THE persistence and severity of the drought in the Murray-Darling Basin has been described as "unprecedented" after late summer inflows to the river system fell to a 117-year low. The "bleak'' outlook for next three months was adding to the grim news, the Murray-Darling Basin Authority said. Irrigation water for Australia's food bowl will be dependent almost entirely on rainfall as basin states hold back water for critical human needs. "The persistence and severity of this drought, particularly over the past three years, is unprecedented,'' authority chief executive Rob Freeman said as he delivered the basin's latest drought update.