New Delhi feels like it is on fire. The heat comes off the road in blistering waves, and the water that flows from the cold tap is too hot to touch. Daytime temperatures have hit 44 degrees Celsius (111 Fahrenheit) and often do not fall below 30 in the night. A giant landfill on the outskirts of the capital spontaneously combusted recently, and the 17-story high dump that contains millions of tons of garbage continues to smolder, worsening the city’s already dangerously polluted air.

Daily power outages driven by a surge in demand for electricity have resulted in blackouts as long as eight hours in some parts of India, while coal stocks — the fuel that accounts for 70% of the country’s electricity generation — are running low, prompting warnings of a fresh power crisis. The northern wheat crop is scorched. It was the hottest March in 122 years. Spring just didn’t happen, and those extreme temperatures continued into April and May 2022. Still, it’s not until June that the monsoon is expected to arrive and provide any kind of relief.

What’s most alarming about this heatwave is that it’s not so much a one-time ordeal as a taste of things to come as the effects of global warming push India and its neighbors to levels where the climate is a core threat to human health.

The most worrying weather measurement is not the heat typically reported in forecasts but the wet-bulb temperature, which combines heat and humidity to indicate how much evaporation can be absorbed into the air. At wet-bulb temperatures above 35 degrees Celsius, we become unable to reduce our temperature via sweating and will suffer potentially fatal heat stroke after only a few hours, even with shade and water. Similar effects can result for those working outdoors when wet bulb temperatures exceed 32 degrees, and measures as low as 28 degrees caused tens of thousands of deaths in the European and Russian heatwaves of 2003 and 2010.

Humidity falls as temperature rises, so such events were once thought to be extraordinarily rare. One 2018 study concluded that the most severe temperatures of close to 35 degrees “almost never occur in the current climate." In fact, closer analysis of data from weather stations done in 2020 suggests they’re already happening relatively frequently, particularly in the heavily populated belt from the Persian Gulf through Pakistan and northwest India.

Just 12% of India’s 1.4 billion citizens have access to air conditioning, which means hundreds of millions of people are simply unable to cool themselves when their bodies reach the point of heatstroke. It’s a situation mirrored in neighboring Pakistan, which is experiencing similarly catastrophic heatwave conditions. Daily wage earners, who toil in the fields, work in factories and construction, sweep streets and build roads, have no escape.

Multiple regions of India have already been edging close to critical wet-bulb temperatures, according to government data, though the maximum humidities haven’t necessarily been occurring at the same time as the peak temperatures. In the eastern Odisha state, peak temperatures and humidities in parts of the capital Bhubaneswar would have produced wet-bulb temperatures of 36.6 Celsius if they happened at the same time, the data show.

The risk is that, even if the most hazardous levels are avoided in the current heatwave, each hot season is a fresh roll of the dice on whether a freak event will occur that will lead to vast numbers of deaths. The odds lengthen with each passing year. The world is currently in the grip of a La Nina climate cycle, which typically brings cooler summer weather to India. When that next flips to El Nino, the risks will ramp higher still.

That the government hasn’t declared a national disaster and rolled out an appropriate response will come as no surprise to those who lived through the nation’s deadly Covid-19 epidemic.

India does have a “National Action Plan on Heat Related Illnesses" and the federal government on 1 May 2022 issued an advisory to states urging them to ensure hospitals were ready to deal with an expected surge in demand. But given that the India Meteorological Department (which started collecting nationwide records in 1901) has been raising the alarm with heat wave warnings on 25 April 2022, it all feels a little underdone. Recommended measures such as whitewashing roofs to cool building interiors would be insufficient to deal with a major heatwave. Advice to ensure secure power supply to health centers won’t help if heat and the load from millions of air conditioners cause the power grid to fall over when it’s most needed.

Dew Point and Dry Bulb Temperatures

• Dry Bulb Temperature:
  • The Dry Bulb temperature, usually referred to as "air temperature", is the air property that is most commonly used.When people refer to the temperature of the air they are normally referring to the dry bulb temperature.
  • The Dry Bulb Temperature refers basicallyto the ambient air temperature. It is called "Dry Bulb" because the air temperature is indicated by a thermometer not affected by the moisture of the air.
  • Dry-bulb temperature can be measured using a normal thermometer freely exposed to the air but shielded from radiation and moisture.
  • The dry-bulb temperature is an indicator of heat content.
• Dew Point Temperature:
  • The Dew Point is the temperature where water vapour starts to condense out of the air(the temperature at which air becomes completely saturated).
    • Above this temperature the moisture stays in the air.
  • If the dew-point temperature is close to the dry air temperature - the relative humidity is high.
  • If the dew point is well below the dry air temperature - the relative humidity is low.
  • The Dew Point temperature is always lower than the Dry Bulb temperature and will be identical with 100% relative humidity(the air is at the saturation line).