El Nino pattern breaks down Dave McRae 02/03/07
In the latest El Nino wrap-up available at www.bom.gov.au the Bureau of Meteorology states that 2006/2007 El Nino event has ended. While the end of the El Nino is usually associated with a return to more normal rainfall pattern, it should not be seen as a start to drought-breaking rains. This particularly applies to eastern and southern Australia, which in some instances will require several years of good rainfall to recover.
However we can be optimistic that there will be a general easing of dry conditions in drought affected areas. This may not be an issue for the recently wetter parts of north Queensland but will hopefully bring more than just relief rain to southern and central Queensland.
As autumn is a key time for the establishment of climate phenomena such as El Nino and La Nina DPI&F climate staff will continue to closely monitor what happens over the next few months. In terms of a state wide improvement in seasonal conditions a year of consistently positive SOI values and a La Nina (and maybe a bit of luck) would help.
Despite the rise in monthly SOI values from minus 8.9 for January to minus 2.8 for February the SOI is still is a "Consistently Negative" phase.
An analysis of historical rainfall records and a Consistently Negative SOI phase indicates a 30 to 50% of getting median rainfall throughout the northern half of Queensland and a 40 to 60% and in a few locations 70% chance of getting median rainfall throughout southern Queensland for March through to the end of May.
As the autumn predictability gap approaches it will be interesting to see what direction the SOI takes. At this a time of year consistently negative values are not really a major concern. However if the SOI does not return to consistently positive values during autumn it would be a warning sign for a likely dry winter/spring.
Low probabilities (20 to 40%) of getting median rainfall persist throughout the north east corner of New South Wales, western half of Tasmania, south west Western Australia and the northern half of the Northern Territory. Throughout the rest of Australia the chance of getting median rainfall during March to May has improved to a reasonable 50 to 70% chance.
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%.
The latest rainfall probability maps are at http://www.dpi.qld.gov.au/climate For more on rainfall probabilities for your location refer to Rainman StreamFlow or contact 132523 or (07) 3404 6999.
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 March to May in the following years since 1900; 1900, 1903, 1915, 1919, 1941, 1942, 1952, 1958, 1959, 1969, 1970, 1983, 1992, 1993 and 1998. Work out your long term average rainfall for March to May and see how many times rainfall was well below, well above or close to average.
For example at Wallumbilla, well below average rainfall for March to May in those years was recorded 3 times, close to average rainfall was recorded 7 times with above average rainfall recorded 5 times. Therefore rainfall during March to May at Wallumbilla is more likely to be average to above average than well below average.
The MJO is currently crossing northern Australia. Some forecasts suggest several tropical cyclones may develop in conjunction with this passage of the MJO/ monsoon trough development. It will be interesting to see what, if any rainfall events it triggers. Widespread rain is still needed promote pasture growth and improve soil moisture levels for the coming winter cropping season.
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). It is next expected in mid April.
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.