On Tuesday afternoon, Delhi recorded a temperature of 43.5 degrees Celsius. But the felt heat was far higher. The city’s high humidity pushed the wet-bulb globe temperature to a dangerous threshold, a metric that combines air temperature, solar radiation and moisture. For the 33 million residents of India’s capital, the difference between recorded and perceived heat is a matter of life and death.
This is not an isolated event. South Asia is experiencing a multi-week heatwave with temperatures exceeding 50C in parts of Pakistan. Yet as the planet warms, even nations accustomed to high heat are finding their infrastructure and public health systems straining. Here, the experience of a country not typically associated with extreme heat – Britain – offers unexpected lessons.
Britain’s 2022 heatwave, which pushed temperatures above 40C for the first time, exposed deep vulnerabilities in a nation built for a cooler climate. Rail tracks buckled, runways melted and hospitals struggled to cool wards. The national response was rapid and data-driven. The Met Office introduced a new heat-health alert system based on multiple metrics, not just maximum temperature. Infrastructure agencies began retrofitting railways with heat-resistant alloys. Public health campaigns emphasised hydration, checking on the elderly and staying indoors. The result: despite record heat, heat-related mortality did not spike as severely as in previous European heatwaves.
For nations like India, the analogy is not about copying specific policies but about the underlying principle: adaptation must be both immediate and structural. Delhi is not London. Its population density, poverty and air pollution compound heat stress. But the British model of measuring multiple environmental variables, rather than relying on a single thermometer reading, can be replicated. India’s meteorological department could adopt wet-bulb globe temperature as a standard forecast metric. This gives communities actionable information. ‘It will be 43C but feels like 48C’ is a warning; ‘wet-bulb temperature exceeds 32C, limit outdoor activity’ is a directive.
The physics is straightforward. Human bodies cool themselves by sweating. In high humidity, sweat evaporates more slowly, reducing the cooling effect. When wet-bulb temperature exceeds 35C, even healthy humans cannot survive more than a few hours without artificial cooling. Delhi’s wet-bulb temperature on Tuesday reached 33C, dangerously close to that limit.
Britain’s retrofit of its rail network is another lesson. Delhi’s metro system, vital for millions, lacks adequate ventilation in many stations. Installing reflective roofing, planting shade trees along routes and ensuring all stations have cooling systems are expensive but non-negotiable. The cost of inaction is measured in lives. India’s heat action plans, pioneered in Ahmedabad in 2013, have reduced mortality but require constant updating.
Technology exists to manage the crisis. Low-cost sensors can provide hyperlocal heat data. Cool roofs – white or reflective coatings that reduce indoor temperatures by 2-5C – are cheap and effective. India has the capacity to manufacture these at scale. The British example shows that investing in resilience is less costly than recovering from disaster.
But there is a deeper problem. Delhi’s heat is amplified by the urban heat island effect: concrete, asphalt and lack of green spaces trap heat. India is urbanising rapidly, and every new development should incorporate heat-resilient design. This is not just a short-term fix. It is a long-term restructuring of how cities function.
The urgency cannot be overstated. Global temperatures are rising. Heatwaves that were once rare are becoming annual events. Countries like India, Pakistan and Bangladesh are on the front line. They did not cause the climate crisis, but they must survive it. The British experience proves that measured, data-driven adaptation saves lives. It is time for Delhi and other vulnerable cities to adopt and adapt these lessons. The heat is not waiting.
Dr. Helena Vance is Science & Climate Correspondent. She holds a PhD in Astrophysics and has reported from the world’s most vulnerable regions.
