Heat Waves in India, IMD warned Maximum Temp to be 3-5°C higher than the Long-term Average

Heat Waves in India

Heat Waves in India: With the growing challenges of global warming and climate change, the heat waves in India have become a real threat to health and wellbeing of Indian people. Heat Waves in India 2023 is also important for UPSC Prelims 2023 and UPSC Mains Exam (GS Paper 1- Salient Features of world’s Physical Geography)

Heat Waves in India in News

Last week, 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. On February 21, 2023, the national capital recorded its third hottest February day (33.6° C) in more than five decades.

What is a heat wave?

According to the IMD, a region has a heat wave if its ambient temperature deviates by at least 4.5-6.4°C from the long-term average. There is also a heat wave if the maximum temperature crosses 45°C (or 37°C at a hill-station).

Heat waves in India 2023

Heat waves are expected to become longer and more intense and frequent over the Indian subcontinent. In 2022 itself, the heat waves started early and were more numerous. They also extended further south into peninsular India due to a north-south pressure pattern set up by the La Niña, a world-affecting weather phenomenon in which a band of cool water spreads east-west across the equatorial Pacific Ocean.

Impact of El Niño on Heat Waves in India

The last three years have been La Niña years, which has served as a precursor to 2023 likely being an El Niño year.  As we eagerly await the likely birth of an El Niño this year, we have already had a heat wave occur over northwest India.

• Heat waves tend to be confined to north and northwest India in El Niño years.
• The El Niño is a complementary phenomenon in which warmer water spreads west-east across the equatorial Pacific Ocean.

Formation of Heat Waves, How do heat waves occur?

Heat waves are formed for one of two reasons — warmer air is flowing in from elsewhere or it is being produced locally. It is a local phenomenon 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.

Formation of Heat Waves and Impact of Global Warming

A study published on February 20, 2023, in Nature Geoscience offers explanations as to how different processes contribute to the formation of a heat wave.

Wind Direction

• In spring, India typically has air flowing in from the west-northwest. This direction of air-flow is bad news for India for several reasons.
• In the context of climate change, West Asia 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.
• While air flowing in over the oceans is expected to bring cooler air, the Arabian Sea is unfortunately warming faster than most other ocean regions.

Westerly Winds System

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, we need to remember that the winds are blowing faster than the planet itself, which is also rotating from west to east. The energy to run past the earth near the surface, against surface friction, can only come from above. This descending air compresses and warms up to generate some heat waves.

Declining Lapse Rate

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.

Role of Air Mass

The other factors that affect the formation of heat waves are the age of the air mass and how far it has travelled. The north-northwestern heatwaves are typically formed with air masses that come from 800-1,600 km away and are around two days old. Heat waves over peninsular India on the other hand arrive from the oceans, which are closer (around 200-400 km) and are barely a day old. As a result, they are on average less intense.

Given that these are the processes that contribute to the formation of a heat wave, and the ways in which global warming affects them, it is clear why once-a-decade heat wave events have started to occur once every few years, and are also more intense.

Improving Early Warning System for Heat Wave Prediction

In sum, heat waves have a sophisticated anatomy with important implications for how well we can predict them. Nonetheless, early-warning systems can take advantage of the processes, modes of formation, location, and age of the air mass to improve the quality of warnings and also increase how soon they can be issued.

• Sizeable investments in human and computational resources have already increased India’s forecast skills in the last decade.
• We should further improve forecast warnings, issue them as soon as possible, and couple them with city-wide graded heat action plans to protect the vulnerable.

Heat Waves in India FAQs

1. What is a Heat Wave?

Ans. According to the IMD, a region has a heat wave if its ambient temperature deviates by at least 4.5-6.4°C from the long-term average. There is also a heat wave if the maximum temperature crosses 45°C (or 37°C at a hill-station).

2. What is Lapse Rate?

Ans. The lapse rate is the rate at which temperatures cool from the surface to the upper atmosphere.

3. What is the impact of El Niño on heat waves in India?

Ans. Heat waves tend to be confined to north and northwest India in El Niño years.

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