Explainer: What is Heat Wave? Impacts on India

A Heat Wave is a period of exceptionally high temperatures that exceed the typical maximum temperature during the summer season in North-Western India. Heat Waves normally occur from March to June, and in a few unusual instances, they might even last until July.

Those who live in these areas are negatively impacted by the excessive temperatures and accompanying climatic conditions because they produce physiological stress, which can occasionally result in death.

The Indian Meteorological Department (IMD) has defined heat waves as follows:

Heat Waves should not be anticipated until a station's maximum temperature reaches at least 40°C for plains and at least 30°C for hilly regions.

when a station's average maximum temperature is 40°C or less the heat wave is 5 to 6 degrees Celsius above usual. A severe heat wave is defined as an abnormality of 7°C or above.

Heat Wave Departure from Normal is 4 to 5°C when the maximum normal temperature of a station is greater than 40°C. A severe heat wave is defined as an abnormality of 6°C or higher.

When it is declared as Heatwave?

Heat waves should be declared when the actual highest temperature is 45°C or higher, regardless of the typical maximum temperature. Climate change is making longer, more intense heat waves and higher daily peak temperatures more common worldwide. India is also experiencing the effects of climate change in the form of an increase in the frequency and intensity of heat waves, which are fatal to human health and increase the number of heat wave deaths.

Effects of Heat Waves on Health:

• Heat cramps, heat exhaustion, heat stroke, and/or dehydration are frequently the health effects of heat waves. The following are the symptoms and signs:
• Heat Cramps: Ederna (swelling) and Syncope (fainting) are typically associated with fevers lower than 39°C, or 102°F.
• Heat exhaustion: Symptoms include weakness, exhaustion, headaches, nausea, vomiting, cramping in the muscles, and perspiration.
• Heat Stroke: A state of delirium, seizures, or coma that is accompanied by body temperatures of at least 104°F (40°C) or higher. This condition carries a risk of death.

India Under Heat Stress:

While 2022 broke the previous record with 200 heatwave days in India and some of the warmest months since 1901, which affected almost 70% of the nation, spring also failed to arrive in 2023. This year's February was recorded as being the warmest in 123 years, the first time since 1901.

An analytical evaluation of the heat index shows that more than 90% of the country is at extremely cautious or dangerous levels. Heatwave is impacting adaptive livelihood capacity, food grains yield, vector-borne disease spread and urban sustainability.

April 2022 in India was the hottest in 122 years and followed the hottest March in 2023 on record, reportedly killing at least 25 people. The cumulative heatwave-related mortality in India is over 24,000 deaths since 1992.

Daily temperature increases

While there were occasional heat waves in March, April started off hotter than the rest, with daily temperature increases. The state-run India Meteorological Department (IMD) has already projected an increased likelihood of heatwaves in April and May. The majority of the Central, East, and across various sections of Northwest India have already experienced maximum temperatures that are settling in the range of 40°C-44°C.

In Gangetic West Bengal, Coastal Andhra Pradesh, Bihar, and across some areas of the northwest plains including Punjab, Haryana, and Uttar Pradesh, heatwave conditions have already arrived. Yet, due to the combination of the coastal region's severe humidity and Wet Bulb Temperatures, the situation in coastal areas is more worrying than it is in the northwest plains.

After a heat-related power shortfall issue last year, the government has already begun increasing fuel imports to meet surging demand during the coming summer months.

National Thermal Power Company, a state-owned power producer, has already estimated that it will require 250 million metric standard cubic metres of coal to meet peak demand over the two-month period of April and May.

Impact on labourers

The poor who are working as urban or rural labourers without access to cooling suffer most in an overpopulated nation like India from the excessive heat. Long-term exposure to hot weather and moist circumstances can have a variety of physiological effects, including a significant risk of heat stroke.

In 2022, 90 deaths attributed to severe heat stress were recorded. Rising worldwide mean temperatures due to more intense and frequent heat waves would result in insufficient conditions, as few places meet and surpass human survivability standards.

India will experience intense heat waves

A research by Global Weather Attribution found that climate change induced by humans raised the likelihood of an occurrence like the 2022 heatwave in India by 30 times. Future global warming will increase the frequency and severity of heatwaves like this one.

