Does recent rainfall mean the drought in Queensland has ended? Dave McRae Qld Climate Change Centre of Excellence 12th June 2007
No not yet. Most of eastern Australia requires several years of good rainfall to fully recover. Although climate forecasts are starting to show higher rainfall probabilities (especially when compared to this time last year) the rainfall deficits that have built up over the last decade mean that large amounts of rainfall are needed to "break the drought".
Using Bell on the northern Darling Downs as an example, records show that rainfall from November 1999 through to April 2007 (90 months) has been in the driest 10% recorded. During that period Bell has accumulated a rainfall deficiency or shortfall of approximately 1175 mm which is close to twice its long term average of 650 mm.
As the northern half of Australia is entering its "dry" season it generally does not receive high overall amounts of rain during this period. Therefore, although climate forecasts are indicating a gradual improvement in seasonal conditions this does not necessarily translate into the high rainfall amounts that are needed to fill irrigation systems, dams and water courses.
So while the impact of the current 'agricultural' and 'meteorological' drought should weaken this year throughout much of Australia, it would be reasonable to expect the 'hydrological' drought to persist in many areas unless a substantial La Nina event were to develop and maintain its intensity through the coming spring and summer. This would help increase the strength of the Australian monsoon trough and increase the occurrence of rain depressions (and cyclones).
Outlook Improves Dave McRae 12th June 2007
According to the Bureau of Meteorology autumn climate review (www.bom.gov.au/climate/) all four eastern states had their warmest autumn on record with many places in Queensland setting new temperature records.
For Queensland the average maximum temperature for autumn 2007 was 2.1 degrees warmer than average which was the highest on record, while the average minimum temperature for autumn was 1.3 degrees warmer which was 4th warmest on record.
Autumn average maximum temperature records were broken at Georgetown with 34.6Â°C (long term average 32Â°C, previous record 34.3Â°C, 113 years of record), Mitchell with 30.7Â°C (long term average 27.1Â°C, previous record 29.7Â°C, 86 years of record) and Charleville with 30.6Â°C (long term average 27.7Â°C, previous record 29.9Â°C, 65 years of record).
This is on the back of a warm start to the year. For example across the Murray Darling Basin for January to April the mean temperature has been +1.46oC above the 1961-90 average. This betters the previous record of +1.3oC set in 2006.
So as well as being warmer than normal, rainfall for autumn was below average over central and southeast Queensland, central west Queensland and the Maranoa and Warrego. Elsewhere rainfall totals although patchy were generally near average.
There has been a slight improvement in the seasonal outlook for Queensland. Based on a Near Zero SOI phase at the end of May there is currently a 50 to 60% (with a few locations up to 70%) chance of getting median rainfall during June to August.
As most of the southern two thirds of Queensland will require several years of good rainfall to fully recover this should not be interpreted as the automatic start to drought-breaking rains. For there to be a lift in rainfall probabilities and a sustained and significant improvement in seasonal conditions, the development of consistently positive monthly SOI values would help.
The 30day average of the SOI has continued to trend slowly upwards to plus 4.3 as of the 11th June. Daily updates on the SOI are available on (07) 46881439 or at www.longpaddock.qld.gov.au
The next passage of the MJO is due to cross northern Australia in the second half of June (around the 20th). The timing of this MJO should coincide well with the onset of the Indian Summer Monsoon. 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). For more information try www.apsru.gov.au/mjo/
In the latest El Nino wrap-up available at www.bom.gov.au the Bureau of Meteorology state that sea-surface temperatures in the Pacific remain close to average following the breakdown of the 2006/07 El Niño event with trade winds and Pacific cloud patterns currently in a neutral pattern. Although computer models show there is an increased chance of a La Niña developing over the next 1 to 3 months, at this stage it has not occurred. The positive news is that there is only a low risk of a return to El Niño conditions in 2007.
In very general terms a La Nina event has the potential in increase rainfall over Australia, Papua New Guinea, Indonesia, New Zealand, India, Thailand, southern Africa, the Sahel and Central America. This type of pattern has the potential to reduce rainfall over parts of Europe, the United States and parts of Central Asia and South America.
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 June to August in the following years since 1920; 1920, 1922, 1926, 1932, 1933, 1937, 1944, 1948, 1949, 1954, 1959, 1966, 1967, 1976, 1982, 1984, 1986, 1996 and 2003. Work out your long term average rainfall for June to August and see how many times rainfall was well below, well above or close to average for June to August in those years.
For example at Proston, well below average rainfall for June to August in those years was recorded 4 times, close to average rainfall was recorded 8 times with above average rainfall recorded 7 times. Therefore rainfall during June to August at Proston is more likely to be average to above average than well below average.
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%.
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. The 'Climate Variability In Agriculture' (CVAP) research and development program 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. An interesting site http://www.managingclimate.gov.au/