SAM and regional rainfall in IPCC AR4 models: Can anthropogenic forcing account for southwest Western Australian winter rainfall reduction?

Wenju Cai*, Tim Cowan

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Winter rainfall over southwest Western Australia (SWWA) has decreased by 20% since the late 1960s. Why has the reduction occurred in the Southern Hemisphere (SH) winter months but not in summer? To what extent is this reduction attributable to anthropogenic forcing and congruent with the Southern Annular Mode (SAM)? Using reanalysis data and the Intergovernmental Panel on Climate Change 4th Assessment Report (IPCC AR4) 20th century model experiments, we show that a SAM-SWWA relationship exists in winter and not in other seasons. An ensemble result from 71 experiments reveals that anthropogenic forcing contributes to about 50% of the observed rainfall decline. Approximately 70% of the observed trend is congruent with the SAM trend, whereas for the models it is 46%. Our result suggests that other forcing factors must be invoked to fully account for the observed rainfall reduction.

Original languageEnglish
Article number24708
Number of pages5
JournalGeophysical Research Letters
Volume33
Issue number24
DOIs
Publication statusPublished - 28 Dec 2006
Externally publishedYes

Keywords

  • HEMISPHERE CLIMATE-CHANGE
  • SOUTHERN ANNULAR MODE
  • CIRCULATION
  • TRENDS
  • VARIABILITY

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