May, generally the hottest month in most of India, is likely to be particularly scorching in large parts of eastern India but Delhi, Punjab, Haryana, Rajasthan, Gujarat — while still sizzling — are likely to see increased rain and limited heatwaves, according to the India Meteorological Department (IMD) on April 28.
“Normal to above-normal rainfall is expected over northwest India, parts of west-central India and the northern part of peninsular India,” the IMD’s monthly-outlook statement said. “Below-normal rainfall is likely over most parts of northeast India, east-central India and south peninsular.”
There will be more than usual heatwave days over Bihar, Jharkhand, Odisha, Gangetic West Bengal, East Uttar Pradesh, coastal Andhra Pradesh, Chhattisgarh, Madhya Pradesh, Telangana, and coastal Gujarat. Heatwaves in these parts of India do not see mercury levels rise as high as in north and northwest India but greater humidity levels combined with the heat, pose a relatively higher health risk.
Rainfall in May is likely to be “normal” or within a 10% window of what’s usual for the month, the statement added. Heatwaves are defined by temperatures being persistently over 45 degrees Celsius or 4-5 degrees more than what’s normal for a region.
“Our current forecasts suggest that there may not be many days of heatwaves in northwest, primarily due to rain that will keep temperatures [relatively] low,” said Mrutunjay Mohapatra, Director-General, IMD.
In April, the IMD indicated a 4% shortfall for the coming monsoon season. Though still categorised as “normal” it is — at 96% of the Long Period Average (LPA) — at the lowest end of what the agency categorises as normal rainfall. The key factor believed to be playing spoilsport this year is the development of an ‘El Nino’, a cyclical phenomenon of warming in the Central Pacific that is linked to diminished rainfall in west, northwest and western parts of Central India.
Since 2019, India has been under the influence of the converse ‘La Nina’ or a cooling in those regions, and therefore substantial monsoon rain. “The latest ‘El Nino’ outlook suggests that warming has begun in the equatorial Pacific and is likely to rise by 1 degrees Celsius during July, August and September. That would be a moderate ‘El Nino’,” said Mr. Mahapatra.
A greater than 1.5°C rise is a ‘strong El Nino’ but over 1°C a ‘moderate El Nino’. From 1951-2022, there have been 15 ‘El Nino’ years, defined as a greater-than-half-degree Celsius rise in temperatures in the Central, Equatorial Pacific Ocean with nine of those years witnessing ‘below-normal’ rain. The last ‘strong El Nino’ year ( >1.5°C rise), 2015, saw monsoon rain shrivel by 14%. A ‘weaker El Nino’ (sub-1°C rise) in 2018 saw a contraction of 7.4%.