This investigation is an extension of earlier work on rainfall patterns in eastern Australia. Using district averages rather than rainfall data for individual cities or towns, further evidence is provided for cyclic variations in precipitation with periods of 18–19, 10–11 and 6–7 years. Results from various regional areas in western Queensland and western New South Wales differ from those found further south in Victoria, and connections are suggested between El Niño/southern oscillation events and the incidence of drought in these two separate areas. Such findings are consistent with ecological aspects of the quasi-periodic occurrence of bushfire seasons as observed in both Victorian eucalypt forests after prolonged drought, or after intermittent widespread rains in the semi-arid Mallee rangelands of western New South Wales.
The ~19-year cycles may be at least partly a reflection of solar and lunar tidal components and the ~11-year cycles (connected with the Sunspot cycle) could be the result of absorption of short wavelength solar emissions in the stratosphere and resultant photochemical events magnified to produce sea surface temperature changes. The ~19-year cycles are apparently associated with either increased or decreased rainfall, and such connections appear to reverse in parts of Australia about every 100 years. These reversals have been associated with major droughts at the end of the 19th and 20th centuries.
