Delhi’s vanishing urban trees: The overlooked solution to the city’s pollution crisis

As Delhi residents grapple with hazardous air pollution levels, the government has introduced short-term measures like anti-smog guns and mechanical street cleaning to alleviate the crisis. However, long-term issues remain unaddressed, with the continued removal of trees, a key factor in controlling air pollution.

On November 3, a dense layer of smog blanketed Delhi, as the Air Quality Index (AQI) surged past 500 in the aftermath of Diwali. Areas like Shahdara and Anand Vihar recorded AQIs above 500 by 11:30 AM. The city’s air pollution levels remain in the “hazardous” category (AQI above 400), with PM2.5 concentrations over 59 times the WHO’s recommended limit, posing severe health risks.

In response to this ongoing environmental crisis, data from Delhi’s Forest Department reveals that nearly five trees have been cut every hour between 2019 and 2021. This data, submitted to the Delhi High Court, highlights the city’s diminishing green cover. The High Court has since mandated the Forest Department to release quarterly reports on tree felling, though compliance has been inconsistent. “The instruction given by the Delhi High Court is not being followed even after a year,” said Aditya Prasad, an environmentalist and lawyer. “The Forest Department shows disregard for the court’s order.”

Role of urban trees

The harmful effects of air pollution, especially particulate matter (PM2.5), present serious health threats to Delhi’s residents. PM2.5 particles, which are less than 2.5 microns in diameter, can penetrate deep into the lungs and bloodstream, leading to respiratory diseases, asthma, and cardiovascular problems. These particles are small enough to bypass the body’s natural defences and are about 30 times smaller than a human hair.

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Urban trees offer a natural solution to countering pollution. According to a study by the Brown University Center for Environmental Studies, titled “Trees and the Urban Heat Island Effect,” trees trap particulate matter on their leaves and absorb pollutants like ozone, nitrogen dioxide, and sulfur dioxide, which are associated with respiratory issues such as asthma. Trees also play a significant role in reducing the Urban Heat Island (UHI) effect, where cities become hotter due to the heat retention of materials like concrete. Trees cool the surrounding air through shade and transpiration, with studies indicating that tree-shaded areas can reduce surface temperatures by up to 45ºF.

A study titled “Modeled PM2.5 Removal by Trees in Ten US Cities and Associated Health Effects” found that trees in New York removed up to 64.5 tonnes of PM2.5 annually, contributing to a reduction in mortality rates associated with pollution. However, Delhi’s urban development is rapidly encroaching on green spaces, increasing UHI effects and undermining these natural defenses. Research by NASA’s ASTER satellite revealed that between 2001 and 2005, surface temperatures in Delhi’s urban areas rose by 5 to 7.22°C due to an increase in concrete structures and a decrease in greenery.

Impact on public health

The long-term health effects of Delhi’s rising temperatures and persistent air pollution are particularly concerning for young residents. A study by the Pulmocare Research and Education Foundation, Lung Care Foundation, and CSIR Institute of Genomics and Integrative Biology, titled “Association between Air Pollution, Body Mass Index, Respiratory Symptoms, and Asthma among Adolescent School Children Living in Delhi, India,” found that one in three children in Delhi suffers from asthma, linked to the city’s poor air quality.

Expert’s take

Environmentalist Bhavreen Kandhari highlights the importance of protecting urban trees, noting that their role in maintaining clean air is critical. “Amidst all the debates about air pollution, there’s an often overlooked contributor to clean air: our trees. Every hour, five fully-grown trees are cut down for urban redevelopment, road widening, and infrastructure expansion in one of the world’s most polluted capitals. Trees aren’t just greenery; they are natural oxygen towers, irreplaceable in their role. Mature trees take decades to develop the vast canopies and complex root systems that allow them to clean the air, cool surroundings, and support biodiversity. No sapling can compensate for the destruction of a fully-grown tree,” said Kandhari.

She further emphasised that while discussions often centre on vehicular emissions, construction dust, and stubble burning, the gradual depletion of urban forests is frequently sidelined. “The loss of trees cuts to the heart of the clean air conversation. By overlooking this, we ignore one of nature’s most effective solutions for air quality. Protecting our mature trees must be prioritised; they’re not merely part of the landscape but vital, living infrastructure essential to a healthier, breathable city.