Context: Heatwave conditions have been declared by the India Meteorological Department (IMD) in various regions of Maharashtra, including Mumbai, Palghar, Thane, Konkan, central Maharashtra, and Vidarbha. This is the fourth heatwave alert for the Konkan region and the first for the month of May, according to the IMD.
Heat Wave
- 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.
Extreme temperatures and resultant atmospheric conditions adversely affect people living in these regions as they cause physiological stress, sometimes resulting in death.
Criteria for Heat Wave
IMD has given the following criteria for Heat Waves:
Two conditions which need to be satisfied:
- Heat wave is considered if maximum temperature of a station reaches at least 40°C or more for Plains, 37°C or more for coastal stations and at least 30°C or more for Hilly regions. Following criteria are used to declare heat wave:
- Based on Departure from Normal
- Heat Wave: Departure from normal is 4.5°C to 6.4°C
- Severe Heat Wave: Departure from normal is 6.4°C
- Based on Actual Maximum Temperature (for plains only)
- Heat Wave: When actual maximum temperature 45°C
- Severe Heat Wave: When actual maximum temperature 47°C
Declare heat wave, above criteria should be met at least in 2 stations in a Meteorological subdivision for at least two consecutive days.
Favourable Conditions for Heat Wave
- Transportation/Prevalence of hot dry air over a region (There should be a region of warm dry air and appropriate flow pattern for transporting hot air over the region).
- Absence of moisture in upper atmosphere (As presence of moisture restricts the temperature rise).
- Sky should be cloudless (To allow maximum insulation over the region).
- Large amplitude anti-cyclonic flow over the area.
- Heat waves 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 wave may also develop over any region in situ under the favourable conditions.
What are the heat wave prone states over India?
Heat wave generally occurs 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 Telengana. Sometimes it occurs over Tamilnadu & Kerala also. Heat waves adversely affect human and animal lives. However, maximum temperatures more than 45°C observed mainly over Rajasthan and Vidarbha region in month of May.
Impacts of Heat waves:
Heat waves affect each and every aspect of life. Following picture shows its multiple impacts in various dimensions:
Health Impacts of Heat Waves?
The health impacts of Heat Waves typically involve dehydration, heat cramps, heat exhaustion and/or heat stroke. The signs and symptoms are as follows:
♣ Heat Cramps: Ederna (swelling) and Syncope (Fainting) generally accompanied by fever below 39 degree C
♣ Heat Exhaustion: Fatigue, weakness, dizziness, headache, nausea, vomiting, muscle cramps and sweating.
♣ Heat Stoke: Body temperatures of 40 degree C or more along with delirium, seizures or coma. This is a potential fatal condition
To cope up with heat waves, IMD issues colour based warnings as follow:
Resilience Strategies For Extreme Heat
- Identifying vulnerable populations and creating heat preparedness plans with all residents in mind, which may include steps like opening cooling centers during periods of extreme heat and adopting workplace heat stress standards.
- Installing cool and green roofs and cool pavement to reduce the urban heat island effect.
- Planting trees to provide shade and to cool the air through evapotranspiration.
- Pursuing energy efficiency to reduce demand on the electricity grid, especially during heat waves.
- Reducing concretisation in urban areas.
- Adopting architectural designs to reduce heat load on built structures.
- Emergency Measures: Democratization of access to public cool spaces in adverse heat waves. Ex. Metro Stations with air-cooled atmosphere should be made accessible to poor.
- IMD should start measuring Heat Index and Wet Bulb Temperatures, which is a better indicator of heat.
