Rainfall probabilities fall/increased risk of El Nino climate pattern. Dave McRae, Qld Climate Change Centre of Excellence, 03/07/09
The monthly value of the SOI for May was minus 4.9 and for June was minus 2.8. This places the SOI in a Consistently Near Zero SOI phase. Based on a Consistently Near Zero SOI phase and historical rainfall records there is a 30 to 40% chance of getting above the long term median rainfall for July through to the end of September across most of Queensland (or depending on how you look at things a 60 to 70% chance of getting below median rainfall).
The exception is for the region to the south east of the Gulf of Carpentaria where there is a 50 to 70% chance of getting above median rainfall for July to September. However median rainfall levels at this time of year in that region are low. For example Normanton has a July to September median rainfall of 1mm, Julia Creek has a July to September median rainfall of 6mm and Richmond has a July to September median rainfall of 8mm.
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 1950 that have had a 'Consistently Near Zero' SOI phase at the end of June; 1954, 1960, 1961, 1969, 1976, 1979, 1980, 1991, 1995 and 1999. For example at Kingaroy, below average rainfall for July to September in those years was recorded 4 times, close to average rainfall was recorded 4 times and above average rainfall was recorded only 2 times. Therefore rainfall at Kingaroy during July to September is more likely to be below average to average than well above average. For more information on historical rainfall data for your region try Rainman Streamflow or www.longpaddock.qld.gov.au
It will be interesting to see if strongly negative SOI values develop over coming months. If the 30 day average of the SOI where to fall into strongly negative values and remain there, it would increase the chance of a dry late winter/spring. You can receive a text message with the latest SOI values sent to your mobile phone. To subscribe to this free service, call me on (07) 4688 1459 or e-mail firstname.lastname@example.org
According to the latest ENSO Wrap-up from the Bureau of Meteorology www.bom.gov.au/climate/enso more evidence of a developing El Nino climate pattern has emerged during the last few weeks. This is reflected by central and eastern Pacific Ocean sea surface temperatures being significantly warmer than the long-term average and a distinct warming of sub-surface temperatures throughout the eastern Pacific during June. This is a trend away from the La Nina like climate pattern that was a feature of the last 9 months.
This trend is also consistent with the output of the surveyed international climate models which all indicate the development of an El Nino climate pattern later this year. None of the surveyed climate models are forecasting any potential return of La Nina or La Nina like conditions.
The message should not be "doom and gloom" another El Nino may be approaching. Rather this is an opportunity to take a risk management approach. Review your business, cropping, stocking, fodder, water use plans for the coming winter and spring, assess the seasonal conditions experienced in your area to date and the resources (soil moisture, grass, water, money, equipment) you have available, monitor changes in the seasonal climate outlook over coming months and adjust your plans if and as necessary.
Typically during an El Nino event, there is a low chance of getting above median rainfall during winter, spring and early summer throughout Queensland. The impact of an El Nino around the state will vary depending on the seasonal conditions experienced during summer (e.g. water supply levels for urban and agriculture, sub-soil moisture profile for cropping/horticulture/pasture/tree growth). As most of central and northern Queensland recorded average to above average rainfall over the summer rainfall season, the immediate impact of a potential El Nino event this year on food production and water supply etc is likely to be minimal.
This is in contrast however, to parts of southern Queensland such as the Darling Downs and south west of the state where average to below average rainfall was recorded over the summer rainfall season. This is following on from a number of years of drought.
Also of some interest is the recent trend to positive values in the Indian Ocean Dipole (IOD). If this trend is maintained (and if coupled with an El Nino climate pattern) there is an increased risk of below average winter rainfall especially throughout south-eastern Australian. For more information try www.bom.gov.au/climate/IOD/
SOI influence on climate varies across Australia (greatest skill is for eastern Australia) and between seasons (usually greatest skill is for winter, spring and early summer). Therefore users of the SOI and any other seasonal forecasts are urged to investigate skill level for their location by using such tools as Rainman StreamFlow.
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.