A drier than normal outlook has been issued for central and southern parts of the wheatbelt over the next three months, while a wetter than normal winter is more likely for the Northern Agricultural Region (NAR).
Confidence in Department of Agriculture and Food’s Statistical Seasonal Forecast (SSF) is reasonably high, based on medium to good predictive skill using May conditions.
Department research officer Fiona Evans said most areas of the wheatbelt received a good break to the season, with above or near-average rainfall over the past month, except for parts of the south coast and central agricultural area.
“Soil water modelling indicates good soil moisture levels throughout two thirds of the wheatbelt up to the start of June,” Dr Evans said.
“By contrast, some areas of the central and southern wheatbelt had relatively low levels of soil moisture.
“Maximum and minimum temperatures were also much warmer than normal in the last month, which has accelerated crop growth and increased evaporation.”
The updated SSF maps show a decile 2-3 outlook for most of the wheatbelt for June, July and August, with a decile 5-10 outlook for the northern agricultural region.
“Higher than normal rainfall in the NAR is likely to be dependent on tropical cloud bands and cut-off lows to trigger rain, both of which are difficult to forecast seasonally,” Dr Evans said.
Dr Evans said the DAFWA SSF forecast was one of the most consistent models available to industry.
“The consistency of the forecast between the statistical and dynamic models gives us more confidence in the outlook,” she said. “These models are consistent with the Bureau of Meteorology’s (BOM) three month forecast for a drier than normal winter.”
The Bureau of Meteorology is forecasting an El Niño event later in the year, which historically has little impact on Western Australian rainfall.
In addition, some climate models are predicting the development of a positive Indian Ocean Dipole (IOD) event in spring.
“If a positive IOD event does develop in conjunction with an El Nino event in the Pacific Ocean, the combined impact on WA rainfall is stronger,” Dr Evans said. “This may mean a wet spring is less likely.”
DAFWA Grains Principal Research Officer David Bowran urged growers to consider this latest climate information carefully when planning their management strategies for the rest of the season.
“Given the outlook that the season is drier than normal, water use by weeds should be minimised so early weed control in crops and pastures is strongly advised,” Dr Bowran said.
“Growers should also be aware that crops on shallow soils or those sown after strong legume crops last year, which produced excess nitrogen inputs, may be at risk of haying off and higher screenings.”
Landholders can get a forecast for their local weather station by visiting the department’s website agric.wa.gov.au, searching for ‘seasonal climate information’ and clicking on the black dots on the maps. They can also see maps indicating stored soil moisture and plots of how soil moisture has changed at each weather station.
For updates and further agronomic advice see the regional AgTactics newsletters, available via the ‘newsletters’ tab on the department’s website.