Seasonal Climate Outlook Message for January to April 2011

Commentary on rainfall probabilities based on 'phases' of the SOI

The extremely high rainfall (PDF)* during December, which contributed to major flooding throughout much of Queensland, occurred during a Consistently Positive phase of the SOI, which increased from +16.3 in November to +26.4 in December.

Based on previous years when the SOI has been in a 'Consistently Positive' phase at the end of December, there is a 50 to 70% probability that rainfall during January to March will be above the long-term median throughout much of Queensland. The exception is the coastal region running from the Hervey Bay district through to north of Rockhampton where the probability of having above median January to March rainfall exceeds 70%.

In assessing this information, it is worth considering other years with a Consistently Positive SOI phase at the end of December. Other years since 1950 that have had the same SOI phase at the end of December include: 1950, 1955, 1959, 1960, 1961, 1970, 1973, 1975, 1988, 1998, 1999, 2000, 2007 and 2008.

When using a climate forecast you should remember that the probability, or percent chance, of something occurring is just that – a probability. For example, if there is a 70% probability of above-median rainfall, then there is also a 30% chance of below median rainfall. It does not mean that rainfall will be 70% more than the median.

From a risk management point of view, the SOI-Phase system highlights the potential for further significant rainfall this summer.  While this does not necessarily equate to ongoing flooding, it is a risk that should be monitored.

Users are advised not to rely on a single climate outlook alone and should consider the range of climate risk assessment information that is available. Further seasonal climate outlook information is available at www.longpaddock.qld.gov.au and www.bom.gov.au 

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