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University of New South Wales (UNSW) 2011

Continuous rainfall simulation for design flood estimation in Australia

Pui, Alexander

Titre : Continuous rainfall simulation for design flood estimation in Australia

Auteur : Pui, Alexander

Université de soutenance : University of New South Wales (UNSW)

Grade : Doctor of Philosophy (PhD) 2011

Résumé
The temporal and spatial variability of Australia’s climate has a profound impact on water resource management across broad disciplines, ranging from agricultural practice to flood risk assessment. In the context of flood estimation practice, stochastic sequences of rainfall are generated via continuous rainfall simulation models over a given region of interest such that it can be used as input for rainfall-runoff models at a catchment scale to simulate continuous flow sequences for flood frequency analysis purposes. However, while many continuous rainfall models within the literature are able to capture extreme rainfall behavior well, their inability to represent other characteristics of low frequency climatic variability that are important for realistic flood design estimation serves as a major limitation. As such, this thesis first explores the nature and impact of low frequency climatic variability in Australia on fine temporal scale rainfall variables, and utilizes this insight to develop a state-based continuous rainfall generation model capable of representing observed rainfall characteristics impacted by low frequency climatic variability.The first part of this thesis reviews and critically evaluates a number of widely applied rainfall disaggregation models at several point locations across Australia. Specifically, the ability of these models to simulate a range of statistics important from a flood design perspective is assessed. Next, a comprehensive study to ascertain the impact of inter-annual climatic variability attributed to climate modes such as the El Niño Southern Oscillation (ENSO) on fine temporal scale rainfall variables across East Australia is undertaken, revealing that the frequency of rain events, but not changes to the intensity of these events, are the primary cause of changes to changes at coarser time scales. The third evaluation investigates the role of antecedent catchment (approximated by antecedent rainfall) conditions in explaining observed differences to flood risk on inter-decadal time scales, and found that antecedent rainfall, but not extreme rainfall fluctuated according to inter-decadal climatic regimes. Lastly, insight gained from earlier findings in the thesis are used to develop a state-based continuous rainfall model that is capable of representing low-frequency structures in rainfall that are important from a flood design perspective.

Mots clés : Australia ; Rainfall ; Flood design ; Modelling ; Risk

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