Urban development is something that we and our audience are passionate about, and the process in which our cities grow is certainly paramount to our future prosperity as a community and society. However there is a phenomenon discovered by Luke Howard in the early 19th century that gets a bit lost amongst the construction and development. This phenomenon is known as the urban heat island effect (UHI) and it occurs when urban development replaces natural permeable surfaces such as grass land or bush land with dry and impermeable surfaces such as concrete and asphalt.
UHI is defined by a metropolitan area having an increased temperature of 1-3 degrees Celsius higher compared to that of surrounding rural or vegetated areas. Further to temperature changes, UHI can also affect localised meteorology by altering wind patterns, creating fogs and clouds and changing the rates of precipitation. The main cause of UHI is that buildings block surface heat from radiating into the relatively cold night air as the changes in thermal properties of the surface materials and the lack of evapotranspiration (i.e. natural cooling effect in vegetated areas) significantly alter the heat capacity and the thermal conductivity compared to rural areas.
So why should we care about UHI? What sort of implications could there be for the inhabitants of metropolitan Melbourne? The elevated temperatures from UHIs during the summer months can affect the community's environment and quality of life. Some effects can be positive via the lengthening of plant growth seasons, the majority are negative and can include:
An example of UHI effects can be seen below in the image showing the emissivity (i.e. heat distribution) at your average shopping centre complex which clearly shows the asphalt and paved areas absorbing and radiating much more heat (indicated by the red and orange colours) than the roofs of the shopping centre complex. Although this does not appear correct, the "cool" roofs (indicated by the blue colour) are regarded as an abnormality in the data collection approach because corrugated iron has low emissivity and therefore appear to be cold.
Furthermore an additional image of a metropolitan area, which is typical of much of metropolitan Melbourne's sprawl belt comprising of detached houses, show roofs and pavement radiating plenty of heat whilst the vegetated areas, namely the gardens and the lawns, not emitting heat into the surrounding environment.
Even though some may see these effects as somewhat vague and not clear, the impacts that they have collectively in a large metropolitan setting such as Melbourne may have the potential to cause long lasting effects if they aren't addressed appropriately. As a result of many studies, appropriate mitigation strategies are available, and local councils have been working hard to gain an understanding of the effects of UHI in their particular municipalities. These mitigation strategies and the desired effects include:
Increasingly, urban development both in vertical sense and horizontal sense is happening in Melbourne. Even though we face many different challenges including the effects of UHI as Melbourne develops, it is encouraging to know that there are practical and somewhat simple ways that could be incorporated either pre- or post-development and as a result we can help mitigate these effects as we move forward into a more sustainable future.