Interpreting rainfall probabilities
- Have a plan. Climate outlooks are based on probabilities, so it is best to plan for a range of possible outcomes.
- It is important to bear in mind that an outlook based on probabilities is not a definitive forecast. For example, if an outlook indicates a 70% probability of rainfall being above the long term median, then it is also indicating a 30% probability of rainfall being below the long term median.
- Climate outlooks do not always indicate a strong probability of either wet or dry conditions.
- If an outlook is for a specific season (e.g. winter), then it is important not to apply that information to the following season or to the rest of the year (wait until a new outlook is issued for that season or period).
- If a climate outlook indicates the ‘probability of exceeding median rainfall’ for instance, then it may be helpful to know what the long-term median rainfall is for your location.
- A management decision should never be based solely on a climate outlook as there are many other factors which may need to be considered (e.g. soil moisture status, crop type, pasture availability, commodity prices, machinery, labour, transport and finance costs).
- Before making a major management decision, a cost benefit analysis may be useful. A cost benefit analysis weighs up the benefits (e.g. financial gain) of a successful outcome against the costs (e.g. financial loss and personal stress) of a failed outcome. A cost benefit analysis may also consider alternative options which may involve less risk.
- Taking the above steps will ensure that normal risk management procedures are not overlooked or that a decision is not overly influenced by a single piece of information (such as a seasonal climate outlook).
- It is also important to ensure, before acting on a climate outlook, that the information comes from a reliable source. Don’t immediately assume that information in the newspaper or on the TV, radio or internet is correct or applies to your location.
- Always take into account a range of information from reliable sources. For example, seasonal outlooks tend to based on the current or projected state of the El Niño-Southern Oscillation (ENSO) which can be assessed using the Southern Oscillation Index (SOI), sea surface temperatures or global climate models).
- It may be useful to use climate outlooks in parallel with a range of other risk assessment tools (e.g. AussieGRASS, FORAGE, Rainman StreamFlow or SILO).
- It goes without saying that if you are not ‘comfortable’ with probability based outlooks, you should not use them. Rather you should seek further information and perhaps investigate how climate outlooks are being used by others. You may also choose to participate in a ‘Managing for Climate and Weather Workshop’.
Last updated 25 November 2016