Weekly update - 29 September 2022

For the week ending 28 September 2022, a low-pressure system and onshore flow brought moderate to heavy rainfall to large areas of eastern Australia, with troughs and cold fronts resulting in isolated falls in other parts of the country. Weekly rainfall totals exceeding 50 millimetres were recorded in parts of eastern New South Wales and Victoria, as well as south-east Queensland and the far north of the Northern Territory. High-pressure systems over western and southern parts of the country resulted in clear, dry conditions.

In Australian cropping regions, rainfall totals of between 10 and 50 millimetres were recorded across most of New South Wales, southern Queensland, Victoria and isolated parts of south-eastern South Australia. Rainfall in excess of 50 millimetres was recorded in isolated parts of New South Wales. Little to no rainfall was recorded in remaining cropping regions of northern Queensland, South Australia and Western Australia for the week ending 28 September 2022.

Another week of moderate to heavy rainfall across major cropping regions of eastern Australia has exacerbated waterlogging in low lying areas. Major flooding was also recorded across rivers in northern New South Wales, including the Culgoa, Bogan, Gwydir, Lachlan, Macquarie, Namoi and Narran rivers. The flooding is expected to result in isolated crop losses. More broadly, wet conditions will delay crop development and increase the risk of fungal damage. Root zone soil moisture levels remain well above average across most eastern and southern cropping regions, with further rainfall likely to diminish yield potentials.

Harvesting of winter crops is underway in Central Queensland, with the pace of activity expected to increase over the coming weeks if conditions allow. There are also reports of early harvesting in parts of Western Australia, however harvesting activity is unlikely to get underway in earnest for some weeks yet. The risk of frost and extreme heat will weigh on yield potentials through flowering and grain filling. Wet conditions across New South Wales, southern Queensland, Victoria and South Australia are expected to delay the start of harvesting of winter crops, especially for late sown crops.

Rainfall for the week ending 28 September 2022

The northern rainfall onset occurs when the total rainfall after 1 September reaches 50 millimetres. This is considered approximately the amount of rainfall required to stimulate plant growth. Coastal parts of northern Australia usually accumulate 50 millimetres of rainfall by late October or early November, spreading to inland areas over subsequent weeks. The presence of La Niña conditions is associated with earlier than normal northern rainfall onset. Negative Indian Ocean Dipole conditions may also contribute to a higher likelihood of an earlier than normal northern rainfall onset.

Median northern rainfall onset in La Niña years 1981 to 2018

Since 1 September 2022, rainfall in excess of 50 millimetres has been recorded across most of southern Queensland, as well as isolated parts of northern Queensland, Western Australia and the Northern Territory. For summer cropping regions, rainfall in excess of 50 millimetres has been recorded across New South Wales and most of Queensland. Rainfall in excess of 100 millimetres has also been received in parts of eastern and northern New South Wales and southern Queensland, causing localised flooding. The northern rainfall onset across cropping regions of eastern Australia is likely to impede the harvesting of winter crops and the sowing of summer crops, especially in areas that have already received above average rainfall throughout winter. However, the rainfall will boost soil moisture for summer crops and northern pastures.

Month-to-date rainfall at 28 September 2022

Over the 8-days to 6 October 2022,low-pressure systems and troughs are forecast to result in showers across eastern and north-western Australia. High-pressure systems will provide clear, dry conditions across remaining parts of the country.

In Australian cropping regions, rainfall totals of between 10 and 50 millimetres are expected across New South Wales, Victoria, South Australia, most of Queensland and isolated parts of the south of Western Australia. Little to no rainfall is forecast for remaining cropping regions in northern Queensland and Western Australia during the next 8-days.

Limited rainfall in parts of Central Queensland over the coming week will allow the harvest of winter crops and the sowing of long-season summer crops to gather pace. Significant rainfall across remaining cropping regions of eastern and southern Australia will contribute to ongoing issues of waterlogging across low-lying areas. These wet conditions are expected to prolong inundation of crops, negatively impacting yield potentials, as well as restricting the ability to access fields for disease management. Yield potentials remain above average across cropping regions, but rainfall over the coming weeks is unlikely to improve them further.

The biggest threat to yield potentials across eastern and southern cropping regions remain waterlogging and frost as winter crops enter flowering and grain filling. For Western Australia, frost and extreme heat present the biggest downside risk, given the favourable conditions to date. The continued influence of a negative Indian Ocean Dipole and the establishment of a La Niña event in the Pacific Ocean suggests a continuation of wet conditions over the coming months for eastern Australia. A likely consequence will be delays in harvesting winter crops and planting summer crops, as well as increased crop damage.

Total forecast rainfall (mm) for the period 29 September to 6 October 2022