Ahmedabad's dengue problem is no longer confined to the rainy season. Two new research papers by scientists from the Ahmedabad Municipal Corporation (AMC) and Ahmedabad University (AU) reveal that rising night-time temperatures, persistent humidity, and rapid mosquito breeding cycles are transforming the city into an increasingly efficient habitat for Aedes aegypti, the mosquito that transmits dengue. The conclusion is stark: dengue in Ahmedabad is shifting from a seasonal outbreak to a near year-round urban threat.
Ideal Breeding Conditions
The studies indicate that the mosquito thrives most aggressively in what researchers call a climatic 'Goldilocks zone'—temperatures between 25°C and 27.5°C combined with humidity above 60%. Under these conditions, the mosquito's reproductive cycle shrinks dramatically. Eggs hatch in just three days, and the insect completes its life cycle in approximately 3.5 days, allowing populations to explode before civic response systems such as fogging operations can catch up.
Outside this narrow temperature band, mosquito breeding slows down. At 15°C or 35°C, egg hatching stretches to seven days. However, researchers warn that Ahmedabad now remains inside this ideal dengue-breeding window for longer periods each year due to climate change and urban heat retention.
First Study: Climate and Dengue Trends
The first study, titled 'Emerging combinations of climatic parameters for dengue proliferation in urban landscapes,' analyzed climate and dengue data from 2012 to 2022. Conducted by researchers Vaibhavi Patel, Subhash Rajpurohit, Chirag Shah of the AMC, and Aditya Vaishya of the School of Arts and Sciences and The Climate Institute at AU, the study found that Ahmedabad's warming nights are among the most worrying signals.
According to the study, night-time temperatures in the city have risen by 0.41°C per decade, while average temperatures increased by 0.29°C and relative humidity by nearly 1% every decade during the study period. Earlier, cooler nights interrupted mosquito activity and reduced survival rates. That natural brake is weakening. The researchers cite previous urban climate studies showing that Ahmedabad has recorded one of the sharpest increases in night-time land surface temperatures among comparable Indian cities due to rapid urbanization.
The mosquito itself appears biologically prepared for this new climate. Research referenced in both papers found that Aedes aegypti eggs can survive dry periods by altering their fat and chemical metabolism. The eggs remain dormant until humidity crosses the 60% threshold, after which they hatch simultaneously—creating sudden surges in mosquito populations after brief wet spells or humid conditions.
Second Study: Dengue Spread Across Neighbourhoods
The second study moves beyond weather and examines how dengue actually spreads across Ahmedabad's neighbourhoods. Titled 'M-SDT: A modelling framework for dengue transmission, forecasting, and intervention strategies in Ahmedabad Municipal Corporation,' the research was led by Sourav Roy and Indrajit Ghosh from AU's Bagchi School of Public Health in collaboration with AMC officials Rajendra Gadhavi, Bhavin Solanki, Chirag Shah, and Raj Sharma. Using mathematical modelling, the study calculated the city's dengue reproduction number—or 'R0'—at 1.7929.
Epidemiologists use R0, pronounced 'R-naught,' to estimate how many people one infected person is likely to infect on average. Any value above 1 means the disease can sustain transmission within a population. Ahmedabad's overall figure is already considered high. But the study identified three particularly vulnerable zones where transmission risks are significantly stronger: the Central Zone with an R0 of 2.2128, the North-West Zone at 2.0562, and the South Zone at 2.0049.
Researchers warn that once the value crosses 2, even modest increases in mosquito density or human contact can rapidly escalate into local epidemics. These areas, the paper notes, effectively function as 'source zones' from which infections spill into neighbouring localities.
One of the study's most striking findings is that nearly 90% of infected individuals may show no symptoms while still contributing to transmission. This silent spread makes containment especially difficult because infected residents continue normal daily movement without realizing they are carrying the virus.
Implications for Public Health
Together, the two papers suggest that Ahmedabad's dengue challenge is no longer simply about stagnant water or delayed fogging. The disease is increasingly being shaped by deeper structural shifts—warmer nights, denser urban landscapes, changing humidity patterns, and a mosquito species evolving to survive them all.
