Rising Temperatures, Rising Dengue
Understanding Climate-Dengue Links and Building a Warning System for a Changing Climate
Summary
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. Without timely interventions, rising temperatures and fluctuating monsoon rainfall could increase dengue-related deaths by 13% by 2030 and 23–40% by 2050.
A pathbreaking study led by Sophia Yacob and Roxy Mathew Koll from the Indian Institute of Tropical Meteorology (IITM), Pune, sheds light on the intricate links between climate and dengue in India. Published in Scientific Reports, the research explores how temperature, rainfall, and humidity influence dengue in Pune, a dengue hotspot.
The study reveals that a combination of warm temperatures above 27°C, moderate and evenly distributed rainfall, and humidity levels between 60% and 78% during the monsoon season (June–September) increases dengue incidences and deaths. Meanwhile, heavy rains above 150 mm in a week reduce the dengue prevalence by flushing out the mosquito eggs and larvae.
The team developed an AI/ML model (model based on artificial intelligence/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.
Temperature and Dengue
In Pune, the mean temperature range of 27–35°C during the monsoon season is ideal for increased dengue transmission. Temperature influences key mosquito factors such as lifespan, egg production, frequency of egg-laying, the time between feeding and laying eggs, the virus’s development inside the mosquito, and the time it takes for symptoms to appear in humans after infection.
This temperature window is specific to Pune and may vary across regions, considering its relationship with other climatic conditions like rainfall and humidity. It is hence important to individually assess the climate-dengue relationship for each region using available health data.
Monsoon Rains and Dengue
The current study reveals that moderate rains during a week (adding up to 150 mm in a week) lead to an increase in dengue mortality, while heavy rains (above 150 mm) reduce dengue mortality in Pune through the flushing effect, where the mosquito eggs and larvae are washed out.
The monsoon rainfall from June to September exhibits strong variability at subseasonal timescales, known as monsoon intraseasonal oscillations, characterized by active (wet) and break (dry) phases of the monsoon. Low monsoon variability—or lower number of active and break days in the monsoon—are associated with high dengue cases and deaths. Conversely, high monsoon variability—or higher number of active and break days in the monsoon—are associated with low dengue cases and deaths. This means that years with high dengue mortality in Pune are associated with moderate rainfall distributed over time. In summary, it is not the cumulative amount of rainfall, but rather the pattern of rainfall, that plays a crucial role in influencing dengue transmission in Pune.
Currently, the India Meteorological Department (IMD) provides extended-range forecasts with information on the active-break cycles of the monsoon, 10-30 days in advance for the entire country. Utilizing these forecasts can offer additional lead time for dengue predictions. Thus, monsoon intraseasonal oscillations could serve as a valuable predictor for dengue, enhancing forecasting accuracy.
Regional Dengue Early Warning System
Existing dengue warning systems in India are rudimentary. The current health bulletin published by IMD provides warning based solely on a generic transmission window of temperature conducive to the development of dengue and overlooks the role of other factors such as rainfall and humidity, and the interplay with these climate factors. Additionally, the climate factor combinations vary regionally, calling for region-specific analysis using local meteorological and health data.
The new study has developed a dengue early warning system that incorporates all potential climate-based dengue factors (predictors) and their combined interactions with dengue at a regional scale. Using observed temperature, rainfall, and humidity patterns, the dengue model is able to predict potential dengue outbreaks by more than two months in advance, with reasonable skill. Such dengue early warning systems can help authorities take proactive measures to prevent and manage outbreaks.
Dengue Model Framework for Early Warning System and Climate Projections, using AI/ML.
Future Rise in Dengue
Temperature and humidity over India are projected to increase further into the future, while the monsoon rainfall patterns will be getting more erratic, dashed with heavy-to-extreme rains. Though heavy rains 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.
Dengue mortality in Pune is projected to rise across all emission pathways:
- Near-term (2020–2040): 13% increase in mortalities, corresponding to global warming crossing 1.5°C.
- Mid-century (2040–2060): 25–40% rise in mortalities, at 2°C warming under moderate-to-high emissions.
- Late century (2081–2100): Up to 112% increase if fossil fuel emissions remain unchecked.
It is important to note that the dengue projections are based on future climatic conditions favorable for dengue spread but do not account for the future socio-economic factors influencing transmission.
The projected change in dengue mortality for Pune under low (SSP1), moderate (SSP2), and high (SSP5) future emission pathways, with the corresponding change in mean temperature.
Data Woes and the Way Forward
Effective dengue early warning systems rely heavily on comprehensive health data collection and sharing. State public health departments play a crucial role in compiling and disseminating health data. One study indicates that dengue is significantly underreported in India, revealing that the actual number of cases is 282 times higher than the reported figures.
“We were able to conduct this study and prepare an early warning system using health data shared by Pune’s health department”, said Koll. “We approached Kerala and other states where dengue cases are high, but health departments there did not cooperate.”
Dengue Deaths in States of India, 2023
“We have meteorological data readily available from the IMD. If health data is shared, we can prepare customized early warning systems for climate sensitive diseases like dengue, malaria, and chikungunya for each city or district in India. Cooperation from health departments is key to saving lives”, Koll emphasized.
States like Kerala, Maharashtra, Goa, West Bengal, Karnataka, Tamil Nadu, Gujarat, Punjab, Haryana, Andhra Pradesh, Telangana, Rajasthan and Uttar Pradesh, which bear a significant dengue burden, can greatly benefit from an advanced early warning system like this to enhance preparedness and reduce the disease’s impact.
The insights from this study could guide policymakers in formulating targeted interventions and resource allocation strategies for managing climate-sensitive diseases.
Quotes
Sophia Yacob, IITM: “This study is a significant step in understanding how climate impacts health,” said Sophia Yacob. “The model we developed can be adapted to other regions, providing a valuable tool for managing climate-sensitive diseases like dengue.”
Roxy Mathew Koll, IITM: “In August 2024, my wife was severely affected by dengue and had to be hospitalized 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 during outbreaks.”
Sujata Saunik, Chief Secretary, Govt. of Maharashtra: “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.”
Abhiyant Tiwari, NRCD India: “This study is a step toward bridging science and action, but it requires cooperation from all stakeholders — researchers, policymakers, and public health authorities — to effectively combat the growing threat of dengue.”
Raghu Murtugudde, University of Maryland: “All predictions are meant for decisions — agriculture, water, health and such. Health applications offer the most stringent tests for weather and climate predictions. We don’t have the luxury of saying there is not enough data. We must use existing data to show what is possible and then identify data gaps to do these much more efficiently and effectively.”
Amir Sapkota, University of Maryland: “Our findings lay the foundation for climate-resilient communities where public health practitioners can anticipate climate-sensitive disease threats ahead of time, prepare for them, and respond when the time comes, rather than simply reacting to them after the fact.”
Rajib Chattopadhyay, IITM: “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”
Reference:
Sophia, Y., Roxy, M.K., Murtugudde, R., Karipot, A., Sapkota, A., Dasgupta, P., Baliwant, K., Saunik, S., Tiwari, A., Chattopadhyay, R. and Phalkey, R.K., 2025. Dengue dynamics, predictions, and future increase under changing monsoon climate in India. Scientific Reports, 15(1), p.1637 [link].
