Rainfall Trends - What are they doing? 05/10/04
Below average rainfall has been recorded across most of Queensland over the last 3 years. It is interesting to see if this is just a short-term phenomenon before seasons return to what many would like to consider "normal" or, part of a longer-term trend.
To estimate rainfall patterns in Australia over the last two to three hundred years, sources of information such as the annual florescence in cores of coral in the Great Barrier Reef and Pacific are measured. These cores suggest that over the past 245 years up to 2001, the 5 wettest years in order were 1887, 1974, 1755, 1768 and 1890 while the driest were 1902, 1867, 1812, 1823 and 1865.
Official rainfall records are available for most locations in Australia from around the mid to late 1800's. Even over this short period there have been significant variations in rainfall (and temperature) over large parts of Australia.
For an example, Blackbutt in the south Burnett has 105 years of rainfall records and a long-term average annual rainfall of 855 mm. However using a 10 year moving average it becomes apparent that there have been prolonged periods of above and below the long term average annual rainfall of 855mm.
The lowest 10 year moving average rainfall was 738 mm in 1926 with the highest being 1037 mm in 1956. Since this peak the 10 year moving average rainfall at Blackbutt has fallen to 780 mm. This is a shift of around 260 mm (or approximately 10 inches). This downward trend since the mid 1950's is evident across most of eastern Australia especially Queensland. Rainfall trend maps are available at www.bom.gov.au
This downward trend in rainfall patterns across most of the state is part of the reason we recommend getting updated accurate information on rainfall levels for your location. This will not only help you interpret seasonal outlooks but provide a more realistic picture of what rainfall may be expected.
This is important when developing management strategies and especially when considering large capital investments such as purchasing property.
I'll do another article detailing what climate phenomena are driving these drying trends later this month. As of the 5th September the 30day average of the SOI is minus 0.1. For more climate information give me a call through the DPI&F Call Centre on 13 25 23.
SOI remains in a "Consistently Near Zero" phase 5th October 2004
The 30day average of the SOI as of the 5th October is minus 0.1 This means the SOI has remained in a "Consistently Near Zero" phase for the second month in a row.
Based on the current SOI phase and the available historical rainfall records for Queensland there is a 40 to 50% chance of getting above median rainfall through to the end of December across most of Queensland. However there are some areas especially in the north and west of the state that have a lower 30 to 40% chance of getting above median rainfall through to the end of December.
For more specific rainfall probabilities, median rainfall levels and significance tests for different locations, we recommend referring to AUSTRALIAN RAINMAN. The latest rainfall probability maps are available at www.dpi.qld.gov.au/climate or www.longpaddock.qld.gov.au
While these rainfall probabilities are an improvement on what would have been the case if the SOI had remained in a "Consistently Negative" SOI phase, given ongoing dry conditions across the state they are not as high as many would want.
For there to be an overall improvement in the seasonal outlook for Queensland, it would help if the SOI rose to a "Consistently Positive" pattern for a couple of months at least.
As with any probability based forecast system it is important to consider the opposite aspect. For example Barcaldine currently has a 30% chance of getting above its long term October to December median rainfall of 115mm. This also means that there is a 70% chance of NOT getting the 115mm through to the end of December.
Another way of looking at this is that in 3 years out of 10 (or around one third) with the current SOI pattern, Barcaldine has received at least 115mm for October to December. Therefore in 7 years out of 10 (or around two thirds), Barcaldine has gotten less than 115mm for October to December.
Sea surface temperatures (SST) in the central Pacific from the international dateline running east towards South America remain warmer than normal (+0.5 to 1.5oC). This pattern can be described as a "border line El Nino". It is worth noting that the USA Climate Prediction Centre www.cpc.ncep.noaa.gov/ expect this pattern to continue into early 2005.
While the current SST pattern is not usually as serious as the El Nino such as occurred between 2002 and 2003, it can still have major impact on Queensland rainfall and water supply, especially if the SOI where to return to a "Consistently Negative SOI Phase".
As an example, we had a borderline El Nino state in 1992 and 1993, both years producing below average rainfall for large parts of Queensland but not to the extent of the 2002/2003 event. The Bureau of Meteorology "El Nino wrap up" www.bom.gov.au/climate/enso/ is a good starting point to find out more on conditions in the Pacific.
Daily updates on the SOI are available on (07) 46881439. Or if you want to receive the SOI update by text to your mobile phone, send me an e-mail or call 13 25 23.