Many parts of India continued to reel under intense heat over the weekend, with rising temperatures showing no signs of relief. According to the India Meteorological Department (IMD), heatwave conditions are expected to persist in isolated places across Odisha from March 13 to 17, Jharkhand from March 14 to 17, and Gangetic West Bengal from March 15 to 17. Additionally, interior Odisha, south Rajasthan, and north Gujarat are likely to experience heatwave conditions during the week of March 21 to 27.
On March 16, IMD issued heatwave warnings and alerts for several districts in Odisha, Chhattisgarh, Karnataka, and Maharashtra. In Jharkhand, temperatures crossed the 40-degree Celsius mark in seven districts. Karnataka’s health minister, Dinesh Gundu Rao, on March 15, urged residents to stay indoors between noon and 3 pm to avoid heat-related health issues.
What Is a Heatwave?
A heatwave is defined as a period of unusually high temperatures over a specific region. The threshold for declaring a heatwave varies depending on the normal temperature patterns in that area during that time of the year. Therefore, what qualifies as a heatwave in one region may not be considered a heatwave in another.
How Is a Heatwave Declared?
According to the IMD, a heatwave is declared when the maximum temperature of a station reaches at least 40°C or more in plains and 30°C or more in hilly regions. The IMD defines heatwaves based on the following criteria:
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Departure from Normal Temperature:
- A heatwave is declared when the departure from normal is 4.5°C to 6.4°C.
- A severe heatwave is declared when the departure exceeds 6.4°C.
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Actual Maximum Temperature:
- A heatwave is declared when the maximum temperature exceeds 45°C.
- A severe heatwave is declared when the maximum temperature crosses 47°C.
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Coastal Areas:
- In coastal areas, a heatwave is declared if the maximum temperature departure is 4.5°C or more from the normal and the actual maximum temperature is 37°C or more.
For a heatwave to be officially declared, the above criteria must be met in at least two stations within a meteorological sub-division for at least two consecutive days. In such cases, the heatwave is declared on the second day.
How Does IMD Measure Heatwave Conditions?
IMD monitors heatwave conditions using a widespread network of surface observatories across the country. These observatories measure key meteorological parameters such as temperature, relative humidity, pressure, wind speed, and wind direction. The normal maximum temperature for each day at a specific station is determined based on the climatological average for the period 1991 to 2020. If the observed temperature meets the defined heatwave criteria, the IMD declares a heatwave.
Why Heatwaves Are Dangerous
Heatwaves in India typically occur between March and June and, in some cases, extend into July. The intensity of heatwaves can cause severe health complications, including heat exhaustion, heat stroke, and dehydration. The discomfort level increases when high temperatures are combined with elevated humidity levels, as sweat fails to evaporate efficiently, leaving the body unable to cool down. Moreover, if nighttime temperatures remain high, the body struggles to recover from the day’s heat, increasing health risks.
As temperatures continue to rise, health authorities have advised people to stay hydrated, avoid direct sunlight during peak hours, and wear light, breathable clothing. The IMD continues to monitor the situation closely and issue updates as necessary.
