Forecasts point to below-average rain
WA graingrowers have been advised to plan their 2017 cropping program carefully, with below-average rainfall forecast during the growing season.
There is consistency between 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 WA 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 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 subsoil moisture across the regions due to widespread summer rainfall, could make it tricky for growers to roll out their cropping programs.
“Currently, 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,” he 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 in areas where storms had occurred.
“Canola growers should not 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 system has indicated a 30 to 60 per cent chance of exceeding average rainfall across the grainbelt for the three months April to June.
The SSF indicated rainfall was 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 current seasonal outlook was consistent. It has predicted a 20 to 35 per cent chance of exceeding average rainfall from April to June, based on a predictive skill of moderate to good.
The bureau was also expecting early season temperatures to be warmer than normal, with a 60 to 70 per cent chance of above-normal daytime 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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