Heatwaves in several parts of India: Why has April been hotter than usual?
- May 1, 2024
- Posted by: OptimizeIAS Team
- Category: DPN Topics
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Heatwaves in several parts of India: Why has April been hotter than usual?
Subject: Geography
Sec: Climatology
Tags: Anticyclone, Heat waves
Context:
- In the first 26 days of the month of April, either a small pocket or a considerably large geographical area in India experienced heatwave conditions, according to the India Meteorological Department (IMD).
More on news:
- While the southern peninsular and the southeastern coast areas have been the worst affected, the northern plains are yet to experience heatwave conditions this season.
About Heat Waves:
- A Heat Wave 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.
- Heat Waves typically occur between March and June, and in some rare cases even extend till July.
- The extreme temperatures and resultant atmospheric conditions adversely affect people living in these regions as they cause physiological stress, sometimes resulting in death.
The Indian Meteorological Department (IMD) has given the following criteria for Heat Waves :
- Heat waves need not be considered till the maximum temperature of a station reaches at least 40°C for Plains,37°Celsius for coastal areas and 30°C for hilly regions.
- When the normal maximum temperature of a station is less than or equal to 40°C:
- Heat Wave: Departure from normal is 5°C to 6°C
- Severe Heat Wave: Departure from normal is 7°C or more.
- When the normal maximum temperature of a station is more than 40°C:
- Heat Wave: Departure from normal is 4°C to 5°C
- Severe Heat Wave: Departure from normal is 6°C or more.
- When actual maximum temperature remains 45°C or more irrespective of normal maximum temperature, heat waves should be declared.
Which areas in India are prone to heatwaves?
- The Core Heatwave Zone (CHZ) spanning central, north, and peninsular India between Gujarat and West Bengal is prone to heatwave conditions every year.
- Rajasthan, Punjab, Haryana, Chandigarh, Delhi, West Madhya Pradesh, Uttar Pradesh, Chhattisgarh, Odisha, Vidarbha in Maharashtra, parts of Gangetic West Bengal, coastal Andhra Pradesh, and Telangana are the most heat-wave-prone states or regions.
Why has April been so hot?
El Nino:
- 2024 is a year that began in an El Niño state.
- El Niño, a weather pattern, refers to an abnormal warming of surface waters in the equatorial Pacific Ocean, which leads to extreme heat in many parts of the world and the ocean.
- It is the large-scale ocean-atmosphere climate interaction linked to periodic warming in sea surface temperatures across the central and east-central Equatorial Pacific.
- It is associated with high pressure in the western Pacific.
- El Nino adversely impacts the Indian monsoons and hence, agriculture in India.
- It developed in June 2023 and generally, the years which begin in an El Niño state, experience extreme temperatures, harsh, multiple and extended heatwave spells, and lack of pre-monsoon rainfall.
Anticyclonic conditions:
- The persistent presence of anticyclone systems over southern peninsular and southeastern coastal areas is also partly responsible for such a hot April.
- An anticyclone is an area of high pressure where air moves apart and sinks.
- It typically indicates fair weather.
- Winds in an anticyclone blow clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere.
- These high-pressure systems, which exist at about the altitude of 3 km and extend between 1,000 and 2,000 km in length, push the air underneath them towards the Earth, in a process called air subsidence.
- The forcefully sunk air generates more heat on the surface closer to the Earth.