The importance of understanding drivers of hydroclimatic variability for robust flood risk planning in the coastal zone

Abstract Previous work has established that the risk of climate related emergencies (eg. floods, droughts, bushfires, etc.) in Australia, and many other parts of the world, is non-stationary. That is, the chance of an extreme climatic event occurring is not the same from one year to the next and is in fact dependent on the state of the various ocean-atmospheric phenomena that are responsible for Australia’s hydroclimatic variability. This previous work demonstrated how, on average for New South Wales, the probability of a flood occurring that is equal in magnitude to the 1-in-100 year flood is about five times greater during La Niña events compared to all other years and 12 times greater during a La Niña event that occurs during the negative phase of the Inter-decadal Pacific Oscillation compared to all other years. This work has recently been extended to focus specifically on urban coastal areas where it has been found that the non-stationarity of flood risk is even further enhanced when compared to the non-coastal catchments. Also investigated is whether this non-stationarity of flood risk is due to non-stationarity of antecedent conditions or non-stationarity of extreme daily and sub-daily rainfall events, with the finding being that both are important. This is contrary to recent studies that claim there is no evidence of non-stationarity in extreme daily and sub-daily rainfall across Australia. The implications of these results are significant given the large populations and infrastructure investment along the eastern seaboard and also timely given current updates to Engineers Australia’s Australian Rainfall and Runoff: A Guide to Flood Estimation, the standard for flood estimation in Australia.

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