Heat Waves

#GS 01 Geography, #GS 03 Science and Technology

As per Indian Meteorological Department, a region can be said to experience heat wave if its ambient temperature deviates by at least 4.5-6.4°C from the long-term average.
Climate change is expected to make heat waves longer and more intense and frequent over the Indian subcontinent.
The maximum temperatures over northwest, west, and central India is expected to be 3-5°C higher than the long-term average.

The causes of heat waves can be one of the two such as; warmer air flowing in from elsewhere or being produced 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, it is a local phenomenon.
India has air flowing in from the west-northwest typically in spring.
Due to climate change, West Asia warms faster than other regions in latitudes similarly located with respect to the equator.
This along with air flowing in from the northwest rolls in over the mountains of Afghanistan and Pakistan serves as a source of the warm air that blows into India.
Even though, air flowing in over the oceans typically brings cooler air, unfortunately the Arabian Sea is warming faster than most other ocean regions.
Another source is the strong upper atmospheric westerly winds, that come in from the Atlantic Ocean over to India during spring which control the near-surface winds.
These descending air masses compresses and warms up which will generate some heat waves.
The final cause can be considered as the lapse rate which is the rate at which temperatures cool from the surface to the upper atmosphere.
Global warming results in the warming of the upper atmosphere at a faster rate compared to the air near the surface.
This in turn makes the sinking air warmer and thus produces heat waves as it sinks and compresses.

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