In the heat of the moment

In 2023, northern India suffered record-breaking heat. In 2024, it broke its own record. In 2025, the Indo-Gangetic plains and the Nepal Tarai suffered a prolonged pre-monsoon heat wave and humidity, forcing closure of schools and workplaces.

This week, southern Europe is suffering the worst heat wave since temperature records began. Football matches, tennis tournaments have been affected, and tourist sites have been closed off. Qatar has ordered a midday work curfew for Nepali and other migrant workers are the maximum temperature this week touched 45°C.

Kathmandu Valley experienced its highest temperature in 25 years in May 2024 at 35.3°C. This year, the maximum temperature exceeded 30°C on many days — heat that till a decade ago would be considered unusual. Rains in early June also meant that towns in the mountains sweltered under high heat plus humidity.

maximum average temperature in Kathmandu — Source: DHM

Measuring just temperature does not give a true picture of how hot it is. When humidity is factored in, the heat index this summer has been much higher in northern India and Nepal. Also, the hotter the air temperature the higher the concentration of water vapour in it.

“We feel it is getting hotter, and our statistics back that up,” says Shanti Kandel at the Department of Hydrology and Meteorology, which issued two heat wave warnings this year, compared to 11 last year. “We need more research to analyse how humidity is make this situation worse.”

A recent analysis by the Indian Meteorological Department has found that heat stress in that country has increased by nearly 30% over the past 40 years. Similarly, India’s Council on Energy, Environment and Water (CEEW) noted that cities like Delhi, Chandigarh, Jaipur, and Lucknow have experienced a 6-9% rise in relative humidity in the last decade.

It also states that 60% of Indian districts, home to three-quarters of the country’s 1.3 billion people face a high to very high risk from extreme heat, with rising night-time temperatures and humidity.

The heat index is also called ‘wet-bulb temperature’ and is a measure of how hot the human body feels when humidity levels are also high — usually much hotter than the recorded temperature. For example, a wet-bulb temperature of 35°C is considered the maximum limit of heat and humidity that humans can handle, beyond which the body cannot cool by perspiration, leading to death.

One indicator of increasing humidity is a rise in average minimum temperature, and Nepal recorded the highest figure since 1981 last year, with a peak of 15.8°C. Higher minimum temperature denotes warmer nights, which in turn is an indication of heat stress caused by increasing humidity, which in turn is a result of global warming.

Aside from higher average temperatures worldwide this year, what makes heat and humidity more unbearable is that cities are always hotter than their surroundings. This is due to the urban heat island (UHI) effect – for example the temperature inside Kathmandu’s Ring Road can be hotter by up to 4°C during the daytime and by 1 to 3°C in the evening compared to the outskirts.

“Climate change is one reason for rising temperature, but there are other factors like increased heat in urban spaces due to concrete buildings and infrastructure, emissions from vehicles, industries, and home appliances,” explains urban planner Bhushan Tuladhar.

He adds: “Much of this comes down to how we have developed our cities, not just our roads and buildings but also our water system, waste management, culture and customs as well as economy.”

There is a feedback loop at work: as it gets hotter, more energy is used for fans, coolers, and air-conditioners which in turn add to the urban heat bubble. The way to reduce the UHI effect is to have more parks, tree-lined streets and water bodies to cool cities down.

A recent study published in the journal Urban Climate by Nepali researchers at the University of Massachusetts, Tribhuvan University, University of Groningen, etc showed that even within Kathmandu, urban forests cooled neighbourhoods by as much as 1.2°C while ponds reduced the temperature by up to 0.85°C compared to nearby houses.

urban heat island in Kathmandu — Source: URBAN CLIMATE et al.

‘Our results demonstrate that blue-green spaces provide significant cooling benefits across the Kathmandu Valley, with distinct patterns by type, size, design, and urban context,’ concluded the paper, whose lead author is Saurav Bhattarai at Jackson State University in the United States.

The old towns in Kathmandu Valley with traditional brick and tile architecture, ponds and trees managed hot summers better. Compact houses around a courtyard gave people just the right amount of sunlight, and use of clay mortar and bricks insulated houses in winter while cooling them in summer. There were open spaces, fertile land along the floodplains for farming, and brick pavements that allowed for seepage.

“Our cities were planned taking nature into account,” says Sangeeta Singh, a professor of urban planning at the Institute of Engineering. “Kathmandu Valley is now built up, but we can still reintegrate blue-blue spaces into town planning with vertical gardening, urban forestry, using local material and harvesting rainwater.”

Kathmandu’s municipalities have by-laws controlling building design and structure, but strict enforcement of land use and zoning are missing. Extreme heat disproportionately affects the urban poor who may not have access to fans or air-conditioners, exacerbating poverty.

Cities in the plains have it even worse. As heat and humidity rise simultaneously, it could reverse the current mass migration of people from the mountains to the Tarai, where 53% of Nepal’s population lives.

A World Bank study put the cost of a 1°C rise in temperature at 17.1% increase in poverty globally. Estimates put the total number of urban poor in developing countries exposed to the worst heat extremes at 26 million presently, this number is bound to grow to 215 million by mid-century, an over eight-fold increase. Meanwhile, 489,000 health-related deaths occur each year, 45% of them in Asia alone.

“Heat has to be seen from a class perspective,” says Singh. “Those with money can afford gadgets and appliances to keep their homes and offices cool, but not day labourers or poor families living in cramped housing with poor ventilation.”

Climate breakdown is going to widen the class divide in cities, as summers become unliveable. Says Singh: “We need policy intervention to address this class injustice. Our building by-laws and new town development must urgently integrate climate and energy efficiency elements.”