A net-zero Perth will need more trees – but how will we water them?

Alongside the COP27 global climate conference,we have presented a series of columns from community leaders and Net Zero Perth members,outlining a pathway to net zero. Here is the final – for now.

Dean of Sustainable Futures,Curtin University

My interest in sustainability has modest roots in my first veggie patch as a teenager. The act of growing something productive intuitively made sense to me. So too did planting trees for shade,shelter and beauty.

This interest soon blossomed into a full-blown fascination with how cities work as systems and the role that plants and water play in making them liveable. What started as an interest in gardening 30 years ago has become a lifelong journey of learning,incorporating the practical and theoretical,and what began as an intuition – that plants are good for us – is now supported by asound evidence base.

Perth is going to need to balance its need for greening with its need to conserve dwindling water sources.

Perth is going to need to balance its need for greening with its need to conserve dwindling water sources.Kathleen Adele

Urban greening and contact with nature have significant health and wellbeing benefits such as reducing stress,improving attention and mental restoration,providing noise buffering,reducing air pollution and optimising sun exposure. Urban greening can also support biodiversity and provide space for localised stormwater infiltration. This is just a snapshot of why urban greening is an important part of the sustainability agenda,but what does it have to do with climate change and the notion of a net-zero Perth?

Firstly,it’s about mitigation. Simply put,thoughtful landscaping with minimal paving,well irrigated gardens and appropriately placed shade trees makes houses more thermally comfortable. This means less energy is needed to heat and cool them,and fewer emissions generated through reduced reliance on air conditioning. The same principle applies to landscaping around apartments and commercial buildings.

People are also more likely to choose active transport such as walking,scooting and bike riding in environments that are shaded and pleasant to be in,resulting in reduced transport emissions.

Urban greening is also about adaption. Climate change is contributing toincreased temperatures and heat wave conditions in Perth. Coupled with urban infill and the changing urban form with reduced garden size and reduced green space,a hotter and drier Perth is projected. Creating healthy,resilient and cool green spaces will be essential for liveability and minimising the potential impacts from climate change and increased urban heat. This is particularly important for vulnerable populations.

Sprawling Perth is Australia’s least-vegetated capital.

Sprawling Perth is Australia’s least-vegetated capital.Nearmap

The importance of urban greening is widely understood with most local government authorities across Perth now actively engaged in developing and administering urban forest strategies,albeit withmixed results. The main frustration is the good work being done planting trees in public areas is being undone through loss of trees on private land.

At a state government level,the Department of Planning,Lands and Heritage provides guidance on urban greening requirements for new developments through its suite ofdesign guides and codes,but application and enforcement is proving elusive with the outcomes often falling short of expectations. The net result is the percentage of green space and tree canopy coverage across Perth is generally static,or going backwards.

Water is an essential ingredient for successful urban greening,and will be even more so in a hotter,drier climate. Declining rainfall linked to climate change has impacted our traditional water sources including dams and aquifers. The challenge is how to balance the benefits afforded by green space with the need to conserve this vital resource.

Much work is being done by government and industry to transition Perth to a more waterwise future. TheWaterwise Perth Action Plan 2,or Kep Katitjin – Gabi Kaadadjin aims to make Perth a leading Waterwise City by 2030 through strategic initiatives and fostering collaboration across government and the community.

Periodic auditing of progress is undertaken via theWater Sensitive City Index against a benchmark established in 2016. The Index includes seven goals for a waterwise city,including “quality urban space” which incorporates indicators related to urban greening,and “productivity and resource efficiency” which considers indicators such as water use and water recycling,as well as greenhouse gas emissions.

Greenery is a priority at my house.

Greenery is a priority at my house.Robert Frith/Acorn Photo

The auditing process shows that we are making some progress as a waterwise city,butwe are also becoming increasingly water constrained – and the energy requirements and associated emissions from the water sector are growing.

Large-scale seawater desalination now makes up around half of Perth’s scheme water supply,despite being the most energy intensive of all primary water sources at around 4 kilowatt hours per kilolitre.Groundwater accounts for around 70 per cent of all water used in the Perth region,despite being under pressure from overuse and reduced recharge.

Access to both sources is restricted to preserve supply and protect groundwater dependant ecosystems. Meanwhile,the vast majority of Perth’s wastewater is pumped long distances,treated and discharged to the ocean – a legacy of \20th century engineering and a reluctance to adapt to new opportunities.

An alternative to this approach is to recycle wastewater locally. At the most basic level this can be done at the household scale using greywater (shower and laundry water) for garden irrigation. Wastewater can also be recycled at the precinct or development scale,using advanced treatment technologies. When incorporated into new urban developments or retrofitted into existing areas as part of urban renewal projects,this can meet the water demands for public and private green space and alleviate pressure on both scheme and groundwater supplies. There are precedents for this approach in other cities around Australia,but none in Perth.

I was a consultant on water use at the White Gum Valley urban infill development,which has achieved an overall 65 per cent reduction in mains water use.

I was a consultant on water use at the White Gum Valley urban infill development,which has achieved an overall 65 per cent reduction in mains water use.Robert Frith/Acorn Photo

I was fortunate to attend COP27 in Sharm El-Sheikh,Egypt earlier this month. The sense of urgency to achieve a meaningful reduction in global emissions was palpable. So too was the sense of reality that we may well miss the target of limiting the global temperature increase to 1.5°C. But we still have time and the ability to come close if we act now. The enormity of the tasks to achieve this can at times feel overwhelming and it is undoubtably the great challenge of this decade. The role of urban greening in contributing to climate change mitigation and adaption is clear and we can all start in our backyards and community spaces now. Better still if this is supported by more ambitious urban planning and integrated urban water management policies for greater impact.

As my own children approach the age when I first fell in love with gardening,I hope they too find joy in the act of growing plants,and eventually realise it is more than just a hobby,but a critical part of making Perth liveable and contributing to a ‘Net Zero’ future.

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Josh Byrne is an environmental scientist with expertise in water-sensitive and energy-efficient urban development. He is also the presenter on Gardening Australia and author of three books on sustainable gardening and low-carbon living.

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