Using spatial modelling to develop flood risk and climate adaptation capacity metrics for vulnerability assessments of urban community and critical water supply infrastructure

Using spatial modelling to develop flood risk and climate adaptation capacity metrics for vulnerability assessments of urban community and critical water supply infrastructure

The aim of this study was to develop a new spatially-explicit analytical approach for urban flood risk assessment and generation of climate adaptation capacity metrics for assessing urban community and critical water supply network vulnerability. Using the January 2011 flood in Queensland (Australia) with the core suburbs of Brisbane City as the study area, the research issues with regards to the sufficiency of indicating variables and suitability of climate risk modelling were addressed in this study. A range of geographical variables were analysed using high resolution digital elevation modelling and urban morphological characterisation with 3D analysis, spatial analysis with fuzzy logic, and geospatial autocorrelation techniques with global Moran's I and Anselin Local Moran's I. The issue on the sufficiency of indicating variables was addressed using the topological cluster analysis of a 2-dimension self-organising neural network (SONN) structured with 100 neurons and trained by 200 epochs. Furthermore, the suitability of flood risk modeling was addressed by aggregating the indicating variables with weighted overlay and modified fuzzy gamma overlay operations using the joint conditional probability weights based on Bayesian theory. Variable weights were assigned to address the limitations of normative (equal weights) and deductive (expert judgment) approaches.
The analyses showed that 186 ha (8%) and 221ha (10%) of the study area were exposed to very high flood risk and very low adaptation capacity, respectively. Ninety percent (90%) of the study area revealed negative adaptation capacity metrics (-31 to < 0) which implies that the resources are not enough to increase climate resiliency of the urban community and critical infrastructure (i.e. water supply network). This scenario was further exacerbated by the findings that government infrastructures in Queensland were uncovered by flood insurance. In the water supply network vulnerability assessment, eight (8) out of 107 critical trunk-reticulation main connection points were assessed as highly vulnerable critical water supply assets. Furthermore, utility network analysis showed that turbid water may flow along 246km of pressure main lines (i.e. trunk and reticulation mains) covering the north east to north west sides of the study area. In the absence of immediate mitigation measures, increased risk of fluvial flooding to water supply may significantly impacted the health conditions of urban residents. The newly developed spatially-explicit analytical technique, identified in this study as the flood risk-adaptation capacity index/metrics-adaptation strategies (FRACIAS) linkage model, will allow the integration of flood risk and climate adaptation assessments which have been treated separately in the past. This study provides a tool of high level analyses (e.g. building floor space, water supply connections, etc.) and identifies adaptation strategies to enable urban communities and the water supply industry to better prepare and mitigate future flood events. Furthermore, the results generated from the model can be used to improve insurance and land-use planning policies. These include the deliberation of risk-based premium pricing of flood insurance that should not heavily based on the geographic location of risk but should also take into consideration the adaptation capacity (e.g. income, severe disability, poor access to emergency services, etc.) of the community at risk. Through this approach, the governments (i.e. local, state, and federal) may provide financial and development support to areas of very high flood risk and very low adaptation capacity; thereby strengthening public-private partnership. As precaution, insurance policies may not be used solely as a decision tool for urban development on areas of very high flood risk but also consider the poor land-use planning inherited from the past. Further disaster risk reduction measures identified in this study include the 'flood proofing' of residential houses and commercial buildings, implementation of 'property buy-back' scheme and 'land swap' program, and amendment of Queensland Development Code to regulate the construction of buildings on areas identified with very high flood risk and very low adaptation capacity.

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