Picture this: you’re working from home and it’s sweltering outside. You venture out for a coffee and move between patches of shade as you go. Good thing you wore your sunglasses, because the glare of the new footpath almost blinds you. You order your coffee – make it iced – before hurrying back to your air-conditioned paradise.
If you live in an urban area in Australia, chances are this scenario resonates. Our cities are becoming ever hotter – due to both the way they’re built, as well as climate change and the extreme heat events it brings.
But the design and management of our cities is changing. In particular, reflective materials – such as light-coloured footpaths and roofs – are increasingly used to bounce solar radiation (and heat) back into the atmosphere, to reduce temperatures on the ground.
Efforts to cool our cities are welcome. Heatwaves are Australia’s most deadly type of natural disaster, and severely affect our quality of life. However, these measures may have unintended consequences. Light-coloured materials reflect not only heat, but ultraviolet (UV) radiation. This type of radiation is the dominant cause of skin cancers.
Our new research shows UV exposure is rarely considered in urban planning policies. Unless the problem is addressed, efforts to cool our cities may exacerbate a serious public health problem.
Understanding UV radiation
Darker surfaces reflect very little solar radiation – instead, they mostly absorb it. That’s why bitumen roads, for example, can get so hot in summer. Surfaces such as glass or metal facades, however, are far more reflective and bounce the sun’s rays – including both heat and UV radiation – back into the urban environment.
Studies have shown this reflection significantly increases people’s exposure to UV radiation. One study, for example, found reflective walls can increase UV exposure by up to 300% compared to walls with non-reflective materials.
UV radiation can cause melanoma and other skin cancers as well as sunburn, skin ageing and eye damage.
Australia has the highest melanoma rates in the world; more than two in three of us will be diagnosed with skin cancer in our lifetime. In 2019, more than 15,600 new cases of melanoma were diagnosed in Australia and the figure is growing each year.
So to what extent does urban planning policy in Australia take account of the risk of UV radiation when trying to cool our cities? Our latest research examined this question.
What we found
The research involved RMIT experts and Sun Smart, a Victorian skin cancer prevention program jointly funded by Cancer Council Victoria and the Victorian government.
The first step was to audit relevant health-policy documents for all 79 local government areas in Victoria, looking for mentions of skin cancer, skin cancer prevention, and UV and sun protection. We found where sun protection was mentioned, it was mostly in relation to reducing urban heat rather than UV exposure.
Second, researchers analysed a sample of seven relevant planning policies across both local and state government. Collectively, they included 102 specific policy items that required or recommended shade or surface material changes to improve health and comfort in urban outdoor environments.
Of these, 21 related to surface materials – mostly changing paving colour to reduce urban heat. The City of Melbourne also considered roof and façade materials.
For example, one requirement found in several planning schemes required new apartment developments to:
shade outdoor areas exposed to summer sun […] and use paving and surface materials that lower surface temperatures and reduce heat absorption.
However, there was no mention in these policies of UV radiation, skin cancer or related terms. That means decision-making in local government is unlikely to consider UV radiation and the public health risk.
We also conducted a workshop with 14 urban planners from government and industry. It highlighted a need to support planners in their decision-making, by providing guidance on matters such as:
how to encourage people to be active while not increasing their exposure to health risks such as UV radiation
which populations are most vulnerable to UV exposure
which locations present the greatest UV risk
the best policy and design responses.
Where to now?
Clearly, urban cooling policies should aim to reduce both UV radiation and heat.
Planners and designers should consider the location and type of reflective materials being proposed. For example, highly reflective materials may be best located away from the street level – such as on roofs – so they can reflect heat without exacerbating UV exposure.
Local governments are increasingly planting trees to provide shade. This both cools urban areas and provides UV protection. Establishing more trees in cities – particularly trees with large canopies – should become a planning priority.
Evidence-based guidance should be provided to local planners to ensure people are not unnecessarily exposed to UV radiation. And more research is needed to understand, for example, how urban design can best reduce UV exposure.
Climate change is set to worsen, and city planners will be looking for more ways to keep people cool. These measures must better balance the need to cool the city while addressing the risk of UV radiation, to keep people both comfortable and safe.
This work was funded by RMIT's Enabling Impact Platforms Strategic Impact Fund.
Joe Hurley receives funding from the Australian Research Council and Australian Urban Research Infrastructure Network (AURIN). This work was funded by RMIT University Strategic Impact Fund. Joe is on the technical advisory committee for the Council Alliance for Sustainable Built Environment.
This article was originally published on The Conversation. Read the original article.
