Seasonal Climate Outlook Message for April to July 2006

The bottom line

How long will the mini La Niña last? 04/04/06

There has been increasing media coverage of the mini La Niña sea surface temperature pattern currently in the central Pacific. So what impact on rainfall across eastern Australia will it have and how long will it last? Probably not much and not long.

The mini La Niña has developed so late in the season that it will probably have not much impact on our expected rainfall. It is also unlikely to persist past autumn into winter and spring when the positive impacts for rainfall across Queensland would be greatest.

For example of 12 surveyed reputable ocean or coupled ocean/atmosphere forecast models, 11 are showing a continuing neutral SST pattern through to July and one is showing the development of an El Nino SST pattern. For more on conditions in the Pacific try the Bureau of Meteorology at www.bom.gov.au/climate/ahead/

It should be noted though that April to June is the period when the ability to predict future ENSO conditions is at its lowest. So for those looking out to the longer term (>6 months) autumn is THE key time to watch for developing trends in both the SOI and sea surface temperatures (SST).

D. McRae Qld DPI&F

The full story

Climate Watch Dave McRae Qld Dept of Primary Industries and Fisheries 03/04/06

SOI Rises Again

The monthly value of the SOI rose from minus 0.6 for February to plus 11.4 for March. Part of the reason for the rise in monthly value of the SOI was the redevelopment of an active monsoonal trough across northern Australia and cyclone activity.

Based on this shift in monthly value, the SOI in now in a 'Rapidly Rising' phase. Using historical rainfall records for April to June and a Rising SOI phase at the end of March there is a 40 to 60% chance of getting above median rainfall across most of Queensland.

It will be interesting to see if the SOI can maintain its current positive values over the next few months or drops back to near zero or negative values as has been the case over the last four years. Sustained positive monthly SOI values would help provide the basis for a widespread improvement in seasonal conditions.

There has been increasing media coverage of the mini La Niña sea surface temperature pattern currently in the central Pacific. So what impact on rainfall across eastern Australia will it have and how long will it last? Probably not much and not long. The mini La Niña has developed so late in the season that it will probably have not much impact on our expected rainfall. It is also unlikely to persist past autumn into winter and spring when the positive impacts for rainfall across Queensland would be greatest.

For example of 12 surveyed reputable ocean or coupled ocean/atmosphere forecast models, 11 are showing a continuing neutral SST pattern through to July and one is showing the development of an El Nino SST pattern. For more on conditions in the Pacific try the Bureau of Meteorology at www.bom.gov.au/climate/ahead/ It should be noted though that April to June is the period when the ability to predict future ENSO conditions is at its lowest.

So for those looking out to the long term (>6 months) autumn is the key time to watch for developing trends in both the SOI and sea surface temperatures (SST). For more information try the DPI&F 'Climate Note', a summary of current climate conditions which is distributed by e-mail once to twice a month. To subscribe or for more information contact 132523.

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 April to June in the following years since 1940 that have had a 'Rapidly Rising' SOI phase at the end of March; 2005, 1990, 1988, 1986, 1973, 1970, 1969, 1964, 1960, 1959, 1952 and 1947.

For example at Emerald well below median rainfall for April to June in those years was recorded three times, close to median rainfall was recorded five times and above median rainfall was five times. At Gatton well below median rainfall for April to June in those years was recorded three times, close to median rainfall was recorded five times and above median rainfall was recorded five times. More information on what rainfall patterns where like for April to June in those years can be found in Rainman StreamFlow.

Generally there is less than a 50% chance of getting above median rainfall during April to June across the other states of Australia. For more information on rainfall probabilities at your specific location refer to Rainman StreamFlow. This forecast does not indicate the potential distribution or expected timing of rainfall over this period. The forecast is for a full three-month period and does not suggest that any expected rain will fall evenly across these three months.

As with any probability based forecast system it is important to consider the opposite aspect. For example, Cooyar has an 80% chance of getting at least 60 mm during April to June. This also means that there is a 20% chance of NOT getting at least 60 mm during April to June. Another way of looking at this is that in eight times out of ten with the current SOI pattern, Cooyar has received more than 60 mm during April to June. Therefore two times out of ten with the current SOI pattern, Cooyar has received less than 60 mm over April to June.

When looking at rainfall probabilities for your area it may make it easier to think of them in these terms:

1. Probabilities above 80% highlight a high chance 2. Probabilities above 60% highlight an above average chance 3. Probabilities below 40% highlight a below average chance 4. Probabilities below 20% have a low chance

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).

Forecasts as well do not always give a strong signal as to likely conditions for your location. In assessing climate forecasts as a management tool consider the level of signal for the key decision times in your location. Rainman StreamFlow is a useful tool for this.

An interesting site http://www.managingclimate.gov.au/ from the 'Climate Variability In Agriculture' (CVAP) research and development program is well worth looking at. It 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.