Extreme weather events are increasing India's infectious disease risks, say experts

Extreme weather events like heatwaves, droughts, erratic rainfall, and flash floods are reshaping the ecology of infectious diseases across India by altering how long pathogens survive and changing the distribution of disease-carrying insects. The Intergovernmental Panel on Climate Change warns that heatwaves and extreme rainfall are projected to increase. A 2025 study by IPE Global and Esri India warns that extreme weather could become more severe by 2030, with heatwaves doubling in major cities and extreme rainfall rising by 43 percent across the country. Health experts stress the need to prevent climate-related outbreaks rather than simply responding to them after they happen.

Waterborne and Vector-Borne Diseases

Heavy rainfall and flooding create ideal conditions for infections to spread. Floods overwhelm sewage systems and mix human and animal waste into water sources. A 21-year study from Kolkata found a biannual pattern in cholera cases, with peaks during summer temperatures and the monsoon. In Delhi and Mumbai, major hepatitis E outbreaks have been linked to sewage entering water supplies after heavy monsoon rains. Furthermore, a Chennai study found that the risk of hospitalisation for gastrointestinal illnesses was 60 percent higher in the 15 days following an extreme rainfall event. Climate change is also making these seasonal patterns unpredictable, with infections appearing more frequently and throughout the year. Floods drive rodents out of burrows into homes, spreading leptospirosis, a bacterial disease. Data from the Integrated Disease Surveillance Project shows that after the 2018 flood, Kerala witnessed 1,318 leptospirosis cases, including 53 deaths. Changes in temperature and rainfall also alter mosquito behaviour. In 2024, Pune reported surges in Zika virus infections following heavy monsoon rains and flooding, while malaria-carrying mosquitoes are now persisting in parts of the Himalayan foothills previously considered too cold.

Infrastructure Challenges

These health risks are amplified by weaknesses in basic infrastructure. Many Indian cities rely on outdated stormwater drains designed under old guidelines to handle rainfall occurring once every one to two years, or a maximum rainfall intensity of 25 millimetres an hour. Recently, cities like Bengaluru, Delhi, and Mumbai received more than 100 millimetres of rain in 24 hours. A 2022 Comptroller and Auditor General of India report notes that municipal authorities in many cities lack updated underground drainage maps, and parts of the network in Mumbai and Kolkata are over a century old. In Assam, around 60 percent of the state's 4,800 kilometres of embankments are estimated to need repairs. Droughts and water shortages also drive people and wildlife to share limited water sources, increasing pathogen transmission.

Context

Climate change alters natural habitats and weather cycles, which directly influences how disease-carrying vectors like mosquitoes and rodents multiply and spread into new areas. When public infrastructure like drainage and sewage systems fail to handle heavy water pressure, waste mixes directly with drinking water supplies, leading to sudden public health crises.