HEAT WAVES (Syllabus: GS Paper 3 – Env and Eco)
Context: The first heat wave of the summer-the season starts April across India-was recorded over parts of north interior Karnataka on Monday, presaging what the Indian weather office has forecast will be an uncomfortably hot summer in many parts of the country.
Heat Waves
- Meaning: 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.
- Seasonal Occurrence: Heat Waves typically occur between March and June, and in some rare cases even extend till July.
- Regional Variability: In certain countries, it is defined in terms of the heat index based on temperature and humidity or based on extreme percentile of the temperatures.
Criteria for Declaring Heat Waves:
- Maximum Temperature Thresholds: Declared when the maximum temperature of a station reaches at least 40°C.
oDeclared when the maximum temperature of a station reaches at least 30°C.
- Departure from Normal Heat Wave: Departure from normal temperature ranges from 4.5°C to 6.40°C.
oDeparture from normal temperature is greater than 6.4°C.
- Actual Maximum Temperature Heat Wave: Declared when the actual maximum temperature is equal to or exceeds 450°C.
oDeclared when the actual maximum temperature is equal to or exceeds 470°C.
- Conditions for heat wave
oTransportation / prevalence of hot dry air over a region
oAbsence of moisture in the upper atmosphere: As the presence of moisture restricts the temperature rise.
oThe sky should be practically cloudless
oLarge amplitude anti-cyclonic flow over the area.
