East–West asymmetry in intensity, duration, frequency of heatwaves over Northern India

Abstract Anthropogenic global warming has led to widespread increase in the heatwave intensity, duration, and frequency (HIDF) of events across the globe. Although the three characteristics of heatwaves are closely interconnected, they are often studied separately, especially over the Indian subcontinent. Here, we assess the HIDF over India during the period 1961–2023, and show that there exists a systematic East–West asymmetry in their characteristics over northern India. Specifically, we show that a substantial increase (decrease) in HIDF exists over major cities in the western (eastern) parts of North India. For example, Ahmedabad (a city in the western part) shows a 67.5% increase in the likelihood of four-day heatwaves in the recent decades (1991–2023) compared to the reference period 1961–1990. On the other hand, in the city of Patna (in the eastern part), we notice a 78% decrease in the likelihood of four-day heatwaves in the recent decades. Furthermore, we show that the East–West asymmetry in the HIDF is caused by a major climatic mode, i.e. the Atlantic Niño. Overall, our study provides a first insight into the contrasting characteristics of heatwaves over Northern India and their potential drivers. Such information is vital for the design of regionally appropriate adaptation strategies across India.