- Area-averaged rainfall in Australian cropping regions during winter 2018 was the fifteenth lowest on record, implying this winter has been in the driest 13% of years.
- August rainfall was extremely low to well below average in southern cropping regions in New South Wales.
- Prospects for winter crop in the eastern states (including South Australia) will be highly dependent on timely spring rainfall because of low levels of soil moisture.
During winter 2018, rainfall was average to extremely low in cropping regions in Victoria, Queensland and South Australia and below average to well above average in cropping regions in Western Australia. Rainfall was severely deficient to well below average in many cropping areas New South Wales (Map 1).
For the Australian cropping region, area-average rainfall during winter 2018 was the fifteenth lowest on record (Table 4). For the New South Wales cropping region, the area-average winter rainfall total was the ninth lowest on record and the lowest area-average winter rainfall total since 2002. In New South Wales, this follows the sixth lowest area-average autumn rainfall total on record.
Table 4 Area-average rainfall
|Lowest on record|
|Lowest on record|
|New South Wales||54.2||9||26.9 (1982)||19.6||23||1.9 (1914)|
|Victoria||101.9||28||32.8 (1914)||37.8||46||2.9 (1944)|
|Queensland||43.6||26||5.2 (1946)||16||53||0 (1991)|
|South Australia||111.5||34||41.9 (1914)||57.4||88||5.1 (1914)|
|Western Australia||160.2||63||86.1 (2006)||61.3||102||12.1 (1956)|
|Australia||87.7||15||57.6 (1940)||33.9||51||8 (1914)|
Notes: Rank ranges from 1 (lowest) to 119 (highest). The figure within brackets in the lowest on record columns refer to the year in which lowest on records area-average rainfall was recorded.
During August 2018, rainfall was generally average in cropping regions in northern New South Wales, Victoria, eastern South Australia and Queensland (Map 2). Rainfall was average to extremely high in Western Australia and on the Eyre and Yorke Peninsulas in South Australia. However, rainfall was extremely low to well below average in southern cropping regions in New South Wales.
Map 3 and Map 4 show the relative levels of modelled upper layer (~0.1 metres) and lower layer (~0.1 to ~1 metres) soil moisture for cropping zones across Australia for August 2018. Soil moisture estimates are relative to the historical long-term average (1911 to 2015) and presented in percentiles.
Upper layer soil moisture responds quickly to seasonal conditions and often shows a pattern that reflects rainfall and temperature events in the days leading up to the analysis date. Lower layer soil moisture is a larger, deeper store that is slower to respond to seasonal conditions and tends to reflect the accumulated effects of events that have occurred over longer periods.
Relative upper layer soil moisture for August 2018 was predominantly average in cropping regions in north-eastern New South Wales, Victoria, eastern South Australia and Queensland (Map 3). It was generally above average to well above average in cropping regions in Western Australia and in the Eyre and Yorke Peninsula regions of South Australia. In southern and central cropping regions in New South Wales relative upper layer soil moisture was extremely low to well below average.
Relative soil moisture in the lower layer for August 2018 was generally extremely low to well below average in most cropping regions in New South Wales, northern and eastern Victoria, and the eastern Eyre Peninsula and upper north cropping regions of South Australia. It was generally average for most cropping regions in Western Australia, south-western Victoria, and much of the Eyre and Yorke Peninsulas in South Australia (Map 4).
Prospects for winter crop in areas of well below average lower layer soil moisture will be highly dependent on in crop rainfall during the remainder of the growing season.
The current outlook reflects the neutral state of broad-scale climate drivers, such as El Niño, La Niña and the Indian Ocean Dipole (IOD), meaning they are currently having little influence on Australia's climate. However, current observations and model outlooks indicate El Niño and a positive IOD could develop in spring. The latest model run from the Bureau of Meteorology's operational climate model also suggests that sea surface temperatures will continue to be cooler than average to Australia's northwest which is likely acting to suppress rainfall over southern and central Australia.
