Understanding climate-dengue links, building an early warning system

“Such dengue early warning systems can help authorities take proactive measures to prevent and manage outbreaks,” Prof Roxy Mathew Koll, climate scientist from the Indian Institute of Tropical Meteorology, told The Indian Express.

The new study, led by Sophia Yacob and Roxy Mathew Koll from the IITM, sheds light on the intricate links between climate and dengue in India. Published in Scientific Reports, the study explores how temperature, rainfall, and humidity influence dengue in Pune, a dengue hotspot.

Researchers from the University of Maryland, US, University of Pune, University of Nottingham, and Maharashtra and Pune health department officials, among others, were also part of the study, titled Dengue Dynamics, Predictions, and Future Increase under Changing Monsoon Climate in India.

Without timely interventions, rising temperatures and fluctuating monsoon rainfall could increase dengue-related deaths by 13 per cent by 2030 and 23–40 per cent by 2050, the researchers said.

The global burden of dengue, one of the fastest-spreading mosquito-borne diseases, is escalating under the influence of climate change, with India contributing a third of the total. Temperature and humidity in India are projected to increase further into the future, while monsoon rainfall patterns will become more erratic, marked by heavy-to-extreme rains. The climate model shows that the overall increase in warmer days is dominating the future changes in dengue.

The study reveals that a combination of warm temperatures above 27°C, moderate and evenly distributed rainfall, and humidity levels between 60 per cent and 78 per cent during the monsoon season (June–September) increases dengue incidences and deaths. Heavy rain above 150 mm in a week reduces dengue prevalence by flushing out mosquito eggs and larvae.

The team developed a model based on artificial intelligence or machine learning for dengue predictions, offering more than two months of lead time for dengue outbreak preparedness.

“This can give adequate time for the local administration and health department to enhance preparedness and response strategies, potentially reducing dengue cases and deaths,” Prof Koll told The Indian Express. He also said that if health data is shared by the state and health departments, customised early warning systems for climate-sensitive diseases like dengue, malaria, and chikungunya could be prepared for each city or district in India. “This will give a two-month advance time for authorities to take precautions and manage disease outbreaks. Cooperation from the health departments is key to saving lives,” Prof Koll said.

“In August 2024, my wife was severely affected by dengue and had to be hospitalised in the ICU. Hospitals in Pune were overwhelmed with dengue patients, and this experience showed me that even as a climate scientist, no one is spared,” Prof Koll added.

Currently, the India Meteorological Department (IMD) provides extended-range forecasts with information on the active-break cycles of the monsoon, 10 to 30 days in advance for the entire country. Utilising these forecasts can offer additional lead time for dengue predictions. Thus, monsoon intra-seasonal oscillations could serve as a valuable predictor for dengue, enhancing forecasting accuracy.

IITM’s Rajib Chattopadhyay, who is also one of the authors, said, “The study can help improve the existing vector-borne disease outlooks provided by IMD by focussing on a more regional threshold analysis-based decision support system”.

Sujata Saunik, Chief Secretary, Maharashtra, said, “This collaboration highlights the importance of bringing together expertise from diverse fields to address complex climate-health challenges. It is a perfect example of how scientists, the health department, and the government can work together to improve our health warning system.”

Future rise in dengue in Pune

Though heavy rain can wash out mosquito larvae, the model shows that the overall increase in warmer days is dominating the future changes in dengue.

Under low-to-high fossil fuel emissions, Pune is expected to experience a 1.2–3.5°C average temperature rise by the end of the century, according to the study.

Dengue mortality in Pune is projected to rise across all emission pathways:

Near-term (2020–2040): 13 per cent increase in mortalities, corresponding to global warming crossing 1.5°C.

Mid-century (2040–2060): 25–40 per cent rise in mortalities, at 2°C warming under moderate-to-high emissions.

Late century (2081–2100): Up to 112 per cent increase if fossil fuel emissions remain unchecked.

It is important to note, the researchers said, that the dengue projections are based on future climatic conditions favourable for dengue spread but do not account for the future socioeconomic factors influencing transmission.