Impacts of long-term climate variability and climate change on flood frequency: Susannah Brook, Western Australia

In this paper we investigate the propagation of long-term climate variabilities and climate changes through a catchment system to the flood frequency curve, through the use of a rainfall-runoff model that captures rainfall and water balance variability at a multiplicity of time scales, ranging from event to seasonal, inter-annual and inter-decadal time scales. This modelling investigation is carried out in the Susannah Brook catchment, Western Australia. Analysis of the results shows that, for example, a 10-year flood may change over to a 15-year flood over the next 50 years, due to a possible declining rainfall trend. Similarly, the 25-year flood may become a 40-year flood over the same period. These results suggest that engineers will need to come up with creative changes to traditional flood frequency estimation procedures to deal with long-term climate variability and changes.