Improving your confidence in using climate model guidance
Dale Grey, DPI Cobram and Maria Rose, DPI Maffra
As far as weather forecasts go, we are quite familiar with those that predict four and up to seven days ahead; generally feeling pretty confident about their short term accuracy. When it comes to longer term planning of seasonal farm management activities however, climate forecasts that cover the current and following season are certainly more appropriate. With such longer term predictions, in order to use them for effective decision making, we also need to be comfortable and confident with their outputs.
Given, that a number of organisations throughout the world are involved in the development of seasonal weather predictions using varying methods (sometimes over different months) that have differing results, the use of one source only is a low confidence option. We can greatly improve our confidence in seasonal outlooks using a decision making process involving "climate model guidance". Essentially this process requires the simultaneous comparing of a number of these world wide seasonal predictions to make an overall assessment representing a 'best fit' forecast.
To explain how this works, the table on the next page contains 11 worldwide sources of weather forecasts for this spring and summer. Across the top title row, you will notice three types of prediction models used; Coupled GCM (General Circulation Model): Sometimes referred to as a Global Climate Model, which includes the physics of the atmosphere and often the ocean, sea ice and land surface as well.
Ensemble: A set of simulations using a single GCM or multiple models to average out chaotic behaviour in the weather, resulting in a better match to climatological observations.
Statistical: A weather forecast based upon a systematic statistical relationship between past behaviour of the atmosphere or ocean and local rainfall and temperature.
Within each prediction model type on the second title row of the table, you will notice the organisation and country source. In the case of the Coupled GCM column, models are from Europe, Australia (Bureau of Meteorology - BoM), Japan and the USA. Ensemble models are sourced from the UK, USA and Korea whilst the statistical models are all from Australian organisations including the BoM and ENSO Sequence System in the Department of Agriculture & Food in western Australia (ESS DAF WA).
So what does the table indicate for the current spring?
The "climate model guidance" indicates that average rainfall with the possibility of slightly drier than normal for spring is the best bet. This has been deduced from the fact that average appears in 11 predictions and the drier signals are erratic. Whilst for the spring temperature, predictions are mixed, but slightly warmer is favoured by the majority.
And for the coming summer?
The "climate model guidance" at this stage is mixed in that average or slightly drier rainfall and average temperatures for summer are mostly predicted.
For relevant dairy farm management ideas throughout the state of Victoria on how to deal with this current spring based on an average rainfall with a possibility of being slightly drier than normal and slightly warmer temperatures favoured, refer to the article "Managing the Spring Ahead" (pgs 6 & 7).
|System 4 ECMWF Europe||POAMA BoM Australia||SINTEX JAMSTEC Japan||CFSv2 NCEP USA||GSM COAPS USA||UKMO UK||IRI USA||APCC Korea||BoM Seasonal Forecast||QDNRM Qld Australia||ESS DAF WA|
|Month of Run||August||August||August||August||August||August||August||August||August||August||August|
|Spring Pacific Ocean NINO3.4||Warm (weak El Nino)||Slightly warm||Warm (weak El Nino)||Warm (weak El Nino)||Warm (El Nino)||Slightly warm||Slightly warm|
|Spring Eastern Indian Ocean||Slightly cool (IOD+ like)||Slightly cool (IOD+ like)||Neutral||Slightly cool||Neutral||Slightly cool|
|Spring Rainfall||Average||Average, slightly drier NE||Slightly drier central and east, average W||Slightly drier N, average S||Average||Average||Average||Average||Slightly drier, average Gipps||Average, slightly wetter SW, slightly drier Gipps||Average|
|Spring Temperature||Slightly cooler?||Average||Slightly warmer||Average||Average||Slightly cooler?||Slightly warmer||Slightly warmer||Warmer|
|Summer Pacific Ocean NINO3.4||Warm (Weak El Nino)||Slightly warm||Warm (weak El Nino)||Warm (weak El Nino)||Warm (El Nino)||Slightly warm||Slightly warm|
|Summer Eastern Indian Ocean||Neutral||Neutral||Slightly warm||Neutral||Neutral||Neutral|
|Summer Rainfall||Average?||Average, slightly drier NE||Slightly drier||Average||Slightly drier||Average||Average|
|Summer Temperature||Average?||Average||Slightly warmer||Average||Average||Average||Slightly warmer E, average W|
|Comments||Experimental||Experimental||Experimental 20 CGCM models summarised in an ensemble||Comparison between current SST's and historic rainfall||5 phase system based on previous 2 months SOI||David Stephens and team. NINO3 SST|