Climate change increases dengue risk in Keralam; cases may rise by 20% by 2040, says study
A study projects that dengue risk in Kerala could rise by roughly 16-20% during 2021-2040, and by up to 113% by the end of the century (2081-2100), depending on the emissions pathway used.
The study identifies rainfall, humidity, and the El Nino-Southern Oscillation (ENSO) as key climatic drivers of dengue transmission in the state.
It finds that atmospheric pressure, temperature, and relative humidity shifts during the active and break phases of the monsoon influence localised mosquito breeding and dengue risk.
Locally, warmer pre-monsoon temperatures (around 30.5-32.5°C), moderate humidity (66-79%), and moderately high monsoon rainfall (180-450 mm/month) were found to favour higher dengue incidence.
The findings point to a need for climate-informed public health planning to manage the projected rise in dengue cases.
El Nino-Southern Oscillation (ENSO) and Disease Transmission
ENSO is a recurring climate pattern involving periodic warming (El Nino) and cooling (La Nina) of sea-surface temperatures in the central and eastern equatorial Pacific Ocean, coupled with atmospheric pressure shifts, occurring in irregular cycles of roughly two to seven years.
Key Details
- ENSO has three phases: El Nino (warm phase), La Nina (cool phase), and a neutral phase; an El Nino event is typically defined as a sea-surface warming episode lasting 12-18 months.
- ENSO alters rainfall and temperature patterns globally, including the Indian monsoon, and is documented (including by IPCC assessments) as a background driver of vector-borne and water-borne disease outbreaks such as dengue, malaria, chikungunya, and leptospirosis.
- Mechanistically, ENSO-linked warming and altered rainfall change mosquito breeding-site availability and the extrinsic incubation period of the dengue virus inside the mosquito vector.
The Kerala study specifically models ENSO alongside rainfall and humidity as a predictor of future dengue risk, linking a global climate oscillation to a localised, state-level public health projection — a typical UPSC "global phenomenon, local impact" bridge.
IPCC Findings on Climate-Sensitive Vector-Borne Diseases
The IPCC's Sixth Assessment Report (AR6), Working Group II, dedicates a cross-chapter analysis to infectious diseases and climate change, concluding that dengue transmission has expanded globally since 1990 and that rising temperatures are increasing the geographic range of climatic suitability for dengue transmission.
Key Details
- AR6 WGII notes that while urbanisation, vector-control gaps, and human mobility all contribute to dengue's spread, warming has independently increased the physiological suitability of many regions for transmission.
- The relationship between temperature and the mosquito's "extrinsic incubation period" (time for the virus to become transmissible inside the mosquito) is non-linear, meaning small temperature increases in certain ranges can sharply raise transmission risk.
- This global assessment framework is the scientific basis cited by India-specific and state-specific dengue-climate studies, including for South Asia.
The Kerala projection is a localised application of the IPCC's global finding that climate change is expanding dengue's transmission window — useful for a Mains answer connecting international climate science to Indian public health policy.
Aedes aegypti and India's Vector-Borne Disease Control Architecture
Dengue in India is transmitted primarily by the Aedes aegypti mosquito, a "container-breeder" that lays eggs in stagnant water in domestic and peri-domestic containers (tanks, drums, coolers, discarded tyres) rather than in open water bodies, and which feeds during the daytime.
Key Details
- Aedes aegypti has a strong preference for human blood and typically breeds close to human dwellings, making urban and semi-urban water-storage practices a key determinant of outbreak risk — distinct from Anopheles (malaria vector, breeds in cleaner, larger water bodies) and Culex (a vector for Japanese Encephalitis and lymphatic filariasis).
- India's vector-borne disease control programme (covering dengue, malaria, Japanese Encephalitis, chikungunya, kala-azar, and lymphatic filariasis) is administered under the National Center for Vector Borne Diseases Control (NCVBDC), Directorate General of Health Services, Ministry of Health and Family Welfare, and implemented through the National Health Mission.
- Dengue has four distinct virus serotypes (DENV-1 to DENV-4); infection with one serotype does not confer immunity against the others, and repeat infection with a different serotype raises the risk of severe dengue.
Rising climate-driven dengue risk sharpens the case for strengthening India's existing vector-control institutional architecture (NCVBDC/NVBDCP) and integrating climate projections like Kerala's into vector-surveillance planning, rather than relying only on reactive outbreak response.
- Projected Kerala dengue risk increase: 16-20% during 2021-2040; up to 113% by 2081-2100 (low- to high-emission scenarios)
- Key local risk conditions: pre-monsoon temperature 30.5-32.5°C, humidity 66-79%, monsoon rainfall 180-450 mm/month
- ENSO cycle length: roughly 2-7 years; El Nino event duration: typically 12-18 months
- Dengue virus serotypes: four (DENV-1 to DENV-4)
- Primary dengue vector in India: Aedes aegypti (container-breeder, day-biting)
- Nodal agency: National Center for Vector Borne Diseases Control (NCVBDC), under the Directorate General of Health Services, MoHFW