Heatwave:

According to qualitative definitions, a heatwave is an extreme temperature that can become fatal to the human body. In terms of quantitative measurement, it is determined by analysing the change in temperature thresholds in a region depending on whether the temperature is normal or not. It is defined in some countries by using the heat index, which is a combination of temperature and humidity, or by using the extreme percentile of temperature.

Favourable conditions for a heatwave:

• The movement and prevalence of dry, warm air over a region (There should be a pattern of warm, dry air existing over a region with the appropriate flow to transport it).
• Moisture is absent from the upper atmosphere [As moisture relates to temperature rise (limits it)].
• To ensure maximum insulation, the sky should be cloudless.
• An anticyclonic flow with a large amplitude is observed over the area.

Heatwaves usually develop over Northwest India and move slowly eastward and southward, but not westward (Westerly to northwesterly winds prevail during the season). Occasionally, under favourable conditions, any region in situ can also experience heat waves.

Effects:

• Usually, a heatwave lasts for a few days,  and during this time, there are many deaths related to heat.
• While heat may be more pronounced in cities due to the Urban Heat Island (UHI) effect, non-urban communities can also suffer critical effects during and after periods of abnormally hot weather.
• During heatwaves, the health care sector and emergency services may be stressed, and transportation, energy, and water supplies may be short, resulting in power outages.
• If crops or livestock are lost as a result of extreme heat, food and livelihood security may also be compromised.
• In a heatwave, those with chronic diseases that take regular medications, as well as children and older people, are at a higher risk of complications and death.

As a result of climate change, global temperatures as well as the frequency and severity of heatwaves will increase in the this  century. High air temperatures can harm people’s health and cause more fatalities. Extended periods of high daytime and nocturnal temperatures put the body under cumulative physiological stress, which makes the world’s leading causes of death, such as diabetes mellitus, cardiovascular disease, and kidney illness, worse. Heatwaves often result in public health emergencies, have a significant negative influence on public health, and have a domino effect on other aspects of society (e.g. lost work capacity and labour productivity).