HEAT WAVE

• The IMD says heatwave is considered when the maximum temperature of a station touches at least 40 degrees Celsius or more for plains, 37 degrees Celsius or more for coastal regions and at least 30 degrees Celsius or more for hilly regions.
• Heatwave is declared when the departure from normal temperature is by 4.5 to 6.4 degrees Celsius and a severe heatwave is when the departure from normal is more than 6.4 degrees Celsius.
• For plains, based on actual maximum temperature, IMD considers heatwaves when actual maximum temperature is more than 45 degrees Celsius and severe heat wave when it is more than 47 degrees Celsius.
• This apart, if the locality records over 45 degrees and 47 degrees on any given day, then the IMD declares heatwave and severe heatwave.

4. Present Temperature Fluctuations

• The maximum temperature in February, averaged over the country as a whole, is expected to be around 28 degrees C based on the record of the 30-year period from 1981 to 2010. This is taken to be the “normal”. The minimum temperature is expected to be around 15 degrees C.
• This varies across regions, with states in northwestern, western, central, and eastern India having higher normal temperatures.
• Over the past week, however, maximum temperatures have been 5-11 degrees C higher than normal in most parts of northern and western India.
• Rajasthan, Gujarat, and Maharashtra have been the most conspicuously hot, with temperatures in a few places reaching almost 40 degrees C.
• If temperatures in the plains exceed 40 degree C, or are about 4.5 degree C higher than the normal, these areas are said to be experiencing a heatwave.
• For the mountains, this threshold is 30 degrees C, and for the coastal areas, 37 degrees C.

5. Absence of western disturbances and weak sea breezes

• Any abnormal or extreme weather events are attributed to climate change these days. In most cases, particularly those related to unusually high temperatures, climate change is indeed the underlying or aggravating factor.
• But the observed abnormalities in weather do not always follow a fixed pattern, which might be expected if climate change was the sole determinant of these events.
• The randomness in extreme weather events is due to a variety of local and short-term meteorological coincidences.
• The IMD has attributed the current spell of hot weather to a combination of factors, including the absence of western disturbance activity in February, which brings some rainfall in this month and keeps temperatures down.

6. Weakening La Niña raises fears of a global heat record

• Globally, this year is widely expected to be a little hotter than the previous two years, mainly because of the expected end of the strongest ever La Niña event.
• La Niña refers to cooler than normal surface waters in the equatorial Pacific Ocean, which influences global weather. La Niña conditions tend to have a temporarym cooling effect on the Earth’s atmosphere as well.
• The last two years have been cooler only in relative terms. Average global temperatures in 2022 were 1.15 degrees C higher than the pre-industrial average, making it the fifth or sixth warmest year on record.
• It was the fifth warmest year in India as well. The World Meteorological Organisation said it could have been substantially warmer in the absence of the La Niña event.

7. Abnormal is the new normal

• Unusually high temperatures, or other extreme weather events, should hardly be a surprise now. Almost every month and year sees a record or two fall. Global warming has affected weather systems in very complicated ways, triggering unpredictable impacts.
• So, not all places are showing a consistent rising trend in temperatures. Several unusually colder months have also been recorded. Periods of extraordinarily intense rainfall have been interspersed with prolonged dry spells.
• The predictable patterns present difficult challenges for weather agencies around the world, who are finding it increasingly difficult to issue accurate forecasts and early warnings.
• An essential part of adapting to the new realities is to expect the unexpected, and to build resilience to the extent possible. 

For Prelims & Mains