Climate Watch Dave McRae 03/05/05
SOI in 'Rapidly Falling' Phase
Monthly values of the SOI fell from minus 1.3 at the end of March to minus 10.8 at the end of April. Based on a 'Rapidly Falling' SOI phase at the end of April there is a 50 to 80% chance of getting above median rainfall for coastal areas of south east Queensland and the northern tropical coast.
Across the rest of the state, there is generally less than a 50% chance of getting above median rainfall for May to July. Some areas mainly in western Queensland have as low as a 20 to 30% chance of getting above median rainfall for May to July.
For example there is a 70% chance of getting above its May to July median rainfall of 160 mm at Gympie, around a 40% chance of getting above their May to July median rainfall of 170 mm, 85 mm and 75 mm for Mackay, Taroom and Emerald and a 33% chance of getting above its May to July median rainfall of 50 mm at Longreach.
If SOI values remain consistently negative for the rest of this month there will be a further corresponding fall in rainfall probabilities across most of the state. Daily updates on the SOI are available on (07) 46881439. The latest rainfall probability maps for Queensland, Australia and the world are at www.dpi.qld.gov.au/climate or www.longpaddock.qld.gov.au
Many people like to follow the relationship between the SOI and rainfall patterns in more detail. To do that, have a look at what happened in your area over May to July in the following years; 2004, 1997, 1995, 1994, 1993, 1976, 1969, 1967, 1965 and 1952 and compare the rainfall recorded with your 'normal' rainfall for May to July.
Information on what rainfall patterns where like for May to July in those years can be found at www.longpaddock.qld.gov.au or in Australian Rainman.
Similar to rainfall probabilities across most of Queensland, across the rest of Australia there is generally less than a 50% chance of getting above median rainfall for May to July with some regions as low as 20%.
The MJO can currently be found in the western Indian Ocean. It should therefore be due to cross northern Australia in mid May hopefully triggering some useful relief rain. The MJO is a band of low air pressure originating off the east coast of central Africa travelling eastward across the Indian Ocean and northern Australia roughly every 30 to 60 days. Research has shown the MJO to be a useful indicator of the timing of potential rainfall events (but not amounts) across much of Queensland.
For more information on the MJO including its location try www.apsru.gov.au/mjo/ or for more technical blurb try www.bom.gov.au/climate/tropnote/tropnote.shtml
Given the limited useful rain over spring and summer across much of Queenslands winter cropping area, soil moisture status at time of planting this year will be a major constraint. For example, over the 6-months from October 2004 to March 2005, Dalby has recorded 290 mm of rain. This compares to its' long term average for those 6-months of 455 mm, which is a shortfall of 165 mm (or 6.6 inches in the old scale). This in the lowest 10% of rainfall recorded historically at Dalby for this 6-month period.
This lack of useful rain is reflected in the current soil water status in many cropping areas. Looking at the aggregated soil water status in the cropping regions as at 31 March 2005 ranked relative to all years (1901 to 2004 with a fallow simulated from 1 October) most of Queensland has a below average ranking in terms of aggregated soil water status with some regions such as surrounding Dalby being in the lowest 10% and surrounding Roma and Kingaroy in the lowest 20%.
Given the potential for an El Niño to develop later this year, an awareness of current soil water status should be part of management strategies in case the likelihood of usual in crop rainfall decreases. For more information on the current soil moisture status as projected by the APSIM model contact Andries Potgieter from APSRU/DPI&F on (07) 4688 1417.
At present there are a number of 'warning signs' that suggest the development of an El Niño in 2005 is a possibility. According to the Bureau of Meteorology El Niño 'Wrap-Up' the chance of an El Niño this year is estimated at between 30 and 50%, which means that the risk is around double what may normally be expected at this time of year.
The development of an El Niño event in 2005 though is by no means a certainty. El Niño events usually develop in mid to late autumn so there is still some time for conditions in the Pacific to change. As well there is a lack of consensus among the computer models forecasting El Niño events. This is also why March to June is known as the "predictability" barrier: model skill is at its lowest predicting El Niño events across this span of months.
However given the physical evidence our policy remains to recommend a cautious approach when considering the longer-term outlook this year. As part of the DPI&Fs' response to these changes we have initiated an "El Niño watch" and will regularly monitor any developments in the Pacific and pass on this information on as it becomes relevant.
To find out more on conditions in the Pacific try the Bureau of Meteorology "El Niño wrap up" at www.bom.gov.au/climate/enso/ or the International Research Institute for Climate Prediction at http://iri.ldeo.columbia.edu/news/monthlyproduct.html or the US Climate Prediction Centre at www.cpc.ncep.noaa.gov/ For the latest sea surface temperature maps have a look at www.cpc.ncep.noaa.gov/products/ or at www.longpaddock.qld.gov.au/
Because rainfall probabilities and median rainfall levels vary between regions, we recommend referring to Rainman StreamFlow for more specific information for your location. Otherwise call the DPI Call Centre on 13 25 23 or (07) 3404 6999.