Vulnerability to Flooding in Cities at Local Scale: New Methodology with Application to a Local Council in Sydney

Abstract

Background. Flood studies are conducted mostly at city or catchment scales. While such studies are necessary for developing flood policies, municipalities require, in addition, place-specific data and strategies that can identify population at risk and develop tailored measures to reduce vulnerability and increase resilience. Local authorities commonly conduct their own flood studies, concentrating on the geophysical aspects of floods without considering their differential social impacts. Different communities and individuals may be at risk for different reasons and for effective flood risk management and better adaptation to floods, it is important to know not only how significant the aggregate flooding risk is, but who is at risk and what are the drivers of their vulnerability. Objectives and Methods. The objective of the study is to develop a new methodology for assessing urban flood risk at local scale by constructing a Flood Social Vulnerability (FSV) model and use it assess the extent to which vulnerability to flooding is likely to change under different scenarios of climate change. The model is based on a hybrid approach, combining hydrological and hydraulic flood simulations with social vulnerability and built-environment indicators. The methodology is tested by applying it to the Marrickville Study Region (MSR), which consists of a number of suburbs in Sydney’s Inner-West known to be prone to flooding. The study area is divided into a set of local spatial units, determined by the smallest unit at which aggregated data is available. This is, in the case of MSR, the SA1 scale of the Australian Bureau of Statistics. A set of indicators under each dimension of a flood risk pyramid – hazard, exposure and social vulnerability – are extracted from simulation analyses and socio-economic databases, for each local unit, and combined into a flood social vulnerability index (FSVI). Moreover, this research investigated how vulnerability might change in the future due to the impact of climate change under today’s demographic, socioeconomic and built-environment conditions. To test the suitability of FSVI in informing flood mitigation policy making within a local government, results were discussed with the local government authority (the Inner-West Council) of the MSR. Findings. FSVI developed in this study helped in detecting local flood vulnerability hotspots. There was little overlap between the spatial distribution of the three sets of indicators (hazard, exposure and social vulnerability). Hence, drawing on socio-economic information to assess vulnerability to flooding was found to be useful. Simulation of climate change scenarios show noticeable increases in the duration of floods, but limited changes in flood depths, velocities and extents. Stakeholders at the Inner-West Council stated that the study’s findings could inform the Council’s current flood management planning, especially in relation to emergency services.