How an El Niño winter could worsen pollution in Delhi

Delhi’s pollution is expected to worsen because several sources will continue releasing pollutants as winter begins. These include vehicle emissions, construction activity, and stubble burning. Winter weather already allows pollutants to accumulate more easily than in summer or the monsoon season.

The main mechanism is weaker air movement. Lower winter wind speeds reduce the dispersal of pollutants. A strong El Niño could weaken local winds further by slowing large-scale global wind circulation. It could also reduce western disturbances, which bring rain and snow to the Himalayas and rain to north-western India. That rain helps flush pollutants out of the air.

Delhi-NCR’s AQI reached 244 on October 21, the worst level in 100 days. The article describes this as the start of the air pollution season. As El Niño is expected to peak between November and January, pollutants may remain suspended longer and air quality may become worse during those months.

El Niño is a climate pattern that repeats every few years. It is influenced by warming sea surface temperatures in the tropical Pacific Ocean. The warming can increase heat and reduce rainfall in different parts of the world. This makes El Niño important far beyond the Pacific itself.

Its reach comes through changes in large-scale wind circulation. During El Niño, Pacific winds that usually move from South America toward Asia weaken, slow, or sometimes reverse. This shifts rainfall patterns, bringing very wet conditions to South America’s west coast while leaving Asia unusually dry. These global changes influence regional weather.

The changed background winds can also affect local conditions near the ground. In India, slower global circulation may make already weak winter winds even weaker. Those weaker winds disperse pollutants less effectively. The article links an active El Niño this year with India’s 13% monsoon deficit and warns of possible effects on winter air quality.

The expected El Niño is unusually strong. The World Meteorological Organisation has predicted that tropical Pacific sea surface temperatures could rise 3.8 degree Celsius above average. That level is described in the article as making this year a “Super El Niño” year.

Timing matters because the predicted peak overlaps with the most pollution-prone part of Delhi’s year. The event is expected to peak between November and January. These are winter months, when wind speeds are normally lower and pollutants already disperse less effectively. A strong El Niño could intensify those conditions.

The likely implication is not that El Niño directly produces pollution. Instead, its associated weather changes may help pollutants stay in the air longer. Slower large-scale winds could weaken local winter winds, while fewer western disturbances could reduce rainfall that normally flushes pollutants from north-western India. The article therefore expects air quality pressures to grow as winter progresses.

Pollutants accumulate when the atmosphere cannot move or remove them efficiently. In winter, wind speeds are already lower, so pollutants disperse less than they do during hotter months or the monsoon. Hotter air and faster winds normally help pollutants rise and spread away from a region.

El Niño may worsen both parts of the problem. It can slow large-scale wind circulation, making Delhi’s already weaker winter winds even weaker. It may also reduce western disturbances. These weather systems bring rain and snow to the Himalayas, which can lead to rain in north-western India. Rain helps flush pollutants out of the air.

With less wind, pollution is carried away less effectively. With less rain, fewer pollutants are washed out. Vehicle emissions, construction, and stubble burning can therefore remain concentrated near Delhi for longer. The article says this trapping may become much stronger than normal as El Niño peaks and winter pollution intensifies.

Western disturbances are a weather phenomenon that causes rain and snow in the Himalayas. Their effects can extend into north-western India, where they bring rainfall. This rainfall matters for air quality because it helps remove pollutants from the atmosphere.

A strong El Niño could reduce the occurrence of these disturbances, according to Gufran Beig. Fewer disturbances would mean fewer rain events in north-western India. Without as much rain, pollutants released by vehicles, construction, and stubble burning would have fewer opportunities to be washed out.

The result could be longer-lasting pollution during winter. Lower winter wind speeds already reduce the dispersal of pollutants. If rainfall also becomes less frequent, both major natural clearing processes become weaker. The article says these conditions could allow pollutants to remain suspended for much longer than they normally do during the season, adding pressure to Delhi’s worsening winter air quality.

Evidence from recent air-quality records suggests that pollution was worse during the 2023–24 El Niño year than during the preceding La Niña years. The Council on Energy, Environment and Water compared data from 2020 to 2024. The comparison covered November through January, when winter pollution is most relevant.

In December 2023, the El Niño year recorded 27 “very poor” and “severe” AQI days. The previous three years, influenced by La Niña, recorded 25, 21, and 20 such days. The difference was larger in January. The El Niño year had 30 such days, while the other years had 20 or fewer.

CEEW’s Prarthana Borah cautioned that the study covered only four years. Still, she said the number of polluted days increased during the El Niño year. The finding shows a correlation, not a complete explanation, and points to the need for deeper study of how El Niño and air quality are connected.

Air pollution depends partly on how well the atmosphere mixes and moves air. In summer and the monsoon season, hotter air helps pollutants rise, while faster winds disperse them. Winter is different: cooler-season wind speeds are lower, so pollutants accumulate more easily near the ground.

Local and global winds both matter. Local weather operates over smaller regions and closer to the ground. Coastal winds, for example, can be driven by differences between ocean and land temperatures. Global background winds influence overall wind behaviour. When large-scale circulation slows, local winter winds can become even weaker, reducing the atmosphere’s ability to spread pollutants.

The balance determines whether pollution disperses or remains concentrated. Stronger winds and greater vertical movement carry pollutants away. Weaker circulation leaves them suspended for longer. El Niño can alter the global background winds, while temperature changes and reduced rain can further affect local conditions. Together, these processes help explain seasonal pollution differences.