Persistent humidity, rising temperature make Delhi sweat

The city’s maximum temperature on the day touched 39.4 degrees Celsius (°C), five degrees above normal, while the humidity peaked at 82%

A brutal combination of high humidity and rising temperature gave Delhi an unusually sticky and uncomfortable Friday, with the weather taking a turn for the worse after a three-day pause in monsoon rains.

The combination of humidity with heat is worse for human health since people cool down by sweating. (HT Photo)

The city’s maximum temperature on the day touched 39.4 degrees Celsius (°C), five degrees above normal, while the humidity peaked at 82%.

The two together gave Delhi a wet-bulb temperature of 29.4°C, a level at which the outdoor heat becomes risky, even for healthy people. The combination of humidity with heat is worse for human health since people cool down by sweating. Wet-bulb temperature reflects the condition someone will feel outdoors — once this measure passes 32°C, people are at extreme risk of adverse health effects.

Another measure is the heat index (HI), which too accounts for humidity in how the temperature affects a person, but this reflects conditions in shade. On Friday, the HI in Delhi touched 50°C. This year, this number peaked at 51°C on June 14.

The India Meteorological Department (IMD) predicted similar weather for the weekend, with high humidity and isolated showers. It did, however, forecast increased rains from Monday till Wednesday, which will consequently push down temperatures and bring residents some relief from the prickly heat of the past week. “High humidity will continue to persist and this is a feature of the monsoon season. Even with the trough away, moisture content can stay around 50-60%, which makes it uncomfortable to be outdoors. We can expect an increase in rain intensity from Monday onwards, with chances of moderate rainfall between Monday and Wednesday,” said Kuldeep Srivastava, scientist at IMD.

Delhi remained dry on Friday, barring a hyper-local spell of sharp rain over Mungeshpur, which received 21mm of showers in the afternoon. Weather experts said this relatively lengthy dry spell was due to a shift in the monsoon trough, which is now over south Rajasthan. As a result, over the past few days, there has been a gradual rise in the city’s maximum temperature.

Safdarjung, representative of Delhi’s weather, hit a maximum of 39.4°C on Friday; 38.4°C on Thursday; 36.5°C on Wednesday and 33.4°C on Tuesday. This has also translated into a gradual rise in the wet bulb temperature at the same time. On Tuesday at 2.30pm, it was 28.5°C. This rose to 29.2°C on Wednesday, 29.5°C on Thursday and 29.6°C on Friday. At 5.30pm on Friday, this crept up to 29.7°C.

Experts say being outdoors when the wet bulb nears 30°C, presents the risk of heatstrokes, possible light-headedness and nausea.“From 28 degrees onwards, there is considerable discomfort being outdoors and as it edges towards 30 degrees and beyond, there is a significant risk of heatstroke. This is because even though the body is sweating, it is not being evaporated to cool down the body, as there is already a lot of moisture in the air,” said Mahesh Palawat, vice president at the private forecaster Skymet.

“Human body can still withstand dry heat, but as humidity levels increase along with heat, the ability to spend outdoors slowly decreases. Sweating is a body’s reaction to cool itself, but beyond a point our body starts getting dehydrated and there can be serious health issues, including the risk of death among senior citizens and children when heat and humidity combine,” said Dr Dilip Mavalankar, director, Gandhinagar-based Indian Institute of Public Health.

In a March 2023 report, the Centre for Policy Research (CPR) analysed 37 heat action plans (HAPs) across 18 Indian states, finding that while most states included measures on dry heat, humid heat spells had not been factored in when it came to policy making. A 2022 Lancet study found a 55% spike in fatalities in India between 2000-2004 and 2017-2021 due to extreme heat and high wet bulb temperatures.

The Met’s forecast for Saturday shows that Delhi could see light rain in some places, with a maximum of around 38°C. The minimum, recorded at 29.5°C on Friday, is meanwhile expected to touch 30°C on Saturday.