The recent discovery of a significant spatial shift in the occurrence of heatwaves across India has made headlines. This shift, which sees heatwaves transpiring in regions they were previously absent, was noticed in a research study reviewing heatwave patterns from 1951-2016. The study also predicted that the eastern and western coasts, currently unaffected, will experience severe heatwaves in the years to come.
The Emerging Pattern of Heatwaves
A warming pattern was detected over northwestern and southern parts of India, contrasted by a cooling trend over the northeastern and southwestern regions. The research emphasized a ‘spatio-temporal shift’ in heatwave occurrences, especially in three heat-prone regions – northwestern, central, and south-central India. The highest increase in these weather events was recorded in west Madhya Pradesh at the rate of 0.80 events per year. While northern states such as Uttar Pradesh, Bihar, and Delhi typically face heatwaves, these weather events are now being reported in usually unaffected regions like southern Madhya Pradesh, Andhra Pradesh, Karnataka, and Tamil Nadu. Notably, heatwave increases in Karnataka and Tamil Nadu could signify increased events in the future. On the contrary, the eastern region of Gangetic West Bengal witnessed a decrease in heatwaves by 0.13 events per year.
Heatwaves: A Detailed Overview
A heatwave is an unusually prolonged period of excessively high temperatures beyond the usual maximum temperature prevalent during the summer season. Commonly occurring between March and June, and in some rare instances, extending until July, heatwaves predominantly affect the North-Western and South Central parts of India. The India Meteorological Department (IMD) designates heatwaves based on regional temperature ranges and sets specific criteria for what constitutes a heatwave. For plains, the maximum temperature must reach at least 40°C, and for hilly regions, it must reach at least 30°C. If the normal maximum temperature is less than or equal to 40°C, a rise of 5°C to 6°C is classified as a heatwave condition. If the temperature rises by 7°C or more, it is considered a severe heatwave condition.
Impacts of Heatwaves
Heatwaves can bring about several critical impacts such as heat stress, increased heat-related mortality, heat strokes, amplified energy demands, and decreased worker productivity. High humidity levels can thwart the body’s evaporative cooling process, leading to heat stress. Research indicates that an increase of 0.5 degrees Celsius in mean summer temperatures can hike heat-related mortality rates by 2.5% to 32%. The mortality risk can further rise by 78% if the duration of a heatwave extends from 6 to 8 days. Individuals most susceptible to heatstroke include older people and those with chronic illnesses such as heart disease, respiratory disease, and diabetes, as their ability to regulate body heat diminishes with age. Yet another impact of sweltering heatwaves is the skyrocketing demand for electricity, causing higher rates. Furthermore, extreme heat can hamper worker productivity, especially for the more than 1 billion workers regularly exposed to high heat, often reporting reduced output due to heat stress.
Mitigating Factors
The study identified two elements that have intensified the heatwave conditions in the country – the escalating nighttime temperatures, which inhibit heat discharge during the night, and the rising humidity levels, which exacerbate the impact of high temperatures on the human body. These findings call for urgent measures to mitigate these factors and ensure better preparedness for future heatwave events.
