Monthly Climate Statement for January 2013

The Science Delivery Division of the Department of Science, Information Technology, Innovation and the Arts (DSITIA) considers that there is a 50 to 70 per cent probability of receiving above-median rainfall for the next three-month period (January to March) across most of Queensland. DSITIA also considers that, for the summer as a whole (November 2012 to March 2013), the most likely outcome is for decile 3 to 7 rainfall for much of Queensland. However, the odds shift towards a drier summer for southern parts of Queensland. Read more (PDF, 216K, last updated 09:53AM, 11 January 2013)*

This assessment is based on the current and projected state of the El Niño-Southern Oscillation (ENSO) phenomenon and on factors which alter the impact of ENSO on Queensland rainfall (e.g. the Pacific Decadal Oscillation (PDO)). The outlook for summer as a whole (i.e. November to March) is based on the sea-surface temperature pattern in the tropical and extra-tropical Pacific leading up to summer. The outlook for the January to March period is based on an historical analysis of Queensland rainfall and the behaviour of the Southern Oscillation Index (SOI) over the last two months.

The Queensland Regional Office of the Bureau of Meteorology has indicated in its Tropical Cyclone Seasonal Outlook for the Coral Sea, that a return to near average, or slightly below average, tropical cyclone activity is likely in Queensland this season (November to April). So far this season there has been one tropical cyclone (TC ‘Freda’) in the Coral Sea and the possibility remains of one or more tropical cyclones making land-fall over Queensland this cyclone season.

The SOI, an atmospheric measure of ENSO, currently remains within the ‘ENSO-neutral’ range. Sea-surface temperature anomalies in the central equatorial Pacific also remain near-average and within the ‘ENSO-neutral’ range. The majority of international global climate models and those surveyed by the Bureau of Meteorology (‘ENSO Wrap-Up’ (PDF)* 3 January) suggest that sea-surface temperatures in the tropical Pacific Ocean will remain within the 'ENSO-neutral' range throughout summer and into autumn.

In addition:

• The SOI, a key atmospheric measure of ENSO, fell from a slightly positive value (+3.8) in November, to a negative value (-7.4) in December. However, the 3-month mean SOI value (-0.4) to the end of December was close to average.
• In December, observed sea-surface temperatures in the key Niño 3.4 region were only slightly cooler (-0.1 ºC) than average.

DSITIA has closely monitored sea-surface temperatures in specific regions of the Pacific Ocean since April last year, to provide long-lead rainfall probabilities for the coming summer. These long-lead outlooks are based on the experimental Seasonal Pacific Ocean Temperature Analysis (SPOTA-1) scheme. SPOTA-1 takes into account both ENSO and a more persistent, but related, coupled ocean-atmosphere phenomenon known as the PDO. November’s SPOTA-1 update was the final update for the current 2012/13 summer season (November to March).

Rainfall outlook

There are various approaches used to provide rainfall outlooks. These approaches tend to differ in terms of the components of the climate system that are considered and, for this reason, each approach may convey a different outlook, particularly for specific locations.

DSITIA produces two statistical climate risk assessment schemes. They are:

• the experimental SPOTA-1 scheme, which integrates sea-surface temperature information, including indices of ENSO and the PDO; and
• the SOI Phase scheme, which relies solely on the SOI, an atmospheric measure of ENSO.

The experimental SPOTA-1 scheme provides long-lead probabilities of summer (November to March) rainfall for Queensland from mid-April through to mid-November each year. The final assessment of rainfall probabilities for the 2012/13 summer, based on the experimental SPOTA-1 scheme as at 1 November 2012, indicated that decile 3 to 7 rainfall is most likely for much of Queensland this summer (November to March). However, the odds shift towards a drier summer for southern parts of Queensland. This assessment is based, in part, on an index of March sea-surface temperature anomalies which reflected a ‘cool’ state of the PDO. This assessment also takes into account a monthly ENSO index, based on the sea-surface temperature gradient (west to east) across the South Pacific Convergence Zone (i.e. between eastern Australia and the central Pacific).

DSITIA’s SOI Phase scheme provides probabilities of rainfall for the coming three-month season based on SOI values over the previous two months. The SOI Phase scheme currently indicates that the probability of above-median rainfall across most of Queensland is 50 to 70 per cent for the next three-month period (January to March). This analysis is based on the SOI being in a ‘Rapidly Falling’ phase at the end of December, as discussed further in the Australia's Variable Rainfall poster (PDF, 9.3M, last updated 03:09PM, 29 July 2016)*, or the Department's archive of historical rainfall maps).

Each of the above schemes may have their own particular following. Although such schemes cannot provide outlooks with absolute certainty, users of the information who follow a skilful scheme should benefit from doing so in the long-term. Users should consider the historical track record of any scheme, and such historical information is becoming increasingly available.

DSITIA's Long Paddock website provides the historical archive of SPOTA-1 reports and past commentaries on the SOI Phase scheme. Users should also consider the wide range of information available each month describing the current state of the ocean/climate system, for example the 'ENSO Wrap-Up' (PDF)*.

ENSO influences other climate variables apart from rainfall (e.g. temperature, pan evaporation and vapour pressure). This means that the impact of ENSO on crop or pasture growth can be stronger than on rainfall alone. The impact of ENSO on pasture growth is also dependent upon current pasture condition and soil water status. DSITIA’s AussieGRASS model takes these factors into account in producing seasonal pasture growth probabilities.

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