Context: A recent analysis by the Banaras Hindu University (BHU), in collaboration with the Department of Science and Technology(DST) and the Ministry of Earth Sciences(MoES), has found a spatial shift of heatwaves in India. With this shift weather events are now occurring in new regions in the country. 
About the study

• The study has looked at temperature data from the India Meteorological Department, spanning 65 years from 1951-2016, to assess the monthly, seasonal, decadal and long-term trends in heatwaves in the country.  

Key findings of the study

• The study has found a warming pattern over northwestern and southern India, while a progressive cooling phase over northeastern and southwest regions of the country. 
• The study found three prominent heatwave prone regions — northwestern, central, and south-central India, with the highest being in west Madhya Pradesh (0.80 events/year). 
• The study has also found a significant decrease in heatwaves over the eastern region, that is Gangetic West Bengal (−0.13events/year).
• The study has also found severe heatwave events have shown a “southward expansion and a spatial surge during the decades of 2001–2010 and 2010–2016”. The increase in heatwaves in Karnataka and Tamil Nadu are particularly significant and will increase in the future.

Key Factors

• Two elements that have exacerbated the heatwave conditions in the country are the increase in night time temperatures, which disallows heat discharge at night, and increasing humidity levels.

About Heatwave

• It is a period of abnormally high temperatures, more than the normal maximum temperature, that occurs during summer. 
• It is a period of abnormally high temperatures, more than the normal maximum temperature that occurs during the summer season in the North-Western parts of India in the month of March to June. 

Factors: The possible factors responsible for Heat Waves include shifting of jet streams, El-Nino and La-Nina, anthropogenic factors like heat islands etc. 
Heatwave is considered if the maximum temperature of a station reaches

• at least 40 degrees C or more for Plains 
• at least 30 degrees C or more for Hilly regions. 

Categories of Heat Wave
Based on Departure from Normal 

• Heat Wave: Departure from normal is 4.5 degrees C to 6.4 degrees C 
• Severe Heat Wave: Departure from normal is >6.4 degrees C 

Based on Actual Maximum Temperature 

• Heat Wave: When actual maximum temperature ≥ 45 degrees C 
• Severe Heat Wave: When actual maximum temperature ≥47 degrees C 

Favourable conditions for Heat Wave

• Transportation / Prevalence of hot dry air over a region (There should be a region of warm dry air and an appropriate flow pattern for transporting hot air over the region).
• Absence of moisture in the upper atmosphere (As the presence of moisture restricts the temperature rise).
• The sky should be practically cloudless (To allow maximum insulation over the region).
• Large amplitude anticyclonic flow over the area.
• Heatwaves generally develop over Northwest India and spread gradually eastwards & southwards but not westwards (since the prevailing winds during the season are westerly to north westerly). 
• But on some occasions, heat waves may also develop over any region in situ under the favourable conditions.

Implications of Heat Waves

• It leads to physiological stress, which sometimes can claim human life. 

There are five physiological mechanisms that are triggered by heat exposure

• Ischemia (reduced and restricted blood flow), 
• heat cytotoxicity (cell death), 
• inflammatory response (swelling), 
• disseminated intravascular coagulation (abnormal blood clotting), and 
• rhabdomyolysis (breakdown of muscle fibres).

These mechanisms affect seven vital organs: The brain, heart, intestines, kidneys, liver, lungs and pancreas. 

• There are 27 lethal combinations of these mechanisms and organs that have been shown to be caused by heat.
• Severe heat waves have caused catastrophic crop failures, thousands of deaths from hyperthermia, and widespread power outages due to increased use of air conditioning.

The signs and symptoms are as follows

• Heat Cramps: Ederna (swelling) and Syncope (Fainting) generally accompanied by fever below 39°C i.e.102°F.
• Heat Exhaustion: Fatigue, weakness, dizziness, headache, nausea, vomiting, muscle cramps and sweating.
• Heat Stroke: Body temperatures of 40°C i.e. 104°F or more along with delirium, seizures or coma. This is a potential fatal condition.
• It affects the transmission of diseases, health service delivery, air quality, and critical social infrastructures such as energy, transport, and water.

Strategies To Address Heat Waves

• Establishment of  Early Warning System and Inter-Agency Coordination for prediction of heatwaves and issuance of alert. 
• Public Awareness and community outreach to increase public awareness on how to protect against extreme heat through different mediums. 
• Capacity building and training programme for health care professionals at different levels to recognize and respond to heatwave related illnesses. 
• Collaboration with non-government organisations (NGOs) and civil society to provide support in distress situations.
• Encourage traditional methods of handling heat waves like wearing cotton clothes etc.
• Reviewing labour laws and other regulations taking climatic conditions into account.
• Improving the infrastructure setup like including shadowed windows, insulated houses etc.

By: Shubham Tiwari