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Context:

According to UN Economic and Social Commission for Asia and the Pacific (ESCAP) report Asian megacities face deadly heatwave risk.

What are heatwaves?

A heat wave is a prolonged period of abnormally high temperature, often combined with high humidity, that exceeds the normal climatic patterns of a region and poses significant health, environmental, social, and economic risks.

Criterion for declaring heatwave (according to India Meteorological Department):

Based on Actual Maximum Temperature

A heatwave is declared when:

• Maximum temperature ≥ 40°C in plains, OR
• Maximum temperature ≥ 37°C in coastal areas, OR
• Maximum temperature ≥ 30°C in hilly regions 

Departure from Normal

Heatwave:

• Departure of +4.5°C to +6.4°C from normal

Severe Heatwave:

• Departure of >6.4°C from normal 

Absolute Temperature Threshold (Fixed Criterion)

Heatwave:

• Maximum temperature ≥ 45°C

Severe Heatwave:

• Maximum temperature ≥ 47°C

What are the favourable conditions for developing heatwave in India?

• Persistent high-pressure systems create atmospheric blocking, preventing cloud formation and trapping heat over a region.
• Clear skies allow intense solar insolation, which rapidly heats land surfaces during the pre-monsoon months.
• Dry soil and drought conditions reduce evaporative cooling, causing more absorbed heat to convert into sensible heat.
• Hot and dry continental air masses, such as the Loo winds in northwest India, raise temperatures sharply.
• Weak or delayed monsoon onset prolongs heating and suppresses convective activity.
• El Niño conditions weaken monsoon circulation and promote warmer, drier weather conducive to heatwaves.
• Urban Heat Island effects intensify heat by trapping radiation in built-up areas and preventing night-time cooling.
• Low relative humidity accelerates surface heating, while high humidity elevates the heat index and exacerbates heat stress.
• Meandering jet streams and amplified Rossby waves stabilize high-pressure areas, extending the duration of heatwaves.

IMD colour-coded warnings for Heatwave:

Why Asia’s megacities are at extreme heat risk?

According to UN Economic and Social Commission for Asia and the Pacific (ESCAP) report

Urban Heat Island (UHI) Intensification

• Asian megacities like Delhi, Dhaka, Karachi, Manila, Seoul, Shanghai could see 2–7°C higher local temperatures on top of global warming.
• UHI adds heat due to:
  • Dense concrete surfaces
  • Limited vegetation
  • High energy use
  • Traffic congestion

Chronic Heat Exposure Across South & Southwest Asia (Broad One-Line Statements)

• South and Southwest Asia are entering a phase of chronic heat exposure, with UN ESCAP warning that India, Pakistan, and Bangladesh may face over 300 days each year with a heat index above 35°C, indicating sustained severe heat stress.
• The region may also experience more than 200 days annually with heat index values exceeding 41°C, a threshold of extreme danger associated with a high likelihood of heat stroke and mortality.

Heat as the fastest-growing climate hazard

• Heat has now become Asia-Pacific’s fastest-growing climate-related hazard, overtaking cyclones and droughts in frequency and impact.
• The year 2024 was the hottest ever recorded globally, marking an unprecedented acceleration in regional heat extremes.

Socio-economic inequality and heat

• Extreme heat deepens urban inequality as poorer neighbourhoods can be up to 7°C hotter than wealthier, greener areas, as shown in the Bandung (Indonesia) study.
• Groups most exposed to dangerous heat include outdoor low-wage workers, children, the elderly, and slum populations lacking access to cooling, water, and healthcare.

Heat–air Pollution feedback loop

• Extreme heat interacts with air pollution in a reinforcing feedback loop, where higher temperatures accelerate wildfire frequency and intensity, increasing PM2.5 and PM10 concentrations.
• Persistent heat enhances ground-level ozone formation, worsening respiratory conditions and raising smog levels in urban areas.

