Why in the news?

A Nature Communications study reveals the human heat stress safety limit is 31°C wet-bulb temperature, not 35°C as previously thought, necessitating a revision of climate resilience strategies.

What is Wet-Bulb Temperature (WBT)?

Wet-Bulb Temperature (WBT) is the lowest temperature to which an object can be cooled by the evaporation of water into the air at constant pressure. 

For humans, it is the most critical measure of heat stress because it represents the limit of the body's ability to cool itself through sweating.

How it is Measured

It is measured by wrapping a wet cloth around the bulb of a thermometer and blowing air over it. As the water evaporates, it cools the bulb.  

• Low Humidity: Water evaporates quickly, significantly lowering the temperature on the wet-bulb thermometer compared to a standard "dry" thermometer.
• High Humidity (100%): No evaporation can occur; therefore, the Wet-Bulb Temperature equals the Dry-Bulb Temperature. 

Socio-Economic Vulnerabilities to 'Wet Heat'

Impact on Labour Force: Over 75% of India's workforce (agriculture, construction, street vending) is exposed to heat. 

• The ILO projects India will lose 5.8% of its working hours by 2030 due to heat stress, equivalent to 34 million full-time jobs (Source: ILO Report).

Gig Economy Risks: Delivery agents and gig economy workers often lack formal occupational safety nets, facing prolonged heat exposure without mandatory rest or cooling facilities.

Urban Heat Islands (UHI): Concrete structures and asphalt roads in cities absorb and retain heat, making urban areas several degrees hotter than surrounding rural areas. This prevents night-time cooling, increasing the risk of heat stress.

Why Current Heat Action Plans (HAPs) are Inadequate?

Blindness to Humidity: The India Meteorological Department (IMD) declares heatwaves based on dry-bulb temperature thresholds (e.g., 40°C in plains). 

• Most HAPs follow this metric and fail to trigger alerts when moderate temperatures combine with high humidity to create lethal conditions.

Lack of Local Context: A study of 37 HAPs found that most are generic and do not account for local vulnerabilities, such as slum populations or specific humidity patterns. (Source: CPR Report)

Poor Implementation: The majority of HAPs are underfunded, advisory in nature, and not legally binding, leaving implementation at the discretion of employers and local bodies.

Way Forward for India

Redefine Heatwave Metrics: Adopt the Heat Index (which includes humidity) for declaring heatwaves. HAPs must be updated to use the 31°C WBT as a critical danger threshold.

Enact Legally Binding Safety Standards: Implement the Occupational Safety, Health and Working Conditions Code (2020) to mandate paid breaks during peak heat hours (12 PM - 4 PM), shaded rest areas, and access to hydration for all outdoor workers.

Design Cooler Cities: Urban planning must prioritize green-blue infrastructure, such as green roofs, urban forests, and wetlands. Building codes should mandate features that ensure cross-ventilation and reduce heat absorption.

Ensure Dedicated Funding: National Disaster Management Authority (NDMA) must allocate specific, ring-fenced budgets for HAP implementation, shifting the focus from post-disaster relief to pre-disaster mitigation.

Learn from Best Practices

• The Ahmedabad Model: South Asia's first HAP (2013) uses an early warning system, promotes cool roofs with reflective paint, and builds medical capacity.  
• Chief Heat Officers: Cities like Athens and Miami have appointed dedicated officials to coordinate heat responses across all government departments, breaking down administrative silos.
• Singapore’s "Cooling Singapore" Initiative: Focuses on urban design, creating ventilation corridors for sea breezes and mandating cool paints on buildings to combat the UHI effect.

Conclusion

India must adopt a proactive, humidity-aware heat strategy by legally protecting workers, mandating NDMA funding for HAPs, and implementing climate-resilient urban design best practices.

Source: INDIANEXPRESS