Context:
Recent research indicates that the occurrence and geographical distribution of moist heatwaves in India are strongly influenced by the active and break phases of the Southwest Monsoon (SWM). The study suggests that such events can be predicted weeks in advance, improving preparedness for heat-related health risks.
Key Highlights:
Scientific Principle
- Moist heatwaves occur due to the combined impact of high temperature and high atmospheric humidity.
- Unlike dry heatwaves, the presence of high humidity significantly increases heat stress on the human body.
Wet Bulb Temperature as Key Indicator
- The combined effect of temperature and humidity is measured using Wet Bulb Temperature (WBT).
- Wet bulb temperature is defined as:
- The lowest temperature to which air can be cooled through evaporation of water at constant pressure.
- It mimics the cooling process of human sweating.
- The human survivability threshold for wet bulb temperature is about 35°C.
- Beyond this limit, the human body cannot effectively cool itself even in shade or with ventilation.
Link with Southwest Monsoon (SWM)
- Research indicates that moist heatwaves are influenced by the active and break cycles of the Southwest Monsoon.
- During break periods of the monsoon, atmospheric conditions favour:
- High temperatures
- Elevated humidity
- This combination leads to intense moist heat stress events.
Stakeholders Involved
- India Meteorological Department (IMD)
- Climate scientists and meteorological institutions
- Public health agencies
- Urban planners and disaster management authorities
Significance
- Predictability of moist heatwaves weeks in advance improves early warning systems.
- Helps authorities prepare health systems and disaster response mechanisms.
- Important for climate adaptation planning in densely populated tropical regions.
Relevant Prelims Points:
- Heatwave
- Defined by IMD based on temperature thresholds and departures from normal temperature.
- Typically occurs when maximum temperature exceeds 40°C in plains or 30°C in hilly regions.
- Moist Heatwave
- Characterized by high temperature combined with high humidity levels.
- Causes greater physiological stress than dry heatwaves.
- Wet Bulb Temperature
- Indicator measuring combined effect of temperature and humidity.
- 35°C WBT is widely considered the upper limit of human survivability.
- Southwest Monsoon (SWM)
- Occurs from June to September.
- Responsible for about 75% of India’s annual rainfall.
- Characterized by active and break cycles affecting regional weather patterns.
Relevant Mains Points:
Moist Heatwaves as an Emerging Climate Risk
- Climate change is increasing the frequency, duration, and intensity of heatwaves worldwide.
- Moist heatwaves are particularly dangerous in tropical and coastal regions due to high humidity levels.
Public Health Implications
- High humidity reduces evaporative cooling from sweating, causing:
- Heat exhaustion
- Heatstroke
- Hyperthermia
- Increased physiological stress may aggravate:
- Cardiovascular diseases
- Respiratory illnesses
- Kidney disorders
- Vulnerable groups include:
- Elderly people
- Outdoor workers
- Urban poor
- Children
Urban and Environmental Dimensions
- Urban areas experience Urban Heat Island (UHI) effects, worsening heat stress.
- Poor ventilation, dense infrastructure, and limited green cover amplify heat risk.
Way Forward
- Strengthen heatwave early warning systems using climate modelling and forecasting.
- Implement Heat Action Plans (HAPs) in vulnerable cities.
- Promote urban greening, cool roofs, and climate-resilient infrastructure.
- Improve public awareness on heat safety and hydration practices.
- Integrate climate science into disaster risk reduction strategies.
UPSC Relevance:
- Prelims: Wet bulb temperature, heatwave definition, Southwest Monsoon dynamics.
- Mains (GS III – Environment): Climate change impacts, extreme weather events.
- Mains (GS III – Disaster Management): Heatwave preparedness and public health response.