What are heat waves?

• A Heat Wave is defined as a period of abnormally high temperatures over a region. 
• The heat wave is considered when the maximum temperature of the region reaches at least 40 degrees Celsius for plains and at least 30 degrees Celsius for hilly regions.
• Higher daily peak temperatures and longer, more intense heat waves are becoming increasingly frequent globally due to climate change. 
• India too is feeling the impact of climate change in terms of increased instances of heat waves which are more intense in nature with each passing year.

Vulnerable Regions

• Heat waves are common over the Core Heatwave Zone (CHZ) — Rajasthan, Punjab, Haryana, Chandigarh, Delhi, West Madhya Pradesh, Uttar Pradesh, Chhattisgarh, Orissa, Vidarbha in Maharashtra, parts of Gangetic West Bengal, Coastal Andhra Pradesh and Telangana, as categorized by India Meteorological Department.
•  The regions in the extreme north, northeast, and southwestern India are less prone to heat waves.

Causes for increasing heatwave events in the country

• According to the India Meteorological Department (IMD), the average temperature in India has increased by approximately 0.6°C over the last century. Thus global warming has resulted in increasing heat waves.
• The number of days with temperatures exceeding 30 degrees Celsius has also increased of late. While a temperature of 33 degrees Celsius was recorded between 1961 and 1990 for around 70 days every year, from 1991 to 2022, this temperature was recorded for 89 days a year.
• Clear skies, low humidity, and lack of wind are favorable conditions for heat waves formation as they result in an increase in temperature.
• The urban heat island effects can make ambient temperatures feel 3 to 4 degrees more than they are.
• More heat waves were expected as global temperatures had risen by an average of 0.8 degrees in the past 100 years. Night-time temperatures are rising too.

Impacts

• The health impacts of Heat Waves typically involve dehydration, heat cramps, heat exhaustion, and heat stroke. 
• The extreme temperatures and resultant atmospheric conditions adversely affect people living in these regions as they cause physiological stress, sometimes resulting in death.
• Heatwaves can also increase strain on water, energy, and transportation resulting in power shortages or even blackouts. 
• Food and livelihood security may also be strained if people lose their crops or livestock due to extreme heat. 
• Multiple areas of the economic sector experience reduced worker productivity during heatwaves, especially agriculture and construction.
• Heatwaves can lead to water shortages and increased stress for plants, particularly in arid regions. This has the effect of reducing plant growth, the basis of energy production and the food chain, with an overall drying-out of the landscape.

Why in news?

• Heatwave alerts have been issued across many states in North and Central India.