Granular monitoring gives city sharper picture of local weather
Extreme temperature recordings across Delhi have shown a notable spike over the past decade, with the India Meteorological Department (IMD) expanding its monitoring network, with several stations in the Capital logging readings that deviate sharply from the base weather gauge at Safdarjung.
IMD data from the past week shows that 80-90% of the 11 stations in Delhi recorded temperatures higher than the official maximum, which is collected at Safdarjung. Experts said this meant that most residents of Delhi are likely experiencing higher temperatures than Safdarjung, warning that it was not an accurate representation of the city’s weather.
On Sunday, for instance, which was the city’s hottest day so far this year, nine stations recorded maximum temperatures higher than Safdarjung. Mayur Vihar was the only station cooler than Safdarjung.
Safdarjung recorded a maximum temperature of 45.6°C, around four degrees lower than stations in north-west Delhi’s Mungeshpur and south-east Delhi’s Najafgarh, where the mercury tipped past 49°C, a number never before clocked on any of the city’s weather gauges. To be sure, IMD set the two stations up just a year ago, so no previous data is available.
On Monday, too, when temperatures dropped across Delhi, all but one weather station (Mayur Vihar) recorded a maximum higher than Safdarjung.
The peak temperature at Safdarjung settled at 42.4°C, even as Najafgarh, Mungeshpur, Sports Complex, Pitampura and Jafarpur went above 44°C.
Scientists from IMD explained that the Safdarjung weather station is considered Delhi’s representational observatory because the recordings are done using mercury thermometers, with readings logged manually to present a more accurate picture.
“Most observatories in Delhi have automatic systems, which have a scope for error, because they use bi-metals, which can contract and expand during different weather conditions. The Safdarjung and Palam observatories are also older stations that have comparative data to show if the spikes are abnormal. We always stress the use and mention of representational stations for a more precise idea of the temperature,” said one senior Met official who asked not to be named.
Delhi has five manual weather stations – at Safdarjung, Palam, Lodhi Road, Ridge and Ayanagar. Readings here are collected manually, with a Met official using several instruments to note recordings at various intervals through the day. The rest — Najafgarh, Mayur Vihar, Sports Complex, Mungeshpur, Jafarpur and Pitampura — are all automatic stations (AWS), where data is recorded automatically and transmitted through servers by pre-calibrated weather instruments.
IMD officials say these AWS began to be installed across the city from 2010, due to IMD needing better coverage during the Commonwealth Games adding that they require minimal space against a full-fledged observatory.
“While they are not as accurate as a manual reading, AWS are still used to get an idea of the temperature in an area. If it appears that the reading is inaccurate, stations are re-calibrated to ensure precision,” said another IMD official who asked not to be named.
Mahesh Palawat, vice-president (meteorology and climate change), Skymet Weather Services, said a single weather station cannot provide representational data for the entire city.
“Safdarjung weather station is located in a fairly green area, as compared to the rest of Delhi, which has a lot of heavily concretised spaces without much green cover. Temperatures in these parts of the city will therefore, understandably, be higher. A station can throw up data for a 3-4 km radius. But for a better picture of the entire city, the Met could average out readings from seven or eight stations,” said Palawat.