Climate and Us | India should expect, and prepare for, unexpected weather

IMD forecast above-normal maximum temperatures and a higher-than-normal frequency of heatwave days from April to June. What do we make of these aberrations?

New Delhi: Unexpected weather conditions since February have taken meteorologists by surprise and caused much concern in the farm sector. It began with the early onset of extreme heat in February particularly across India’s west coast, making it the warmest February in 122 years. Then early pre-monsoon showers set in over most parts of the country in March when spring was expected.

Such warming led to increased concerns that the wheat crop quality and yield will be impacted for the second year in a row. (PTI)

Almost all of the second half of March was dominated by unusually long spells of thunderstorm activity, accompanied by hailstorms, lightning and gusty winds that harmed the wheat crop in Uttar Pradesh, the largest grower, Madhya Pradesh, the second-largest producer, Punjab, Haryana and Rajasthan, according to farmers, meteorologists, traders and officials. Now, India Meteorological Department has forecast above-normal maximum temperatures and a higher-than-normal frequency of heatwave days over most parts of the country from April to June. What do we make of these aberrations?

Anti-cyclone over the Arabian Sea triggered early heat

The monthly average maximum temperature in February was 29.54°Celsius (C), 1.73°C above normal over the Indian region — the highest during February since 1901. The average minimum/night temperature was 16.82°C, 1.33°C above normal over the Indian region — the fifth highest during February since 1901. There were below-normal rains over the country with a deficiency of 68%. Central India recorded 100% rain deficiency. Large parts of west and northwest India, as well as many Himalayan towns, recorded temperatures 5-10°C higher than what is normal for mid-February. For example, on February 15, Bhuj recorded 40°C, some 10° higher than normal.

On February 16, such a high departure from normal was recorded in Bikaner in Rajasthan, where the maximum was 36.8°C. In Jammu and Kashmir (J&K), the deviations were 7-9° above normal. The Capital recorded a maximum temperature of 29.8°C — 6° above normal. This unusual heat that lasted till the end of February over most parts of west and northwest India and the Western Himalayas were linked to the development of an anti-cyclone over the northeast Arabian Sea which was sending dry and hot winds from Sindh and Balochistan westwards, over parts of India.

In addition, western disturbances over the Himalayan region were too feeble to bring adequate rain or cause clouding. Clear skies and dry land created a feedback loop that led to exceptional heating even in higher altitudes. Such warming led to increased concerns that the wheat crop quality and yield will be impacted for the second year in a row. The spring heatwave in 2022 led to at least 90 deaths across India and adjacent Pakistan, triggered a glacial lake burst in northern Pakistan, and led to forest fires in the hills of Uttarakhand. March 2022 eventually had the highest-ever average temperature recorded nationally. It also hit India’s wheat output significantly.

IMD forecast more heat in March. Monthly maximum and minimum temperatures for March are likely to be above normal over most parts of the country except peninsular India, where normal to below normal maximum temperatures are likely, IMD warned.

Early onset of pre-monsoon showers in March

Far from what IMD had forecast for March, an unusual spell of thunderstorms and hail starting March 16 accentuated worries for wheat and several other horticultural crops. While not very unusual for March, experts said pre-monsoon activities started relatively early this year. Early heat in February that warmed the dry land surface acted as a trigger for the early onset of pre-monsoon showers.

"Convective clouds develop when there is heating. During February we saw temperatures that are over 5 to 6°C above normal over most parts. The soil was very dry and hot which creates a triggering mechanism. Over the head Bay of Bengal and Central Arabian Sea, two anti-cyclones formed which brought in a lot of moisture. Plus, other low-level cyclonic circulations formed and a western disturbance also impacted the Western Himalayas," explained M Mohapatra, director general, IMD on March 22. "But one of the main factors in triggering widespread hailstorms in many parts of the country are upper level westerly winds blowing at 120 kmph and penetrating up to Peninsular India. These colder winds brought down the freezing level so it started to rain in the form of ice which is hail," added Mohapatra.

