IMD says reading at Najafgarh is accurate, blames heat island effect

Increased concretisation and inadequate green cover have led the daytime temperatures to soar at Najafgarh in southwest Delhi, making it the hottest location compared to the rest of the country. On Sunday, the weather station logged a maximum of 47.8°C — effectively edging out conventionally hot regions in north India like Rajasthan, Gujarat and Haryana.

The Met department has attributed the intense weather conditions “urban heat island effect” — when an area is significantly hotter than the surrounding areas — due to a combination of factors like weak winds and secondary sources like “waste heat” generated due to energy consumption.

Officials at IMD clarified that the readings at Delhi stations were accurate. “There is no problem with the calibration of the station, as these are regularly checked. Readings have been high – over 44°C in most places in Delhi NCR. Some locations can be hotter than others due to the urban heat island effect as there could be concretisation in the area,” said an IMD official, on condition of anonymity.

Close behind Najafgarh was Agra in UP and Mungeshpur, in northwest Delhi, where a maximum of 47.7°C was recorded, followed by Datia in Madhya Pradesh (47.5°C). In Rajasthan, the hottest location was Ganganagar at 46.7°C; Surendranagar in Gujarat (45.3) and Bathinda (46.4°C) in Punjab.

RK Jenamani, senior scientist at IMD said it was wrong to compare urban stations with semi-urban or rural stations, as the surroundings may be fairly different. “The density is less in terms of people and buildings in semi-urban or rural areas. In urban cities, particularly Delhi, we have a lot of concretisation and buildings, which is also one of the reasons why we are seeing such high readings,” he said.

Mahesh Palawat, vice president at IMD echoed similar views. “In an automatic weather station, it is important where the station is placed. Sometimes, if it is near a lot of concrete or areas around it that receive direct heat, the air temperature can be 1-2°C hotter. At Safdarjung, where manual observations are made around a metre above the ground, this is done in the shade and in an area where there is grass underneath. This gives the most accurate reading of the air temperature,” he said, adding that stations like Najafgarh are still an accurate representation of the urban heat island effect.