Quick questions on Millennium Drought and the water cycle: HSC Geography Biophysical Interactions

El Nino-Southern Oscillation (ENSO). Four El Nino events between 1997 and 2009 (1997-98, 2002-03, 2004-05, 2006-07, 2009-10) suppressed eastern Australian rainfall. El Nino conditions push warm surface water eastward across the Pacific, reducing evaporation and rainfall over Australia.

Rainfall. Murray-Darling Basin rainfall averaged 466 mm during 2001-2009 against a long-term average of 530 mm (12 percent below).

Wetlands. The Macquarie Marshes (RAMSAR-listed) lost an estimated 40-50 percent of its core wetland area. Coorong salinity rose above marine levels (over 200 g/L in places, three times seawater), killing fish and aquatic plants.

Agriculture. Murray-Darling agricultural production fell by around $1 billion per year. Rice production fell by 99 percent at the trough; dairy in northern Victoria lost roughly 30 percent of capacity.

Four El Nino events between 1997 and 2009 (1997-98, 2002-03, 2004-05, 2006-07, 2009-10) suppressed eastern Australian rainfall. El Nino conditions push warm surface water eastward across the Pacific, reducing evaporation and rainfall over Australia.

Positive IOD phases (warm western Indian Ocean) in 1997, 2006, 2007, 2008 reduced moisture transport to southern Australia from the Indian Ocean side.

Negative SAM phases brought drying westerly winds further north in winter, reducing winter rainfall in the Murray-Darling.

The Bureau of Meteorology has attributed a portion of the drought severity to anthropogenic warming. The 2010-2019 decade was Australia's warmest on record.

Murray-Darling Basin rainfall averaged 466 mm during 2001-2009 against a long-term average of 530 mm (12 percent below).

Inflows into the Murray system fell by around 65 percent during 2001-2009. Total inflow to the Murray-Darling in 2006-07 was around 800 GL against a long-term average of 9,500 GL.

The Murray Mouth closed periodically from 2002 to 2010, sustained only by dredging. The Lower Lakes (Alexandrina and Albert) dropped below sea level for the first time in recorded history, exposing acid sulfate soils.

Groundwater extraction increased as surface water disappeared. Levels in the Great Artesian Basin and the Goulburn-Murray groundwater system fell, and recovery has been slow.

The Macquarie Marshes (RAMSAR-listed) lost an estimated 40-50 percent of its core wetland area. Coorong salinity rose above marine levels (over 200 g/L in places, three times seawater), killing fish and aquatic plants.

Up to 75 percent of river red gum forests along the Murray showed canopy decline.

Murray cod and golden perch populations collapsed in the lower Darling. Fish kills at Menindee Lakes in 2018-19 (over 1 million fish) followed two decades of altered flow regimes.