El Niño and the southern oscillation Fluctuations in rainfall have several causes that are not fully understood. Probably the main cause of major rainfall fluctuations in Australia is the southern oscillation , which is a major air pressure shift between the Asian and east Pacific regions. The strength and direction of the southern oscillation is measured by a simple index called the Southern Oscillation Index (SOI). The SOI is calculated from monthly or seasonal fluctuations in air pressure between Tahiti and Darwin. In an average rainfall year with ‘typical’ pressure patterns, the SOI is between −10 and +10. If the SOI is strongly negative (below −10), this means that the air pressure at sea level in Darwin is higher than in Tahiti, and an El Niño event occurs. During an El Niño event, less-than-average rainfall is experienced over much of Australia. During this period, drought will occur. If the SOI becomes strongly positive (above +10), this means the air pressure in Darwin is much lower than normal and a La Niña event occurs. During this period, above-average rainfall will occur. In recent years, scientists have made great advances in understanding and forecasting El Niño and southern oscillation events. The National Climate Centre in Australia produces outlooks on rainfall three months ahead. These outlooks are proving to be of great value to farmers, and especially valuable for ecologically sustainable development in rural areas. 9.6.6 Water availability and accessibility Imagine that it is lunchtime on a regular school day. Your stomach has been rumbling all morning and it is finally time for lunch. You open your bag and staring back at you is a lunchbox filled with all your favourite foods. We can say that your lunch is available because it is there for you, ready to be used. We can also say that your lunch is accessible because you can easily get to it. If you have lunch in your bag but it’s not yet lunchtime, then your lunch is available but it is not accessible. This simplified example can be used to explain the difference between a location’s water availability and accessibility. The distinction between these two terms is important — firstly, to understand the reasons a location may not have reliable water and, secondly, to develop solutions to improve the supply of water. Although 70 per cent of the Earth is water, a tiny proportion of that water is available for human consumption. Of that 70 per cent, 96.5 per cent is contained in our oceans, with only 2.6 per cent present as freshwater. However, the majority of that water is trapped with glaciers, icecaps and groundwater, with just 1.2 per cent of that 2.6 per cent present in surface water. If we keep following this surface freshwater, we discover that, again, a remarkably small percentage of water is available for direct human consumption, largely in rivers and lakes. These statistics (see FIGURE9 ) clearly demonstrate that the availability of fresh water on a global scale is significant issue. With the seemingly never-ending increase of human population, the scope of this issue becomes even more apparent. For some countries, water accessibility is a greater concern than availability. Papua New Guinea can be used as an example of such a country. Located directly to the north of Australia, Papua New Guinea is the third wettest country in the world, with an average annual rainfall of over 3000 millimetres. This incredibly large amount of rain shows us that it is not the availability of water that is the problem for Papua New Guinea. Instead, the accessibility of water in Papua New Guinea is affected by the country’s extremely mountainous topography and its dense jungle environments. These geographic characteristics make it difficult for the people of Papua New Guinea to collect and distribute water across the country. Sadly, this means that although Papua New Guinea has strong water availability, it has poor water accessibility. This, in turn, negatively influences Papua New Guinea’s economic capability, making it one of the poorest countries in the world.
276 Jacaranda Humanities Alive 7 Victorian Curriculum Third Edition
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