El Nino official: rainfall probabilities low till summer
GroundCover™ Issue: 41
THE SEASONAL outlook remains a cause for concern. Based on the recent pattern of the Southern Oscillation Index (SOI), the probability of receiving or getting above the long-term median rainfall for August to October remains relatively low (30- 50 per cent) across most of the major cropping regions of Australia (see map).
As always when dealing with probabilities, it is essential to consider the additional information that probabilities provide. For example, based on the recent pattern of the SOI, there is only a 38 per cent chance of getting the long-term August-October median rainfall of 155 mm at Wagga Wagga in NSW. Therefore, there is a 62 per cent chance of not getting the long-term August-October median rainfall.
See probabilities in year patterns
Another way of looking at this is that, in approximately one-third of years (3-4 years out of 10) with the current SOI pattern, Wagga Wagga has received its long-term median August-October rainfall. Therefore, in around two thirds of years (6-7 years out of 10) with the current SOI pattern, Wagga Wagga has recorded below-median rainfall for August-October.
For the specific rainfall probabilities for your location, refer to Australian Rainman.
EI Nino pattern official
Currently an EI Nino sea-surface temperature (SST) pattern exists in the central Pacilic Ocean. Normally 'his type of pattern, once developed, will last until the following autumn before breaking down.
Therefore, at this stage, rainfall probabilities would be expected to remain relatively low until early to mid-summer. Rainfall probabilities would then usually rise marginally (across northern cropping regions mainly) due to increasing storm activity. However, as most readers would be aware, storm activity is generally patchy and may provide only limited relief rain.
References to 'weak' or 'strong' EI Nino events can be misleading, as these refer to the magnitude of SST anomalies and not the impacts of an EI Nino. For example, many of the sea temperature anomaly patterns observed in the Pacific during 1991 to 1994 were regarded as 'very weak' EI Nino events, yet the impact on eastern Australian rainfall was considerable.
Each EI Nino unique
It is worth noting that each EI Nino event is unique with respect to rainfall patterns and areas affected by dry conditions. The Bureau of Meteorology has an interesting web site www.bom.gov.au/climate/ahead which provides a good summary of the rainfall patterns that have occurred in previous EI Nino years.
For those who like to follow historical patterns more closely, some of the years in the past that had a 'consistently Near Zero' SOI Phase at the end of July include 2001, 2000, 1991 , 1990, 1983, 1980, 1978, 1971, 1969, 1967,1966 and 1962. What were the rainfall and/or farming conditions like for August-October in your area for those years?
The Long Padaock Internet site www.longpaddock.qld.gov.au has details on the rainfall received in those years.
Our strong advice, as always, remains to closely monitor SOI trends and SST patterns. As an EI Nino event is occurring, we encourage readers to consider what repercussions and/or benefits an EI Nino could mean to their businesses.
For more information, try the DPI climate web site www.dpi.qld.gov.au/climate on which the 'Climate Note' can be found.
Region North, South, West