India is entering a potentially difficult public-health phase as a strengthening El Niño threatens to reshape temperature and rainfall patterns across South Asia. The World Health Organization’s Global Public Health Situation Analysis – El Niño 2026 has placed India among the countries facing high or very high health risks, with South Asia expected to experience drier-than-normal conditions and above-normal heat during August-October. The warning assumes added significance as mosquito-borne diseases are already showing signs of an increase in Delhi, where dengue and malaria cases climbed sharply in August.
The WHO assessment, released on September 5, does not suggest that El Niño itself directly causes disease. Instead, it describes the climate phenomenon as a “risk modifier” capable of changing the environmental conditions in which infectious diseases spread and heat-related illnesses intensify. The report says the greatest health consequences occur when climate anomalies combine with vulnerable populations, weaker health systems and conditions favourable to disease transmission.
El Niño is characterised by unusual warming of surface waters in the central and eastern tropical Pacific Ocean. Although the phenomenon originates thousands of kilometres away from India, its atmospheric effects can influence rainfall and temperature patterns across the subcontinent.
For India and other parts of South Asia, the current WHO assessment points towards a particularly important combination: below-normal precipitation and above-normal temperatures during August-October. Such conditions can create several health pressures simultaneously. Heat can directly produce dehydration, heat exhaustion and heatstroke, while also worsening cardiovascular, respiratory, renal and other chronic illnesses.
At the same time, changes in rainfall and water-storage practices can influence mosquito breeding. A prolonged dry spell may encourage households and communities to store water, creating additional breeding opportunities, while sudden rainfall can leave stagnant pools in drains, construction sites, discarded containers and other urban spaces.
The WHO report classifies heat stress as a very high-risk consequence under warmer and drier El Niño conditions. It also places dengue and other arboviral diseases, as well as malaria, in the high-risk category. Under wetter conditions, the organisation again identifies dengue and malaria as high-risk concerns because accumulated standing water can increase mosquito breeding.
The situation in Delhi illustrates why climate-health preparedness cannot be treated as a seasonal exercise alone.
According to the latest MCD figures, the capital recorded 90 dengue cases in August, its highest monthly tally of 2026. The cumulative number reached 311 by August 29. Malaria cases also increased dramatically, from 17 in July to 53 in August, taking the year's total to 119. Chikungunya cases reached 22.
The August dengue figure is particularly significant because it was more than twice the July count of 40. MCD data also showed that 39 dengue cases were reported in the week immediately preceding its latest report, suggesting that transmission was gathering momentum as the city moved deeper into the mosquito-borne disease season.
There is, however, an important discrepancy in Delhi's official numbers. While MCD reported 311 dengue cases through August 29, Delhi Health Minister Pankaj Singh was reported to have cited around 2,200 cases through August 25. The difference has not been clearly explained and highlights the importance of consistent disease surveillance and transparent reporting.
The health challenge is not simply about rising mosquito numbers. Climate variability can alter the entire chain of disease transmission.
Temperature affects mosquito development, viral replication and the duration of the pathogen's development inside the vector. Rainfall, humidity and water availability determine where mosquitoes can breed. When these variables become unusually erratic, conventional assumptions about the beginning and intensity of disease seasons can become less reliable.
The WHO itself cautions that the relationship between El Niño and disease is not uniform. Local climate, ecological conditions, population vulnerability and the capacity of health systems all determine the eventual impact. Therefore, an El Niño warning should not be interpreted as a prediction of a nationwide epidemic, but as a signal to strengthen preparedness before risks materialise.
This distinction is particularly important for Indian cities. Rapid construction, inadequate drainage, water-storage practices, crowded settlements and extensive outdoor activity can create multiple points of vulnerability. Even relatively small changes in weather conditions can therefore have consequences when large populations are exposed.
The second side of the emerging crisis is heat stress.
WHO identifies extreme heat as an important occupational and public-health hazard. Outdoor workers, street vendors, construction labourers, traffic personnel and others who spend long hours outside can face disproportionate exposure. The danger is not restricted to people working under direct sunlight; high humidity and elevated night-time temperatures can prevent the body from recovering adequately from daytime heat.
Heat also places additional stress on people living with cardiovascular, respiratory, kidney and metabolic conditions. The WHO assessment notes that heat exposure can contribute to severe illness and death by aggravating underlying diseases. It also highlights evidence linking heat exposure with adverse maternal and perinatal outcomes.
This makes the climate-health challenge broader than dengue or malaria surveillance. Hospitals and primary health centres must be prepared simultaneously for febrile illnesses, dehydration, heatstroke and complications among vulnerable patients.
The emerging lesson for India is that vector control and heat management cannot remain separate policy tracks.
The WHO recommends strengthening surveillance and early-warning systems for climate-sensitive diseases, improving coordination with meteorological agencies and ensuring continuity of essential health services. It also stresses the need to identify vulnerable populations and strengthen primary healthcare capacity before risks peak.
For cities, the immediate priorities are practical: eliminate stagnant water, intensify mosquito surveillance, improve drainage, strengthen diagnostic capacity and ensure that hospitals can respond quickly to both vector-borne infections and heat-related emergencies. Public communication must also become more targeted, particularly in densely populated and vulnerable communities.
India has considerable experience managing monsoon-related disease outbreaks and heatwaves. The challenge now is to connect those systems with increasingly sophisticated climate forecasting.
El Niño should therefore be viewed not merely as a distant Pacific Ocean phenomenon but as an early warning for public-health planners. The WHO's message is essentially one of preparedness: climate variability can magnify existing vulnerabilities, but timely surveillance, prevention and health-system readiness can prevent a climate signal from becoming a health emergency.
The rise in Delhi's dengue and malaria figures provides a timely reminder. The real test will be whether India can act before the next wave of heat or mosquito-borne disease arrives, rather than responding after hospitals begin filling up.
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