SOI and SST worth watching this month Dave McRae, Qld Climate Change Centre of Excellence, 14/04/10.
The 30day average of the SOI has continued to maintain the upward trend of the last couple of weeks and is plus 7.0 as of the 13th April. This is up from minus 18.2 for February and minus 10.8 for March.
It will be interesting to see if these positive values are maintained over coming months. At this a time of year, a return to consistently negative values would be a warning sign for a likely dry winter/spring. In terms of a continued improvement in seasonal conditions and outlook, the development of consistently positive SOI values and even a La Nina would help.
According to the latest ENSO Wrap-up from the Bureau of Meteorology, while there is still a typical El Niño sea surface temperature present in the Pacific, the surveyed global climate models indicate the gradual breakdown of the EL Niño will continue to occur with only a very low chance of an El Niño climate pattern redeveloping during autumn.
This expectation is reflected by a distinct cooling trend in sea surface temperatures (SST) throughout the eastern Pacific. There has also been a distinct warming trend in SST's around northern Australia.
As autumn is a key time for the establishment of climate phenomena such as El Nino and La Nina QCCCE climate staff will continue to closely monitor what happens over the next couple of months. 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
Convection associated with a weak MJO became evident in the Indian Ocean during mid-March and travelled eastward across Australian longitudes during the end of March/early April. This coincided with the development of Tropical Cyclone Paul in the Gulf of Carpentaria.
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 try the Bureau of Meteorology at www.bom.gov.au
Based on the shift in monthly SOI value from the end of February (minus 18.2) to the end of March (minus 10.8) the SOI has remained in a "Consistently Negative" phase. Despite the "Consistently Negative" SOI phase at the end of March there is a somewhat mixed seasonal outlook for April through to the end of June across Queensland.
For example, throughout the far north west and peninsular region of Queensland along with isolated pockets of the far south east and far south west of the state, there is a lower 20 to 40% chance of getting above the long term April to June median rainfall. This is in contrast to the rest of the state where there is a higher 50 to 70% chance of getting above median rainfall during April to June.
As always when dealing with any probability based climate forecast system it is important to consider the alternate view. For example, currently there is a 70% chance of getting above the long term April to June medium rainfall of 90mm at Taroom. This also means there is a 30% chance of not getting above 90mm.
Another way of looking at this is that in around 7 years out of 10 (or slightly less than three quarters) with the current SOI pattern, Taroom has received more than 90mm during April to June. Therefore in 3 years out of 10 (or around one quarter) with the current SOI phase, less than 90mm has been recorded at Taroom.
For those who like to follow the relationship between the SOI and rainfall patterns in more detail for their location have a look at what happened in your area during April to June in following years: 2003, 1998, 1993, 1992, 1987, 1983, 1978, 1941, 1926, 1919, 1915, 1912, 1906 and 1905.
It can be very useful to find out what rainfall patterns and seasonal conditions where like during April to June in your area for those years. Work out your long term average rainfall for April to June and see how many times rainfall was well below, well above or close to average.
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.