Local factors explain why some parts of Delhi hotter
The extreme heat seen in the Capital has been unusual in more ways than one, with Safdarjung, the base weather station for Delhi, already touching a maximum of 42.6 degrees Celsius this year on April 11 and 19.
This is the highest maximum for April in the past five years since it touched 43.2°C on April 21, 2017. However, Safdarjung is rarely Delhi’s hottest location. If average maximum temperatures from all 11 weather stations in the fortnight of April 11-25 are analysed, Safdarjung was one of Delhi’s cooler spots, ahead of only Mayur Vihar.
While Safdarjung recorded an average maximum temperature of 40°C in these 14 days, the Yamuna Sports Complex weather station in east Delhi was the hottest, averaging a maximum temperature of 41.9°C, nearly two degrees higher. It has also been the only station to register a maximum temperature of 45°C this year on April 19.
On the other end of the spectrum, the Mayur Vihar weather station has emerged as Delhi’s coolest location, with average a maximum of just 38.7°C, as much as 3.2 degrees cooler than Yamuna Sports Complex.
This difference in local temperatures can be pinned to a phenomenon called the urban heat island effect, Met officials said, although there are other factors at play as well. Urban heat islands occur when cities replace natural land cover with dense concretisation that absorbs and retains heat.
This is best demonstrated at the Yamuna Sports Complex, which is surrounded by congested residential neighbourhoods largely devoid of green cover. At the same time, the weather station at the Delhi Ridge near Delhi University’s north campus has been the third hottest location during the fortnight at an average maximum temperature of 41.3°C. This shows the other factors that determine local temperature.
The location of the station plays a key role in capturing surrounding temperature in the surroundings, said RK Jenamani, scientist at the India Meteorological Department. The Ridge station is surrounded by hard rocks that can heat up fairly quickly, he said.
“The Aravalli terrain is seen at both the Ridge station and Ayanagar, but Ayanagar has been found to be much cooler despite these locations largely surrounded by green areas. However, the Ridge station has a lot of hard rock near it and this is likely to be heating up the area around its vicinity,” Jenamani said. “If the green cover is dense, it can provide shade and a cooling effect; otherwise even parts of the Ridge that are in the open can heat up fairly quickly.”
The Safdarjung station is located in one of the greenest patches of Delhi that also has grass around it that is watered frequently, which explains the relatively lover temperatures recorded. “Safdarjung is located in one of the cities greenest areas and has no structures in the vicinity, thereby allowing air to flow freely,” experts said.
However, this is not the case at Najafgarh, which recorded an average maximum temperature of 41.4°C during this period, making it Delhi’s second hottest spot. Although Najafgarh exhibits similar characteristics as Safdarjung in terms of location — surrounded by fields and open spaces that allows winds to flow freely — warmer westerly winds from Rajasthan are likely to be the reason for such a high reading at this particular station, Met officials said.
“Haryana and the western parts of Delhi have been impacted the most by dry westerly winds blowing in from Rajasthan,” Jenamani said. “Since Najafgarh is the western most station, the rise in temperature there has largely been down to these winds.”
On Tuesday, Delhi’s hottest location was Najafgarh, with a maximum of 42.6°C, followed by Ridge and Yamuna Sports Complex at 42.5°C each. Safdarjung was cooler, recording a maximum of 40.8°C.