Explained: Is India at Risk of Wet-Bulb Events?

Introduction

India is bracing for above-normal temperatures this year, with the India Meteorological Department (IMD) warning of widespread heatwaves from March to May. As global warming intensifies, scientists are increasingly concerned about the possibility of “wet-bulb events” — deadly combinations of heat and humidity that may push the limits of human survival.

---

What is a Wet-Bulb Temperature?

Definition:

The wet-bulb temperature (WBT) is the lowest temperature to which air can be cooled by evaporation at constant pressure. It is measured by wrapping a wet cloth around the bulb of a thermometer.

In simple terms, it represents the point where the human body can no longer cool itself through sweating.

• When WBT exceeds 35°C, human survivability sharply decreases, as even a healthy person sitting in shade with water access cannot regulate body temperature.

• Beyond this threshold, the body’s core temperature rises, leading to heat exhaustion, heatstroke, and potentially death.

---

Why Is It Dangerous?

Under normal conditions, the human body cools itself by evaporating sweat. But when humidity is high, evaporation slows, and the body loses its natural cooling mechanism.

A wet-bulb temperature of 35°C means:

• Air is hot and humid enough to stop sweat from evaporating.

• Prolonged exposure (even 5–6 hours) can be fatal.

• Such conditions are extremely rare but are becoming increasingly frequent due to global warming.

---

India’s Growing Risk

1. Record-breaking Temperatures

   • India recorded its warmest February since 1877, with IMD noting that minimum temperatures were among the top five highest since 1901.

   • The upcoming summer is expected to bring above-normal heat across northeast, eastern, central, and northwest India.

2. Scientific Warnings

   • World Bank (2022) warned that India could become one of the first countries where wet-bulb temperatures exceed 35°C, crossing the human survivability limit.

   • According to Peter Dynes (MEER Project), India is approaching “the limits of human survival” if global temperatures continue to rise.

3. Historical Context

   • The 1995 Chicago heatwave is one of the most infamous wet-bulb events — over 700 deaths, mainly among the elderly and poor.

   • India has already experienced a 55% increase in deaths due to extreme heat, according to The Lancet Countdown (2022).

---

Impact on India

• Health Impacts: Increase in heatstroke, cardiovascular strain, and mortality, especially among outdoor workers, elderly, and children.

• Economic Impacts: Productivity losses in agriculture, construction, and manufacturing.

• Energy Security: Rising demand for cooling and electricity during peak heat periods.

• Food Security: Droughts and heat stress affect crop yield and livestock health.

• Urban Vulnerability: Heat island effect in cities intensifies exposure, especially for the poor living in unventilated areas.

---

Current Preparedness: Heat Action Plans (HAPs)

The Centre for Policy Research (CPR) reviewed 37 Heat Action Plans (HAPs) across 18 states and found major shortcomings:

• Only 2 out of 37 HAPs included vulnerability assessments.

• Most plans do not prioritize vulnerable communities such as daily wage workers, slum dwellers, or the elderly.

• Resource targeting and data-driven planning are weak, leading to limited on-ground effectiveness.

Key Recommendation:

Future HAPs must include:

• Local vulnerability mapping

• Early warning systems

• Community awareness programmes

• Integration of health, disaster, and urban planning departments

---

Way Forward

1. Strengthen Local Heat Action Plans: Incorporate scientific data, real-time monitoring, and vulnerability mapping.

2. Urban Cooling Measures: Promote green roofs, urban forestry, and cool pavements.

3. Agricultural Adaptation: Introduce heat-resilient crops and shift sowing patterns.

4. Public Awareness: Educate citizens about hydration, shade, and rest cycles.

5. Global Climate Action: India, as the fifth-largest contributor to global warming (0.08°C since 1850), must continue investing in renewable energy, energy efficiency, and climate-resilient infrastructure.

---

Conclusion

India stands on the frontline of climate vulnerability, where rising heat and humidity could soon make some regions physiologically uninhabitable during extreme summer events.

The growing threat of wet-bulb temperatures is a stark reminder that climate change is not a distant risk—it’s a current reality.

To ensure resilience, India must adopt proactive adaptation policies, integrate vulnerability assessments, and commit to climate mitigation that safeguards both people and ecosystems.

---

UPSC Relevance

Prelims:

• Terms: Wet-bulb temperature, IMD, Anthropocene, Heat Action Plans (HAPs), The Lancet Countdown.

Mains (GS Paper 3 – Environment):

• “Explain the concept of wet-bulb temperature and discuss its significance in understanding the impact of global warming on India’s climate.”

• “Assess India’s preparedness for extreme heat events in the context of climate change.”

Essay Topics:

• “Adapting to a Warming World: Lessons from India’s Heatwaves”

• “The Silent Killer: Understanding the Human Cost of Rising Temperatures.”