Climate Watch Dave McRae Qld Climate Change Centre of Excellence 3rd September 2007
Moderate improvement in outlook.
Dave McRae, QCCCE, 7th September 2007.
Compared to this time last year, there has been an improvement in the seasonal outlook for Queensland.
Based on a "Rapidly Rising" SOI phase at the end of August there is a 40 to 70% chance of getting median rainfall for September to November with the highest rainfall probabilities (60 to 70%) being found throughout central Queensland. The exception is for the extreme far south west of the state where there is a lower 20 to 40% chance of getting median rainfall.
While these probabilities may not be as high as some would like, there is a reasonable chance of getting some useful rainfall. For example during September to November Kingaroy has a 70% chance of getting at least 140 mm, Jondaryan has a 70% chance of getting at least 120 mm, Roma has a 70% chance of getting at least 100 mm, Emerald has a 70% chance of getting at least 90 mm and St George has a 70% chance of getting at least 60 mm.
When using any probability based forecast you should remember that the probability or percent chance of something occurring is just that - a probability. 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 more on rainfall probabilities for your location refer to Rainman StreamFlow.
To follow the relationship between the SOI and rainfall patterns in more detail have a look at what happened in your area during September to November in the following years: 1904, 1906, 1908, 1928, 1937, 1942, 1943, 1944, 1945, 1954, 1962, 1964, 1966, 1967, 1970, 1971, 1983, 1985 and 2000. Find out your average rainfall for September to November and how many times rainfall was well below, well above or close to average during September to November during those years.
As for the rest of the spring and summer outlook it would help if the SOI went into a 'Consistently Positive' SOI phase and remained there for a number of months. The last time the SOI was in a "Consistently Positive" phase for more than one month was from September 2000 to March 2001.
For those interested daily updates on the SOI are available on (07) 46881439 or at www.longpaddock.qld.gov.au You can also receive a text message with the latest SOI values sent to your mobile phone. To subscribe to this free service call (07) 46881459.
There is another phase of the MJO apparently developing in the Indian Ocean. While still only weak if it continues to develop we could see the next passage of the MJO in 15 to 20 days (late September).
At this time of year the MJO is typically associated with monsoonal bursts over India and eastern Asia, and tropical storms, cyclones and typhoons in the South China Sea and northern western Pacific Ocean. We would usually expect to see a greater impact on our rainfall (northern Australia) as we enter spring and summer.
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/
According to the Bureau of Meteorology in their "ENSO Wrap-up" available at www.bom.gov.au/climate/enso/ the past three months have seen conditions in the Pacific Ocean fluctuate. Since late July though, there has been a gradual strengthening of La Nina indicators.
For example, eastern equatorial Pacific Ocean temperatures have continued to cool, trade winds have been mostly close to normal and the SOI has had a rise in value since July. However for a La Nina to fully develop there needs to be further changes in our climate indicators. This would include consistently stronger than average south east trade winds, positive SOI values (+7 or higher for several months) and further cooling of the eastern equatorial Pacific Ocean.
For our general seasonal outlook it would also be helpful if ocean temperatures off the eastern and northern Australian coastline became warmer than normal.
While the climate models the Bureau have used did predict an increased chance of a La Nina developing, they also suggested the event is likely to be moderate and persist for only a few months. It is also now late in the year for a La Nina to develop as historically most La Nina events were established before the end of winter.
When I'm asked about how climate information can be used I refer to a couple of key points developed from client feedback. Key points include 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) program has an interesting site which highlights some case studies on how producers and businesses have used climate and weather information in their decision-making processes at http://www.managingclimate.gov.au/.