Comparative analysis of heatwaves and heat stress in six climatic zones of India based on observed data

The global phenomenon of climate change has led to the increasing occurrence of heatwaves, significantly escalating heat stress and discomfort. Presently, heatwaves are intensifying in terms of frequency, duration, and severity, causing adverse effects such as increased illnesses, human mortality, and forest fires, both in India and globally. This study investigates six climatic zones in India—Arid, Semi-arid, Montane, Humid subtropical, Tropical wet, and Tropical wet & dry—over 31 years (1990–2020), focusing on the summer season. Daily maximum temperature, relative humidity, wind speed, and solar radiation were used to analyze heatwaves, while the Universal Thermal Climate Index (UTCI) and Humidity Index (HD) measured heat stress and discomfort. Our study shows heatwaves are most prevalent in Semi-arid, Montane, and Humid subtropical zones. These zones exhibited a respective increase of (10.94 %, 21.35 %, and 7.03 %), (11.62 %, 22.03 %, and 7.70 %), and (11.76 %, 22.16 %, and 7.84 %) of heatwave events compared to the Arid, Tropical wet, as well as Tropical wet and dry zones respectively. In April 2010, India experienced widespread heatwaves, except tropical wet zone. The Tropical wet zone experienced minimal heat waves, with individuals facing moderate discomfort and heat stress. Thermal stress impacts were greater in the eastern coastal regions of the Tropical wet and dry climates, with notable instances of great discomfort, strong and very strong stress, and dangerous conditions, potentially leading to heat stroke. However, similar stress levels were also observed in the Arid, Semi-arid, and Humid subtropical zones, particularly in May, June, and July. • Semi-arid and Humid subtropical zones are more severely affected by heatwaves. • East coast areas of the tropical wet and dry climate zone are more susceptible to thermal stress. • Heatwaves in the tropical wet zone are minimal. • Heatwaves were experienced throughout India during April 2010 except in tropical zones.