The incidence of heavy rainfall events in India (64.5 to 115.5 mm) has been the highest this March in the past five years. Around 60 people died, 15 were injured and more than 490 livestock perished due to lightning incidents during March. Due to heavy rain, seven persons died, 29 were injured, and 63 livestock perished in March. Hailstorm led to the death of one person in Chhattisgarh, IMD said on Saturday.

There were 7 western disturbances along with induced circulation that affected the country last month. “Five active western disturbances (against none in February) moved across north and central India. The associated strong westerly jet stream (with wind speed exceeding 120 kmph to 200 kmph sometimes at the height of about 12 km) provided upper-level divergence and hence lower-level convergence of air mass and uplifting of air leading to the formation of deep clouds. The occurrence of lower-level cyclonic circulations led to the development of thunderstorm clouds. There was the feeding of moisture from the Bay of Bengal and the Arabian Sea in association with the anti-cyclonic circulation over the north Bay of Bengal and the central Arabian Sea. There was also lowering of freezing level in the atmosphere helping in the formation of hail,” IMD had explained on Saturday.

“The models may not have been able to capture the local phenomenon that triggered thunderstorm activity in many parts of the country. Apart from early heat in February, there was a lot of moisture incursion in March which causes instability in the atmosphere and induces thunderstorms. This was clearly not captured by the models,” explained OP Sreejith, head, climate monitoring and prediction group, IMD, Pune.

Brace up for heat stress

During summer (April to June), most of the country is expected to experience above-normal maximum temperatures, except for southern peninsular India and some parts of west-central India where normal to below normal maximum temperatures are likely, IMD warned on Saturday, adding that in April, above-normal to normal maximum temperatures are likely over most parts of the country, except some areas in peninsular, central northwest and northeast India.

Why is IMD so confident that there will be a higher-than-normal frequency of heatwaves and high day temperatures? “Global warming has an imprint. The models reflect above-normal maximum temperatures because of the impact of climate change. The other reason is local circulation features that may make heat spells intense. There have been research studies last year that concluded that climate change contributed to the spring heatwave last year. Some research has also linked thunderstorm activity with climate change but that needs to be studied carefully. Unexpected weather features are to be expected in view of climate change,” added Sreejith.

Intergovernmental Panel on Climate Change (IPCC)’s Synthesis Report released on March 20 has warned that every region in the world is projected to face further increases in climate hazards, increasing multiple risks to ecosystems and humans. Hazards and associated risks expected in the near term include an increase in heat-related human mortality and morbidity, food-borne, water-borne, and vector-borne diseases, and mental health challenges (associated with heat extremes), flooding in coastal and other low-lying cities and regions, biodiversity loss in land, freshwater and ocean ecosystems, and a decrease in food production in some regions. Heat stress will be particularly acute in the tropics including all of South Asia and India. Annual hottest-day temperatures, for example, are projected to increase the most (by 1.5 to 2 times) in some mid-latitude and semi-arid regions and the South American monsoon region with every increment in global warming, IPCC has warned.

IMD in its long-range forecast has said a transition to El Niño is expected by July-September, with chances of El Niño increasing through the fall. There is a 48% chance of El Nino establishing during the June-July-August season which is expected to impact the monsoon.

El Niño is characterised by an unusual warming of waters in the eastern equatorial Pacific. Its opposite, La Niña, is defined by unusually cooler waters in the same area. The phenomenon together is called the ENSO (El Niño Southern Oscillation). It has a high correlation with warmer summers and weaker monsoon rains in India.

“All we can say is there have been three good monsoon years consecutively. With El Niño, we may not see a bounty of rain or an excess rain year. Whether it will be a normal or below normal monsoon year will be known later in April or May,” said M Ravichandran, secretary, ministry of earth sciences said on March 6.

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