Article 2: Heat Stress & Climate Adaptation
Why in News: A recent study in Nature Communications suggests that human tolerance to heat stress (wet-bulb temperature) may be lower than previously estimated, raising concerns for countries like India.
Key Details
- Heat stress depends on temperature + humidity, not just dry temperature.
- Traditional threshold of 35°C wet-bulb temperature is being reconsidered; 31°C may be dangerous for vulnerable groups.
- Indian cities increasingly face urban heat islands and high heat index values.
- Existing Heat Action Plans (HAPs) are often inadequate and not aligned with humidity-based risks.
Wet-Bulb Temperature & Heat Stress
- Concept of Wet-Bulb Temperature: It measures combined heat and humidity, indicating the lowest temperature achievable through evaporation. It directly reflects human cooling capacity via sweating.
- Human Thermoregulation Limits: The human body maintains ~37°C through sweating, but high humidity reduces evaporation, leading to heat exhaustion or heat stroke.
- Revised Threshold (31°C vs 35°C): Earlier, 35°C was considered the survival limit; new studies indicate 31°C can be critical, especially for elderly and outdoor workers.
- Heat Index vs Dry Temperature: A temperature of 35°C with high humidity can feel like 45–50°C, making heat index a better indicator of risk than ambient temperature.
India’s Heat Vulnerability
- Geographical Exposure: India lies in the tropical and subtropical belt, making it highly vulnerable to extreme heat waves, especially in northern and central regions.
- Urban Heat Islands (UHI): Cities like Delhi, Ahmedabad, and Mumbai experience 2–5°C higher temperatures due to concrete structures, reduced vegetation, and pollution.
- Case Study – Navi Mumbai Tragedy: In 2023, 13 deaths due to heatstroke occurred at ~35°C, highlighting that humidity and exposure duration matter more than temperature alone.
- Night-time Heat Stress: Urban areas fail to cool at night due to heat retention, leading to chronic exposure and increased mortality risk.
Socio-Economic Dimensions of Heat Crisis
- Vulnerable Populations: Outdoor workers such as construction labourers, farmers, street vendors, and gig workers face direct exposure without adequate protection.
- Inequality in Adaptive Capacity: Poor households lack access to cooling devices, ventilation, and healthcare, making them disproportionately vulnerable.
- Occupational Hazard: Heat stress reduces productivity and increases health risks, affecting sectors like agriculture and construction, contributing to economic losses.
- Gendered Impact: Women, especially in rural areas, face additional burden of water collection and household work, increasing exposure to extreme heat.
Urban Planning & Environmental Factors
- Concrete-Dominated Infrastructure: Rapid urbanisation has replaced green spaces with heat-absorbing materials, intensifying local temperatures.
- Decline in Green Cover: Trees provide shade and evapotranspiration cooling, but deforestation and poor urban planning reduce this natural buffer.
- Poor Ventilation & Housing Design: Informal settlements often lack proper airflow, increasing indoor heat stress, even during nights.
- Climate Change Linkage: Rising global temperatures (≈1.1°C above pre-industrial levels) have increased frequency, intensity, and duration of heatwaves.
Policy Response & Gaps
- Heat Action Plans (HAPs): Cities like Ahmedabad pioneered HAPs, focusing on early warning systems, public awareness, and emergency response.
- Dry Heat Bias: Most HAPs rely on temperature thresholds, ignoring humidity, thus underestimating real risk.
- Lack of Localisation: Plans are often generic, not tailored to city-specific climate, demographics, and infrastructure.
- Implementation Challenges: Weak coordination, limited funding, and lack of data reduce the effectiveness of HAPs across states.
Global & Institutional Frameworks
- IPCC Reports: Highlight increasing heat extremes and recommend adaptation strategies for urban resilience.
- National Disaster Management Authority (NDMA): Provides guidelines for heatwave management, but needs updating to include wet-bulb metrics.
- SDG Linkages: Heat crisis impacts SDG 3 (Health), SDG 11 (Sustainable Cities), and SDG 13 (Climate Action).
- Global Best Practices: Cities like Paris and New York use cool roofs, heat shelters, and real-time heat alerts.
Way Forward
- Adopt Wet-Bulb Based Metrics: India should revise heat thresholds to include temperature-humidity indices for accurate risk assessment.
- Strengthen Heat Action Plans: Develop city-specific, data-driven HAPs integrating local climate, vulnerable populations, and infrastructure gaps.
- Climate-Resilient Urban Planning: Promote green roofs, urban forests, reflective materials, and water bodies to reduce urban heat islands.
- Protect Vulnerable Workers: Introduce heat-safe labour policies, flexible work hours, hydration breaks, and occupational safety norms.
- Public Awareness & Early Warning: Use digital platforms and local governance to disseminate heat advisories and health precautions effectively.
Conclusion
The emerging understanding of heat stress marks a paradigm shift from viewing temperature in isolation to recognising the combined impact of heat and humidity. For India, this is not merely a climatic issue but a public health, economic, and social justice challenge. Addressing it requires scientific recalibration, policy innovation, and inclusive governance to ensure that the republic protects its most vulnerable citizens in an era of climate uncertainty.
EXPECTED QUESTIONS FOR UPSC CSE
Prelims MCQ
Q. Wet-bulb temperature is a measure of:
(a) Atmospheric pressure
(b) Combined effect of temperature and humidity
(c) Wind speed variation
(d) Solar radiation intensity
Answer: (b)
Descriptive Question
Q. Evaluate the effectiveness of Heat Action Plans in India. Suggest measures to make them more climate-responsive and inclusive. (250 Words, 15 Marks)