Doubt over Delhi's 52.9 degrees Celsius reading: How air temperature is measured, how it can go wrong

On Wednesday, Delhi recorded its highest ever temperature of over 52 degrees Celsius.

The Mungeshpur weather station in northwest Delhi recorded the temperature.

On Tuesday, the same weather station noted a temperature of 49 degrees Celsius.

But now the India Meteorological Department is saying that it is possible that the station is an outlier or suffering from a sensor error.

“The maximum temperature over Delhi-NCR varied from 45.2 degrees Celsius to 49.1 degrees Celsius in different parts of city. Mungeshpur reported 52.9 degrees Celsius as an outlier compared to other stations. It could be due to error in the sensor or the local factor. IMD is examining the data and sensors,” the IMD said in a statement.

Union minister Kiren Rijiju posted on X:

A team of specialists has been dispatched to Mungeshpur to check the temperature sensor, according to several media reports.

But how is air temperature measured? And why does it sometimes go wrong?

Let’s take a closer look:

How is air temperature measured?

First, let’s briefly examine the IMD.

Established in 1875, the agency is the country’s national meteorological service.

It is the principal government agency in all matters relating to meteorology and allied subjects.

According to Hindustan Times, the IMD currently has over 550 surface observatories to forecast weather.

However, this manual network is inadequate for constantly keeping an eye on cyclones and monsoons.

The IMD has now added Automatic Weather Stations (AWS) to the mix.

Since summer 2022, the IMD has established AWS in 15 locations across Delhi and NCR.

These measure factors such as ambient air temperature, relative humidity, precipitation, wind speed, and wind direction  every hour.

Ambient temperature is the temperature of the air surrounding a component.

In this case, ambient air temperature is measured via an electrical resistance thermometer.

The ambient air temperature is recorded in degrees Celsius.

How can it go wrong?

According to CNBC, an inaccurate sensor can result in faulty data.

“If sensors are not properly calibrated or maintained, they can give false readings that do not accurately reflect the weather conditions,” the piece stated.

It is also important to remember that ambient air temperature can also vary in urban areas.

This is because local features such as proximity to water bodies, barren land, concrete, dense urban clusters, and green areas all play a part in impacting it_._

NDTV quoted IMD director general M Mohapatra as saying that local factors could have played a part in Mungeshpur.

Experts have blamed hot winds from Rajasthan for the current situation in Delhi.

India Meteorological Department (IMD) regional head Kuldeep Srivastava said Delhi’s outskirts are the first areas to be impacted by hot winds from Rajasthan.

“Parts of Delhi are particularly susceptible to the early arrival of these hot winds, worsening the already severe weather. Areas like Mungeshpur, Narela and Najafgarh are the first to experience the full force of these hot winds,” Srivastava told PTI.

Mahesh Palawat, the vice president of Meteorology and Climate Change at Skymet Weather, said, “In open areas with vacant land, there is increased radiation. Direct sunlight and lack of shade make these regions exceptionally hot.”

“When wind blows from the west, it affects these areas first. As they are on the outskirts, temperatures rise rapidly,” Palawat explained.

With temperatures soaring, the city peak power demand rose to an all-time high of 8,302 MW at 15:36:32 hours on Wednesday, according power discom officials.

This is the first time in the history of the National Capital that its power demand has crossed the 8,300-MW mark. Power distribution companies had estimated the demand to peak at 8,200 MW this summer.

The National Capital is also facing water shortage due to unprecedented summer heat.

Water minister Atishi has directed the Delhi Jal Board (DJB) to deploy 200 teams across the city to prevent water-wasting activities like car washing with a hose, overflowing water tanks, and use of domestic water supply for construction and commercial purposes.

The IMD has, however, predicted that the heatwave conditions would ease.

“It has rained at many places in Delhi in the afternoon resulting in further fall of temperature. Heatwave conditions will reduce during the next 2 - 3 days due to gradual fall in temperature in association with approaching western disturbance, rainfall/thunderstorm and southwesterly wind blowing from the Arabian Sea to northwest India,” the IMD release stated.

With inputs from agencies