Published Sep 19, 2026 | 6:20 PM ⚊ Updated Sep 19, 2026 | 6:20 PM
Aedes aegypti mosquito. (Creative Commons)
Synopsis: A new study finds Keralam’s dengue burden is closely tied to monsoon rainfall, temperature, humidity and El Niño. Researchers project dengue incidence could rise 16 percent–20 percent by 2040 and up to 113 percent by century-end under high emissions. The findings point to climate-based early warnings months before dengue cases peak.
Keralam’s dengue numbers track the monsoon, and as the climate shifts, that link could push cases higher for decades, a new study finds. The state logs about 5,000 cases most years, but spikes hit 21,993 in 2017, 16,766 in 2023 and 20,088 in 2024.
Researchers project dengue incidence could climb 16 percent–20 per cent between 2021 and 2040. Under a scenario where emissions keep climbing through the century, that figure could reach 113 per cent by 2100.
The study, published in the journal GeoHealth, comes from teams at the Indian Institute of Tropical Meteorology, ICMR-National Institute of Translational Virology and AIDS Research, Keralam University of Health Sciences and Government Medical College, Thrissur. They worked through 14 years of dengue and weather data, from 2006 to 2019, to trace how climate drives outbreaks in the state.
“Dengue fever has emerged as a major public health threat in India, with its burden projected to rise under climate change,” the authors wrote. “This study investigates the influence of climate variability on dengue incidence in Keralam, a dengue hotspot in southern India.”
Cases cluster tightly around the southwest monsoon. About 60 per cent of Keralam’s dengue burden falls between June and September, and June alone carries the peak.
“Dengue seasonality in Keralam closely follows its rainfall cycle, with cases rising in May and peaking during the southwest monsoon, reaching a maximum in June-July,” the authors noted.
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The team traced dengue back to a mix of temperature, rainfall, humidity and a Pacific Ocean weather cycle called El Niño, which swings between warm and cool phases and reshapes rainfall patterns across Asia.
Temperatures between 30.5°C and 32.5°C, paired with humidity of 66 per cent to 79 per cent before the monsoon breaks, lined up with sharper case rises. Add 180–450mm of monthly monsoon rainfall, and the risk climbs further.
But none of these signals arrives on cue. Each climate variable takes its own time to show up in the case data.
Mean and maximum temperatures lead dengue by three months. Minimum temperature runs two months ahead. The daily swing between a location’s high and low temperature, and humidity, stretches furthest, showing their strongest link five months out. Rainfall, by contrast, hits almost immediately.
“Locally, warmer temperatures and moderate humidity during the pre-monsoon season, together with moderately high rainfall during the monsoon season, favour high dengue incidence,” the authors wrote.
That lag, researchers argue, hands health planners a window rather than a warning.
The study then turns to the Pacific. El Niño and its cooler counterpart La Niña appear to reach all the way into Keralam’s dengue numbers.
Researchers found a positive link between dengue cases and Pacific sea surface temperatures, with the connection showing up strongest three months later.
“Remotely, El Niño-like conditions increase dengue incidence by shifting large-scale circulation toward warmer and drier pre-monsoon conditions over Keralam, while La Niña-like conditions have the opposite effect, providing about three months of potential predictability,” the authors wrote.
The numbers back this up. Climate model runs showed 40 per cent of high-dengue years coincided with El Niño. Not one high-dengue year lined up with La Niña.
The reverse held too. 57 per cent of low-dengue years fell during La Niña, and none touched El Niño.
“El Niño events are associated with higher dengue risk by creating warmer and drier conditions, while La Niña events are linked to cooler and wetter conditions that reduce the risk,” the authors said.
They stop short of calling this Pacific cycle the whole story. “It was an important, but not exclusive, driver of dengue variability,” the study noted, pointing to the short 14-year dataset as a limit on how far the finding can travel.
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To pull these threads together, researchers tested four computer models built to learn patterns from data and forecast outcomes.
One approach, called XGBoost, which builds its forecast by correcting its own errors step by step, outperformed the rest, explaining 72 per cent of the variation in dengue cases against 48–52 per cent for the other methods. The team trained it on data from 2006 to 2016, then tested it against 2017–2019 figures it had never seen.
“Using a machine learning approach, we developed a model that captures the complex relationship between climate and dengue incidence over Keralam,” the authors wrote.
Temperature and rainfall carried the most weight in the model’s predictions.
“The results from the current study provide important insights that can enhance prevention strategies, inform policymaking, and support climate-adaptive public health planning, aiding in the mitigation of dengue outbreaks in a warming climate,” the authors wrote.
Researchers then fed the model six sets of future climate data, run under three tracks that map out how far the world cuts, or fails to cut, greenhouse gas emissions this century.
Every track pointed the same direction: up.
For 2021–2040, dengue incidence could rise 16–20 per cent against case numbers recorded between 1995 and 2014. By 2041–2060, that grows to 32 per cent under the track with the deepest emission cuts, 33 per cent under a middle track and 44 per cent under the track with the least action on emissions.
By 2081–2100, the spread widens further: 46 per cent under the low track, 63 per cent under the middle track, and up to 113 per cent under the high track.
“Future simulations project an increase in dengue incidence by 16%-20% in the near future and 46%-113% in the far future under low-to-high emission pathways,” the authors wrote.
Keralam’s temperatures track a similar climb. The study projects a rise of 0.91°C per century under the low track, 2°C under the middle track and 4.4°C under the high track, all measured across 2015–2100.
Rising daily maximum temperatures carry the heaviest weight behind that dengue rise, contributing 4–22 per cent across the tracks, the study found.
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Rain does not always help the mosquito. The study flags a twist: while moderate rain fills containers where mosquitoes breed, heavy rain can wash eggs and larvae away.
Researchers tested this by stripping out the heaviest rainfall events, those that historically ranked among the top 10 per cent for intensity, then rerunning the model.
Dengue projections rose 3–7 per cent once those extreme events disappeared from the data.
“These findings suggest that future extreme rainfall events can suppress dengue transmission to some extent, thereby potentially offsetting the projected increase in dengue incidence by three to seven per cent for Keralam,” the study noted.
The paper closes by calling on health authorities to fold climate signals into dengue surveillance.
“These findings highlight the need for climate-informed dengue early warning and future risk planning in Keralam,” the authors wrote.
They caution that the projections track only climate-driven change. They leave out mosquito control programmes, population growth and shifting immunity levels in the population, all of which could bend the numbers further.
“Despite these constraints, the dengue model demonstrated reasonable forecasting accuracy, providing region-specific insights that can support early warning systems and public health planning to control dengue in Keralam,” the authors wrote.
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