The new heat threat: Why India’s cities are feeling hotter even after monsoon arrives

SAlespeople, day-after-day wagers, a police force police on a break away, a couple up of foreign tourists, and a waste picker — Delhi’s largest “cooling zone” outside Jama Masjid metro station was packed to capacity. Some queued up for cold water while others huddled close to fans and coolers.Squeezing in quietly, autorickshaw driver RK Shukla asked hesitantly if the air cooler could be adjusted: “It’s the same problem at home. When it gets humid, my desert cooler throws warm air.” This was late June when the pre-monsoon heat index—which measures how hot it feels—made Delhi suffocating. The highest it touched this month was 53° Celsius.The monsoon has reached northern India since, but rainfall alone does not guarantee thermal comfort. Heat index records from 2021 to 2025 show that Delhi often felt hotter than its air temperature due to high humidity. In July-August, the heat index often exceeded 46-50°C, causing oppressive conditions. This discomfort extended the duration and intensity of high electricity consumption as cooling systems, mainly air conditioners, worked harder and longer, according to a policy brief from the Centre for Science and Environment last September.Also Read: Monsoon has arrived in Delhi, but where is the rain? Experts explainAs part of its heat action plan (HAP), the Delhi administration has launched temporary cooling zones, mobile vans, and cool wards in hospitals. Emergency measures are understandably seasonal, but experts warn that Indian cities must act swiftly to adopt informed, targeted, and year-round programmes to safeguard against changing heat patterns. The heat resetThere is an alarming rise in warm nights; increased relative humidity in the Indo-Gangetic Plain; and heightened heat exposure in dense, urban and economically important districts such as Delhi, Mumbai, Ahmedabad, Hyderabad, Bhopal, and Bhubaneswar. The Council on Energy, Environment and Water (CEEW) analysed heat risk across 734 districts to highlight these key trends last year.Also Read: Delhi set to see rain from July 6 to 11; IMD warns of heavy showers as monsoon finally takes effectMore recently, on June 24, a study by US-based non-profit Climate Central revealed that since the 1970s, India has experienced an increase in dangerously humid heat days, from 101 to 141 per year. Globally, the number went up from 10 to 23. The benchmark for such days is a wet-bulb temperature — a measure of how much an object can cool down through evaporation — of 25°C or higher.Over five decades, Delhi saw the number of such dangerously humid days rise from 96 to 135; Ghaziabad from 99 to 137; Nagpur from 44 to 119; Raipur from 82 to 150; Ahmedabad from 137 to 162; and Jaipur from 55 to 101.Scientists link these changes to ocean warming. In India, the Arabian Sea and the Bay of Bengal push moisture inland. Due to high mean temperatures driven by factors like excessive urbanisation, the Urban Heat Island effect dominates the drying impact (also known as the Urban Dry Island effect) when there’s moisture in the environment. This humidity also hampers normal cooling at night. If there are extended periods of high humidity without rain and nighttime temperatures remain high, the next day’s maximum is kept elevated.Nighttime heat waves were persistent in 15 smart cities, including Delhi, Agra, Kanpur, Varanasi, Jhansi, Gwalior, and Kochi, said a study published in the journal Physics and Chemistry of the Earth released in March this year. Analysing March-June data between 2001 and 2024 for all 100 smart cities of India, the study found another 16 cities of them — including Aurangabad, Bhopal, Indore, Nagpur, Raipur, Warangal, and Puducherry — experienced persistent compound heat both day and night.Most city HAPs neglect the full diurnal dimension of heat risks, focusing largely on measures such as providing drinking water, raising awareness, improving medical preparedness, and adjusting work and school timings, said Kashif Imdad, one of the study’s authors and an associate professor at CSJM University in Kanpur.To combat nighttime heat, Imdad suggests cool roofs, green cover, natural ventilation, and reliable electricity; additionally, 24-hour response systems, health preparedness, and passive techniques to cool homes and workspaces for cities facing intense heat both day and night.Common solutionsPrioritising context-specific solutions over purely theoretical ones is essential. Rajan Rawal, a professor at Ahmedabad’s CEPT University and a specialist in passive design and urban climate, highlights this with the commonly cited solution of cool roofs — surfaces engineered to reflect sunlight and reduce heat.Since urban heat is not solely about daytime sun exposure, blocking or reflecting sunlight cannot significantly improve indoor comfort. This physical comfort depends not only on roof surface temperature but also on air temperature and humidity, Rawal wrote in an essay he co-authored with Radhika Khosla, an associate professor at Oxford University’s Smith School of Enterprise and the Environment.Also Read: Water supply to be disrupted in parts of Delhi due to maintenance work. Check if your area