How and why are floods changing in Australia?

Abstract

One of the open questions about climate change is how future flood risk in Australia will change. Although changes to rainfall extremes are expected in most locations, it is not clear how these changes translate into flood risk due to the potential additional feedback of altered catchment characteristics (e.g., storage volumes, soil moisture, vegetation cover and fire disturbance) on runoff due to the changing climate and/or direct human-led changes. Flood damages have increased over the instrumental period in Australia, but it is not known if this is due to changes in population densities, increased infrastructure in flood prone locations (the exposure), improved reporting or actual changes in the occurrence of flood-producing meteorological events (the hazard). This paper reviews the existing literature on historical and expected future flooding in Australia, focusing on the flood hazard. Trends and changes in flood-producing mechanisms are also reviewed. Three flood case studies, namely the 2007 Pasha Bulker storm, the flood characteristics of the Fortescue Marsh area in the Pilbara and the 1956 Murray River floods are used to highlight the complexities of flood behaviour and to illustrate remaining challenges. We show that short instrumental records, large natural variability and the interrelated nature of other catchment changes limit our ability at this stage to understand how the flood hazard has changed in the historical period. Research efforts to both address this gap and continue to develop methods to best use projections from climate models are required to quantify future flood hazard. This information can then serve as an input to risk models that combine flood hazard with projections information, flood exposure and vulnerability.