Green Spaces Can Combat Urban Heat Stress

Adelaide has just come out of one of its worst spells of prolonged heat on record with blazing 42-degree-plus temperatures for five days straight in January.

Adelaide has just come out of one of its worst spells of prolonged heat on record with blazing 42-degree-plus temperatures for five days straight in January. Winning the dubious honour of the title “hottest city in the world” on January 16, in the confines of the city square mile the intensification of those temperatures was debilitating. Packed with concrete, asphalt, glass, traffic and the man-made heat given off from over-stretched air conditioning systems, there was a strong sense of being marooned on an Urban Heat Island. It is little wonder there are urgent calls for increased green space in urban areas to mitigate the impact of heatwaves. All predictions indicate the intensity and frequency of these conditions will increase as the planet warms. The Bureau of Meteorology predicts a higher frequency of stronger and longer prevailing heatwaves for Australia. Finding ways to design, reshape and build our cities to adapt to climate change is a matter of urgent concern and one university researchers are set to tackle. As we have seen from recent experience this is not just a matter of comfort or securing commercial productivity – it is a matter of life and death. At the peak of this episode, 163 people needed treatment in Adelaide hospitals because of the heatwave (mainly for risk of heat stroke and dehydration). The number of heat-related deaths in Adelaide is expected to more than double by 2030. The greatest number of deaths occurs in those aged 75 or older. Sustainable urban development principles recommend the use of green roof gardens and green walls, as vegetation cools the air temperatures; in addition, we should use construction materials that don’t store, but reflect, the heat. Research shows a 10 percent increase in urban green space can decrease surface temperatures by up to four degrees Celsius, as well as reducing air conditioning costs and greenhouse gas emissions. Green spaces could also reduce heat-related fatalities. Aiming for a healthy, liveable and sustainable city, we need better models of urban infill and gardens to successfully reintroduce greenery and natural habitat into a more compact urban environment. The federal government’s 2013 State of Australian Cities report found people living in cities could be more susceptible to the effects of heatwaves. It said the urban heat island was “caused by the prevalence in cities of heat-absorbing materials, such as dark-coloured pavements and roofs, concrete, urban canyons trapping hot air, and a lack of shade and green space’’ The urban heat island effect is lifting city centre temperatures by up to six degrees Celsius between the city centre and suburbs. If built with the wrong materials and too little green space, cities trap and store heat like a baking oven. During heat waves, the night cooling effect doesn’t work anymore. In the past, cities used to cool down overnight – when you came into the CBD of a morning, the heat from the previous day had dissipated. Now, due to an excess of anthropogenic heat, that is just not happening. Usually you open the windows at night and it’s nice and cool in the morning when you get up. But in such periods of extensive heat, cities don’t cool down overnight because the way we have built our cities stores and traps heat. It’s timely to think about changing Australia’s building code to mandate more heat-resistant designs and materials. We have to have more green roof gardens, green walls and community gardens, and use materials that reflect the heat. The City of Melbourne has implemented the ‘Urban Forest’ concept, with the aim of doubling its canopy cover over the next 25 years – so from 22 percent to 40 percent by 2040. As a transformational project, Adelaide could engage in a massive tree planting initiative that brings back street trees and gardens. It’s also timely to rethink the role of the parklands and create distinctive meeting places within the parklands. Luckily, we have not minimised the size of the parklands and the City of Adelaide has always protected these unique public recreational areas from any construction attempts. Interestingly, today we know that trees make perfect business-sense, save energy and help to keep cities cool. With a project grant of more than $1 million, UniSA is leading a comparative research study to tackle heat stress in Australian cities, which has at its heart an investigation into building and construction design. The study brings together three universities and eight industry and government partners, including SA Urban Renewal Authority, BlueScope Steel, Hassell Architects, the Cities of Adelaide and Sydney and the NGIA. Part of this large three-year research project is the investigation of use patterns and behavior of people in public space. We are asking what happens in public spaces when older people and young children are not able to go out because of the heat. How do we build cities and new types of public spaces that mitigate heat stress and reduce the storage of heat? The urban heat island effect is found in metropolitan areas where an urban microclimate is created due to human activity. It causes the city centre to be considerably warmer than its surrounding areas. Urban development is a big culprit as original land surfaces are diminished and replaced with dark energy-absorbing roads and buildings. It is also caused by waste heat from air-conditioning units, which often need to be used more to combat the effects of heat increases, further exacerbating the problem. Today, as effective and innovative as they are, we need to look far beyond green roofs to solve the problem, because when you move into a suburban context these sorts of innovations cannot be effectively applied. Every one degree Celsius temperature reduction means around five percent energy saving through reduced cooling load. In a large city like Adelaide this amounts to significant saving potential. We know that building materials, surface colours and pavement all have a significant effect on heat buildup and transfer. For example, the fashion for black tiles on roofs is really not something we can afford to indulge if we are serious about building heat-resistant cities and suburbs. Black tiles are one of the worst things you can have on a roof if you are hoping to efficiently manage heat. Black roofs absorb considerably more heat energy, driving a much greater cooling load and in turn lifting both greenhouse gas emissions and energy costs. Changing building codes so that black or other heat trapping tiles are legislated and not able to be used in cities such as Adelaide, Melbourne and Perth would be a simple and immediate step towards improving heat resistance. We know that cities were never intended to be completed. All cities are inherently evolutionary, in constant transformation and much of their character lies in the complexity and diversity of urban spaces. However, with impact of population growth, demographic change, an ageing population, climate change and the urgency of global warming, achieving sustainable urban development with meaningful and sustainable ‘places’ has become significantly more urgent and complex. The bigger task ahead is to transform our existing cities to become more walkable, compact, sustainable and liveable – and that includes a notion of cooler, more heat-resistent cities. In this process it is essential to better understand the interplay between higher densities and the risk of the urban heat island effect. Already one year into the research, we are are well on the way to building a better understanding of the essential characteristics of urban micro-climates in key Australian cities – working with Adelaide, Melbourne and Sydney. Our goal is to disseminate and promote policy dialogue and peer-learning among cities, researchers and industry partners to encourage city-to-city knowledge transfer. We also hope to provide capacity development programs for stakeholders in cities that are striving to become ‘Cool Cities and reduce cooling energy loads, and design a comprehensive framework to monitor and assess urban micro-climates with key indicators and measurements, so that we can build mixed use and vibrant urban centres that withstand the worst effects of heatwaves in the future. Our research will also deliver cost-benefit and risk analysis of the urban heat island mitigation options so that future planning options can be evaluated. This work will give urban local governmenr authorities, state/regional planning and public health agencies, developers, industry and infrastructure/service providers the tools to make better planning decisions for a future which will undoubtedly include hotter and more frequent heatwaves. Professor Steffen Lehmann will be one of the feature presenters at the University of South Australia sponsored Planet Talks at WOMADelaide Friday, March 7 to Monday, March 10