The Science Division of the Department of Science, Information Technology, Innovation and the Arts (DSITIA) considers that, for most of Queensland, there is a slightly lower than normal probability of exceeding median rainfall over the next three-month period (February to April). This view is based on an analysis of the historical relationship between Queensland rainfall and the Southern Oscillation Index (SOI) Read more (PDF, 428K, last updated 02:29PM, 27 February 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 climate outlooks (including outlooks for El Niño or La Niña development) are least reliable – a period known as the ‘autumn predictability gap’.
Although definitions of ‘El Niño’ vary, DSITIA’s ‘Australia’s Variable Rainfall’ poster (PDF, 9.3M, last updated 03:09PM, 29 July 2016)* stipulates a six-month period, ending in any month between November and March, having an average SOI value less than -6.0. Based on the Bureau of Meteorology’s calculation of the SOI, the six-month average SOI values were -6.9, -7.6 and -8.4 in November, December and January respectively, in each case meeting the above criterion for an El Niño event. Likewise, since November, warm sea-surface temperature anomalies in the central equatorial Pacific have met the World Meteorological Organisation’s operational ‘consensus’ definition of El Niño (three-month anomalies at or above +0.5 ºC).
Rainfall over the last three-month period (November to January) was mostly near-average or above-average across Queensland except for Cape York where three-month totals were extremely low in some parts (see map below).
Summer rainfall outlook (Nov-Mar 2014/15)
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 (November to March) rainfall in Queensland. The accuracy of this outlook increases as the evolving ENSO-related SST pattern is also taken into account from June through 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. The outlook was strongly related to the extra-tropical SST pattern measured in March last year, which was indicative of a warm phase of the Inter-decadal Pacific Oscillation.
Seasonal rainfall outlook (Feb-Apr 2015)
An analysis of rainfall probabilities as at 1 February based on the SOI being in a ‘Consistently Negative’ phase indicates, for most of Queensland, a slightly below normal probability of exceeding median rainfall over the next three-month period (February to April - see map below).
Furthermore, it should be noted that:
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