Heat Waves: A Natural Hazard

A Heat Wave is a period of abnormally high temperatures that causes physiological stress and can lead to illness or death.

It is a climatic extreme, increasingly frequent in India due to global warming and urban heat island effect.

🔥 How a Heat Wave Forms

Let’s visualise it scientifically and simply:

1️⃣ A ridge of high pressure develops and sits over a region for several days.
2️⃣ This causes air to sink downward (subsidence).
3️⃣ As the air sinks, it gets compressed and heated (adiabatic heating).
4️⃣ The descending air suppresses cloud formation → clear skies → more direct sunlight.
5️⃣ The ground heats up quickly and re-radiates heat → further warming the lower atmosphere.

In short: High pressure + clear skies + stagnant hot air = Heat Wave.

🧭 Criteria for Declaring a Heat Wave (IMD Norms)

Region	Temperature Threshold	Heat Wave Criteria
Plains	≥ 40°C	5–6°C above normal (Heat Wave); ≥ 7°C (Severe)
Hilly areas	≥ 30°C	Same departure logic
When normal > 40°C	4–5°C (Heat Wave); ≥ 6°C (Severe)
Absolute Criterion	≥ 45°C (anywhere)	Automatically declared Heat Wave

👉 WMO definition: ≥ 5 consecutive days where max T > average + 5°C.

🇮🇳 Heat Wave Risks in India

• Season: April – June (sometimes March & July).
• Hotspots:
  • Northwest India — Rajasthan, Punjab, Haryana
  • Gangetic Plains — UP, Bihar, Jharkhand, West Bengal
  • Central India — MP, Vidarbha
  • East coast — Odisha, Andhra Pradesh, Telangana
• Urban vulnerability: Cities are hotter than rural areas due to the Urban Heat Island (UHI) effect — concrete, vehicles, and pollution trap heat.
• Casualties: NDMA (1992-2015) — > 24,000 deaths (likely under-reported).

👥 Who suffers most?
Outdoor workers, slum dwellers, elderly, children, and the poor — those with least access to cooling, water, or healthcare.

📘 NDMA Guidelines (National Guidelines for Action Plan — 2016)

Even though heat wave is not officially notified as a disaster under the DM Act 2005 or NDRF norms, NDMA issued detailed guidance on planning and preparedness.

1️⃣ Government Engagement

• Mandate participation of state & district governments, municipal health agencies, DM authorities, NGOs, and private partners.
• Appoint Nodal Officer / Agency to coordinate drills, simulations, and communication before summer.

2️⃣ Vulnerability Assessment

• Identify high-risk districts/urban wards.
• Establish Heat-Health threshold temperatures in coordination with IMD to trigger alerts.

3️⃣ Early Warning System

• Develop colour-coded alert system (usually yellow → orange → red).
• IMD to provide seasonal forecasts and daily warnings to SDMAs and media.

4️⃣ Drafting a Heat Action Plan (HAP)

• Each city/district should have a HAP with:
  • Local coordination structure
  • Communication channels
  • Roles and responsibilities
  • Early-warning dissemination strategy

5️⃣ Implementation & Communication

• Disseminate Do’s & Don’ts in local languages via TV, radio, social media, loudspeakers, and health workers.
• Emphasise hydration, shade, and rest.
• Involve ASHA, Anganwadi, SEWA, Mahila Arogya Samiti etc., in outreach.

6️⃣ Evaluation & Updating

• Review effectiveness every season; update threshold values and institutional roles.

7️⃣ Long-Term Mitigation

• Urban design interventions: cool roofs, white reflective paints, ventilated housing.
• Increase green cover & restore water bodies to counter UHI effect.
• Environmental sustainability: promote tree plantations along streets and open spaces.

⚙️ Four-Pillar Mitigation Strategy (NDMA Focus)

Pillar	Example Activities
1. Forecasting & Early Warning	Localized IMD alerts, colour codes
2. Health System Preparedness	Training doctors & paramedics for heatstroke cases
3. Community Outreach	Public awareness drives, media messages
4. Inter-agency Coordination	Convergence between IMD, NDMA, health dept., ULBs

🏙️ Heat Action Plans (HAPs)

NDMA promotes city-specific HAPs, first pioneered in Ahmedabad (2013) — now replicated in several cities.

Key Components

1️⃣ Monitoring Network

• Dense grid of weather stations for micro-climate mapping.

2️⃣ Preparedness Measures:

• Adjust work/school hours
• Ensure public drinking water, shade shelters, and rest breaks
• Train health workers for heat-related illnesses

3️⃣ Long-Term Urban Solutions:

• Restore ponds & rivers
• Promote green roofs, cool roofs, urban forestry
• Enhance ventilation & shade in housing and public spaces

4️⃣ Institutional Support:

• Dedicated “heat officers” at city level.
• Joint funding by local bodies, state, centre & private sector.

⚠️ Challenges in Heat Wave Management

1️⃣ Data Gaps: Lack of granular (sub-district/ward-level) vulnerability mapping.
2️⃣ Limited Research: Few studies linking climate, health, and socio-economic exposure.
3️⃣ Weak Communication Use: Under-utilisation of mass messaging tools (radio, SMS, call alerts).
4️⃣ Low Public Awareness: Neglect of traditional coping habits — loose clothing, mid-day rest, indoor stay.
5️⃣ Urban Design Neglect: Few cities adopt shading, insulation, or ventilation measures.
6️⃣ Infrastructure Deficit: Many homes lack indoor toilets and piped water, forcing outdoor exposure.

🌿 Mitigation & Adaptation Measures

Domain	Actions
Immediate Response	Early warning, water kiosks, shaded rest areas, medical camps
Urban Planning	Cool roofs, green corridors, open parks, reflective pavements
Ecosystem Approach	Tree plantation, restoring ponds, urban wetlands
Behavioural Change	Shift work hours, encourage hydration, avoid alcohol/dehydrating drinks
Health Sector	Heat-stroke wards, IV fluids, awareness among doctors
Governance	Annual review of HAPs; coordination among IMD-NDMA-SDMA-ULB

💡 Conceptual Understanding

Think of a heat wave as a “pressure cooker” atmosphere —
The lid (high-pressure ridge) traps the hot air beneath, clouds disappear, and sunlight cooks the land.
Cities, with their concrete and pollution, trap this heat even more — creating a human-made oven effect.

🌞 For UPSC Mains (Value Addition)

“India’s battle with heat waves is no longer a meteorological issue — it’s an urban planning and public health challenge.”

You can conclude answers with:

• Need to mainstream heat-wave resilience into Smart City, AMRUT, and Climate-Action Plans.
• Recognise heat waves as a notified disaster to access NDRF/SDRF funds.
• Promote community-based adaptation through local HAPs and green urban design.