Climate Watch Dave McRae Qld Dept of Primary Industries and Fisheries 02/02/05
Based on the SOI value at the end of January, chances for average to above average rain over the next three months (February to April) across most of Queensland are generally between 30 to 50%. The main exception is for a belt running from the north west into the central west of the state where the probability of getting average to above-average rainfall for this time of year is slightly higher (50 to 60%).
As of the 2nd February the 30-day average of the SOI is plus 1.2. Daily updates on the SOI are available on (07) 46881439. The latest rainfall probability maps for Queensland, Australia and the world are at www.dpi.qld.gov.au/climate or www.longpaddock.qld.gov.au
Based on the SOI and historical rainfall records, the chance for average to above average rain for February to April across NSW, Victoria, Tasmania, the southern half of South Australia and the south west corner of Western Australia is generally between 20 to 50%. This does not mean there will be no rainfall at all for the 3-month period. What it does means though, is that rainfall recorded for February to the end of April in the affected areas will, more likely than not, be below average for this time of year.
For the rest of Australia the chance for average to above average rain for February to April is generally between 50 to 70%. Because rainfall probabilities and median rainfall levels vary between regions, we recommend referring to Rainman StreamFlow for more specific information. Otherwise call the DPI Call Centre on 13 25 23 or (07) 3404 6999.
As with any probability based forecast system it is important to consider the opposite aspect. For example, Cunnamulla has around a 40% chance of getting above its normal February to April rainfall of 95 mm. This also means that there is a 60% chance of NOT getting the 95 mm over February to April.
Another way of looking at this is that in around 4 years out of 10 historically (or slightly less than one half) with the current SOI pattern, Cunnamulla has received at least 95 mm over February to April. Therefore in 6 years out of 10 historically (or slightly more than one half), Cunnamulla has gotten less than its normal 95 mm over February to April.
When looking at rainfall probabilities for your area it may make it easier to think of them in these terms:
1. Probabilities above 80% highlight a high chance 2. Probabilities above 60% highlight an above average chance 3. Probabilities below 40% highlight a below average chance 4. Probabilities below 20% have a low chance
For those looking for some more rain the next passage of the MJO due around mid-February will hopefully trigger it. The last passage of the MJO was in early January.
The MJO is simply 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 across much of Queensland. Given the growing interest in the MJO, and with funding from the DPI&F, GRDC and CRDC we have developed a site www.apsru.gov.au/mjo/ that will allow anyone interested to track its passage.
A borderline El Niño continues to persist in the central Pacific Ocean. The changes that occur in sea surface temperature patterns in the central Pacific especially in the coming autumn will be crucial in terms of whether this El Niño event continues to persist throughout the rest of the year.
To find out more on conditions in the Pacific try the Bureau of Meteorology "El Niño wrap up" at www.bom.gov.au/climate/enso/ or the US Climate Prediction Centre at www.cpc.ncep.noaa.gov/ For the latest sea surface temperature maps have a look at www.cpc.ncep.noaa.gov/products/ or at www.longpaddock.qld.gov.au/
In a recent media release the Bureau of Meteorology www.bom.gov.au stated that based on the best available and most recent information the lengthy run of relatively quiet cyclone seasons was likely to continue for Queensland with the number of tropical cyclones in the Coral Sea this season having only an outside chance of exceeding 2 or 3, and not all will cross the coast.
In a reflection of the lack of cyclone activity the Bureau also state that the last 15 years have been relatively quiet in terms of both cyclone activity in the Coral Sea and the incidence of significant cyclone impacts along the Queensland coast with the past 3 cyclone seasons being particularly unusual in that only 1 cyclone has crossed the east Queensland coast ("Fritz" a low Category 1 in the far north last February). For more information on cyclones try the Queensland Tropical Cyclone Warning Centre at www.bom.gov.au/weather/qld/cyclone
On a positive note, the early summer storm rain received across much of southern Queensland and northern NSW has provided a good start to the grain sorghum cropping season. However, there is some considerable variation in the Queensland sorghum yield outlook.
At the end of December, current soil water conditions and the seasonal rainfall outlook indicated a below average chance (30 to 40%) of bettering the long-term median grain sorghum yields in most areas of Central Queensland. This contrasts with parts of southern Queensland and northern NSW, which had mainly above average chances of bettering the long-term median grain sorghum yield.
At this stage of the growing season widespread rain is still needed to ensure good planting opportunities and to improve the current sorghum outlook across the entire cropping belt.
