Pacific and Indian Ocean climate variability: implications for water resource management in eastern Australia

The impacts of multi-temporal scale climate variability occurring over the Pacific and Indian Oceans on the rainfall and runoff regimes of eastern Australia are explored in this thesis. Three modes of natural climate variability are studied, the El Niño/Southern Oscillation (ENSO), the Interdecadal Pacific Oscillation (IPO) and the Indian Ocean Dipole (IOD). An analysis of historical rainfall and streamflow data for Queensland (QLD), New South Wales (NSW) and Victoria (VIC) reveals strong relationships between indices of ENSO and IPO variability and seasonal rainfall and streamflow totals in the spring and summer months. In addition, it is shown that a strong connection exists between a number of Indian Ocean SST indices and winter rainfall in eastern Australia, offering an improved understanding of year-round seasonal climates. A climate impact assessment is carried out for a regulated irrigation and domestic water supply system located in NSW (the Lachlan River Valley) to determine the main climatic drivers in the region. It is shown that ENSO, the IPO and the IOD have a strong impact on rainfall, evaporation and inflows, while storage volumes, water allocations and sustainable crop areas are also related to the state of ENSO and the IPO. The research presented in this thesis highlights the importance of understanding the role that natural climate variability plays in influencing the climate, water resources and agriculture in eastern Australia. A simple stochastic framework for use in long term drought risk assessment is developed that specially incorporates multi-decadal persistence of rainfall, brought about by changes in the IPO. The drought risk framework is applied to water resource assessment in the Lachlan River Valley, providing greater insight into the frequency, magnitude and duration of hydrological droughts than present approximations that use the limited instrumental record alone. Importantly, the results presented in this thesis highlight the fact that water resource management in eastern Australia must be developed to cope with the full range of natural climate variability, irrespective of future impacts of anthropogenic climate change, to aid in drought proofing our climate sensitive infrastructure.