Modelling best placement of green infrastructure to reduce urban heat

A numerical tool for designing Water Sensitive Cities — a concept closely aligned with water wise cities — is creating demonstrated impact in places like the City of Unley, Adelaide.

Unley faced a problem common to many urban communities. How can planners and utilities best configure their implementation of green infrastructure — elements like trees in streetscapes, vegetated green walls and roofs, and technology for recycling stormwater?

For Unley, a specific question centred on mitigating rising heat in its major streets, reflecting that familiar city experience in which hard impervious surfaces retain the day’s heat to create ‘islands’ that remain hotter than surrounding areas. Greening streetscapes can powerfully cool those same concreted environments — a specific benefit for which communities are willing to pay. In fact, households in Melbourne and Sydney are willing to pay between $47–81/year for cooler summer temperatures according to research by the Cooperative Research Centre for Water Sensitive Cities (CRCWSC).

But deploying green innovations effectively requires data on where and how implementations will improve temperatures — and by how much. This has traditionally been an information gap, with some planners recently resorting to drone flyovers and state-of-the-art thermal imaging equipment. Despite the expense of such methods (which can cost $60K for just 4 flight hours), the data from aerial surveys are more detailed than required, and may not represent how the surveyed area’s temperature behaves over time.

Now, a new tool — part of the Water Sensitive Cities Modelling Toolkit — allows planners to replace or complement drone data by drawing on recent advances in urban heat modelling.

Designed by the CRCWSC, the evidence-based Toolkit provides a range of tools for quantifying the benefits of installing green infrastructure in a particular context. Importantly, it empowers users to be more strategic when guiding their planning and decision-making.

“The tool lets you map out a region so that you can pick areas [for implementing green infrastructure] that make sense,” explained CRCWSC researcher Dr Peter Bach. “You can use it to validate your existing drone data to determine if they are representative. And you can construct alternative scenarios — like ‘What happens under X, Y, or Z plans for a particular area?’

“And with the Toolkit’s microclimate module, the Unley case study also showed that we can really efficiently input local data to simulate heat mapping, and to visualise different strategies for mitigating heat.”

For professionals such as Mellissa Bradley from Water Sensitive SA, the tool is well timed. She is dealing with challenges like ‘underperforming asphalt’ and needs innovative approaches. “The true value of the Toolkit is in its cost-effectiveness, and its capacity to let users explore and compare scenarios,” said Bradley.

For councils and water utilities, the other big benefit is that the heat models provide an invaluable communications aid. Maps of heat across streetscapes, and visuals of ‘before-and-after’ scenarios, enable people to ‘see’ the outcomes of infrastructure work and participate in discussions without needing to engage with the technical details.

But with integrated urban water management at its core, the Toolkit has intuitive benefits for utilities as well as governments.

It supports needs ranging from planning at regional scales to quantifying the benefits of harvesting and recycling water sources like stormwater as part of a portfolio of supply options.

Those linkages recognise the inter-agency value of greening cities. Not only can organisations such as councils and water utilities benefit individually from more powerful ways to strategically plan their projects, but the new generation of tools — such as the Toolkit — increasingly enable councils, utilities and communities of water wise cities to band together to achieve benefits for livability, cooling, wellbeing, water and irrigation.

For more on the Water Sensitive Cities Toolkit, visit: https://watersensitivecities.org.au/solutions/water-sensitive-cities-toolkit/.