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IMD is already sensing heat waves

  • February 27, 2023
  • Posted by: OptimizeIAS Team
  • Category: DPN Topics
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IMD is already sensing heat waves

Subject :Geography

Section :Climatology

Context: In the week of February 21, the India Meteorological Department (IMD) warned that the maximum temperatures over northwest, west, and central India would be 3-5° C higher than the long-term average.

Origin of heat waves

  • Heat waves are formed for one of two reasons: because warmer air is flowing in from elsewhere or because something is producing it locally.
    • Air is warmed locally when the air is warmed by higher land surface temperature or because the air sinking down from above is compressed along the way, producing hot air near the surface.
  • A study published in Nature Geoscience offers some clues as to how different processes contribute to the formation of a heat wave.
    • In spring, India typically has air flowing in from the west-northwest. In the context of climate change, the Middle East is warming faster than other regions in latitudes similarly close to the equator, and serves as a source of the warm air that blows into India.
    • Likewise, air flowing in from the northwest rolls in over the mountains of Afghanistan and Pakistan, so some of the compression also happens on the leeward side of these mountains, entering India with a bristling warmth.
    • The air flowing in over the oceans is expected to bring cooler air, since land warms faster than the oceans. The Arabian Sea is warming faster than most other ocean regions.
    • The strong upper atmospheric westerly winds that come in from the Atlantic Ocean over to India during spring control the near-surface winds. Any time winds flow from the west to the east. The descending air compresses and warms up to generate some heat waves.
    • The so-called lapse rate – the rate at which temperatures cool from the surface to the upper atmosphere – is declining under global warming. In other words, global warming tends to warm the upper atmosphere faster than the air near the surface. This in turn means that the sinking air is warmer due to global warming, and thus produces heat waves as it sinks and compresses.

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 and South Central parts of India.
  • It is a condition of air temperature which becomes fatal to the human body when exposed.
  • The IMD declares a heatwave when the maximum temperature crosses a certain threshold — 40°C in the plains, 37°C along the coast, and 30°C in hilly regions.
  • Alternatively, a heatwave is declared if the maximum temperature rises by between 5°C and 6.4°C above normal.
  • A severe heatwave is declared when the maximum temperature rises more than 6.4°C above normal.
  • A third condition for a heatwave arises when an area records a maximum temperature of more than 45°C and up to 47°C on any given day.
Geography IMD is already sensing heat waves

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