Winter Cropping Analysis 2021: Analogue years and GCMs
/What is an analogue year? This is a “like” or “similar” year when the ocean and air pressure conditions are almost the same. A study by CSIROs Jaci Brown et. al. (2018) found a combined GCM analogue year approach can be useful in decision making for winter cropping in eastern Australia. Here’s what we know;
One floated analogue by Accu Weather Climatologist, Jason Nicholls (US) is 1989. A look at this 1989 year shows neutral ENSO, neutral/wet IOD and neutral/wet Modoki index. This is the only year that sticks out since 1980 that ticks these boxes in line with global forecasts. Check your rainfall records for that year for May-October. (1989 rain decile map bottom).
The GCM outputs reviewed last week showed average rainfall and temperatures for the next 3-months. Most models showing decile 4-6 rain, with the exception of the IRI model, which favour decile 7 for NSW. Longer-term IRI prediction favour a wet spring. (top chart with yellow border, below).
The subtle difference between 1989 obs. and the forecast is that in 1989 the Modoki index was in wet phase for winter, then faded to neutral. The outlook in 2021 is for Modoki and possible IOD to strengthen from neutral to wet phases, which is worth keeping an eye on. ENSO looks to be neutral, consistent with 1989/2021.
Jaci Brown’s paper here: https://doi.org/10.1016/j.agrformet.2018.06.001
