Weakening El Niño, but check regional climate history by Dave McRae DPI Centre for Climate Applications

Monthly SST Anomaly (°C) February 2003

AS READERS would be aware, an El Niño sea temperature pattern has been the dominant feature of the Australian climate over the last 9 to 12 months. The 2002-03 El Niño event will be remembered for its negative impact not only on rainfall patterns but also on expected crop yields and animal production Australia-wide

At the time of writing (March), the El Niño pattern (warm sea temperature anomalies) could still be found in the central Pacific Ocean.

The map highlights the February sea surface temperature pattern. Areas coloured red and yellow are warmer than normal and areas coloured blue are cooler then normal. As can be seen on the map, an El Niño pattern (red and yellow areas) still persists in the central Pacific. Current sea temperature maps can be found at www.long paddock.qld.gov.au

Quick or slow end to El Niño?

There is increasing optimism that this pattern is starting to break down. While this is good news, it's worth remembering that there remains around a 30 per cent chance of El Niño regeneration in some form past autumn.

Normally this would not be considered a high risk. However, given the current shortage in many areas of available agistment, fodder, surface water, irrigation water and lack of crop planting opportunities etc, it certainly should be taken into account in terms of any longer-term risk management strategy.

Even if this pattern breaks down at the end of autumn, conditions may not improve in all areas for several months, as unfortunately the breakdown of major drought events rarely occurs evenly across all affected areas.

Previous El Niño events include autumn 1902 to autumn 1903, 1905-06, 1911-12, 1913-14, 1914-15, 1919-20, 1925-26, 1940-41, 1941-42, 1946-47, 1951-52, 1957-58, 1964-65, 1965-66, 1969-70, 1972-73, 1977-78, 1982-83, 1987-88, 1991-92, 1993-94,1994-95 and 1997-98. For planning purposes it may be helpful to find out when conditions improved in your area following these events.

Check regional patterns post-El Niño

In many areas, the winters following an El Niño event provide the best chance for average to above-average winter rain and potential high winter crop yields. Examples of this pattern include 1978, 1983,1988 and 1998 (although 1998 was actually too wet in many areas, with resultant crop diseases).

Autumn 1992 is a good example of a partial breakdown in an El Niño pattern when it reformed in early winter (not necessarily as a classic El Niño but something close to it). Some relief rain followed by a fairly dry winter usually characterises this pattern. It is comparatively rare, but this type of pattern occurred previously in 1992, 1993, 1994, 1940, 1941, 1912, 1913, 1914 and 1915.

The Climate Prediction Centre (CPC) in the United States (www.cpc.ncep. noaa.gov/) and the International Research Institute (http://iri.ldeo.columbia.edu/) are a good source of information on El Niño development.

For those interested, ocean and coupled ocean/atmosphere forecast models (GCMs) give an indication as to likely ENSO development nine months ahead. Of the 10 models that forecast to July 2003, seven indicate the development of neutral sea temperature patterns, two indicate an ongoing El Niño (or warm) sea temperature pattern and one indicates the potential development of a La Nina (or cold) sea temperature pattern.

Of the seven models that forecast to October 2003, six indicate the development of a neutral sea temperature pattern, while one indicates the development of a La Nina sea temperature pattern.

GCM outputs should be viewed cautiously at this time of year, as we are approaching the so-called 'predictability barrier' between March and June. More details can be found at www.bom.gov.au/ climate/ahead/ENSO-summary.shtml

For the latest and most up-to-date information on the seasonal outlook for your location, try the 'Climate Note' at www.dpi.qld.gov.au/climate