February Fog: Climate Change Rewriting City’s Weather Profile?

Chennai:As February is usually marked by rising heat and clear mornings, dense fog settling over Chennai these days has raised fresh questions about whether the city’s weather is quietly but decisively changing.

In recent mornings, visibility across arterial roads, suburban rail corridors, and even near Chennai airport dropped sharply, disrupting traffic and flight operations.

Meteorologists say that while fog is not uncommon in coastal Tamil Nadu, its timing, persistence and spread in February are unusual and increasingly difficult to dismiss as a one-off anomaly.

Traditionally, Chennai experiences fog or mist during late December and early January, when cooler nights, residual winter moisture, and calm winds coincide. February, by contrast, is expected to mark a transition into warmer conditions, with steadily rising daytime temperatures and clearer mornings.

The Regional Meteorological Centre (RMC) attributed the fog to a combination of high humidity, cooler night-time temperatures, and light winds, which allowed water vapour near the surface to condense into tiny droplets in the early hours.

While such conditions are typical of late winter, the department has indicated that early morning fog or mist may persist across Chennai and parts of Tamil Nadu through the end of February, even as daytime temperatures continue to rise.

“This is not classic winter fog,” said V. Prabhakaran, an environmental activist with Poovulagin Nanbargal. “It is a hybrid phenomenon, influenced by climate change rather than purely seasonal cycles.”

One of the drivers behind this shift is Chennai’s expanding urban heat island effect, in which dense built-up areas retain heat at night and alter local atmospheric behaviour. Concrete surfaces, asphalt roads, glass façades and shrinking green cover absorb heat during the day and release it slowly after sunset, leading to warmer nights, weaker air circulation and moisture trapped close to the ground.

“When warm air near the surface interacts with cooler upper layers under high humidity, fog forms,” Prabhakaran said. “Cities like Chennai are now creating their own microclimates.”

Satellite-based studies have shown that night-time temperatures in core city areas are 2–4°C higher than in surrounding semi-urban zones, a difference large enough to affect dew points, cloud formation, wind patterns, and atmospheric stability.

The February fog cannot be viewed in isolation. It forms part of a broader pattern of weather volatility Chennai has experienced in recent years, including intense heat waves, sudden cloudbursts, prolonged dry spells and floods that overwhelm infrastructure.

Climate experts warn that rapid urbanisation amplifies global climate change at the local level. As green spaces shrink and wetlands vanish, the city loses natural systems that once moderated heat and moisture.

“Chennai is warming overall, but paradoxically also seeing conditions that support fog,” a senior meteorologist said. “That contradiction is a hallmark of climate-stressed cities.”

The loss of wetlands such as the Pallikaranai marsh, encroachment on floodplains and reduction in tree cover have weakened Chennai’s ability to balance temperature and humidity. Wetlands once acted as thermal buffers, absorbing heat and releasing moisture gradually. Their degradation has made atmospheric changes sharper and less predictable. The result is fog when it should not occur, floods when rainfall should not overwhelm, and heat when relief should arrive.

Long-term data on fog over Chennai airport reinforces this trend. Studies show that fog occurrences have risen steadily over the past five decades, with nearly 400 instances recorded. The mean annual fog frequency at the airport now stands at 21.5 days, with January remaining the most favourable month, followed closely by February and March.

Researchers have also observed a sharp rise in low-level temperature inversions and surface isotherms over the past two decades. Rapid urbanisation, increased vehicular movement, and higher concentrations of suspended particulate matter, sulphur dioxide and nitrogen oxides have contributed to greater atmospheric stability and provided condensation nuclei for fog formation.

Though pollution levels have reduced in recent years, concentrations still frequently exceed national ambient air quality standards.

During December to March, low-level atmospheric inversions have become an almost day-to-day phenomenon, particularly in February, in the last decade. Once fog forms under these conditions, the stable atmosphere prevents dispersion until sunlight breaks the inversion later in the morning. Meteorologists stress that inversion alone does not cause fog, but in combination with high humidity, calm winds and pollutants, it sustains and intensifies it.

Experts caution against treating such events as isolated anomalies. “Climate change does not announce itself with a single disaster,” said an environmental planner. “It rewrites patterns quietly. February fog is a warning signal, not an outlier.”

As Chennai continues to expand vertically and horizontally, the city is likely to face more off-season weather events — fog in warmer months, heat during traditionally mild periods, and rainfall that defies historical models.

The question now is whether Chennai is prepared to redesign its urban systems, from buildings and roads to green spaces, wetlands and drainage, for a climate that no longer follows the old calendar. February’s fog suggests the answer may determine not just how the city moves, but how it survives in the decades ahead.