Such a heatwave would become 2-20 times "more likely" and 0.5-1.5°C hotter than those in 2022 at the global mean temperature scenario of +2°C. Experts feel that limiting further warming is critical, and the emphasis has turned to the need to adapt to rising climate change-related heat threats.

Research has shown that heat action plans (HAP), which incorporate early warning and early intervention, awareness-raising and behaviour-changing messaging, and supportive public services, can lower mortality.

Study on Ahmedabad

The Ahmedabad HAP was cited by the IPCC's Working Group II Report on "Climate Impacts, Vulnerability and Adaptation" as the best example of urban heat adoption in all of South Asia. This report was part of the IPCC's sixth assessment report cycle.

According to research, one of India's largest cities, Ahmedabad, prevented almost 1,190 deaths annually after implementing the HAP in 2013. The national government of India is collaborating with around 130 cities and districts, 23 states that are prone to heat waves, and 23 other states to develop and deploy HAPs nationwide.

Nearly all HAPs are underfunded, are not designed for local contexts, and fail to identify and target vulnerable people, according to the most recent analysis from the Centre for Policy Research (CPR). Extreme heat adaptation will increase resiliency while lowering mortality. But according to the IPCC sixth assessment cycle's Synthesis Report, if emissions are not limited to 1.5°C warming, we will pass the point at which humans will no longer be able to adapt to or survive extreme weather events like heat waves.

Experts' Opinion on Heatwave

Raghu Murtugudde, Visiting Professor, Earth System Scientist at IITB and Emeritus Professor at University of Maryland tells us about the impact of El Niño on Monsoon 2023. While an El Niño tends to produce a deficit monsoon, only about 60% of the deficit monsoon years have occurred during an El Niño year.

He said that this could be turned around to say that 40% of the El Niño years have resulted in normal or above normal rains. However, analysis of past monsoons shows that an El Niño that follows a La Niña year tends to be the worst-case scenario in terms of monsoon deficits. We have just emerged from a record 3-year La Niña and are likely heading into an El Niño.

"If the forecasts say the monsoon will still be normal, we need to wait and see what compensating factors may play a role," he added.

Visiting Professor said that one also needs to keep in mind that seasonal rainfall totals now have very little meaning considering the erratic distributions with extreme wet and dry spells expected in any monsoon year - normal, deficit or excess. Floods, droughts, crop damages, health impacts and such need to be dealt with as effectively as possible with short (days 1-3), medium (days 3-10) and extended (weeks 2-4) range forecasts.

He said that, all states down to municipalities and panchayats have to pay attention to IMD warnings. However, despite the LaNiña of 3-years long, the Eurasian precipitation has been slightly below normal which would favour a stronger monsoon and may offset the El Niño impact. Unclear if this is what is happening in the IMD forecast.

The Hottest City Today Is..

India is in for a particularly hot summer, as 36 weather stations in various locations throughout the nation registered highs of 42 degrees Celsius on Monday. The list of cities with the highest temperatures today was provided by the India Meteorological Department (IMD), with the top-ranking city scorching at 44.6 degrees Celsius.

Prayagraj in Uttar Pradesh grabbed the top rank on the list published by the weather office today. Baripada in Odisha measured a blistering 44.2 degrees, while Jhasi in Uttar Pradesh boiled at 43.6 degrees.

18 of the 36 weather stations recorded maximum temperatures around 43 degrees Celsius, while the remaining weather stations recorded maximum temperatures around 42 degrees. The highest temperature recorded in Delhi was 40.6 degrees Celsius, which is four degrees above average.

Here are some measures that you can take to cope with heat waves

Stay hydrated: Drink plenty of water and other fluids such as coconut water, lemon water, or fruit juice to keep your body hydrated.

Stay indoors: Stay indoors during the hottest parts of the day, typically between 11 am to 4 pm. If you must go outside, try to stay in the shade or wear a hat and light-coloured clothing.

Use fans or air conditioning: Use fans or air conditioning to cool down your body and your home.

Take cool showers: Take a cool shower or bath to lower your body temperature.

Avoid strenuous activities: Avoid strenuous activities such as exercise or sports during the hottest parts of the day.

Eat light and healthy: Eat light, healthy, and easy-to-digest meals such as salads, fruits, and vegetables.

Stay connected: Keep in touch with family and friends, especially those who may be more vulnerable to the effects of heatwaves.

Check on others: Check on neighbours, friends, and family members who may be at risk.