Seasonal Climate Outlook Message for June to September 2010

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SOI in Consistently Positive Phase Dave McRae QCCCE 15/06/10

Based on a monthly SOI value of plus 12.1 for April and plus 10.5 for May the SOI is in a 'Consistently Positive' phase. The last time the SOI was in a consistently positive phase was in February 2009.

Based on historical rainfall records and a consistently positive SOI phase at the end of May, there is a 40 to 60% chance of getting above median rainfall for June through to the end of August throughout most of Queensland. This is in comparison to last year when there was a lower 20 to 40% chance of getting median rainfall throughout the southern half of the state as well as along the central and northern coastal strip.

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 June to August in the following years since 1950 that have had a Consistently Positive SOI phase at the end of May: 1950, 1956, 1960, 1961, 1963, 1971, 1974, 1975, 1985, 1989 and 2000. Find out your average rainfall for June to August and see how many times rainfall was well below, well above or close to average during June to August in the listed years. For more information on historical rainfall data for your region try Rainman Streamflow.

Based on soil moisture levels and the seasonal climate outlook at the end of May, there is a 40 to 70% chance of getting above median wheat yields throughout most of Queensland's wheat growing regions for the 2010 season. This is a small reduction from the yield outlook based on conditions at the end of April.

The current state wheat outlook shows a forecast median yield at the end of May this year as 1.34 t/ha, which is close to the long-term median of 1.41 t/ha. However, it is very early in the growing season and the situation can change considerably as the season progresses. Useful rainfall totals are still needed in most of the wheat growing regions to ensure widespread planting and crop growth.

The regional wheat crop outlook is based on the assumption of cropping after a summer fallow and does not take into account effects of poor crop nutrition or damage due to pests, diseases, heat or frosts. For more information on the seasonal crop outlook contact Andries Potgieter, DEEDI on (07) 4688 1417.

For those looking for a planting rain opportunity the next passage of the MJO is expected to cross Australian longitudes during mid to late June. The MJO is a band of low air pressure which originates off the east coast of central Africa. It travels eastward across the Indian Ocean and northern Australia roughly every 30 to 60 days. Because of the timing of the MJO the phenomenon is also known as the forty day wave. It can be used as an indicator for the timing of potential rainfall events.

It is worth noting that the impact of the MJO on rainfall varies between the different seasons and location. For example the MJO has a greater influence on rainfall throughout northern Australia during summer and southern Australia during winter. For more information on the MJO go to www.bom.gov.au

According to the latest ENSO Wrap-up from the Bureau of Meteorology, a neutral sea surface and climate pattern currently exists in the equatorial Pacific Ocean. However, there is an increased chance of a La Niña developing during the next couple of months.

This is reflected by the cooling of surface and sub-surface ocean temperatures that is occurring throughout the key ENSO regions of the Pacific. For example sub-surface ocean temperatures along the central equatorial Pacific are around 3 to 4 degrees cooler than normal. At this time of year this is indicative of the potential development of a La Niña. As well, the majority of the surveyed global climate models are indicating the potential development of a La Niña during the next couple of months. Historically, about 40% of El Niño events are followed by a La Niña. For example the 98/99 La Niña developed onto the end of the 97/98 El Niño.

If surface and sub-surface ocean temperatures in the central Pacific continue to cool coupled with ongoing positive SOI values it will increase the likelihood of a La Niña developing. Also of interest is that SST's around eastern and northern Australia are warmer than normal which may assist the inflow of moisture across the Queensland coastline.

As autumn is the key transition time for the development and breakdown of El Niño and La Niña events we recommend monitoring SST and SOI values. Updates on the development of these climate patterns can be found at www.bom.gov.au/climate/enso or www.longpaddock.qld.gov.au or www.cpc.ncep.noaa.gov

The 30day average of the SOI has continued to remain in positive values. As of the 14th June the 30day average of the SOI is plus 5.9.

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.