Directory : Water Directory 2014
WATER DIRECTORY 2014 AUSTRALIAN WATER INFORMATION AND STATISTICS Climate Water supply and use in the Australian economy needs to be considered in the context of Australia's climate. Mean annual rainfall in Australia varies substantially across the continent and between regions. Large areas of Australia have a mean annual rainfall of 600--1500mm, an amount comparable with most of Europe and North America. However, a key feature of Australia's climate is not the amount of rainfall but the variability in rainfall from year to year and season to season. Annual rainfall variability is greater for Australia than any other continental region. Any assessment of water supply and use over time must take this variability into account, including comparisons between the Water Accounts for 2010--2011 and 2011--2012. The major driver of interannual climate variability in Australia, particularly eastern Australia, is the El Niño--Southern Oscillation phenomenon. El Niño is an anomalous large warming of the central and eastern tropical Paci c Ocean, while La Niña, the reverse phase of the system, is an anomalous cooling. The Southern Oscillation refers to a see-sawing of atmospheric pressure between the northern Australian--Indonesian region and the central Paci c Ocean. El Niño events are strongly associated with abnormally high pressures in the northern Australian--Indonesian region and abnormally low pressures over the central Paci c, while the reverse is true during La Niña events. The Southern Oscillation Index (SOI) is an index of the pressure differences between Darwin and Tahiti and has traditionally been used as an indicator of El Niño events (which are often, but not always, associated with a strongly negative SOI). However, with modern satellite and oating buoy observations developed over the last 30 years, ocean temperature anomalies, both at and below the surface, can be monitored directly and hence proxy measurements, such as the SOI, are less important than they once were. El Niño events characteristically develop during the southern autumn and continue for about nine to 12 months until the following autumn. The 2002--03 and 2009--10 El Niño events followed this pattern, developing in May--June and dissipating in February--March. In contrast, the 2006--07 event developed unusually late in August--September 2006 (although dry conditions were well established in many areas by then), before breaking down in February--March 2007. On occasion, El Niño events are followed immediately by La Niña events (or vice versa), but it is more common for them to be followed by near-normal (neutral) ocean conditions. Events lasting for more than one year are rare, but not unknown. There are typically two to three El Niño events per decade, but there is large variation from decade to decade in their frequency and the balance of El Niño and La Niña events. Between 1980 and the mid-2000s, El Niño events have been predominant, whereas La Niña events were frequent in the 1950s and 1970s. There have been two major La Niña events in the last few years, and the event of 2010--11 was one of the strongest of the last century. It was accompanied by widespread heavy rain and ooding. Climate variability (in rainfall, temperature and evaporation) affects the performance of water utilities in a variety of ways. A key example is decreased rainfall, which affects water availability and can trigger demand management measures. Demand management activity incurs operating costs and also reduces the volume of water supplied. In turn, that affects revenue from water consumption charges, which then affects pro tability (net pro t after tax) and the dividend (if any) to shareholders. The charts opposite are examples of some interesting trend relationships between climate-related indicators (rainfall and temperature) and Urban NPR indicators.
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