Water is the only thing, which is of a crucial importance for the Australian continent. From the earliest times until the present it has received a considerable effect on the pattern of human habitation, landscape, people's lifestyle, prosperity and their relationship with the land.
Australia is a continent of extremes: geography, climate, population and water resources are often abnormal and subjects to scientific studies. First of all, it has a diverse range of climate zones. This contrast from tropical regions in the north through the arid expanses of the interior to the temperate climate in Sydney and the rest of the south. On the whole, eighty percent of the Australian land is an arid environment with less than six hundred millimeters of rainfall per year. The precipitation of the rest part of continent usually does not exceed three hundred millimeters; thus, it is by the right considered to be the driest inhabited continent on the Earth with highly variable rainfall patterns.
The Australian rainfall varies greatly by location with the least amount, falling in the interior. The temperature and humidity contrast to a great extent as well. The tropical part of Australia receives the most intensive moisture with more rain falling on the eastern side of the continent than the western side. The northern part of the country, which is also a tropical zone, has tropical rainforests, grasslands and a desert. The south-east and south-west corners of the continent belong to a temperate type of climate.
A peculiar feature of the Australia's climate is its high year-to-year rainfall variableness. Such volatility partly explained as a result of the Southern Oscillation influence, which is driven largely from the tropical Pacific Ocean and overlying atmosphere. Southern Oscillation also molds tropical cyclones, heat-waves, bushfires and frost, taking place in Australia. The phenomenon known as El Nino is a part of this ecosystem and makes a significant contribution to the Australian rainfall variability.
Although El Nino and Southern Oscillation result in regular seasonal anomalies in many parts of the globe, Australia experiences the highest pressure. It has extreme droughts that are interspersed with extensive wet periods. The vegetation of the continent had to develop adaptation methods in response to dry conditions, heat and the lack of the water, as the Australian rainfall is simply the lowest of the five continents (excluding Antarctica).
The mystery of this fact is hidden in the high evaporation of the continent. Available Australian water sources consist of surface waters that are rains, falling into streams and rivers, and the groundwater. Only twelve percent of the annual Australian rainfall becomes a runoff of streams and rivers or soaks into the ground. The rest goes back directly to the atmosphere, as a result of the transpiration.
In outcome Australia, which obtains five percent of the world's land area, has only one percent of the water, carried by the world's rivers. All these factors consequence in the environmental concern about the sustainable management of the surface water in Australia, its use, its quality and sometimes even its existence.