Causes of the Major Australian Floods: La Niña, Atmospheric Instability, and Saturated Catchments

Recent widespread flooding in Australia resulted from a convergence of three major factors:

1. La Niña Event

A strong La Niña—cooler-than-average sea surface temperatures in the central/eastern tropical Pacific—drove increased rainfall across eastern Australia. This event was one of the strongest on record and persisted into late 2022.

2. Upper Atmospheric Instability

Unusually unstable air over Australia spawned low-pressure systems and heavy rain. Contributing factors included:

• An exceptionally strong jet stream
• Slow-moving cut-off lows
• Upper-level troughs extending through the atmosphere

3. Saturated Catchments

Months of prior rainfall left soils, vegetation, and ground cover unable to absorb more water. Even moderate rain caused immediate runoff and flooding in New South Wales, Queensland, and Victoria.

The combination led to loss of life, widespread damage, and major disruption.