When rain isn't enough: Why Indian cities are struggling with heat despite downpour

India’s cities must move beyond seasonal heat response measures and adopt year-round, localised strategies to tackle rising humidity and persistent nighttime heat, experts have said, warning that conventional approaches are becoming inadequate as climate patterns evolve.

The warning comes even as the southwest monsoon has advanced across northern India. While rainfall may bring relief from soaring daytime temperatures, experts note that high humidity often keeps conditions uncomfortable, with the heat index — which reflects how hot it feels after accounting for humidity — remaining significantly higher than the actual air temperature.

Delhi illustrates the challenge. Heat index records between 2021 and 2025 show that during July and August, the capital frequently experienced 'feels-like' temperatures of 46°C to 50°C despite lower recorded air temperatures. Higher humidity also prolonged electricity demand as cooling systems, particularly air conditioners, operated for longer periods.

The Delhi government has introduced temporary cooling zones, mobile cooling vans and dedicated cool wards in hospitals under its Heat Action Plan (HAP). While such interventions provide immediate relief during extreme weather, researchers argue that they need to be complemented by permanent measures tailored to changing heat patterns.

Heat risk changing across cities

Studies published over the past year indicate that India's heat risk is increasingly being driven by humidity and warmer nights rather than daytime temperatures alone.

An assessment by the Council on Energy, Environment and Water (CEEW), covering 734 districts, identified rising nighttime temperatures, increasing humidity across the Indo-Gangetic Plain and greater heat exposure in densely populated urban centres including Delhi, Mumbai, Ahmedabad, Hyderabad, Bhopal and Bhubaneswar.

Separately, a study released on 24 June by the US-based non-profit Climate Central found that the number of dangerously humid heat days in India has risen from 101 annually during the 1970s to 141 in recent years. The study used a wet-bulb temperature threshold of 25°C or above, beyond which the human body's ability to cool itself through perspiration becomes increasingly limited.

Several cities recorded substantial increases over the five decades, including Delhi, Ghaziabad, Nagpur, Raipur, Ahmedabad and Jaipur.

Scientists attribute the trend partly to warming waters in the Arabian Sea and the Bay of Bengal, which transport greater moisture inland. Combined with rapid urbanisation and the urban heat island effect, the additional humidity reduces nighttime cooling and can keep daytime temperatures elevated.

Warm nights emerging as a major concern

Nighttime heatwaves are becoming an increasingly important public health challenge.

A study published earlier this year in the journal Physics and Chemistry of the Earth, which analysed data from 100 Indian smart cities between 2001 and 2024, found persistent nighttime heatwaves in cities including Delhi, Agra, Kanpur, Varanasi, Jhansi, Gwalior and Kochi. Another group of cities, including Aurangabad, Bhopal, Indore, Nagpur, Raipur, Warangal and Puducherry, experienced prolonged heat during both day and night.

Kashif Imdad, an associate professor at CSJM University in Kanpur and one of the study's authors, told Hindustan Times most city heat action plans continue to focus primarily on daytime measures such as drinking water, public awareness campaigns, medical preparedness and revised work schedules.

He said future plans should also prioritise measures aimed at reducing nighttime temperatures, including cool roofs, expanded green cover, natural ventilation, reliable electricity supply and round-the-clock emergency response systems.

Passive cooling alone may not be enough

Experts also caution against relying on single solutions.

Rajan Rawal, a professor at CEPT University and an expert on passive building design, said cool roofs — widely promoted as an effective intervention — have limitations because indoor comfort depends not only on roof temperatures but also on humidity, surrounding air temperatures and heat absorbed through walls, windows and floors.

He noted that while cool roofs help reduce heat retained by concrete structures, they are less effective for lightweight roofing materials such as tin or cement sheets, which cool rapidly after sunset. In northern India, where winters can be cold, seasonal or removable cooling solutions may prove more practical than permanent installations.

Traditional architectural features such as courtyards, high ceilings and ventilators also have reduced effectiveness in densely built urban environments where surrounding temperatures remain elevated.

Rawal and other researchers instead advocate integrated passive building designs that improve insulation, ventilation and heat management through construction materials and building layouts. Although such designs may involve higher initial costs, they can reduce long-term dependence on air conditioning while limiting waste heat released into urban environments.

Vishwas Chitale of CEEW said active cooling would remain necessary in many cities experiencing increasingly humid conditions, although ensuring affordable access to efficient cooling technologies remains a significant challenge.

Greening strategies need local adaptation

Researchers say urban greening also requires a more nuanced approach.

Trees provide shade and cooling through evapotranspiration, but in humid environments excessive moisture combined with restricted airflow can increase heat stress despite lower surface temperatures.

A study by IIT Gandhinagar, published in Nature Communications, analysed 138 Indian cities and concluded that greening initiatives in humid regions must balance shade, moisture management and ventilation rather than focusing solely on increasing tree cover.

Despite the growing challenges, experts say urban heat planning is becoming more sophisticated.

Newer heat action plans increasingly incorporate local climate conditions, vulnerability assessments and projections for future heat risks.

Thane's 2024 Heat Action Plan, for instance, uses the Intergovernmental Panel on Climate Change (IPCC) risk assessment framework to map hazards, exposure and vulnerability at the ward level. CEEW is currently supporting 145 cities across seven states in preparing similar plans.

Meanwhile, Bhubaneswar is preparing to launch a climate-risk dashboard that will map heat stress at the building level using satellite imagery, weather observations and local sensor data. The platform is expected to support long-term planning by identifying vulnerable locations such as schools, hospitals, transport hubs and government buildings.

Experts say such data-driven tools, combined with locally tailored infrastructure and governance measures, will become increasingly important as Indian cities adapt to more frequent and intense humid heat conditions.