The rainfall outlook for September 2018 indicates that cropping regions in New South Wales and Western Australia have a 50% chance of recording close to median rainfall for the month, and cropping regions in Victoria, South Australia and Queensland have a 50% chance of recording half their median rainfall. This means cropping areas in Western Australia have a 50% chance of receiving between 10 and 25 millimetres in the east and between 25 and 50 millimetres in the south-west in September (Map 5).
In New South Wales it means cropping regions have a 50% chance of receiving between 10 and 25 millimetres in the west and between 25 and 50 millimetres of rain in the east during September 2018. In Victoria, cropping regions have a 50% chance of receiving between 10 and 25 millimetres in the north and between 25 and 50 millimetres in the south. In South Australia, cropping regions have a 50% chance of receiving between 10 and 25 millimetres in the east and north and between 25 and 50 millimetres of rain in southern regions. The south-east of the Queensland cropping region have a 50% chance of receiving between 10 and 25 millimetres, the remainder of the Queensland cropping region has a 50 per cent chance of between 0 and 1, 1 and 5, or 5 and 10 millimetres.
Given the relatively low level of soil moisture in most summer cropping regions of northern New South Wales and Queensland, this rainfall outlook scenario would suggest that planting opportunities are likely to be limited during September 2018.
The Bureau of Meteorology's seasonal rainfall outlook for September to November 2018 indicates that a drier than average spring is more likely for most western and southern Australian cropping regions (Map 6). The highest chance of exceeding average spring rainfall is in cropping regions in Queensland and northern New South Wales. Maximum temperatures are likely to be higher than average across most Australian cropping regions.
Map 7 shows the shire-scale forecast of wheat yields obtained from the University of Queensland's Queensland Alliance for Agriculture and Food Innovation (QAAFI). These forecasts are based on soil moisture conditions and the seasonal outlook, including the most recent trend in the Southern Oscillation Index (SOI). QAAFI uses the most recent trends in the SOI to calculate probabilities of receiving particular amounts of rainfall at a shire level over the next few months. This is different to the methodology used by ABARES and there are regional differences between the QAAFI and ABARES yield forecasts, particularly for Western Australia.
At the beginning of September 2018, the departure of the forecast shire median yield from the long-term median wheat yield, is expected to be high (between 30 and 60%) in most cropping regions in central and northern New South Wales, southern and northern Queensland, central Victoria and some eastern cropping regions in Western Australia. Some central and northern cropping regions in Western Australia, parts of central Queensland, southern New South Wales, northern Victoria and scattered shires in South Australia show slightly reduced chances of exceeding the long-term median wheat yield (between 10 and 20%).
Table 5 Rainfall in major cropping districts, median and actual, June 2018 to August 2018
|District||District no.||June median|
New South Wales|
|NW Plains (W)||52||33||8||30||5||19||18|
|NW Plains (E)||53||37||9||36||10||30||30|
|NW Slopes (N)||54||38||7||41||29||37||37|
|NW Slopes (S)||55||43||11||42||11||41||28|
|N Tablelands (N)||56||43||12||44||43||42||30|
|CW Plains (S)||50||38||35||36||2||30||13|
|CW Plains (N)||51||33||26||28||2||23||15|
|CW Slopes (N)||64||40||24||44||5||36||30|
|CW Slopes (S)||65||47||27||50||5||45||26|
|C Tablelands (N)||62||42||29||45||9||45||35|
|C Tablelands (S)||63||54||45||56||10||59||36|
|SW Slopes (N)||73||57||53||59||16||62||27|
|SW Slopes (S)||72||92||90||102||54||114||82|
|Lower North East||82||107||96||113||66||118||97|
|W Darling Downs||42||27||15||28||16||20||33|
|E Darling Downs||41||29||11||31||22||24||19|
|Moreton S Coast||40||37||22||37||20||29||17|
|Upper South East||25B||50||43||53||47||57||66|
Note: Median rainfall is calculated over the period 1900 to August 2018. Australian rainfall districts are shown in Map 8 of the Australian crop report.
Source: Bureau of Meteorology monthly district rainfall reports