Delhi once had harsh but breathable summers. Now humid heat is making the city harder to endure

For more than 30 years, I have lived through Delhi’s summers. The city’s heat was harsh but dry. The hot winds, called the loo, could feel brutal, yet mornings and evenings often brought some relief. Sweat evaporated quickly. Nights cooled enough for the body to recover.

That Delhi now feels distant.

Today, the city does not simply burn; it suffocates. The heat is often humid, sticky and exhausting. The air feels heavier. Even at night, temperatures remain oppressively high. What was once primarily a semi-arid climate increasingly resembles the humid heat conditions associated with coastal cities.

This transformation has not been caused by a single factor. It is the result of global climate change interacting with intensive urbanisation, pollution, waste burning, a huge number of vehicles and changing land-use patterns.

Together, these forces have reshaped Delhi’s climate into something far more dangerous.

Climate change and urban heat

At the broadest level, Delhi’s worsening summers are linked to global climate change. Across India, heatwaves are becoming more frequent, longer-lasting and more intense. Scientific studies show that average temperatures and the number of extremely hot days have risen significantly over recent decades.

But what many residents increasingly notice is not just daytime heat. It is the lack of cooling at night.

Hot nights prevent the human body from recovering from daytime stress. Continuous exposure to high temperatures creates cumulative impacts on health, especially for vulnerable populations.

Climate change has effectively raised the “baseline” temperature on which all other urban heat effects now operate.

Delhi itself has also become a massive heat-retaining structure. Concrete, asphalt, flyovers, glass buildings, parking lots and densely packed colonies absorb solar heat during the day and slowly release it through the night. This is the urban heat island effect.

Areas with dense construction and limited ventilation can be several degrees hotter than urban peripheries or less built-up parts of the city. The temperature difference between tree-lined zones and heavily built-up areas can be physically felt.

Over decades, rapid urbanisation has reduced natural cooling systems. Soil has been covered by concrete. Wetlands and water bodies have disappeared. Open spaces have shrunk. Air circulation has weakened in dense built-up clusters.

As a result, Delhi increasingly stores heat rather than releasing it.

One of the most disturbing changes is the growing combination of heat and relative humidity.

Delhi traditionally experienced dry summer heat. But in recent years, relative humidity levels during hot periods have risen noticeably. This creates a far more dangerous environment because humidity prevents sweat from evaporating effectively — the body’s primary cooling mechanism.

A humid 38 degrees Celsius (°C) can be more dangerous than a dry 44°C.

The body now struggles continuously to regulate temperature. This is why many people increasingly describe Delhi’s summers as “unbearable”, even when temperatures are similar to those experienced decades ago.

The change is visible not only in weather records but in everyday life. People tire faster. Outdoor work slows dramatically. Nights feel airless and restless. Heat exhaustion appears more common.

Delhi has effectively developed both a heat island and a “humidity island”.

A city that produces heat

Delhi’s heat is not only climatic. It is actively produced by the city itself.

More than one crore vehicles moving daily through congested roads generate enormous amounts of waste heat. Engines, exhaust systems and traffic jams continuously release thermal energy into already overheated streets.

Waste burning contributes in multiple ways. It releases direct heat, emits black carbon and greenhouse gases, worsens air pollution, and dark aerosols can trap heat near the surface.

Construction activities, diesel generators, industries and even air conditioners add to the problem. Air conditioners cool indoor spaces while pushing hot air outdoors, worsening temperatures at street level.

In this sense, the city has become a machine that generates and traps heat simultaneously.

Delhi also presents a striking contradiction.

According to recent assessments by the Forest Survey of India, almost 25 per cent of Delhi’s area is under forest and tree cover, making it among India’s greenest megacities.

Yet heat stress continues to worsen.

The explanation lies in the uneven distribution and fragmentation of greenery. Large sections of the city remain heavily built-up, with limited shade and minimal ecological cooling.

Tree cover alone cannot offset massive concrete expansion, dense traffic corridors, loss of wetlands, high energy consumption and continuous human-generated heat.

Green cover matters hugely, but it cannot compensate for uncontrolled urban heat production.

The long-term trends are revealing. Delhi’s green cover has increased over the decades. Yet heatwave days have also risen sharply. Relative humidity has steadily increased as well.

This shows that urban climate resilience depends not only on the quantity of greenery, but also on urban planning, water systems, building design and reductions in heat-generating activities.

The human cost

The worst impacts are borne by those who cannot escape the outdoors.

Construction workers labour under direct sunlight on roads, metro lines and high-rise projects. Street vendors stand for hours beside traffic-choked intersections. Delivery workers, sanitation workers, rickshaw pullers and daily wage labourers endure temperatures and humidity that are increasingly dangerous.

Many of these workers are migrants or part of the informal economy. They often lack access to shade, regular drinking water, cooling spaces, medical protection and the ability to stop working without losing income.

Heat for them is not simply discomfort. It is a direct threat to survival and livelihood.

One now routinely sees workers slowing down by afternoon, resting under flyovers or trees, covering their heads with wet cloths, or visibly struggling through the day.

What is changing now is the widening circle of vulnerability.

Even middle-class and relatively protected populations are increasingly affected. Elderly people face higher risks of dehydration and cardiac stress. Children struggle in poorly ventilated schools and homes. Families without reliable electricity face dangerous indoor heat, made worse in some homes by cooking fires. Rising energy costs make cooling inaccessible for many.

Extreme heat is no longer only a problem of “the poor”. It is becoming a structural public health crisis for the entire city and the country.

Delhi’s changing climate reflects a larger urban crisis unfolding across India.

Global warming has raised temperatures. Urbanisation has intensified them. Pollution, traffic, waste burning and concrete expansion have amplified them further. Humidity has turned the heat more dangerous. And inequality determines who suffers the most.

The city I once knew was scorching but breathable. Today, it feels heavier, more exhausting and increasingly difficult to endure.

Delhi has become greener on paper, yet less liveable in practice.

That is not merely an environmental contradiction. It is a warning about the future of Indian cities in a warming world.

Soumya Dutta is a trustee of MAUSAM (Movement for Advancing Understanding of Sustainability And Mutuality), an executive member of Friends of the Earth India, a former advisory board member of the UN Climate Technology Centre and Network, and a member of the national working group of National Alliance of People's Movements.

Views expressed are the author’s own and don’t necessarily reflect those of Down To Earth