is affectedThe heat map of cities, derived from satellite data, typically focuses on daytime land surface temperatures and neglects nighttime urban heat island effects, air temperature, and humidity. But it’s these parameters, along with wind speed and solar radiation, which impact the comfort, health, and electricity demand of people in the buildings. And even though cool roofs lower ceiling temperatures, walls, floors, and windows have a greater impact on occupant comfort, they added.According to Rawal, cool roof engineering lowers nighttime temperatures on concrete surfaces, which tend to retain heat. However, it is less effective on tin or cement-sheet roofs as those cool down faster at night anyway. Imdad noted that permanent cool roofs may not suit north Indian cities with near-zero winter temperatures; instead, removable or seasonal solutions would be better.Passive design has limitations. In dense neighbourhoods, a lack of natural ventilation can make homes hot and stuffy. But, Rawal said, ventilation cannot lower indoor temperatures below ambient outdoor temperatures, especially when humidity is high.Traditional architecture with courtyards, perforated screens, high ceilings, and ventilators was effective when the surroundings were relatively cooler, he said. “But with urban sprawls now surrounding most areas, ambient temperatures have risen, and even old neighbourhoods have lost their natural cooling capacity.”Instead, Rawal and Khosla propose a passive design approach that uses building materials, construction methods, and room layouts, with a focus on conduction, convection, and radiation — the three modes of heat transfer. While the upfront cost may be higher, it reduces air conditioning use and the waste heat generated from it, mitigates urban heat island effects, and improves conditions for those without active cooling.Vishwas Chitale from CEEW agreed that with rising humid heat, passive strategies are often inadequate. “We require active cooling solutions. But affordable, innovative solutions, as well as subsidised models and adoption incentives, remain a challenge.”Sky, ground and trees in betweenIn cities, the lack of a “sky view” makes nights hotter, as dense buildings and tree canopies trap heat rather than allowing it to escape into the sky. Open, unpaved spaces cool down efficiently at night due to exposure to the sky, but concrete beneath trees creates heat islands despite greenery, Rawal explained.Trees provide shade and evapotranspiration, which cools the environment. In dry areas, evapotranspiration reduces heat because the air can absorb excess moisture. In humid urban zones, excess moisture trapped near the ground increases heat stress even in the shade.Building on this, a study by IIT Gandhinagar, published in Nature Communications, noted that vegetation’s impact on the heat index varies with climate and morphology, not just canopy cover alone.After analysing 138 Indian cities, the researchers concluded that in cities experiencing humid heat stress, greening strategies must simultaneously provide shade, manage moisture, and maintain airflow.Going forwardDespite challenges, Chitale said that heat mitigation and governance in Indian cities are becoming more structured and refined. Earlier, heat action plans lacked local context, vulnerability assessments, and understanding of crucial parameters like humidity and night temperatures, but newer plans are more comprehensive.For example, Thane’s 2024 HAP incorporates the IPCC AR5 framework—which defines hazard, exposure, and vulnerability as key factors in climate risk—to create a city heat index. The plan includes historical and projected climate extremes in dry conditions, humidity, and warm nights, along with socioeconomic factors to support detailed ward-level planning. It also defines triggers, responsibilities and timelines for action, Chitale said.With this advanced framework, CEEW supports 145 cities in developing HAPs across seven states.Cities like Cuttack and Sambalpur aim to extend cooling solutions beyond six months, while Chennai is integrating heat action into its master plan, he added.Bhubaneswar will soon launch a climate-risk dashboard that maps heat stress at the building level, bringing homes, schools, anganwadis, hospitals, health centres, government offices, roads, bus stops, railway stations, and bus terminals into a single digital view, said Suraj Kumar from Innpact Solutions, which provided technical support for the project.This digital twin uses satellite imagery, weather data, and local sensor feeds to analyse surface and air temperatures, humidity, and urban heat islands. It is part of the Sustainable Urban Mobility — Air Quality, Climate Action, and Accessibility (SUM-ACA) initiative led by GIZ India and the Union ministry of housing and urban affairs.Bhubaneswar’s commissioner, Chanchal Rana, said the dashboard will aid long-term strategic planning for urban heat mitigation projects funded by the state disaster management fund. “It is a highly credible, scalable, open-source tool that has no licence fees, offering long-term benefits by avoiding proprietary software,” he said, and if successful, it would be recommended to other urban local bodies in Orissa.