Challenges of heatwaves:

Public Health Crisis: Heatwaves overwhelm the body’s thermoregulation, leading to heat stress, dehydration, kidney injury, cardiovascular strain and heatstroke. India 2024 heatwave killed around 700, becoming the second deadliest event of the year.

Labour Productivity Loss: Heat stress reduces physical work capacity, impacting labour-intensive sectors such as agriculture, construction, mining, logistics, and gig work. According to ILO report India may lose 34 million full-time jobs equivalent by 2030 due to heat stress.

Agricultural Losses: Heatwaves deteriorate soil moisture, disrupt crop growth cycles, and increase evapotranspiration. According to IPCC (2022) report for every 1°C rise, wheat yields can drop by 6% in South Asia.

Urban Overheating: A Bandung (Indonesia) microclimate study documented a 7°C temperature gap between informal settlements and green-rich neighbourhoods—one of the largest urban thermal disparities recorded in Southeast Asia.

Water stress and power demand peaks: India’s national peak power demand hit 234 GW in June 2023, the highest at the time, directly attributed to severe heatwave conditions across north India. Bengaluru’s 2024 summer water crisis coincided with prolonged heat spells, affecting ~2 million people due to drying borewells and reduced Cauvery inflows.

Government initiatives to address heat risks:

National Action Plan on Climate Change (NAPCC) – Mission on Sustainable Habitat targets cooling, transport, urban planning.

India Cooling Action Plan (ICAP) – First global plan to reduce cooling demand by 20–25% by 2037.

National Disaster Management Authority (NDMA) Heat Action Plan Guidelines (2016):

• Mandatory for all states
• Early warning systems
• Heat shelters
• Public communication

Atal Mission for Rejuvenation and Urban Transformation (AMRUT): AMRUT promotes climate-resilient urban development by expanding green cover, restoring and creating water bodies, enhancing urban wetlands, and improving stormwater drainage—all of which help lower surface temperatures, reduce urban heat island effects, and strengthen long-term heat resilience.

Smart Cities Mission: The Smart Cities Mission integrates heat-adaptive urban design through measures such as cool roofs, reflective and permeable pavements, smart shading systems, green corridors, and climate-responsive building codes, alongside digital monitoring systems that support heat early warnings and urban microclimate management.

Green India Mission (GIM): The Green India Mission advances urban and peri-urban afforestation, ecological restoration, and landscape-scale greening to improve carbon sequestration, enhance ecosystem services, regulate microclimates, and create heat-buffer zones that mitigate rising temperatures in densely populated regions.

Way Forward:

Scale Up Heat-Health Early Warning Systems (HHEWS) Beyond Current Coverage

Only 54% of global meteorological agencies issue heat alerts according to UN ESCAP 2025 report.
India must expand district-level, hyperlocal heat alerts.

Mandate Cool Roofs and Heat-Resilient Building Codes

Hyderabad’s cool-roof initiative (2023–24) covered 300,000 sq. m and reduced indoor temperatures by 2–4°C in low-income households.

Urban Greening Using Microclimate Science, Not Generic Plantation Drives

Cities must adopt heat-mitigating species (Neem, Peepal, Banyan, Rain tree) and continuous green corridors, based on studies showing surface-temperature reduction of up to 5°C around urban forests.

Heat-Safe Work Regulations for Informal & Gig Workers

India lacks binding heat-safety standards. It must adopt

• Mandatory rest–water–shade cycles like OSHA (US)
• Shift work timing for construction, delivery, and street vending
• Cool vests and hydration support for gig workers (piloted in Ahmedabad & Hyderabad).

Conclusion:

Asia’s megacities are entering an era of chronic heat, driven by global warming, UHI, and rapid urbanisation. The UN ESCAP report makes clear that extreme heat is now the fastest-growing climate hazard with deep socio-economic, health, and constitutional implications. Targeted heat-health systems, resilient urban planning, worker protection and regional cooperation are essential to safeguard millions in South and Southwest Asia.

Source: Down to Earth