Abstract
Principal component analysis with varimax rotation was used to identify major spatial patterns of New South Wales (eastern Australia) district rainfalls in each season. Four spatial patterns of the principal components of rainfall, each dominant in a subregion of the State, were evident. Plots of correlation coefficients between the amplitudes of the spatial patterns and the Southern Oscillation Index (SOI) revealed temporal instability of the relationships. Results show that the relationships have changed dramatically with time and that they have changed differently from region to region. Over the 55 years (1933β1987) for which data were available, in some regions the correlation coefficients changed from being highly significant, to showing no relationship, in others the reverse was the case, and in some very little change occurred. This meant that over time the spatial pattern of relationships for a given season also changed quite dramatically.
These findings have profound implications for studies based on assumptions of stationarity of geophysical phenomena and relationships and suggest there are other, as yet unrecognized, phenomena influencing rainfall in the longβterm.