This sorghum yield outlook is based on a shire scale. It does not take into account crop area planted and is purely a yield forecast. Nor does not take into account individual property circumstances or the effects and damage from poor crop nutrition, pests, diseases, frosts, heat stress and distribution of planting rain within a shire. For more information on the sorghum crop yield outlook contact Andries Potgieter on (07) 46881417 or try www.dpi.qld.gov.au/climate where a full copy of the sorghum crop outlook can be found. For detail on farm level crop management strategies for CQ and SQ access www.dpi.qld.gov.au/fieldcrops
Many people like to follow the relationship between the SOI and rainfall patterns in more detail. To do that, have a look at what happened in your area over February to April in the following years; 2003, 2002, 1996, 1986, 1982, 1980, 1977, 1968, 1967, 1963, 1954 and 1953 and compare the rainfall recorded with your 'normal' rainfall for February to April.
Information on what rainfall patterns where like for February to April in those years can be found at www.longpaddock.qld.gov.au or in Australian Rainman.
I thought I'd give a brief summary of what ENSO or the El Niño/Southern Oscillation means and the influence it has on the climatic characteristics (rainfall, temperatures, wind and evaporation) of the whole of eastern Australia.
Changes in sea surface temperature (SST) patterns along the equator from the west coast of South America to around the International Dateline drive shifts in the global circulation patterns (eg Walker Circulation) that influence our local climate. The Southern Oscillation Index (SOI) is a useful way of measuring these changes. The SOI is simply a measure of the difference in barometric air pressure between Darwin and Tahiti. It typically ranges in value from plus 30 to minus 30.
A summary of ENSO follows:
El Niño SST pattern
Sea surface temperatures (SST) along the equator from the International Dateline running east towards the coast of South America become warmer (plus 1.0 to 2.0oC) than normal, with SST to the north of Australia usually becoming cooler than normal.
Negative values of the SOI (eg. average monthly values of the SOI below minus 5) are usually associated with an El Niño because barometric air pressures over northern Australia are higher relative to those in the central Pacific. This may slow or stop the flow of the southeast trade winds that push atmospheric moisture from the Pacific Ocean across Australia as well as reduce the occurrence of rain depressions (and cyclones). Typically, a decline in rainfall is noticeable during winter, spring and early summer.
La Niña SST pattern
Sea surface temperatures (SST) along the equator from the International Dateline running east towards the coast of South America become cooler (minus 1.0 to 2.0oC) than normal with SST to the north of Australia becoming warmer than normal.
Positive values of the SOI (average monthly values of the SOI above plus 5) are usually associated with a La Niña because barometric air pressures over northern Australia are lower relative to those in the central Pacific. This may cause an increase in the intensity of the monsoon trough across northern Australia as well as increase the flow of the southeast trade winds across Australia. There may also be an increase in the occurrence of rain depressions (and cyclones).
Typically, there is an increase in rainfall in a La Niña SST pattern in winter, spring and early summer.
Neutral SST pattern
About half the time the Pacific Ocean is in a neutral SST pattern. When SST patterns are near normal, the SOI is usually associated with near zero (average monthly values between minus 5 and plus 5) values. More information on the SOI is available at www.longpaddock.qld.gov.au and www.dpi.qld.gov.au/climate
When incorporating climate forecasts into management decisions, it could be worthwhile to consider some of the following general rules of thumb developed from feedback from climate users.
1. Be sure of your source of information and what it is actually suggesting. Do not take a quick grab of information from any source including radio, TV or the internet and assume what you heard/saw/read applies to your location.
2. Decisions should never be based entirely on one factor (such as a weather or climate forecast). As always, all factors that could impact of the outcome of a decision (such as soil moisture/type, crop, pasture type/availability, commodity prices, machinery, work force, transport, finance, costs, seasonal outlook etc) should be considered.
3. Access local information or at least be aware of the long-term median for your location so you can correctly interpret the forecast.
4. Do a cost benefit analysis of any decision with a climate risk factor eg What will I gain if I get the desired outcome from this decision? What will I lose if I don't get the desired outcome from this decision? What other cost neutral options do I have if any?
5. Do not to take a forecast for a specific period (eg September to November) and expand it out (eg late summer). Update the information regularly.
An interesting site http://www.cvap.gov.au/mastersoftheclimate/ from the 'Climate Variability In Agriculture' (CVAP) research and development program is well worth looking at. It highlights some case studies on how producers and businesses have used (to varying levels of success) climate and weather information in their decision making processes.