We’re all familiar with the general predictions about population growth, increasing urbanisation and global warming. “Between 2012 and 2050, the world population is expected to increase by 2.3 billion, passing from 7.0 billion to 9.3 billion. By 2050 over 67% of the world’s population are predicted to live in urban areas, or 86% in developed regions.” United Nations Department of Economic and Social Affairs/Population Division 2011
“Australian average temperatures are projected to rise by 1.0 to 5.0 °C by 2070 when compared with the climate of recent decades.” CSIRO and Bureau of Meteorology State of the Climate 2012 report.
Percentages of our cities devoted to roads
“In a motorized city, on average 30% of the surface is devoted to roads while another 20% is required for off-street parking. In North American cities, roads and parking lots account (for) between 30 and 60% of the total surface.” The Geography of Transport Systems by Dr Jean-Paul Rodrigue
Heat island effect
“Air temperatures in densely built urban areas are higher than the temperatures of the surrounding rural country. The intensity of the heat island is mainly determined by the thermal balance of the urban region and can result in a temperature difference of up to 10 degrees.” Heat-Island Effect by M Santamouris, Department of Applied Physics, University of Athens
Currently available thermal imagery clearly illustrates the dominant impact that streets have on the urban heat island effect. www.cityofsydney.nsw.gov.au/vision/sustainability/sustainable-city-living/urban-heat-island
Benefits of urban trees
“Individual urban trees, on average, contain approximately four times more carbon than individual trees in forest stands.” “Planting trees in strategic locations near buildings can reduce building energy usage via enhanced shading and evaporative cooling in summer, and by wind speed reduction in winter, which phenomena lower the demand for electricity needed for cooling and heating and, in most cases, offset the burning of a certain amount of coal, gas or oil.” Nowak, D.J. and Crane, D.E. 2002. Carbon storage and sequestration by urban trees in the USA. Environmental Pollution 116: 381-389.
Nowak and Crane note that the atmospheric CO2 ‘avoidance’ provided by such strategically planted trees is approximately four times greater than the amount of CO2 they physically remove from the air.” Trees in the City:
A New Role for the “Ultimate Urban Multitaskers” by Dr Sherwood B Idso and Dr Craig D Idso
More attractive tree lined streets offer many of the same benefits provided by parks as well as a raft of other supplementary benefits. The presence of trees close to roads: helps reduce traffic speeds, largely due to the perceived risks and helps protect pedestrians from cars; when placed between the road and the footpath increases the shade for pedestrians and hence makes walking a far more attractive transport proposition with all of the positive health implications associated with this.
The presence of trees in medians helps reduce the likelihood of head on collisions which are far more dangerous than say hitting a tree.
Many of the great streets of the world provide excellent examples of the additional benefits provided by implementing such a strategy. The Champs-Élysées in Paris is a massive street by any standards. However the reason it is one of the great streets of the world is that: the tree planting is in scale with the width of the street; and despite it being a major traffic conduit it still generously provides for pedestrians.
In the context of all of the above it seems obvious that our streets represent an excellent, largely untapped, opportunity to extend the health benefits offered by parks and significantly improve our environmental conditions and public amenity. As a corollary to the above it is proposed that Energy saving guidelines, similar to those that apply to all new buildings in Australia, such as NatHERS, NABERS, BASIX, should be developed for our streets with the aim to significantly reduce temperatures in urban areas.