Monthly Climate Statement for April 2014

The Science Division of the Department of Science, Information Technology, Innovation and the Arts (DSITIA) considers that there is a slightly lower than normal probability of exceeding median rainfall over the next three-month period (April to June) for most of Queensland. This view is based on DSITIA’s analysis of the historical relationship between Queensland rainfall and the Southern Oscillation Index (SOI) which, at this time of year, is quite weak. Furthermore, and with higher confidence, the probability of a wet summer (November to March 2014/15) is very low based on DSITIA’s analysis of the current extra-tropical Pacific Ocean sea surface temperature (SST) pattern. Read more (PDF, 132K, last updated 12:03PM, 16 April 2014)*

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 SST pattern in the Pacific Ocean).

About this long-lead rainfall outlook
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 may provide a guide as to the likely development of an El Niño or La Niña event, it is not until late autumn (May) that the prevailing ENSO pattern (as measured by indices such as the SOI or central equatorial Pacific Ocean SST anomalies) provides a useful basis for seasonal forecasting (i.e. for providing rainfall outlooks for winter, spring or summer).

However, DSITIA scientists have shown that extra-tropical SST anomalies, when measured in specific regions of the Pacific Ocean at this time of year, do provide a useful basis for long-lead forecasting of summer rainfall in Queensland. This information 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. 

The El Niño - Southern Oscillation (ENSO)
It is not until late autumn (May) that the prevailing ENSO pattern (as measured by indices such as the SOI or central equatorial Pacific Ocean SST anomalies) provides a 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 an El Niño or La Niña pattern may develop.  Global climate models also provide a more formal means of assessing this likelihood.

Currently:

  • The SOI, a key-atmospheric measure of ENSO, fell sharply from -1.7 in February to -12.0 in March. The three-month mean SOI value from January to March was -0.8, remaining in the ENSO-neutral range.

  • Observed SST anomalies in the key Niño 3.4 region of the central equatorial Pacific Ocean warmed by 0.4 ºC from February (-0.6 ºC) to March (-0.2 ºC).  As at 5 April, the latest weekly SST anomaly (+0.3 ºC) was slightly above average.

  • Most international global climate models currently indicate that central equatorial Pacific Ocean SSTs should continue to warm in the coming months, with a higher than normal probability of El Niño conditions developing over winter. 

What if an El Niño develops this year?
Currently, close to 80 per cent of Queensland remains drought declared under State Government processes. While patchy rainfall during February and March has brought relief to some drought affected regions, the possibility of an El Niño event developing later this year, and with it the threat of another dry summer for some regions, poses a risk of current drought conditions becoming more protracted. This risk should be factored into decision making and allocation of resources. In this context, it should be noted that:

  • The current long-lead outlook is based solely on extra-tropical Pacific Ocean SST anomalies and does not yet factor in central equatorial Pacific Ocean SST anomalies which, in coming months, will define the state of ENSO (‘El Niño’, ‘La Niña’ or ‘ENSO-neutral’) for 2014/15.
  • Central equatorial Pacific Ocean SST anomalies currently remain ‘ENSO-neutral’, but there is a growing body of evidence pointing to the likely development of an El Niño pattern over winter and spring.
  • Should an El Niño event occur, this coupled oceanic and atmospheric pattern would likely persist over the coming summer (November to March).
  •  An El Niño pattern in the central equatorial Pacific Ocean, coupled with the current extra-tropical Pacific Ocean SST pattern, would support a weak atmospheric Walker Circulation, leading to a high probability of dry conditions (< decile 3 rainfall) for much of Queensland over the coming summer.
  • Irrespective of how ENSO develops, the probability of wet conditions (> decile 7 rainfall) for much of Queensland will remain low over the coming summer.
  • DSITIA’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.
  • Updates to the summer rainfall outlook will be reported in future Monthly Climate Statements.

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Last updated: 30 March 2018
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