Managing your climate risk using forecasting tools

Understanding how to use forecasting and weather analysis tools to assess climate risk can assist in better decision making (when managing nitrogen by irrigation decisions and determining crop selection) for the upcoming season. Factoring this information into your cropping plan provides valuable guidance on the use of expensive crop inputs and can also help prepare for extreme climatic events.

What do you need to know?

Forecasting tools rely on imperfect information which can cause variations in reliability but the trends suggested by a range of tools can provide a valuable source of information to consider in risk management decisions.

Relying on one particular model or information source is risky. Computer guidance can be very reliable at certain times of the year, but there may also be strengths or weaknesses with climatic influences that are not always clear to the user.

Seasonal forecasts: rainfall verses temperature

Modelling and simulating rainfall convective processes in various layers of the atmosphere is a challenging science. The accuracy of rainfall seasonal predictions varies throughout the calendar year and by region.

Temperature predictions based on air pressure patterns are generally more accurate than rainfall forecasts.

Evaporation due to hot temperatures is an important component of the moisture balance sheet that should not be overlooked.

Above average temperature forecasts can be a good guide to approaching months of heat waves and extreme weather. Conversely models showing below average three-monthly outlooks can also signal increasing cloud cover and lower evaporation, and hopefully rainfall.

El-Niño Southern Oscillation (ENSO)

ENSO refers to the oscillation in the sea surface temperature and air pressure anomalies in the tropical Pacific Ocean. The Southern Oscillation Index (SOI) is an air pressure measurement calculated between Tahiti and Darwin. The SOI represents a 30-day average of a broad belt of air pressure in the Pacific Region. When the SOI is in a positive phase (La Niña), mean sea level air pressure is lower and historically conditions are more favourable for rain.

Generally, from January to May, temperature and rainfall in most summer cropping regions is poorly correlated with ENSO. However during a definitive ENSO phase, related climate modelling shows stronger results in the winter cropping season and at the onset of summer crop planting.

Recent research has found that climate models have far greater accuracy during defined La Niña or El Niño events than they did in neutral phase years. Neutral years should not be confused with average years; variability will increase during ENSO neutral years, reducing the longer term accuracy of seasonal models.

Indian Ocean Dipole (IOD)

The Indian Ocean Dipole is a Sea Surface Temperature index in the Indian Ocean. This is a secondary moisture source during the winter and spring seasons in Eastern Australia. A negative Indian Ocean value is favourable for moisture supply. The IOD life-cycle starts in June and typically ends in October and impacts southern growing areas from the Macquarie Valley south the most.

Southern Annular Mode (SAM)

The SAM is a measurement of the mean sea level pressure around latitudes in Antarctica. This measurement is the difference or ‘gradient’ of the air pressure patterns that can affect daily variations in eastern Australian rainfall and temperatures.

Fluctuations in the SAM affect agricultural areas of eastern Australia during winter and spring extending into summer in some regions.

A positive SAM will feed moist, convective air from the Tasman and Coral Seas into troughs and frontal systems producing rain events.

A negative SAM reduces the number of cold fronts that originate from the Southern Ocean resulting in a dry, stable westerly air pressure pattern.

The Climate Prediction Centre in the US can provide historical information on the SAM index (referred to as AAO – Antarctic Oscillation) together with accuracy, average values and 14 day forecasts. Click here, and go to the ‘climate and weather’ tab.

General Circulation Models (GCMs)

The Bureau of Meteorology’s GCM is just one of around eight operational seasonal models available internationally. Identifying consensus from these models can give extra confidence in decision making. Variable results can also signal a conservative approach is required.

The GCMs indicate short and long-term precipitation and temperature outlooks, as well as seasonal forecasts.

Most climate models simulating Australian seasonal conditions will be heavily weighted with ENSO information.

Monitoring Seasonal Temperature Forecasts

When planning summer crops, a climate risk assessment can also include regular surveys of international seasonal temperature forecasts. These forecasts can assist in monitoring stored soil moisture and making decisions about likely evaporation rates through the spring and early summer period.

The Australian Bureau of Meteorology releases a seasonal temperature and rainfall forecast on a monthly basis. The results of this forecast should be considered in the context of other models such as leading US, European and Asian forecasts.

Global Circulation Models generally have higher accuracy predicting extremes in temperature than rainfall.

A series of monthly seasonal forecasts of high temperatures may often coincide with low rainfall.

What should you do on your farm?

  • Stay informed about the latest climate risk management information through the CottonInfo Moisture Manager – a monthly summary of international forecasting models, climate indicators, expert opinion and local analysis delivered by CottonInfo. View previous editions of the Moisture Manager here, and subscribe to receive future editions here.
  • Survey information sources widely. Look at a range of models to determine if there is a consistent pattern in the forecasts.

Where should you go for more information?