‘Canyon Effect’ in Australian cities

by Dr. Tony Matthews and Dirk van der Kamp

Published in

The Machinery of Government

8 min readSep 6, 2017

A phenomenon known as ‘canyon effect’ is becoming increasingly common in Australian cities. It occurs when tall buildings flank both sides of city streets, artificially creating a canyon-like effect. It is associated with negative consequences including temperature change, light levels, wind patterns, air quality and even diminished mental health outcomes. Once it has been established, canyon effect is locked into the urban fabric with implications that can last for decades.

The increasing proliferation of canyon effect poses a rising concern for many cities. It became more pronounced in recent years as a direct result of an intense period of urban development. It is most visible in centres and inner suburbs of our largest cities. It is now a common urban feature in areas like West End, Fortitude Valley and Newstead in Brisbane. In Melbourne, it is common in Southbank, Fitzroy, Brunswick and Richmond. Examples in Sydney occur commonly in Chatswood and the Central Business District with more areas likely to follow under the current Central Sydney Planning Strategy.

In this article we investigate the phenomenon of canyon effect and its proliferation in Australian cities. We outline and discuss its negative consequences and reflect on lessons learned from recent policy failures. We conclude that while little can be done to remediate existing canyon effect, there are opportunities for urban policy improvements to reduce its future incidence.

The creep of canyon effect

Australian cities, like their counterparts all over the world, are growing at unprecedented rates. Over 50% of the global population currently reside in cities, a figure expected to increase to 70% by 2050. The rate is even more pronounced in Australia, with close to 90% of Australians already living in urban areas. We may historically be referred to as the ‘Lucky Country’ but perhaps it is now more accurate to refer to us as the ‘Urban Country’.

Rapid urbanisation is profoundly changing the form and density of Australian cities. Demand for high-profile urban development, tall buildings and infrastructure was constant over the last few years. Of course cities always face development pressures but the pace and intensity accelerated during the recent Australian urban development boom. Apartment towers and premium grade office buildings sprung up to meet demand from aspiring city dwellers and companies seeking high-spec office spaces.

A heady mix of cheap credit, sympathetic tax policies, surging urban populations and escalating local government development contributions drove this boom. It left urban planners and other policy-makers scrambling to keep up. High-rise buildings proliferated within this context and reshaped the skylines of Australia’s largest cities. Unfortunately many new high-rise buildings were allowed to cluster too closely together. A proliferation of canyon effect is an unwelcome legacy of this period in Australian urban history.

The consequences of canyon effect

Urban populations are growing in Australia meaning more people are becoming exposed to risk factors originating from the built form of our cities. The linear continuation of dense block structures along city streets, leading to canyon effect, is a growing urban problem. This problem is well established in many cities globally but is a more recent agenda here. The negative consequences of canyon effect now present elevated risk factors in Australian cities, particularly in the larger cities.

Canyon effect can significantly influence street-level temperatures and urban microclimates. Temperatures within an urban canyon are usually above ambient urban air temperatures. They tend to be highest during the day as the clustering of tall buildings traps heat, reducing the potential for it to dissipate. Inflated temperatures can also extend into the evening as heat retained by street canyons is released. Relative increases in temperatures are linked to the width of a street and the height and morphology of buildings along it. In general terms, urban canyons characterised by narrow streets with taller buildings tend to be hotter than those where streets are wider and building heights are lower.

The intensity and speed of wind within a canyon may be artificially increased or reduced based on the surrounding urban form and street orientation. Wind in urban canyons is important for reducing heat and pollutants but excessive wind intensity can reduce pedestrian comfort. The influence of canyon effect on wind can vary. Channelization effect occurs when wind moves parallel to a canyon’s orientation. This is good for reducing pollution but is associated with pedestrian discomfort. Venturi effect intensifies wind speed as wind is funnelled through small openings. It can cause severe gusting at street level and may make walking difficult for some people, especially those with mobility challenges. Changes to wind flow caused by canyon effect may also affect activity and comfort above street level, particularly for apartment dwellers with verandas overlooking the street canyon.

Air quality, noise and light levels may also be negatively impacted by canyon effect. Narrow streets flanked by buildings taller than five storeys may suffer reduced light penetration and increased noise volume at street level. This arrangement may also reduce the capacity for pollutants released by traffic and building ventilation to dissipate. Tree planting may help to dampen noise impacts and remove some pollutants from the atmosphere but can further reduce light levels.

