Urban water metabolism of Brisbane city: a multi-scale interdisciplinary evaluation framework

Continually providing water services for increasing urban population while minimising the impacts of urbanisation on the environment is becoming challenging. The technological/engineering solutions alone are not sufficient. Interventions from other disciplines such as urban design, planning, and social science are needed in addition to engineering solutions to overcome the challenges. However, suboptimal integration of interdisciplinary interventions might lead to unintended and undesirable outcomes. There is a need to holistically evaluate the benefits (and potential drawbacks) of integrated interventions, which is missing from the literature. Urban water metabolism at multiple scales as an evaluation framework for testing and comparing interdisciplinary interventions has been introduced. Urban water metabolism is a conceptual model for describing water flows in and out of urban areas, which can be used to study the interactions between natural landscape, built-environment, and socio-technological systems. It is based on urban water mass balance principles accounting for all water flows including natural and anthropogenic flows. The quantitative capacity of the evaluation framework at the development scale (i.e. site-scale) and city-scale is shown in the Australian city of Brisbane using a set of water performance indicators (e.g. naturalness ratios). Six scenarios were developed representing a variety of demand management strategies (e.g. efficient appliances), on-site water servicing technologies (e.g. rainwater tanks), and architectural design interventions. The results show, depending on the interventions implemented, stormwater runoff spikes between 332 to 392%, evapotranspiration is reduced in the range of 41 to 83%, and infiltration shrinks to 34 to 71% of the flows in the natural landscape (i.e. natural hydrology). More than 36% of water demand can be met internally at the site (i.e. self-sufficiency) if smart irrigation systems are installed, the efficiency of appliances and water fixtures is increased, on-site storage for local harvest is introduced, and architectural design is optimised. The framework developed in our study is useful for evaluating interdisciplinary options quantitatively and systematically. Additionally, it has applications as a design tool to identify and test alternatives to achieve greener and more sustainable urban spaces.