The Science Division of the Department of Science, Information Technology, Innovation and the Arts (DSITIA) considers that the current borderline El Niño conditions and warm phase of the Inter-decadal Pacific Oscillation (IPO) increases the probability of below-median rainfall over most of Queensland for the remainder of this summer (January to March). Read more (PDF, 399K, last updated 10:49AM, 14 January 2015)*
DSITIA’s rainfall outlooks for Queensland are 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 (i.e. the more slowly changing extra-tropical sea surface temperature (SST) pattern in the Pacific Ocean).
At this time of year the prevailing ENSO pattern (as measured by indices such as the Southern Oscillation Index (SOI) or central equatorial Pacific Ocean SST anomalies) offers a useful basis for providing seasonal outlooks for summer.
Monthly values of the SOI have been negative since June, averaging -7.4 for the last six-month period since July and -7.9 for the last three-month period since October. Monthly SST anomalies in the central equatorial Pacific have been warmer than average since April this year and remain close to El Niño thresholds. The six-month average SST anomaly since July was +0.5 ºC and the three-month average since October was +0.7 ºC.
Although October and November rainfall was well-below average to extremely low in many drought affected parts of the state, high rainfall was recorded in parts of Central Queensland during December.
Borderline El Niño
Although the definition of ‘El Niño’ varies between agencies, DSITIA considers current conditions to be bordering on El Niño. However it is immaterial to the rainfall outlooks presented on the following page, as to whether or not an ‘El Niño event’ is eventually declared by national and/or international agencies.
Outlook for summer rainfall
DSITIA scientists have shown that extra-tropical SST anomalies, when measured in specific regions of the Pacific Ocean in March each year, provide a useful basis for long-lead forecasting of summer rainfall in Queensland. This outlook can be modified, with increasing accuracy, as the monthly ENSO-related SST pattern is also taken into account from June to November.
This understanding has been incorporated in an experimental system known as SPOTA-1 (Seasonal Pacific Ocean Temperature Analysis version 1), which has been operationally evaluated by DSITIA scientists for over a decade. As at 1 November, DSITIA’s final long-lead outlook for the whole of summer (November to March 2014/15) indicated a higher than normal probability of below-median to well below-median rainfall for most of Queensland and, conversely, a low probability of widespread drought-breaking rainfall. This outlook is strongly related to the extra-tropical SST pattern measured in March this year, which is indicative of a warm phase of the IPO.
Furthermore, an analysis of rainfall probabilities as at 1 January based on the SOI being in a ‘Consistently Negative’ phase indicates that, for most of Queensland, the probability of exceeding median rainfall over the remainder of summer (January to March) is low.
In summary, it should be noted that:
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