Trees and Temperature
According to a recent report by the Gauteng Department of Agriculture and Rural Development, Gauteng’s temperatures are increasing at double the rate of global temperatures. This is due to two factors, global temperature trends and the heat island effect experienced in an incredibly urbanised province.
How trees help
The Heat Island Effect
That cities have warmer surface temperatures than surrounding rural areas is attributed to the “Heat Island Effect”. Through urbanisation the landscape is transformed from grassland to urban structures. Urban surfaces such as bricks, tar and concrete tend to absorb more heat. This results in higher surface and air temperatures in urban areas.
There are many solutions to help us reduce the effects of urbanisation and climate change. Surfaces such as roofs, walls and paving can be changed into greener surfaces, which absorb less heat. The simplest solution however, is planting trees.
Trees disrupt the warming effects in a number of different ways;
Trees block the sun from warming up city surfaces. Some studies show that trees can reduce surface temperatures by between 11˚C and 25˚C and air temperatures by about 5.5˚C.
As the sun hits the trees, the trees transpire, emitting water droplets that reduce the air temperature
Trees also provide many other benefits to the urban environment, as detailed in the next page.
As such, planting trees in tree-less urban environments is an increasingly important endeavour, not only for the offset of carbon emissions, but also to help the populace adapt and cope with increasing temperatures in the next century.
The combination of indigenous and fruit tree planting through the Trees for All and Trees for Homes programmes, solves this issue, as well as the issue of food security facing the country.
For more information about Trees and the Heat Island Effect you can look at the following:
1. United States Environmental Protection Agency’s Heat Islands Resource https://www.epa.gov/heat-islands and chapter on planting vegetation as a strategy
2. Livesley, S., McPherson E.G., Calfapietra, C. 2016. The Urban Forest and Ecosystem Services: Impacts on Urban Water, Heat, and Pollution Cycles at the Tree, Street, and City Scale. Journal of Environmental Quality. 45:119–124
3. McPherson, E.G., J. R. Simpson, P. J. Peper, S. E. Maco, and Q. Xiao. 2005. Municipal forest benefits and costs in five US cities (PDF) (6 pp, 267K). Journal of Forestry 103(8):411–416.
4. ‘The essential role of trees – adapting to climate change be managing high temperatures and reducing pressure on drainage systems’, Gill S in proceedings Trees and Urban Climate Adaption: a sociable agenda for living cities, 19 November 2009.