Frost in northeast Australia: Trends and influences of phases of the Southern Oscillation

Abstract

A forecast method capable of estimating date of last frost and number of frosts per season in northeastern Australia some months in advance is described. Forecast “skill” is achieved using either Southern Oscillation index (SOI) patterns (phases) during the previous austral autumn or a linear discriminant approach and the SOI. When applying these systems, it is possible to provide significantly different probability distributions of day of last frost and number of frosts, depending on the SOI patterns observed during the previous season. An analysis of the time series of frost frequency and date of last frost suggests an apparent warming trend in the data, resulting in a trend toward earlier dates of last frost and fewer numbers of frosts at many of the locations analyzed. The beneficial implications of the proposed frost forecasting system for enterprises such as winter agriculture in the region are believed to be significant.