The Science Division of the Department of Science, Information Technology and Innovation (DSITI) considers that, for most of Queensland, there is currently an equal likelihood of rainfall being above or below median over the next three-month period (May to July). This view is based on an analysis of the historical relationship between Queensland rainfall and the Southern Oscillation Index (SOI) which, at this time of year, is quite weak. DSITI’s analysis of the March sea surface temperature (SST) pattern in the South-West Pacific indicates that the probability of exceeding median summer (November to March 2015/16) rainfall is currently slightly higher than normal for most of Queensland. Read more (PDF, 278K, last updated 04:40PM, 14 May 2015)*
DSITI’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 SST pattern in the Pacific Ocean).
Rainfall for the last three-month period (February to April) was extremely low (less than the 10th percentile) across extensive areas of northern and western Queensland. However, parts of the state (mainly in the south east) recorded above median rainfall.
More than 80 per cent of Queensland is now drought declared under state government processes. This is an increase since 1 April 2015 (75 per cent).
The El Niño - Southern Oscillation (ENSO)
At this time of year (known as the ‘autumn predictability gap’), the ENSO pattern tends to change very rapidly. Although the change in the ENSO pattern over autumn (March to May) may provide a guide as to the likely development of El Niño or La Niña events, it is not until June that the prevailing ENSO pattern (as measured by indices such as the SOI or central equatorial Pacific Ocean SST anomalies) begins to provide a more useful basis for seasonal forecasting (i.e. for providing rainfall outlooks for winter, spring or summer). However, it is useful to monitor the change in ENSO indices over this time of year as a guide as to whether, for example, the current El Niño pattern may further develop. Global climate models also provide a more formal means of assessing this likelihood.
Seasonal rainfall outlook (May-Jul 2015)
An analysis of rainfall probabilities as at 1 May, based on the SOI being in a ‘Consistently Negative’ phase, indicates for most of Queensland a 40 to 60 per cent probability of exceeding median rainfall over the next three-month period (May to July, see map below). This means that there is an equal likelihood of rainfall being either above or below median over the next three-month period (May to July).
Summer rainfall outlook (Nov-Mar 2015/16)
DSITI 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 May through to October. 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 DSITI scientists for over a decade.
As at 1 April 2015, DSITI’s initial long-lead outlook for the coming summer (November to March 2015/16) indicated a slightly higher than normal probability of exceeding median rainfall for most of Queensland, due to warmer than average sea surface temperatures in the extra-tropical South-West Pacific (east of Australia).However, this outlook may change if the current El Niño event intensifies and the extra-tropical warmth in the South-West Pacific does not persist.
DSITI’s long-lead outlook for summer rainfall will be reassessed in June, and then updated monthly until November, by factoring in the most recent ENSO conditions.
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