Context

New research has found that the regions of central, northwest and south-central India are the new hotspots of intense heat waves in the country in the last 50 years. They also found that there has been an increase in severe heat waves in the country, in recent years.

About Heat Wave:

• A heat wave is a period of unusually hot weather that typically lasts two or more days. To be considered a heat wave, the temperatures have to be outside the historical averages for a given area.
• Criteria for declaring Heat Wave: Heat wave is considered if the maximum temperature of a station reaches at least 40 degree Celsius or more for Plains and at least 30 degree Celsius or more for Hilly regions.
• Period of Heat Wave in India: It is occurring mainly during March to June and in some rare cases even in July. The peak month of the heat wave over India is May.
• The heat wave prone states over India: Heat waves generally occur over plains of northwest India, Central, East & north Peninsular India during March to June. It covers Punjab, Haryana, Delhi, Uttar Pradesh, Bihar, Jharkhand, West Bengal, Odisha, Madhya Pradesh, Rajasthan, Gujarat, parts of Maharashtra & Karnataka, Andhra Pradesh and Telangana. Sometimes it occurs over Tamilnadu & Kerala also.
• Favorable conditions for Heat wave:
• Transportation / Prevalence of hot dry air over a region
• Absence of moisture in the upper atmosphere
• The sky should be practically cloudless
• Large amplitude anticyclonic flow over the area.
• Heat Index: The heat index is the combination of air temperature and relative humidity, it measures how hot it really feels when relative humidity is factored in with the actual air temperature.
• Health Impacts of Heat Waves: The health impacts of Heat Waves typically involve dehydration, heat cramps, heat exhaustion and/or heat stroke.
• Impact based heat wave warning issue by India Meteorological Department (IMD):
  
  

Key Observations in the Recent Research:

• Change in Spatial and Temporal Trends: A team of researchers studied the change in spatial and temporal trends in Heatwaves (HW) and Severe heatwaves (SHW) over the past seven decades in different meteorological subdivisions of India.
• Shift in the Spatio-temporal trend of HW: The study showed a shift in the Spatio-temporal trend of HW events from the eastern region of Gangetic West Bengal and Bihar to North-Western, Central and further to the south-central region of India.
• Expansion and a Spatial Surge in SHW Events: The research also observed an alarming southward expansion and a spatial surge in SHW events in the last few decades that may put a greater population at additional risk of heat stress in a region already characterized by low Diurnal temperature range (DTR), or the difference between the maximum and minimum temperatures within one day and high humidity.
• Correlated with Mortality in Odisha and Andhra Pradesh: Importantly, the HW/SHW events were found to be positively correlated with mortality in Odisha and Andhra Pradesh, highlighting that human health is highly susceptible to severe heatwave disasters.

Way Forward:

Heatwaves emerged as a deadly health hazard, claiming thousands of lives across the globe in recent decades, with episodes strengthening in frequency, intensity, and duration in the past half-century in India as well. This has caused severe impacts on health, agriculture, economy, and infrastructure.  With an ever-increasing extreme-temperature threshold, a heat resilient future is the need of the hour. Dense population with an intensive outdoor work culture calls for an equitable heat resilient mitigation and adaptation strategies covering each section of the society depending on their vulnerability.

To mitigate future disastrous implications of exacerbated heat extremes and frame adequate adaptation measures in the wake of possible emergence of new hotspots, reliable future projections are needed.