Our cities, until recently, have been developed under the assumption that climate is relatively stable. Recent observations suggest that this is not the case and this has been reflected in legislative changes across Australia. For these reasons it will be necessary to adapt and plan for these challenges. This paper focuses on future flooding using existing tools and models coupled with recent predictions in future rainfall.

This paper has taken recent research into future rainfall intensity by the CSIRO (Abbs & Rafter, 2008) and applied them to existing flood models in the Melbourne area. The 2030 and 2070 rainfall intensities derived from the CSIRO paper were used to produce design rainfall and design hydrographs for each catchment.

Peak flows were determined at catchment outlets for design events based on the existing conditions and future conditions for 2030 and 2070. To evaluate changes in the Annual Recurrence Intervals (ARI) relative to current design standards quantile relationships for the Generalised Extreme Value (GEV) distribution were inverted and solved for the GEV parameters. The resulting GEV relationship was used to determine future design events return period for current conditions. While results varied from catchment to catchment typical results from this analysis indicated the 2070 1 in 2 year design ARI event was equivalent to the present 1 in 5 year ARI event and the 2070 1 in 100 year ARI event was equivalent to the 1 in 150 year ARI event. In addition to providing information on return periods the hydraulic model showed increases in the extents of inundation.

The results have important implications on future planning, management and infrastructure. The suggest we may need to revise our infrastructure design standards and some areas currently considered appropriate for development may be vulnerable in the future.