Amid growing adversity from climate change, extreme weather events like rapid tropical cyclone formation in the Bay of Bengal and Arabian Sea, coupled with heavy rain and floods, have severely impacted Indian metros, disrupting daily life. The year 2023 stands out as one of the hottest years since the Industrial Revolution, marked by an increase in both the intensity and frequency of heatwaves. These anomalies, once seen as isolated disasters, have become recurrent and severe, highlighting the present-day reality of climate change. The India Meteorological Department (IMD) warned that the El Niño effect would trigger harsher and prolonged heat waves, exacerbating droughts and disrupting rainfall.

Understanding heat domes

Heat dome is a weather phenomenon where a high-pressure system traps a warm air mass over a region for prolonged time-period, leading to excessive high temperatures. The high-pressure area acts as a lid, obstructing the rising up and dispersion of warm air. Instead, it traps the air and as it descends, it compresses and heats up further. The formation, persistence and behaviour of heat domes are closely linked to jet streams, which are fast-flowing, narrow air-currents found in the upper levels of the atmosphere.

Typically, a jet stream follows a wavy pattern around the globe. When the jet streams form large, slow-moving loops, it can create conditions leading to the development of a high-pressure system and thus trapping the warm air within it, creating perfect conditions for formation of heat domes. “Blocking” of a jet stream in a certain pattern for an extended period can also cause the heat dome to remain stationary and thus lead to prolonged heat.

Formation of a heat dome creates a feedback loop where the high-pressure system and the jet stream sustain and reinforce each other, lengthening the heat-wave period. For instance the Pacific Northwest, during the summer of 2021, experienced an extreme heatwave, partially driven by the ‘Omega block’ pattern of jet stream which trapped the high-pressure system over the region. Stalling of the jet stream prolonged the built-up heat under the heat dome, allowing the high pressure to remain in place.

Previously in 2018, a split in the polar jet stream into two separate paths, north and south, allowed the formation of a heat dome over Northern Europe creating severe heat wave conditions. The heat dome got trapped between the two paths, which prevented any weather system from dislodging the high-pressure area. Thus, heat domes and jet streams are interconnected phenomena influencing each other in significant ways.

Impact of heatwaves 

Heat domes have severely impacted India, particularly during intense heat waves. In the 2022 North India heat wave, temperatures soared above 45°C across Delhi, Uttar Pradesh, Rajasthan, and Madhya Pradesh, with some areas nearing 50°C. A high-pressure system caused stagnant hot air and minimal cloud cover, intensifying the heat. The jet stream, positioned unusually far north, worsened this by blocking cooler air. Similar events occurred in Jaipur (2019), Kolkata (2017), Ahmedabad (2016), and Mumbai (2015).

One of the deadliest heat waves occurred in 2015, affecting Andhra Pradesh and Telangana, causing over 2,500 deaths, severe water shortages, power outages, and strained public health systems. Heat domes during pre-monsoon months pose significant health risks, agricultural damage, and infrastructure challenges.

Extreme heat leads to illnesses like heatstroke and dehydration, especially among the elderly and children. In Delhi, where temperatures exceed 45°C, respiratory and cardiovascular-related hospitalizations rise. Prolonged exposure reduces work productivity, particularly in construction and agriculture. In 2019, India lost 118 billion potential working hours due to extreme heat, according to the Lancet Countdown Report. Urban heat islands (UHI) effect in cities is fast-becoming a pan-India phenomenon, with amplified heat further increasing energy consumption and leading to blackouts in major urban cities like Delhi, Mumbai, Kolkata, Bhopal, Surat,Ahmedabad, Bengaluru, and Chennai.

The 2022 heat dome also reduced wheat and pulse yields, disrupting food supply chains. The combination of reduced labor productivity, crop damage, water shortages, power cuts, and healthcare costs leads to significant economic losses.

Needed robust urban planning

The emergence of heat domes as a new and formidable weather anomaly underscores the urgent need for adaptive and robust urban planning. These events, once rare, are now becoming more frequent and intense, threatening not just the infrastructure of cities, but also the lives and well-being of their inhabitants. This in turn poses a serious challenge to India’s public health, agriculture, economy and its development. Addressing these impacts requires integrated strategies like heat action plans, as well investment in green infrastructure and long-term climate adaptation measures.

 (Dr. Ruchi Sachan is Assistant Professor, Department of Geography, Miranda House, University of Delhi. She holds a PhD degree from Jawaharlal Nehru University on Climate Change, Migration and Conflict in Kenya. Ujjwal Gurdaswani is an Urban Policy Analyst with interest in promoting sustainable and inclusive cities. Views are personal. They can be contacted at ujjwalgurdaswani97@gmail.com.)