Urban tree benefits UK

A July 2010 Woodland Trust report demonstrates the essential part trees play in making towns and cities healthier, cleaner and more prosperous, and underlines the need to green the UK's urban landscapes.

"Towns and cities also tend to put into sharp relief some of the key problems we are facing as a society - physical and mental health problems, childhood obesity and asthma, differences between rich and poor, air pollution, soaring summer temperatures, flash flooding, energy conservation, diminishing wildlife - so they are a good place to start when trying to illustrate just where green space can deliver significant improvements for relatively little cost." Mike Townsend, The Woodland Trust

The report calls on extensive research and urban case studies from across Europe and the USA. Chief amongst its findings are:

Air quality and health


 * Higher temperatures combined with pollution leads to increased ground level ozone – exacerbating respiratory illnesses, including childhood asthma. Urban trees help to keep the air clean and breathable and to reduce ambient temperature, thus improving air quality.
 * Each year, 24,000 people in the UK die prematurely from air pollution. The UK also has one of the world’s highest rates of childhood asthma, around 15 per cent, particularly amongst lower socio-economic groups in urban areas. Research shows asthma rates among children aged four to five falls by a quarter for every additional 343 trees per square km.
 * The Campaign for Greener healthcare and the initiative to establish a National Health Service Forest also illustrate a growing consensus amongst health professionals of the importance of trees to peoples’ general health and wellbeing. Evidence suggests proximity to a wood encourages physical exercise, whilst a woodland walk lowers the heart rate and mental stress.
 * Fewer than 10% of city dwellers have access to local woodland within 500m of their homes.
 * Around £110 billion is spent each year in the UK on healthcare, 8.5 per cent of all income. If every household in England had good access to quality green space it could save around £2.1 billion annually in health care costs.

Urban heat island effect


 * The buildings, concrete and other hard surfaces such as roads act as giant storage heaters, absorbing heat during the day and releasing it at night.
 * Trees provide both direct shade from radiant heat for buildings and people and reduce the ambient temperature through evaporative cooling. A mature tree transpires up to 450 litres of moisture a day – equivalent to five room-sized air conditioners left on for 19 hours.
 * Research at the University of Manchester using computer modelling has shown how increasing urban green space by just 10% could mitigate for a 30C rise in urban temperatures.
 * On some days there is a difference of as much as 10oC between central London and its surrounding suburbs. Climate change projections show that by 2080 London will be between 2oC and 6oC hotter than today.
 * In the 2003 summer heat wave over 2,000 people died in Britain alone and more than 35,000 died across Europe as a result of cardiovascular or respiratory failure or dehydration.

Surface water flooding


 * A major factor (identified in the 2007 floods) is the increase in hard surfaces, unable to absorb rainfall, which often means drains are overwhelmed and water quickly collects on the surface rushing down streets and over paving.
 * Tree canopies (especially older trees with larger spreading crowns) intercept rain and regulate the speed at which rainfall reaches the ground, improving the capacity for slow absorption through the ground and the ability of engineered drains to take away excess water.
 * The University of Manchester has shown that increasing tree cover in urban areas by 10 per cent reduces surface water run-off by almost 6 per cent.
 * Flooding currently threatens up to 3.8 million homes in the UK. The costs around £2.5 billion annually and could rise to £4 billion by 2035.

References