City scientists have just completed a study of twenty areas in Bangalore that prove beyond doubt the filtering and cooling effect that trees have on urban and other areas. Bangalore has lost a lot of its trees in many areas due to widening of roads and construction of huge buildings. Experts said the result of this has been increased temperatures and air pollution.

Harini Nagendra, a scientist at the Ashoka Trust for Research in Ecology and the Environment (ATREE), Bangalore, is one of the authors of a study available online on urban forestry and urban greening.

The study found that streets with trees had a lower temperature, humidity and pollution.

Afternoon ambient air temperatures were found to be lower by as much as 5.6 degree Celsius, road surface temperatures by 27.5 degree Celsius and sulfur dioxide levels reduced by 65 per cent. Suspended Particulate Matter (SPM) levels were very high on exposed roads, with 50 per cent of them showing levels almost twice the permissible limit while 80 per cent of streets with trees had SPM levels within the prescribed limit.

Two locations (with and without trees) were studied each on Bellary Road, Banashankari Road, Magadi Road, Siddapura Road, Bannerghatta Road, Jeevan Bhima Nagar Road, Hennur Road, Sarjapur Road, Assaye Road and Kundanahalli ITPL Road. Prof N H Ravindranath at the Centre for Sustainable Technologies and Centre for Ecological Sciences, Indian Institute of Science, Bangalore, says: “To my knowledge, there is no collaborating programme between the BBMP or any other city-based body and IISc that involves urban greening. In fact, researchers working on climate change suggest urban trees as the solution to global warming as they reduce the need for air conditioning. Having trees around houses and painting roofs white will certainly cool the city and reduce energy requirements and carbon dioxide emissions.”

Nagendra suggests planting long-lived trees with wide canopies.

“The few trees being planted on roads are largely narrow canopied trees which neither provide shade nor reduce pollution. We need more trees near busy signals where people are most exposed to air pollution. Bike and pedestrian lanes need to be identified in the city and screened from traffic by planting trees so that more people can cycle/walk safely and comfortably,” the scientist said.