Australian east coast rainfall decline related to large scale climate drivers

Abstract

Rainfall on the subtropical east coast of Australia has declined at up to 50 mm per decade since 1970. Wavelet analysis is used to investigate eight station and four station-averaged rainfall distributions along Australia’s subtropical east coast with respect to the El Niño-Southern Oscillation (ENSO), the inter-decadal Pacific oscillation (IPO) and the southern annular mode (SAM). The relationships are examined further using composite atmospheric circulation anomalies. Here we show that the greatest rainfall variability occurs in the 15–30 year periodicity of the 1948–1975 or ‘cool’ phase of the IPO when the subtropical ridge is located sufficiently poleward for anomalous moist onshore airflow to occur together with high ENSO rainfall variability and high, negative phase, SAM variability. Thus, the mid-latitude westerlies are located at their most equatorward position in the Australian region. This maximizes tropospheric interaction of warm, moist tropical air with enhanced local baroclinicity over the east coast, and hence rainfall.