surge becomes a full scale emergency.
