A preconditioned event occurs when the impact of a hazard is exacerbated by pre-existing conditions. For example, in March 2021, large parts of New South Wales experienced extensive rainfall that led to widespread flooding. The impact of the rainfall (the extent and severity of the flooding) was exacerbated by the preconditioning of river catchments. The catchments had received above average rainfall caused by La Niña conditions during the previous summer, filling water reservoirs and saturating soils. As such the additional water could not be absorbed by the system and this resulted in significant flooding.