Understanding heat waves: What are the causes, impact, and how to stay safe

Delhi sweltered on Monday as temperatures soared into the mid- to high-forties Celsius, triggering heat wave conditions across the city. Weather forecasters predict this intense heat will persist until at least Wednesday, with the heat index, or "feels-like" temperature, reaching 49 degrees Celsius.

Safdarjung, the city's base station to monitor weather, recorded 45.1 degrees Celsius on Monday, five degrees above normal. This followed Sunday's high of 45.4 degrees Celsius. Monday's minimum temperature was 29.2 degrees Celsius, three degrees above normal. The extreme heat has severely hampered daily activities.

What are heat waves

A heat wave is an extended period of excessively hot weather that can have serious consequences for human health and the environment. In a heat wave, temperatures rise significantly above the average for a particular region and time of year. Heat waves can cause exhaustion, stroke, and even death in extreme cases.

A heat wave is not just high temperature, it is defined by unusual temperature increases. For instance, a location that typically experiences 40 degrees Celsius in summer is not considered to be having a heat wave even if the temperature rises to 42 or 43 degrees. Conversely, a place where the normal temperature is 27 or 28 degrees would be experiencing a heat wave if the temperature reaches 35 degrees.

According to the India Meteorological Department (IMD), a heat wave is considered if the maximum temperature of a station reaches at least 40 degree Celsius or more for Plains and at least 30 degree Celsius or more for Hilly regions. However, it also notes the temperatures at which heat waves are declared differ from place to place based on the temperature climatology of the region.

Also Read: IMD weather: Delhi on heatwave red alert, heavy rain in many states today

Increasing frequency of heat waves

Heat waves have become increasingly frequent in India due to climate change. The heat wave in North India, with temperatures nearing 50 degree Celsius in some areas, is a recent example. The IMD has issued a red alert for several states, including Delhi, Haryana, Punjab, Uttar Pradesh, Rajasthan, Madhya Pradesh, and Gujarat.

Certain regions in India are more susceptible to heat waves due to their location and climate. The northwestern and central parts of the country, including Rajasthan, Madhya Pradesh and Gujarat, are prone to heat waves due to their continental climate characterised by hot, dry summers and sparse rainfall.

This year, a heat wave has triggered a severe water and power crisis in several areas of the Jammu division, prompting the authorities to set up control rooms and appoint nodal officers in each district to cater to public complaints. Jammu has been reeling under an extreme heat for the past fortnight.

On Monday, Jammu recorded its hottest day of the season at 42.8 degrees Celsius, 3.7 degrees above normal for this time of year, according to the meteorological department.

What is causing the high temperatures

Climate researchers say that heat waves occur when there is high pressure in the atmosphere that forces hot air downward and traps it near the ground. This high-pressure system acts like a lock that prevents the hot air from rising, causing the temperature to rise further.

The air compresses and heats up as it sinks, leading to extreme heat conditions. Additionally, climate change contributes to more frequent and intense heat waves by altering global weather patterns and increasing the likelihood of prolonged periods of high pressure.

Why is the heat increasing in India

The IMD reported that a combination of weather patterns is causing temperatures to rise in the breadbasket region.

While summer temperatures in India typically peak in May, the IMD has forecasted 7-10 heat wave days in the northwestern regions this month, compared to the usual 2-3 days.

This increase is mainly attributed to fewer non-monsoon thunderstorms and an active but weakening El Nino, a climate pattern that usually brings hot and dry weather to Asia and heavier rains to parts of the Americas.

Additionally, warm westerly winds from Pakistan are contributing to the heat.

Elsewhere in India, summer temperatures have already reached record highs, particularly in the eastern and southern regions, where April temperatures were among the highest on record.

Last month, the weather department also declared a rare heat wave in the southwestern coastal state of Kerala.

Impact of heat waves on health

Extreme heat can have severe impacts on health. Recent research indicates that there is an increase in premature births during intense and prolonged heat waves.

A team of researchers, including those from the University of Nevada studied 53 million births across the 50 largest metropolitan areas in the US over a 25-year period (1993-2017). They analysed daily counts of preterm and early-term births and found that preterm births increased by 2 per cent, and early-term births increased by 1 percent following a four-day period during which each day's average temperature was among the hottest 2.5 per cent for that region.

“Each 1 degree Celsius increase in mean temperature above the threshold was associated with a 1 per cent increase in the rate of both preterm and early-term birth,” the authors wrote in the study published in The Journal of American Medical Association (JAMA) Network Open.

Apart from that, heat waves are also known to worsen respiratory conditions and lead to breathing difficulties, particularly in areas with poor air quality. High temperatures can also strain the heart and circulatory system, increasing the risk of heart attacks and other cardiovascular issues

Economic implications of high temperatures

As temperatures rise, concerns about the economic impact of heat waves are growing. The negative effects are not limited to human suffering but also affect a wide range of economic activities.

Heat waves often result in decreased workforce productivity. High nighttime temperatures make it difficult for the body to cool down, especially in urban areas experiencing the urban heat island effect, where temperatures are significantly higher than in surrounding regions. This phenomenon worsens the impact of heat waves.

In a country like India, where a large portion of the workforce is engaged in outdoor activities, the consequences are severe. Around 45.76 per cent of the workforce is employed in agriculture, with 83 per cent working in the unorganised sector. Outdoor workers, including farmers, are particularly vulnerable to heat-related illnesses such as heat exhaustion and heatstroke, leading to frequent breaks and reduced productivity.

A study by Cambridge University last year warned that extreme heat could reduce outdoor working capacity by 15 per cent, potentially lowering the quality of life for millions and causing a 2.8 per cent decline in India’s GDP by 2050.

What is ‘Nautapa’

Nautapa are tge nine days when heat is at its worst in India. It is also known as ‘Navtaap’. The term Nautapa translates to ‘nine hot’ (nau = nine, tapa = heat). . These days are also the hottest of the year. In 2024, Nautapa began on May 25 and will continue until June 2.

During Nautapa, the sun is directly over Central India, minimising the distance between the Earth and the sun. This results in more direct and intense solar radiation, causing severe heat. Temperatures are expected to reach close to 50°C in some areas, particularly in Rajasthan, Haryana, Punjab, Madhya Pradesh, and Gujarat.

How to protect yourself in the sweltering heat

To protect yourself during this period of extreme heat, doctors have recommended that it is essential to stay hydrated, consume a liquid-rich diet, avoid outdoor activities, wear protective clothing, and seek medical attention if you experience any health issues.