Cities as Water Supply Catchments: Green cities and microclimate (Project B3.1)

Overview

Reduced water availability and vegetation cover, as well as the high thermal mass of impervious surfaces associated with urban development, limit evapotranspiration in urban areas, leading to unique urban climates in Australia.

At the city-scale, this transformation can lead to an Urban Heat Island (UHI) effect where the urban areas are often warmer than the surrounding rural areas, especially at night. Drought, water restrictions and the implementation of drought tolerant landscapes all contribute to drier urban landscapes which can exacerbate urban heat. This will be further intensified by the projected increases in the intensity, frequency and duration of extreme heat events under climate change. Implementing stormwater harvesting systems that incorporate vegetation offers unique opportunities to build water sensitive, low-energy and visually attractive cities with improved urban microclimates.

This project aims to understand the climatic benefits of stormwater harvesting, water sensitive urban design (WSUD) and urban greening at the household- to neighbourhood-scale, including the relationship between extreme heat and health outcomes.

Key outcomes

This project, in partnership with the National Climate Change Adaptation Research Facility (NCCARF), identified threshold temperatures above which mortality and morbidity increase in all Australian capital cities, and developed a mapping tool to identify areas of high vulnerability during extreme heat events. The vulnerability maps have been used for emergency response planning by hospitals, the ambulance service and local governments to protect vulnerable residents and plan for the future. Researchers also found a clear association between area-based measures of extreme heat vulnerability and heatwave morbidity and reported on the key characteristics required to reduce temperatures and enhance human thermal comfort and liveability.

Providing fit-for- purpose water to ensure trees and vegetation remain healthy will deliver positive benefits for human thermal comfort. Together with the Victorian Centre for Climate Change Adaptation Research (VCCCAR) and other universities, this project established a framework for prioritising urban greening interventions based on population vulnerability, areas of excess heat and behavioural exposure (areas of high population activity). This framework provides a step-by- step guide to the selection and placement of green infrastructure, especially trees, to maximise cooling benefits. This project also determined how effective stormwater harvesting technologies, tree cover, green infrastructure and WSUD are improving urban climates at a range of scales.