Trees Are the Coolest Way to Reduce Urban Heat Island Effect, Surrey University Study Finds

Published on: 20 Nov, 2020
Updated on: 22 Nov, 2020

Air pollution experts from the University of Surrey have found green infrastructure (GI), such as trees, can help reduce temperatures in many cities and towns.

An urban heat island is a built-up area significantly warmer than its surrounds. Usually, the temperature difference is larger at night.

With the UK government pledging 300,000 new homes every year, many towns and cities could experience temperature rises caused by more vehicles and building activity.

In a paper published by Environmental Pollution, experts from Surrey’s Global Centre for Clean Air Research (GCARE) modelled how a UK town would be affected if its urban landscape included different types of GI.

The study focused on simulating temperature increases in Guildford under different GI cover (trees, grassland and green roofs). The team’s computer modelling systems found 78 per cent of Guildford was covered by grassland and trees.

The research team investigated five scenarios:

1. What is the status quo with the present GI?
2. What would happen if the town had no GI?
3. What would happen if the GI was only trees?
4. What would happen if the GI was only green roofs?
5. What would happen if the GI was only grassland?

The GCARE team found trees are the most effective form of GI, showing Guildford would be 0.128oC cooler if trees replaced all forms of GI.

The team also found trees are the best solution for the reduction in temperature spikes because they can better shade surfaces and influence aerodynamic mixing of air in the atmosphere caused by enhanced turbulence.

Professor Prashant Kumar Photo: University of Surrey

Professor Prashant Kumar, director of GCARE at the University, said: “As policymakers and political leaders rightly look to solve the nation’s housing crisis, it is vitally important they consider how this influx of new urban infrastructure will impact our environment and our planet.

“I hope our study will give decision-makers the information they need when they are deciding which green infrastructure to establish in our communities.

“Our results suggest that, given a choice, trees are the most effective at reducing the urban heat island effect many of our towns face.”

Cllr John Rigg

Borough Cllr John Rigg (R4GV, Holy Trinity), lead for Major Projects, said: “We thank the university for this insightful research.

“One core objective of our Guildford Economic Regeneration Programme is to address the climate emergency through environmental measures, and this new study highlights the role green infrastructure can play in the reduction of urban temperatures and is one we support.

“We look forward to incorporating the latest innovations where possible into our developing master-plan.”

Cllr Jan Harwood.

Cllr Jan Harwood (Lib Dem, Merrow), lead for Environment, said: “Since declaring a climate emergency last year, we have been looking at ways to reduce our carbon footprint across the borough.

“It’s important we work with our partners to find new ways to reduce our carbon emissions to achieve our target of net zero emissions by 2030.

“We will be establishing a borough-wide climate change partnership with representatives from all sectors to find the best way of implementing measures to help us reduce our carbon emissions and monitor all grant funding for projects in relation to the climate emergency.

“Climate change is a global issue and our climate change framework prioritises and encourages model shift to greener forms of transport, working with local landowners and other stakeholders to promote capturing and storing carbon, sustainable agriculture and promoting biodiversity, green spaces and tree-planting.

“We also encourage residents to utilise other ways to reduce their carbon footprint, both in their homes and outside.”

Sam Peters, for Extinction Rebellion, said: “We are pleased to see more excellent research coming from Surrey University which adds to the scientific consensus on climate, environment and biodiversity.

“Not only do urban trees reduce and stabilise temperatures in towns and cities, but they also filter air, help prevent flooding, provide habitats for hundreds of species, store carbon, improve mood, and more.

“Guildford is a popular place to live, and with good reason. But, as Prof Kumar notes, it is vital that as the town develops, it does so in an environmentally responsible manner with care taken over all aspects of sustainability.

“We hope this research can further strengthen the case against unnecessary or unsustainable development, such as the [withdrawn] proposal to tear down 70 trees at Sainsbury’s Burpham, and instead support the positive case for efficient, environmentally conscious green projects alongside investments in rewilding, public transport, renewable energy, and other public goods.”

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