Weekly Australian Climate, Water and Agricultural Update, 12 September 2024

For the week ending 11 September 2024, a series of cold fronts and low-pressure systems brought rainfall to parts of western and southern Australia, and scattered areas of central and eastern Australia. Rainfall totals of up to 50 millimetres were recorded in southern areas of Western Australia, South Australia and Victoria. In Tasmania, cold fronts brought rainfall totals of up to 150 millimetres in the west.

Across cropping regions, little to no rainfall was recorded across most areas this week. Parts of southern Victoria recorded rainfall totals of between 5 and 15 millimetres, with parts of western South Australia and Western Australia seeing between 5 and 25 millimetres. Little to no rainfall across south-eastern and eastern cropping regions has likely contributed to a drawdown of stored soil moisture. Where average to above average levels of stored soil moisture are available, crops and pastures would have been able to draw on these reserves to maintain current yield potentials. However, in areas where stored soil moisture levels are low, little to no rainfall is likely to lead to reduced yield potential, exacerbated by warm and windy conditions in some areas.

Rainfall for the week ending 11 September 2024

Over the 8 days to 19 September 2024, low-pressure systems are expected to bring showers over eastern and northern parts of the country. A maximum of 50 millimetres of rainfall is forecast in the northern tropics, eastern Queensland, eastern New South Wales and southern Victoria. High pressure systems are expected to keep much of western and central Australia largely dry.

Across cropping regions, conditions are forecast to be mixed. In the east, rainfall totals of between 5 and 25 millimetres are expected in Queensland, and between 5 and 50 millimetres in New South Wales. In contrast, much of Western Australia and South Australia are expected to see little to no rainfall, with Victoria forecast to receive between 1 and 10 millimetres. If realised, this lack of rainfall across southern growing regions is likely to contribute to further declines in soil moisture and present a downside risk to winter crop production.

Total forecast rainfall for the period 12 September to 19 September 2024

The El Niño Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) climate drivers are currently neutral and having minimal influence on Australian rainfall. The Southern Annular Mode (SAM) is positive (as at 1 September). Forecasts indicate it is likely to become neutral over the coming week. A neutral SAM has no strong relationship to forecast climate conditions.

The most recent rainfall outlook for October 2024 provided by the Bureau of Meteorology indicates that much of northern and eastern Australia is likely to see above median rainfall (between 55 to 80% chance). There is a roughly equal probability of either above or below median rainfall in much of western and southern Australia, except for parts of central and south-west Western Australia, and western Tasmania which are more likely to see below median rainfall.

According to Bureau of Meteorology’s climate model, for October 2024, there is a 75% probability of rainfall totals of between 10 and 50 millimetres across much of eastern New South Wales, eastern Queensland, the far south-west of Western Australia, Victoria. Meanwhile, Tasmania is expected to see falls of between 25 millimetres in the east to 200 millimetres in western areas. Much of northern and central Australia is expected to receive little to no rainfall. This is consistent with the Bureau of Meteorology’s forecast of a delay northern rainfall onset.

Across cropping regions, there is a 75% chance of receiving between 10 and 50 millimetres of rainfall across much of Queensland, New South Wales and Victoria, with higher rainfall totals expected in eastern regions. In Western Australia and South Australia, rainfall totals are expected to be between 5 and 25 millimetres. These rainfall totals, if realised, are likely to be sufficient to support above average yield prospects of winter crops in regions with ample sub-soil moisture reserves. However, in areas with limited stored soil moisture, these falls are likely to only be sufficient to maintain current close to average yield expectations.

Rainfall totals that have a 75% chance of occurring in October 2024

The rainfall outlook for October to December 2024 indicates an increased probability of above average rainfall across much of the eastern two-thirds of the country. In contrast, below median rainfall is more likely across isolated areas of western and northern Australia as well as western Tasmania. Remaining areas of Australia have roughly equal chance of receiving above or below median rainfall.

Across cropping regions, the probability of receiving median rainfall is greater than 60% in Queensland and New South Wales. In Victoria and South Australia, the probability of above median rainfall is between 50 to 70%, while Western Australia has a roughly equal chance of above or below median rainfall across most regions. As of September 2024, many of these areas have below average modelled lower layer soil moisture. If above median rainfall is realised, this rainfall is likely to support the storage of soil moisture in eastern regions for the summer cropping period and contribute to improving soil moisture in southern regions.

Chance of exceeding the median rainfall October to December 2024

The outlook for October through to December suggests a 75% chance of rainfall totals between 50 and 300 millimetres across much of New South Wales, Queensland, Victoria, Tasmania and the Northern Territory, and across parts of South Australia and Western Australia. Rainfall totals in excess of 300 millimetres are forecast for alpine regions of Victoria and New South Wales, isolated coastal areas of eastern New South Wales and Queensland, western Tasmania and the tropical north of the Northern Territory.

In cropping regions, there is a 75% chance of receiving between 100 and 300 millimetres of rainfall across much of Queensland, and between 50 and 200 millimetres across New South Wales and Victoria. Conditions are expected to be drier in Western Australia and South Australia, with forecast rainfall to between 10 and 100 millimetres, and 25 to 100 millimetres, respectively.

If realised, these expected rainfall totals are likely to be sufficient to support the growth and development of winter crops, boost soil moisture profile and assist in maintaining current winter crop yield expectations in most regions and provide a favourable start to the summer cropping season across eastern Australia. However, a potential downside production risk still remains across isolated regions across southern Australia exhibiting extremely low soil moisture levels leading into spring.

Livestock producers, especially those in the east and far north, are expected to experience improved pasture production given this favourable rainfall outlook over the October to December period.

Rainfall totals that have a 75% chance of occurring October to December 2024