Decadal scale relationship between indices of climate variability and Australian rainfall

Decadal scale relationship between indices of climate variability and Australian rainfall

Australia’s climate is characterised by high intra and inter annual; decadal and longer term variability of such elements as temperature and rainfall. Various drivers are responsible for variability at these tempos, for example: the Madden Julian Oscillation, El Niño Southern
Oscillation (ENSO) and Pacific Decadal Oscillation respectively. Rainfall variability dramatically impacts on the nation’s economy and efforts to understand it can assist in drought mitigation and safeguard farming and infrastructure from its associated weather extrema.

1. A Pearson’s 'r' technique incorporating Lanczos filtering to track the correlation of 24 globally diverse, monthly climate indices with spatially resolved Australian summer rainfall (December, January and February) for the
11 decades from 1900 – 2008.

2. Relationship was scored (ranked) in terms of four criteria:
a. population variance was assessed as non-biased indicator,
b. interdecadal variance change,
c. the area of significant correlation
d. and the temporal stability of a significant correlation pattern.

3. Finally each index was ranked by its overall score.

The highest scoring index was the BEST index a combination of the Southern Oscillation Index (SOI) and the Niño3.4 Index.

A novel aspect of this study is the use of Simple Ocean Data Analysis (SODA) datasets where necessary to overcome poor availability of ocean climate data prior to the satellite age. High correlations were from some of the oceanic warm pool (WP) indices that captured the
size/volume of the WP regions adjacent to the Australian continent, either in terms of ocean heat content, or a Sea Surface Temperature metric. A WP index based on the Pacific Warm Pool (PWP) region achieved a much higher variance than the Southern Oscillation Index (SOI) and the Warm Water Volume West (WWV_W) index achieved equal second rank in
score. There are no pre-existent studies that correlate WP indices with Australian decadal rainfall.

A large variety of climate indices were also correlated against South East Queensland rainfall where an unexplained reduction in summer rainfall had been observed since 1980. The de facto El Niño index, Niño3.4 and SOI fared worse than they do for other regions of Australia. A WP index based on the Warm Water Volume East (WWV_E) was by far the highest scoring index. Derived ENSO indices also scored well.

The thesis expands on the existing literature and a subsequent paper will highlight the significance of WP indices and further investigations and applications.