La Nina & the Australian Floods

The massive flooding across eastern Australia, which began in November, has been associated with the La Nina phenomenon, which tends to peak every 3 to 7 years. Produced by high pressure over the eastern Pacific and low pressure over the western Pacific, this weather pattern results in strong Pacific trade winds, which bring relatively warm ocean waters to the southeast coast of Asia and the northeast coast of Australia. This spawns strong cyclones and excessive rainfall in these areas, generally during an autumn to autumn cycle in the Southern Hemisphere.

Coinciding with a high Southern Oscillation Index, which measures the seasonal variance of sea surface pressure between Tahiti and Darwin, La Nina episodes trigger excessive precipitation across northern and eastern Australia. This year's flooding has been especially severe, disrupting transportation, stranding inland towns, inundating coal mines and wiping out much of the region's wheat crop. The Great Barrier Reef may also be affected, as plumes from the rivers of northeast Australia sweep particulates and pollutants toward that fragile ecosystem.

The current Australian flooding may prove to be the worst in recorded history. Unfortunately, some climatologists project that the La Nina and the opposite El Nino patterns will intensify with the advance of global warming. For eastern Australia, that could mean an alternating pattern of severe floods and prolonged drought.