SOI in Rising Phase Dave McRae Qld Climate Change Centre of Excellence 5th July 2007
Based on the rise in monthly SOI value from minus 2.5 for May to plus 5.4 for June the SOI is now in a 'Rapidly Rising' phase. With the rise in value of the SOI most of Queensland has a 50 to 70% chance of getting median rainfall for July through to the end of September. For example Roma has a 70% chance of getting above its July to September median rainfall of 75 mm, Miles and Emerald have a 65% chance of getting above their July to September median rainfall of 85 mm and 55 mm respectively and Gympie has a 65% chance of getting above its July to September median rainfall of 115 mm.
The exception is for parts of the central north where there is a lower 40 to 50% chance of getting median rainfall.
When using a climate forecast you should remember that the probability or percent chance of something occurring is just that - a probability. For example if there is a 70% chance of recording more than 100 mm there is also a 30% chance of recording less than 100 mm i.e. 70-30; 30-70. It does not mean that you will get 70% more than 100 mm or 100 mm plus another 70%.
For those who like to follow the relationship between the SOI and rainfall patterns in more detail have a look at what happened in your area during July to September in the following years since 1920; 1920, 1922, 1929, 1934, 1945, 1947, 1950, 1951, 1953, 1957, 1958, 1966, 1967, 1970, 1973, 1986, 1996, 1998, 2001 and 2005. Find out your average rainfall for July to September and see how many times rainfall was well below, well above or close to average during July to September in the listed years.
It will be very interesting to see if the recent upward trend of the SOI is maintained over coming weeks or is just a short-term fluctuation. As stated regularly, for there to be an overall improvement in seasonal conditions across the state, it would help if the SOI went into positive values for a couple of months at least. The last time the SOI was in a "Consistently Positive" phase for more than one month was from September 2000 to March 2001.
Similar to Queensland there has been a general rise in rainfall probabilities across Australia. Currently there is a 50 to 70% chance of getting median rainfall during July to September. The main exception is for Western Australia where there is a 40 to 50% chance of getting medina rainfall during July to September.
In the latest El Nino wrap-up available at www.bom.gov.au the Bureau of Meteorology state that there remains an increased chance of a La Niña developing over the next 1 to 3 months, (although at this stage it has not occurred) and only a very low risk of a return to El Niño conditions in 2007.
The basis for the increased chance of a La Niña developing is computer model output, positive SOI values, stronger than normal south east trade winds below average cloud cover across the equatorial Pacific.
In very general terms a La Nina event has the potential in increase rainfall over Australia, Papua New Guinea, Indonesia, New Zealand, India, Thailand, southern Africa, the Sahel and Central America. This type of pattern has the potential to reduce rainfall over parts of Europe, the United States and parts of Central Asia and South America.
The generally useful rainfall that was recorded during mid June coincided with the passage of the MJO. Based on its current timing the MJO is next expected in very late July or early August. 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). For more information try www.apsru.gov.au/mjo/
When I'm asked about how climate and weather information can be used I refer to a couple of key points developed from client feedback. When using any of the number of weather internet sites available now, we strongly recommend that you have look at a number of them to develop a consensus view or find one that you believe works well for your area and stick with that. Do not troll through them all to find the one that says what you want to get and go with that.
Management decisions should never be based entirely on one factor such as a climate or weather forecast. As always, everything that could impact of the outcome of a decision (soil moisture, pasture type/availability, crop and commodity prices, machinery, finance, costs etc) should be considered. For example, the level of soil moisture at planting is the major factor influencing crop yield or success.
A simple cost benefit analysis when making a major decision may also be useful. For example what will I gain if I get the desired outcome? What will I lose (sleep, money, family relationships) if I do not get the desired outcome and what other options (risk neutral) are there? A PART OF THIS PROCESS IS TO HELP MANAGERS TO BE CAREFUL NOT TO CHANGE FROM NORMAL RISK MANAGEMENT TO HIGH LEVEL RISK TAKING BASED ON A PIECE OF INFORMATION (SUCH AS A CLIMATE FORECAST).
The 'Climate Variability In Agriculture' (CVAP) research and development program highlights some case studies on how producers and businesses have used (to varying levels of success) climate and weather information in their decision-making processes. An interesting site www.managingclimate.gov.au/