IMD: Half of April spent under heat wave, no respite till early May

Though March is the month for seasonal transition, it saw two heat waves this year. The season’s first heat wave spell over the country was from March 11 to 19. The next spell, which commenced on March 27, abated only on April 12, making it one of the longest spells in the season so far. Another heat wave spell surfaced on April 17 and lasted till April 20.

A heat wave covering a larger geographical area is set to start on Wednesday, affecting Rajasthan, Delhi, Haryana, Punjab, Uttar Pradesh, Madhya Pradesh, Maharashtra, Chhattisgarh and Telangana, and it could last till early May. Once realised, this will mean that India experienced heat wave conditions for about 30 days during March and April this year.

The ongoing summer has been unusually warm with early heat conditions surfacing along north and northwest India regions, western Himalayan states, Jammu division and Himachal Pradesh.

Usually, heat slowly starts building up post the second half of April over Jammu, Punjab, Delhi, Haryana, Uttar Pradesh, Bihar and Rajasthan. The summers here peak during May and June. Heat abates upon the arrival of the Southwest Monsoon either in late June or early July.

“Since March, the maximum temperatures have consistently remained above normal over northwest and central India regions. The most affected areas include west Rajasthan, Delhi, Himachal Pradesh, west Uttar Pradesh and west Madhya Pradesh,” R K Jenamani, senior weather forecaster at the National Weather Forecasting Centre, Delhi, told The Indian Express.

The IMD declares a heatwave when the maximum temperature of a location crosses 40 degrees Celsius over the plains; 37 degrees Celsius along the coasts and 35 degrees Celsius in hilly areas. A heat wave is also declared whenever the maximum temperature departure from normal ranges anywhere between 4.5 – 6 degrees Celsius. Met officials observed that day temperatures recorded in most areas in west Rajasthan have not dropped below 40 degree Celsius since March. Similarly, maximum temperatures recorded in Delhi have constantly remained above 38 degrees since the commencement of summer season in March. Both Delhi and Rajasthan have already experienced two heat wave spells in this season. On some days, the maximum temperature at many places in northwest India remained 6 to 9 degrees Celsius above normal.

The latest heat wave is set to cover Delhi, Haryana, Punjab, Uttar Pradesh, Madhya Pradesh, Rajasthan, Gangetic West Bengal, Madhya Maharashtra and Vidarbha subdivisions in Maharashtra, Chhattisgarh, Jharkhand and Telangana. So, there doesn’t seem to be any immediate respite from heat till May — the peak of summer months.

However, unlike an arid March, when all-India rainfall was minus 70.7 per cent, April has witnessed widespread rainfall events with multiple heavy spells over south peninsular and northeast India. The month’s rainfall departures (till April 26) from normal over south peninsula and northeast India remained 50.4 per cent and 49.7 per cent, respectively.

Such persistent wet spells in these two homogeneous regions have significantly helped in bringing down the all-India rainfall departure from minus 30 per cent to 8 per cent till Tuesday, between March 30 and April 26.

Five western disturbances have crossed India during March and April. Usually, the interactions between these cooler streams with moist winds from the south cause light rains over northern India regions. But this summer, such a scenario arose only once in the last week when some parts of Jammu, Kashmir and Delhi reported light to moderate rain whereas the weather remained otherwise dry over rest of the country.

Three feeble western disturbances that mostly passed from the extreme northern regions were realised this month. However, none caused significant weather,” added Jenamani. As a result, the month’s rainfall departure from normal over northwest India stood at minus 82.5 per cent (till April 26) followed by central India at minus 51.6 per cent, the IMD’s data suggested.