According to a study published in the journal GeoHealth, Keralam’s dengue burden is closely tied to monsoon rainfall, temperature, humidity, and El Niño cycles, with researchers projecting that incidence could rise between 16 percent and 20 percent by 2040 and up to 113 percent by the end of the century under high-emission scenarios. Teams from the Indian Institute of Tropical Meteorology, the ICMR-National Institute of Translational Virology and AIDS Research, Keralam University of Health Sciences, and Government Medical College, Thrissur, analyzed 14 years of data from 2006 to 2019 to map out how weather patterns drive outbreaks in the southern Indian state.
How Monsoon Weather and Climate Shifts Drive Dengue in Keralam
Keralam typically records about 5,000 dengue cases in most years, but severe outbreaks have pushed those numbers much higher. The state logged 21,993 cases in 2017, followed by 16,766 cases in 2023 and 20,088 cases in 2024, according to the research data. Roughly 60 percent of the state’s total dengue burden falls between June and September, with June alone acting as the annual peak. Researchers noted that the seasonality of the virus closely follows the rainfall cycle, with infections beginning to climb in May before reaching a maximum during the southwest monsoon months of June and July.
The study highlights that local conditions—such as pre-monsoon temperatures ranging from 30.5°C to 32.5°C paired with 66 percent to 79 percent humidity—line up with sharper case increases when combined with 180mm to 450mm of monthly monsoon rainfall. However, these climate variables do not manifest immediately in case counts. Mean and maximum temperatures lead dengue trends by three months, minimum temperatures lead by two months, and daily temperature swings alongside humidity show their strongest correlation five months out. Rainfall, by contrast, influences case numbers almost immediately.
El Niño and Pacific Weather Patterns as Early Warning Signals
Beyond local weather, the study reveals that Pacific Ocean climate cycles reach into Keralam’s disease data. Researchers found a positive link between dengue cases and Pacific sea surface temperatures, with the connection peaking three months later. El Niño conditions tend to increase dengue incidence by creating warmer and drier pre-monsoon conditions over the state, while La Niña phases have the opposite effect, offering roughly three months of potential predictability for health planners.
The historical numbers support this Pacific connection. Climate model simulations showed that 40 percent of high-dengue years coincided with El Niño events, while zero high-dengue years lined up with La Niña. Conversely, 57 percent of low-dengue years fell during La Niña phases, with none touching El Niño. The authors noted that while the Pacific cycle is an important driver, it is not the sole factor influencing Keralam’s disease variability, constrained somewhat by the short 14-year dataset analyzed.
Did You Know? While moderate rain fills the water containers where Aedes aegypti mosquitoes breed, extreme downpours can actually wash away eggs and larvae. When researchers removed the heaviest 10 percent of rainfall events from their models, projected dengue numbers rose by 3 percent to 7 percent, suggesting that extreme storms can suppress transmission to a degree.
Machine Learning Projections Point to Higher Burdens by 2100
To forecast future outbreaks, the research team tested four computer models and found that XGBoost—an approach that builds forecasts by correcting its own errors step by step—outperformed the others. It explained 72 percent of the variation in dengue cases during testing against unseen 2017–2019 figures, compared to 48 percent to 52 percent for competing methods. When the team ran this model against future climate scenarios mapping different levels of global greenhouse gas emissions, every track pointed toward a higher disease burden.
For the 2021–2040 window, dengue incidence is projected to rise 16 percent to 20 percent compared to baseline numbers recorded between 1995 and 2014. By the 2041–2060 period, that increase grows to 32 percent under the track with the deepest emission cuts, 33 percent under a middle track, and 44 percent under the track with the least action on emissions. Toward the end of the century, spanning 2081–2100, the spread widens to 46 percent under the low track, 63 percent under the middle track, and up to 113 percent under high emissions. Rising daily maximum temperatures carry the heaviest weight behind these increases, contributing between 4 percent and 22 percent across the various emission pathways.
Frequently Asked Questions
When does dengue peak in Keralam?
About 60 percent of Keralam’s dengue burden occurs between June and September, with June carrying the highest peak of the year following the onset of the southwest monsoon.
How much could dengue cases increase by the end of the century?
According to the GeoHealth study, dengue incidence could rise between 46 percent and 113 percent by 2081–2100, depending on future greenhouse gas emission tracks.
What weather factors influence dengue outbreaks in the state?
Warmer pre-monsoon temperatures between 30.5°C and 32.5°C, moderate humidity levels, monthly monsoon rainfall between 180mm and 450mm, and El Niño climate cycles all correlate with increased disease risk.
Do heavy rains increase dengue transmission?
While moderate rain creates breeding sites for mosquitoes, extreme rainfall events can wash away eggs and larvae, occasionally suppressing transmission by 3 percent to 7 percent.
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