El Niño and Human Health: Disease Outbreaks and Heat-Related Risks
Published: May 20, 2026 · 8 min read
When Climate Patterns Become Health Threats
The El Niño-Southern Oscillation (ENSO) is a natural climate cycle that shifts ocean temperatures and atmospheric pressure across the Pacific. During an El Niño event, warmer waters trigger dramatic changes in global weather patterns, including extreme rainfall, prolonged droughts, and record-breaking heat. These shifts create a cascade of public health risks, from infectious disease outbreaks to heat-related mortality. Understanding how El Niño amplifies these threats is critical for health systems worldwide.
Vector-Borne Diseases: Mosquitoes on the Move
El Niño’s impact on rainfall and temperature directly expands breeding grounds for disease-carrying mosquitoes. Dengue fever outbreaks often spike during El Niño years, as warm, humid conditions accelerate mosquito reproduction and viral replication. The 2015-16 El Niño was strongly correlated with the emergence of Zika virus in the Americas, where unusual rainfall patterns allowed Aedes aegypti mosquitoes to thrive in regions previously too dry for sustained transmission. Malaria also spreads more readily in East Africa and South America, where heavy rains create stagnant pools for Anopheles mosquitoes. Conversely, drought conditions can concentrate mosquito populations around shrinking water sources, intensifying transmission in localized areas.
Water-Borne Disease Outbreaks
Both flooding and drought during El Niño increase the risk of cholera and typhoid outbreaks. Flooding contaminates drinking water with sewage, as seen in Peru during the 2015-16 event when heavy rains overwhelmed sanitation systems. Meanwhile, drought forces communities to rely on unsafe water sources. The 2015-16 El Niño contributed to severe drought in Ethiopia, affecting over 10 million people and leading to a surge in acute watery diarrhea cases. In both scenarios, weakened water infrastructure and population displacement amplify the spread of water-borne pathogens.
Extreme Heat and Mortality
El Niño years consistently rank among the hottest on record, with extreme heat waves pushing mortality rates higher. Vulnerable populations—including the elderly, outdoor workers, and those without air conditioning—face heightened risk of heat stroke and cardiovascular failure. Urban areas experience the urban heat island effect, where concrete and asphalt trap heat, making cities like Karachi and Jakarta particularly deadly during El Niño summers. The 2015-16 event saw thousands of excess deaths in India and Pakistan linked to heat waves that exceeded 45°C (113°F).
Air Quality Degradation
Drought conditions during El Niño contribute to wildfire smoke that degrades air quality over vast regions. In Indonesia, the 2015-16 El Niño caused prolonged drought that led to massive peatland fires, blanketing Southeast Asia in hazardous haze. This smoke contains fine particulate matter (PM2.5) that penetrates deep into the lungs, triggering asthma attacks, chronic obstructive pulmonary disease exacerbations, and increased hospitalizations for respiratory infections. Children and those with pre-existing lung conditions are most vulnerable.
Mental Health and Climate Anxiety
The indirect health effects of El Niño include mental health crises driven by displacement, economic stress, and agricultural losses. Farmers in drought-stricken regions of Ethiopia and Central America face crop failure and livestock deaths, leading to food insecurity and forced migration. This instability contributes to climate anxiety, depression, and post-traumatic stress disorder. Communities that lose their homes to flooding or wildfires experience long-term psychological trauma, often with limited access to mental health services.
Preparedness: What Public Health Systems Can Do
Integrating seasonal climate forecasting into health planning can reduce El Niño’s toll. Early warning systems that predict rainfall anomalies allow health agencies to pre-position mosquito nets, vaccines, and oral rehydration salts. For example, the International Research Institute for Climate and Society works with ministries of health to issue epidemic risk maps months before El Niño peaks. Strengthening surveillance for vector-borne diseases, improving heat wave response plans (including cooling centers and public alerts), and investing in resilient water infrastructure are essential steps. Public health systems that prepare for El Niño’s cascading risks save lives and reduce the burden on emergency services.