Most parts of Delhi recorded a heat index from 44 to 49 degrees Celsius in April last year, data used for a research article on heatwaves showed.
Parts of Southwest Delhi recorded the highest heat index of 49 degrees Celsius over this period, followed by parts of South Delhi that saw a heat index of 48 degrees Celsius. Pitampura and Mungeshpur in Northwest Delhi followed with 47 degrees Celsius. Parts of New Delhi and Southeast Delhi may have recorded the lowest heat index of around 44 degrees Celsius over the month.
Heat index is a measure of how hot it feels when humidity is factored in along with the air temperature, and the figures were calculated using data from the India Meteorological Department (IMD).
The research article, published in the journal PLOS Climate, notes that the heat index figures recorded across Delhi in April last year are in the ‘danger’ category of the United States National Weather Service classification for heat index, based on the effect of heat on the human body. The ‘danger’ category points to the likelihood of heat cramps and heat exhaustion, along with possible heat stroke in case of continued activity. There is only one higher category of ‘extreme danger’ when heat stroke is “imminent,” according to the classification.
On Delhi’s heat risk, the researchers, Ramit Debnath, Ronita Bardhan, and Michelle L Bell, associated with the University of Cambridge and Yale University, note that aspects that can aggravate the “heat-related vulnerabilities” in Delhi include “concentration of slum population” and overcrowding in areas with high heat index, lack of access to amenities like electricity, water and sanitation, poor housing conditions, and non-availability of immediate healthcare and health insurance.
Debnath said that urban densification and built-up area, along with wind direction are likely to contribute to local variations in heat index within the city. The researchers make a case for contextualised heatwave impact studies, while Bardhan explained that for heat, it is essential to look beyond temperature and combine humidity and human behavioural adaptation while preparing and implementing action plans to deal with heat.
The research article also notes that the Delhi government’s vulnerability assessment, which is part of the state action plan on climate change, does not include heat index estimations. This action plan was finalised in 2019 and is to be updated.
On local temperature variations, Kuldeep Srivastava, scientist, IMD, said that factors like concrete and green areas can determine these variations, along with the location of the weather station, and the type of weather station — with a manual one likely to be more accurate than an automatic one.
