Urban heat is pushing Indian cities towards unliveability

Kumar Subramanian|

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The problem
As I stepped out of our Gurgaon office at around 8pm on 26th May, the air did not feel like night-time at all. My weather app showed a temperature of 40.2°C. But the more alarming number was the “feels like” temperature—54.2°C. At this level, conditions are classified as “Extreme Danger”, where prolonged exposure can become life-threatening.

This “feels like” temperature—technically known as the heat index—captures how humidity interferes with the body’s ability to cool itself through sweat. When humidity rises, sweat cannot evaporate efficiently, trapping heat against the skin. The result is that the human body experiences conditions far harsher than what the thermometer shows.

Delhi’s summers are typically bone-dry. High temperatures, while uncomfortable, have historically been survivable. But on that evening, an unusual combination of haze and thunderclouds pushed humidity levels above 60%, far higher than the usual 20–30%. This single shift was enough to push the heat index into a zone that challenges human survivability.

A worrying trend, not an isolated event
To understand whether this was an anomaly or part of a broader pattern, I analysed historical weather data across the past two decades (2007–2026), focusing on May and June—the hottest months across most Indian cities.

  • The threshold heat index of 52°C, beyond which conditions are considered extremely dangerous
  • The number of days this threshold was breached
  • The peak night-time heat index levels, particularly around 8pm

The results are deeply concerning. Indian metros are not only crossing dangerous heat thresholds more frequently, but they are also reaching higher peaks than ever before.
I focused on three cities—Mumbai, Delhi National Capital Region (NCR), and Chennai—each representing a different climatic profile but all showing signs of escalating risk.
Three cities, three distinct vulnerabilities
1. Mumbai — A humidity tipping point
Mumbai benefits from a moderating sea breeze and significant wetland coverage, which help keep temperatures relatively stable. Night-time temperatures typically remain in the low 30s.

However, the city operates under persistently high humidity (75–80%). This means even a slight increase in temperature—to 35-36°C—is enough to push the heat index into dangerous territory. This tipping point was crossed for the first time in 2024, signalling a growing vulnerability.
2. Delhi NCR — From dry heat to dangerous humidity
Delhi has long experienced intense heat waves, but evenings historically brought some relief, with temperatures cooling to the mid-to-high 30s. Low humidity ensured that the heat index stayed close to the actual temperature.

That pattern is now breaking. Rising night-time temperatures combined with occasional spikes in humidity are pushing the heat index beyond survivable thresholds. The breach in 2024—and again in 2026—could mark a structural shift rather than a one-off anomaly.
3. Chennai — Persistent extreme exposure
Chennai faces a unique and more persistent challenge. During Agni Nakshatram—the peak summer phase—its geographical orientation traps heat, while a delayed sea breeze raises humidity sharply in the evenings.

Even when temperatures hover around 34–35°C, humidity levels of 75–85% push the heat index beyond 52°C. Unlike other cities, Chennai has experienced such conditions almost every year in recent times, indicating a chronic and escalating risk.
Why night-time heat is particularly dangerous
Extreme heat during the day is disruptive—but when temperatures remain dangerously high at night, the implications are far more severe.
1. Infrastructure stress
Millions of air conditioners operate simultaneously, pushing electricity grids to their limits. Transformer failures, fires, and rolling blackouts become increasingly likely.
2. Public health crisis
The human body relies on cooler nights to shed accumulated heat. When this recovery window disappears:
To understand whether this was an anomaly or part of a broader pattern, I analysed historical weather data across the past two decades (2007–2026), focusing on May and June—the hottest months across most Indian cities.

  • Sleep is disrupted
  • Cardiovascular strain increases
  • Risk of heat-related illness and cardiac events rises sharply
3. A deepening inequality
For millions who rely on fans rather than air conditioning, extreme night-time heat becomes a matter of survival, not comfort. Urban heat thus transforms into a powerful amplifier of social inequality.
The real driver: urbanisation amplifying climate change
Climate change is raising baseline temperatures globally—but this alone does not explain the severity of urban heat.
It is unplanned urbanisation that transforms this baseline into a localised crisis.
As cities expand:

  • Green cover and wetlands are replaced with concrete
  • Buildings and roads absorb heat during the day
  • This heat is slowly released at night, preventing cooling
This phenomenon, known as the urban heat island effect, can raise night-time temperatures by several degrees. Studies have shown increases of around 3°C in cities like Chennai.
In effect:
Climate change raises the baseline. Unplanned urbanisation turns it into a dangerous extreme.
The path forward: embedding heat resilience
Urban heat is not a distant climate risk. It is already reshaping how our cities function—and how people live, work, and survive within them.
Addressing it requires embedding resilience into how we design and manage cities:

  • Cool roofs and reflective materials to reduce heat absorption
  • Urban greening and water bodies to mitigate heat islands
  • Augmented climate-sensitive building codes for passive cooling with stronger enforcement
  • Resilient energy systems to handle peak demand
The solutions exist—but they remain fragmented, under-implemented and inadequately financed.
Conclusion
India’s growth ambition will require building the equivalent of a new Chicago every few years. But how we build will decide whether our cities remain engines of growth—or become environments that are increasingly difficult to inhabit.

The challenge now is not recognising the problem. It is acting decisively, at scale, and in time.

Kumar Subramanian

Founding Partner and Managing Director at Sculpt Partners

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