Every year, we Nepalis find ourselves battling two identifiable yet often overlooked enemies—extreme heat and toxic air. But what happens when both strike at once?
A new study by Sweden’s Karolinska Institute of Environmental Medicine has revealed that the combination of intense heat and air pollution could dramatically increase the risk of death. In simple terms, when both air pollution and extreme heat levels are high, the risk of mortality also surges significantly.
The study found that even when only one of these factors is present, the risk of death rises compared to regular days. The findings were published in the journal Environment International.
While previous research has separately highlighted the health impacts of air pollution and heat, there is still limited knowledge about how deadly their combination can be. In Nepal, such a study has yet to be conducted.
This lack of research is also evident in countries like India and Pakistan, where both heat and pollution frequently reach dangerous levels.
To understand this better, researchers affiliated with the Karolinska Institute collected and analyzed daily mortality data from 10 major cities in India between 2008 and 2019.
Analyzing around 3.6 million deaths, they found that during extremely hot conditions, the link between fine particulate matter (PM2.5) and mortality became significantly stronger.
The researchers used advanced scientific methods to study the relationship between air pollution, heat, and deaths over time. Specifically, they examined how the combined impact of pollution and extreme heat increased the risk of death and how one factor intensified the effects of the other.
Key Findings of the Study:
On extremely hot days, a 10-microgram per cubic meter increase in PM2.5 was associated with a 4.6% rise in daily mortality. This is significantly higher compared to the 0.8% rise observed on regular hot days.
Similarly, when the temperature moved from ‘hot’ to ‘extremely hot’, and PM2.5 levels rose to 20 micrograms per cubic meter, the risk of death increased by 8.3%. If the pollution level reached 100 micrograms per cubic meter, the risk of death shot up by as much as 64%.
Professor Jeroen de Bont, one of the researchers involved in the study, noted, “These findings highlight the compounded impact of air pollution and extreme heat, which is particularly dangerous in densely populated cities where both issues are often present simultaneously.”
According to him, immediate action is necessary to curb emissions that drive both air pollution and climate change in order to protect public health.
The study emphasized the need for a unified action plan to tackle both air pollution and climate change, especially as global temperatures continue to rise, which could make the situation worse in the future.
Air Pollution in Nepal
Due to air pollution, Nepal’s capital Kathmandu has been listed among the most polluted cities in the world.
According to the air quality index (AQI) approved by the Government of Nepal:
- AQI of 0–50 is considered good,
- 51–100 is moderate,
- 101–150 is unhealthy for sensitive groups,
- 151–200 is unhealthy,
- 201–300 is very unhealthy,
- and above 301 is deemed hazardous.
AQI primarily measures levels of PM2.5 and PM10—fine particles in the air.
According to IQAir, a Swiss-based real-time air quality monitoring platform, at 10:32 PM on Monday, Kathmandu’s AQI was recorded at 262. On Tuesday at 7 AM, the AQI was 245.
Earlier, on Chaitra 21 (early April), Kathmandu’s AQI had reached 373. At that time, Acting Prime Minister Prakash Man Singh had called a meeting with stakeholders and decided to implement an odd-even vehicle rule, among other measures. However, those decisions have yet to be implemented.
In 2021 (Chaitra 2077), schools were closed for four days due to extreme pollution. The AQI then had reached 470 in Kathmandu. Helicopter flights were grounded due to poor visibility, and many people reported symptoms like eye irritation, throat discomfort, and respiratory issues.
Even now, the number of patients with respiratory problems has increased, according to Dr. Niraj Bam, a pulmonary specialist at Tribhuvan University Teaching Hospital.
The main causes of air pollution include wildfire outbreaks during the dry season, high traffic of fuel-powered vehicles, unregulated construction, and emissions from industries and factories. The situation worsens when rising temperatures add to the burden, exposing Nepalis to dual risks.
Critical care and respiratory disease specialist Dr. Raju Pangeni describes air pollution as a “silent killer.” He explains, “Air pollution contains various harmful chemicals. The dust particles we see with our naked eyes are relatively large—over 50 microns in size. But pollutants in the air are smaller than 10 microns, small enough to reach the inner layers of the lungs. Extremely tiny particles can even enter the bloodstream and affect all organs—potentially causing heart disease, kidney problems, strokes, and cancer.”
Public health expert Kamal Ranabhat also warns that Kathmandu’s air is currently in a very unhealthy state and advises the public to take protective measures. He says, “Unhealthy air can affect the eyes, lungs, and skin. People with respiratory illnesses and children are at greater risk. So, it’s best to stay indoors as much as possible. If going outside is necessary, wear a mask, use protective glasses, and wear full-body covering clothing.”
According to the World Health Organization (WHO), around 7 million people die prematurely each year worldwide due to diseases related to air pollution.
Rising Temperatures and Increasing Impacts in Nepal
According to a report by Nepal’s Department of Hydrology and Meteorology, based on 30 years of data from weather stations across the country, the temperature in Nepal is rising at an average rate of 0.056 degrees Celsius per year.
The year 2024 has already surpassed 2023 as the hottest year on record.
This year too, rising temperatures are expected. Winter and monsoon nights were reported to be warmer than in previous years.
On Asar 1 (mid-June), Kathmandu Valley experienced the highest heat in 35 years, recording a maximum temperature of 35.3°C. This was the highest maximum temperature since 2046 BS (1989), when the temperature reached 36.6°C.
Across many weather stations, both maximum and minimum temperatures during the monsoon were above average.
For example, from 1991 to 2020, Kathmandu’s average July maximum temperature was 28.7°C, and the average minimum was 20.3°C. However, on July 31 this year, Kathmandu recorded a maximum of 33°C and a minimum of 23°C.
In Bhairahawa, Rupandehi, the average July maximum temperature is 33.5°C, but on July 29 it reached nearly 40°C, with a minimum of 30°C.
In Janakpur, the average July maximum temperature is 32.9°C and minimum 26.5°C, but on July 31, it hit 38°C and almost 30°C minimum. Similarly, in other places like Dhangadhi, Nepalgunj, Ghorahi, Biratnagar, and Dharan, monsoon days and nights were hotter than usual.
Nepal’s highest recorded temperature to date was 46.4°C in Dhangadhi on June 16, 1995.
After that, some cities have also seen extreme heat:
- Nepalgunj, Banke: 45.2°C on May 30, 2024
- Dhangadhi, Kailali: 44.1°C on May 30, 2024
- Nepalgunj, Banke: 44.2°C on May 30, 2024
- Bhairahawa, Rupandehi: 43.6°C in April 2024
- Sarlahi: 43°C in 2024
- Dharan, Sunsari: 40°C on April 28, 2024
- Kathmandu: 35.3°C on June 15, 2024
These records confirm that temperatures in several Nepali cities have been rising significantly in recent years, with occurrences of heatwaves becoming more frequent.
All of these statistics show that temperature is rapidly increasing in Nepal, and when combined with pollution, it creates a double blow to public health. In such circumstances, it is essential for the government to develop a solid and coordinated strategy to effectively tackle the dual threats of heat and pollution.
