Climatic and agronomic conditions

Australian Crop Report: September edition

Following above average rainfall from January to April, May to July rainfall was extremely low to below average in most cropping regions in Victoria, Queensland, South Australia and Western Australia. In cropping regions in New South Wales, May to July rainfall ranged from well below average to above average (Map 1).

Despite variable rainfall in June and July, close to average yield potentials were preserved across most cropping regions due to a draw down of soil moisture reserves built up during late summer and autumn.

Map 1 Australian rainfall percentiles, 1 May 2020 to 31 July 2020

Note: Rainfall percentiles are displayed for cropping regions only.
Source: Bureau of Meteorology

August rainfall was generally average to above average in most cropping regions except for some southern cropping regions in Western Australia and South Australia where August rainfall was below average (Map 2). Substantial August rainfall improved soil moisture across most cropping regions, supporting the final stages of winter crop development and providing a reliable base for the early planting of summer crops.

Map 2 Australian rainfall percentiles, 1 to 31 August 2020 

Note: Rainfall percentiles are displayed for cropping regions only.
Source: Bureau of Meteorology

Map 3 shows the relative levels of modelled root zone (0 to ~1 metres) soil moisture for cropping zones across Australia for August 2020. Soil moisture estimates are relative to the historical long-term average (1911 to 2016) and presented in percentiles.
Relative root zone soil moisture for August 2020 was around average to above average for this time of year in most cropping regions in the eastern states. In contrast root zone soil moisture was average to extremely low for this time of year in South Australian and Western Australian cropping regions (Map 3).

Map 3 Root zone soil moisture, August 2020 

Note: Relative root zone soil moisture is displayed for cropping regions only. The extremely high band indicates where the estimated soil moisture level for August 2020 fell into the wettest 10 per cent of estimated soil moisture levels on that day each year between 1911 and 2016. The extremely low band indicates where the estimated soil moisture levels for August 2020 fell into the driest 10 per cent of estimated soil moisture levels on that day between 1911 and 2016.
Source: Bureau of Meteorology.

The rainfall outlook presented here provides an indication of how favourable conditions for agricultural production are likely to be over spring. The latest three-month rainfall outlook (September to November), issued by the Bureau of Meteorology on 3 September 2020, suggests that spring rainfall is likely to be above average in most cropping regions. However, there are roughly equal chances of higher or lower than average spring rainfall in most cropping regions in Western Australia and below average spring rainfall is most likely in the Geraldton zone in Western Australia and part of the Kwinana zone. (Map 4). It is likely rainfall will not be evenly distributed in most cropping regions over spring with a lower chance of exceeding average rainfall in September than in October and November.

Map 4 Chance of exceeding median rainfall September to November 2020 

Note: Rainfall outlook is displayed for cropping regions only.
Source: Bureau of Meteorology

There is a 75% chance of between 25 and 100 millimetres in most cropping regions in Australia during September and October (Map 5). It is highly likely spring rainfall totals will be enough to maintain average to above average crop yields through to harvest in regions where crops were in a good position at the end of winter.

There is a 75% chance of rainfall between 10 and 50 millimetres in most cropping regions in Western Australia and northern cropping regions in Queensland. In areas with low levels of soil moisture at the start of spring these probable September to October rainfall totals are unlikely to be sufficient to sustain the current winter crop yield potentials through to harvest.

The outlook for maximum and minimum temperatures for September to November 2020 indicates that daytime temperatures are likely to be around average in spring in most cropping regions. Night-time temperatures are expected to be hotter than average in most cropping regions except in Western Australia where they are more likely to be around average.

Map 5 Rainfall totals that have a 75% chance of occurring, September to October 2020 

Note: Rainfall outlook is displayed for cropping regions only.
Source: Bureau of Meteorology

Map 6 shows modelled water availability levels that have a high chance of occurring by the end of October 2020. Water available for crop growth comes from water stored at sowing time and in-crop rainfall. On average, the total water requirement to achieve the national 5-year average wheat yield of 2.0 tonnes/ha is 235 millimetres, based on a conversion rate of 16kg of wheat per millimetre of water and a standard soil evaporation loss factor of 110 millimetres.

Indicative estimates of water availability are based on modelled plant available soil moisture as at 30 April 2020, recorded rainfall totals as at 31 August 2020, an estimate of rainfall totals with a 75% chance of falling during September and October 2020 derived from the Bureau of Meteorology latest rainfall outlook released on 3 September 2020.

The crop yield associated with a specific level of water availability varies across regions with variations in soil characteristics. Additionally, in some seasons the responsiveness of crop growth to water availability will be better than average (around 22kg/mm) and in other years it will be worse (around 6kg/mm) as responsiveness depends on factors such as temperature, humidity, soil nutrition and the timing of rainfall.

Map 6 Modelled water availability levels that have a 75% chance of occurring by the end of October 2020

Note: Modelled water availability is displayed for cropping regions only. 
Source: ABARES & Bureau of Meteorology 

At the end of August 2020, there was a 75% chance of achieving at least 265 millimetres of water availability by the end of October 2020 in eastern and central cropping regions in New South Wales, southern cropping regions in Victoria, central and southern cropping regions in South Australia and far western and southern cropping regions in Western Australia. There is a 75% chance of achieving between 140 and 235 millimetres of water availability by the end of October 2020 in north-western and south-western cropping regions in New South Wales, most cropping regions in Queensland, northern cropping regions in Victoria and South Australia, and most cropping regions in Western Australia.

Statistical tables

Last reviewed: 7 September 2020
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