What is drought?
Drought is a natural part of our highly variable climate - and Australian life. Parched landscapes, dying livestock, empty farm dams and wilting gardens are images that we know all too well.
It is not a case of whether drought will occur, but when. The lessons of the past show clearly that it cannot be eliminated.
As former Premier Sir Rupert Hamer said in 1983: "It is impossible to make Melbourne drought-proof... in this sort of continent we will get (water) shortages periodically."
Melbourne Water regards drought as a normal part of climate variability that must be managed, not avoided - and that is why the Melbourne water industry plans for drought.
Drought is a prolonged, abnormally dry period when there is not enough water to meet normal or expected needs. It may include lower than expected water storage volumes and flows to reservoirs, and higher than expected demand for water caused by hot weather.
Drought may last a few months or many years. The current drought is now in its tenth year.
The impact of a drought depends on the amount of water in storage (from rainfall in previous years). For example, the dry conditions of 1997 in and around Melbourne had little immediate impact because water storages were full after a wet 1996. After ten years of below average stream flow, storage levels at the end of 2006 fell below 42 per cent of capacity.
Rainfall varies significantly across Australia in its severity and frequency. For example, Melbourne has more rainy days than Sydney but its average annual rainfall (655 millimetres) is about 40 per cent less than Sydney's (1107 millimetres).
Even across Melbourne, rainfall varies considerably, with averages for the past 20 years ranging from 827 millimetres in the east at Mitcham to 546 millimetres in the west at Keilor.
Rainfall also varies significantly from year to year. For example, Clayton received 1029 millimetres in 1993 and only 486 millimetres in 1997.
Farms and agriculture are often the first to be hit by drought, but eventually everybody feels the impact. It causes environmental and economic damage, often resulting in loss of vegetation and soil erosion, reduced water quality, and increased risks of bushfires and dust storms as well as crop and stock losses.
The main cause of drought in Australia is El Niņo - extensive warming of the central and eastern Pacific Ocean that leads to a major shift in weather patterns across the Pacific.
