Modelling shows below average rainfall

Modelling shows below average rainfall

Grains
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WA grain growers are advised to plan their 2017 cropping program carefully, with below average rainfall forecast during the growing season.

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Plant available soil water at  April 3, 2017, estimated using a simple two-layer model and assuming fallow conditions. The model uses daily rain from BoM and DAFWA stations since November 2016.

Plant available soil water at April 3, 2017, estimated using a simple two-layer model and assuming fallow conditions. The model uses daily rain from BoM and DAFWA stations since November 2016.

WA grain growers are advised to plan their 2017 cropping program carefully, with below average rainfall forecast during the growing season.

There is consistency between 10 out of 11 Australian and international climate forecasts, with none expecting wetter than normal conditions for April to June, suggesting greater confidence in the outlook.

Department of Agriculture and Food research officer Meredith Guthrie said the strong agreement between models was unusual, especially early in the season.

Dr Guthrie said the forecast was driven by the combined effect of a predicted El Nino event and the emergence of a positive Indian Ocean Dipole (IOD) by August, which is historically associated with below average rainfall.

“In past years where an El Nino and a positive IOD have occurred together, the negative impact on rainfall became stronger in the south west and southern parts of WA,” she said

DAFWA research officer David Ferris said the outlook for drier conditions, combined with varying amounts of sub-soil moisture across the regions due to widespread summer rainfall, could make it tricky for growers to roll out their cropping programs.

“Plant available soil moisture is less in the Northern Agricultural region compared with the Central and South Coast regions, where soil moisture levels are high,” Mr Ferris said.

“Those areas with good soil moisture levels can still anticipate above average yields, in spite of the projected forecast for below average rainfall, provided crops emerge early or are sown into moist soils in May.

“Growers that took the opportunity to deep rip compacted soils after summer rain will also benefit from crop roots accessing more of the soil profile this season.”

Dr Ferris cautioned that early, wet-seeding opportunities for canola had largely passed, as the soil surface had dried out, except where storms had occurred.

“Canola growers should not to be tempted to chase soil moisture by seeding deeper than one centimetre, as results from early sown canola trials have consistently shown less emergence and lower yields with increased seeding depth,” he said.

“With a drier than average outlook for April to June, growers’ economic risk should be managed by delaying the bulk of nitrogen fertiliser applications until the season’s potential becomes clearer in areas with limited stored moisture.”

DAFWA’s Statistical Seasonal Forecast (SSF) system is indicating a 30 to 60 per cent chance of exceeding average rainfall across the grainbelt for the three months from April to June.

The SSF indicates rainfall is most likely to be in the 2-3 decile range – the second lowest – based on a poor to good predictive skill (confidence in the forecast).

The Bureau of Meteorology’s seasonal outlook is consistent, which predicts a 20-35pc chance of exceeding average rainfall from April to June, based on a predictive skill of moderate to good.

BOM expects early season temperatures to be warmer than normal, with a 60-70pc chance of above normal day-time maxima, based on moderate to good predictive skill.

DAFWA has several free online cropping decision aids, such as Soil Water and Rainfall to Date tools, which can be found at agric.wa.gov.au under the climate, land and water tab.

The SFF is updated monthly and can retrieved by searching for seasonal climate information.

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