Heat Wave: Criteria and Causes

Heat Wave: Criteria and Causes

Question: India is currently experiencing the second deadliest heat wave in its history. Discuss the criteria for heatwaves and causes for the same.

• Heatwaves are the result of certain configuration of temperature, humidity and air movement that culminate in unusually high temperatures.

• The current heat wave in India has taken more than 1800 lives.

• Heatwaves also cause death of livestock and crop losses apart from damage to rail, road and electrical infrastructure

• Heatwaves occur during the summer season in North western parts of India and they occur between March and June,sometimes extending to July

Criteria

IMD has precribed the following criteria for heatwaves:

• Heat wave will only be considered if maximum temperature of a station reaches 40 degree celsius for the plains and 30 degree celsius for hilly areas
• In case normal maximum temperature of a station is lower or equal to 40 degree celsius, heat wave departure from normal is 5 to 6 degree celsius and severe heat wave departure from normal is 7 degree celsius or more

• In case normal maximum temperature of station is more than 40 degree celsius, heat wave departure from normal is 4 to 5 degree celsius and severe heat wave departure from normal is 6 degree celsius or more

• When actual maximum temperature remains 45 degree celsius or more regardless of normal maximum temperature, heat waves should be declared

B. Causes

• Climate change has resulted in higher daily peak temperatures and more intense heat waves are becoming common globally as well

• High humidity is also linked to heat waves

• When high pressure from aloft 10 to 25 thousand feet remains strong in an area for days to weeks, heat waves occur

• Air sinks towards the surface under high pressure and the buildup of heat results

• Three quarters of heat waves over land can be traced to human activity induced global warming, according to a study in Nature Climate Change

• According to an IPCC report, frequency of heat waves has gone up in EU, Asia and Australia due to global warming and climate change

• The report said human activities more than doubled chances of heat waves in certain parts of the world

Facts and Stats

• The current heatwave gripping India is the 5th deadliest in the world and the second deadliest in the nation

• Prior to this, the worst heat wave was in 1998 when 2541 people died as a result of it

• The worst heat wave till date was the one in 2003 in the EU which left over 70,000 persons dead

• Indian heatwave figures 4 times in list of top 10 world disasters-2015, 2003, 2002 and 1998 according to EMDAT-Emergency Events Database maintained by Centre for Research on Epidemiology of Disasters in Brussels