Using Dynamically Downscaled Rainfall Data to Examine the Impact of Climate Change on the Combined Probability of Extreme Rainfall and Antecedent Soil Moisture

Wednesday, 17 December 2014: 3:25 PM
Andrew Graddon1, Natalie Lockart1, Garry R Willgoose2, George A. Kuczera2, Aaron Coutts-Smith3 and Min Chen4, (1)University of Newcastle, Callaghan, NSW, Australia, (2)University of Newcastle, Callaghan, Australia, (3)Office of Environment and Heritage, Climate Change Impacts and Adaptation Section, Sydney, Australia, (4)Three Gorges University, Department of Hydraulics and Ecohydrology, Yichang, China
The wetness of the soil prior to a rainfall event plays an important role in determining how much rainfall is converted to runoff. This can impact the size and timing of any resulting flood. This study used dynamically downscaled GCM rainfall projections from the NSW / ACT Regional Climate Modelling (NARCliM) project to examine the joint probability of extreme rainfall and antecedent soil moisture prior to extreme rainfall events. The NARCliM project has produced an ensemble of regional climate projections for south-east Australia, in particular 10 by 10 km resolution hourly rainfall data. 12 different projections of rainfall have been produced for three 20 year time periods; 1990-2009, 2020-2039 and 2060-2079. An hourly time series of soil moisture was simulated from each of the rainfall data sets using the Australian Water Balance Model (AWBM). The soil moisture and rainfall time series were then examined to determine the relationship between the extreme rainfall and the median antecedent soil moisture. Rainfall events of varying durations were considered. For short duration rainfall events, an initial analysis showed that a clear relationship exists between the antecedent soil moisture and extreme rainfall; as the rainfall depth increases so too does the antecedent soil moisture. For the site considered in this study, the extreme future rainfall depths are predicted to increase, which will result in an increase in the soil moisture. This implies that extreme flooding events will increase in magnitude for the study site. Results from the 12 rainfall datasets and three time periods will be presented. The impact of climate change on the soil moisture / extreme rainfall relationship will also be presented.