Comparing the outlook in 2010 to 2011
by Bree Walshe, DPI Maffra and Zita Ritchie, DPI Warnambool
Gearing up for spring after a wet winter in many parts of Victoria it is easy to assume we’ll see a repeat of 2010. The big question is, will it? We do not have a crystal ball, but we can compare the model forecasts from this time last year with the current outlook. Of course we must remember models are predictors and only in hindsight can we confirm their accuracy.
This season is shaping up differently to last year’s predicted and experienced conditions. In September 2010 we were in the midst of La Niña and a weak Indian Ocean Dipole (IOD) negative event which strengthened throughout spring. Wet conditions were predicted for the 2010 spring (Table 1) and the persistence of the strong La Niña led to continued rainfall throughout the Victorian summer.
The Pacific Ocean has a big influence on Victoria’s weather patterns. Last year, there were distinct signals from ocean temperatures, air pressure and trade winds which resulted in a slightly wetter than average outlook for 2010. This year, the Pacific ocean is showing ’weaker’ signals, with a cooling trend. The Indian Ocean however, has recently reached IOD positive territory. Historically this increases the chances of a drier spring. Therefore, by combining the two oceans’ behaviour, the models’ predictions have resulted in an average rainfall outlook for spring, based on a number of computer and historical climate models.
As we plan our spring management and weigh up the odds of what may be ahead, making informed decisions about the weather and climatic data helps to minimise the risk.
Given the climatic outlook for the spring, we have to put a ‘risk’ overlay into your planning. On balance current models predict that average spring rainfall is the most likely outcome for Victoria. Alternatively, a few models are reporting a neutral forecast, which historically means that there is still an equal chance of receiving above, below or average rainfall.
It is easy to look to the sky, irrigation dams and soil moisture levels and think the good old days of plenty of rain have returned. However, based on history an average outlook could mean rainfall could go either way, as rainfall events rely on a good moisture feed from the Pacific and/or Indian oceans.
How are you going to manage the risk and opportunities of average rainfall on your farm? Will it aid or hinder your spring fodder production? Are you going to bank on average rainfall, or are you managing for slightly drier conditions?
The temperature outlook offers another important guide. This months models predict higher chances of average temperature, similar to last year. As temperature affects many facets of the growing season, it is good to weigh up the risks associated with this outlook.
What are the potential risks and opportunities to your farm business if we receive average temperatures over spring? Pasture and crop growth rates will increase which may create earlier opportunities to conserve silage or may also create issues with increased evaporation, depleting soil moisture reserves if irrigation isn’t available.
In summary, 2011 looks unlikely to mimic 2010, taking into account the current climatic indicators and model predictions. When comparing the seasonal outlook from year to year, it is important to keep risk in the back of you mind. Many factors affect our weather, with each region having their own specific risks which need to be considered in the context of the broader model forecasts. Managing climatic risk is complex, one of the hardest management decisions is around how all of these outlooks come together and affect your farm.
| Seasonal model forecasts for spring (SON) in Victoria, from the Fast Break newsletter | ||
| 2010 | 2011 | |
|---|---|---|
| Pacific Ocean | Cool | Slightly cool/neutral |
| Indian Ocean | Slightly warm/warm | Neutral/weak IOD positive |
| Rainfall | Slightly wetter/average | Average |
| Temperature | Slightly warmer/average | Average/slightly warmer |