Combinations of the negative consequences associated with canyon effect may also adversely impact the mental health of urban dwellers. Links between the form and characteristics of urban environments and reduced mental health outcomes are now starting to be explored. Cities are increasingly being understood as potentially “depressogenic”. Current research suggests that combinations of heat, noise and light levels may be associated with higher rates of depression and anxiety. Each of these factors is associated with canyon effect and may individually exacerbate negative mental health outcomes. As such, there may be a link between canyon effect and the reality of depressogenic environments. Undoubtedly this connection will be closely scrutinised in future urban research.

Improving urban policy to manage canyon effect

Canyon effect is difficult to remove from the urban fabric once it has become embedded due to the longevity of built environments. As such, there is little that can now be done to remediate canyon effect where it already exists in Australian cities. Instead, attention needs to focus on how future urban policy improvements might prevent its occurrence or at least minimise its negative consequences where possible.

Urban consolidation has traditionally served as the main macro-scale policy response to urban development pressures in most Australian cities. A counter measure to urban sprawl, urban consolidation aims to concentrate growth in existing urban areas through high-density developments. High-rise developments are broadly supported within this policy context. But in recent years there has been some disconnect between the macro-scale focus of urban consolidation polices and micro-scale development realities. This disconnect is seen where planners allowed too many high-rise buildings to cluster together, leading to canyon effect.

Clearly policy improvements are needed to ensure that urban consolidation priorities do not perpetuate canyon effect. A first strategy is to ensure urban policy-makers and planners actually understand the phenomenon of canyon effect. Good policy can only follow where there is clear awareness of an issue and its dimensions. If nuanced policy responses are required, they might need to be pre-empted by professional education. Organisations like the Planning Institute of Australia can help in this regard, as can the universities who are training the urban planners and policy-makers of tomorrow.

Mitigating canyon effect starts at urban planning policy level but needs to be translated into practice. Micro-level policy improvements would perhaps be most helpful if directed at improving development assessment standards. Development approval is a public process, overseen by urban planners working for government. The tension of development approval is always in mediating the profit motive of developers against public good outcomes. If you’re a developer it makes sense to maximise building heights in central urban areas to increase profit returns from expensive development land. However, a planner will use policy where possible to balance this imperative with the need to create positive urban experiences for people.

Planners assess the heights of proposed building through height limit controls imposed by the relevant urban planning instruments. Consideration is given to the height of a proposed development in relation to: the height of buildings currently surrounding it; the height of buildings which have been approved but not yet constructed; and the maximum building height that is permitted in that area. However, these boundaries are often pushed by developers seeking to achieve maximum yield.

Firm policies embedded within development approval systems could specifically discount exceptions to height limit controls. This approach would provide an explicit micro-scale strategy to reduce the potential for canyon effect without undermining macro-scale urban consolidation policy priorities. Moreover, it could provide more certainty for planners, developers and urban residents while supporting the creation of more liveable urban environments.

Looking to the future

Contemporary Australia certainly deserves the title ‘Urban Country’. There is no suggestion that our preference for urban living will change; indeed, it is likely to intensify. Effective urban policy is critical to ensure the liveability of our cities for everyone. Achieving positive outcomes through effective policy and practice is difficult at the best of times. It is even harder during periods of accelerated development like the last five years.

Canyon effect is unwelcome and its proliferation, especially in the centres and inner suburbs of our largest cities, is problematic. The creep of canyon effect in Australian cities is partly explained by the pace and intensity of recent development pressures. However, it is also a consequence of policy disconnect between the macro-scale focus of urban consolidation and development realities at the micro-scale.

The negative consequences of canyon effect are exacerbated by the fact that they will remain locked into urban fabrics. As such, urban policy priorities should now focus on reducing future incidences of urban canyon effect. Australia’s cities will continue grow into the future but nuanced policies across scales can ensure that canyon effect becomes a relic of the past.

ABOUT THE AUTHORS

DR TONY MATTHEWS

Dr. Tony Matthews is a Lecturer in Urban and Environmental Planning at Griffith University. His research interests include managing climate change impacts in urban systems through planning; the role and function of green infrastructure in delivering adaptive interventions; institutional, governance and policy change processes; and community, cultural and spatial rejuvenation led by informal local networks. Dr. Matthews is a member of Griffith’s Cities Research Institute and he co-presents a weekly urban affairs program called The Urban Squeeze with Associate Professor Jason Byrne on ABC Radio.