Drought in Australia is defined by the Australian Bureau of Meteorology as rainfall over period greater than three-months being in the lowest decile of what has been recorded for that region in the past. This definition takes into account that drought is a relative term and rainfall deficiencies need to be compared to typical rainfall patterns including seasonal variations. Specifically, drought in Australia is defined in relation to a rainfall deficiency of pastoral leases and is determined by decile analysis applied to a certain area. Note that this definition uses rainfall only because long-term records are widely available across most of Australia. However, it does not take into account other variables that might be important for establishing surface water balance, such as evaporation and condensation.

The Darling River is the third-longest river in Australia, measuring 1,472 kilometres (915 mi) from its source in northern New South Wales to its confluence with the Murray River at Wentworth. Including its longest contiguous tributaries it is 2,844 km (1,767 mi) long, making it the longest river system in Australia. The Darling River is the outback's most famous waterway.