According to experts, heat waves are a period of unusually high temperatures as compared to what is normally expected over a region. Therefore, the temperatures at which heat waves are declared differ from place to place based on the temperature climatology of that region. The impact of heat waves gets aggravated by supportive meteorological factors such as high humidity, high wind speed, duration of heat wave events, etc. In India, a heat wave is considered if the maximum temperature of a station reaches at least 400C or more for Plains and at least 300C or more for Hilly regions. Most of the states of India are prone to heat waves in varying degrees.
The India Meteorological Department (IMD) recently predicted that heat waves will sweep across most of the states in the country in June 2024. According to the forecast, above-normal monthly maximum temperatures are likely over most parts of the country in June, except many parts of the southern peninsular India. It also said that above-normal heat wave days are likely over most parts of northwest India and adjoining areas of central India. The only relief is expected in the extreme northern parts of northwest India and a few pockets of east and northeast India, where normal to below-normal minimum temperatures are most likely.
Heat waves affect human health and air quality, increase energy consumption, reduce crop yields, increase water loss and intensify droughts. In addition, exposure of crops to temperatures beyond a critical threshold can lead to crop failure. Heat waves also increase temperatures in buildings and cities, cause disruptions in critical infrastructure networks, affect the economy through lower labour productivity, and exacerbate the impacts of other climate-related hazards such as droughts or forest fires. Increased humidity and temperatures can also significantly endanger human life.
Heat waves have claimed more lives in India than other natural hazards, with the exception of tropical cyclones. Vulnerability to heat is shaped by both physiological factors, such as age and health status, and exposure factors such as occupation and socio-economic conditions. Extended periods of high temperatures create cumulative physiological stress on the human body which exacerbates the top causes of death globally, including respiratory and cardiovascular diseases. Further, heat waves can often trigger cascading socioeconomic impacts.
With every additional increment of global warming, changes in extremes continue to become larger. Every additional rise in global warming causes discernible increases in the intensity and frequency of temperature extremes, including heat wave intensity, frequency and duration. Climate change, without mitigation, poses a serious and unique risk to South Asia, a region that is home to about one-fifth of the world’s population, due to an unprecedented combination of severe natural hazards and acute vulnerability. Mitigating climate change by reducing greenhouse gas emissions is imperative and urgent to limit the magnitude of human costs from extreme heat.
