Seasonal rainfall update

Rainfall update 21 August 2018

Rainfall for the month to date

Rainfall has continued through August, with good falls along the west coast and northern grainbelt, as well as the south-west and coastal parts around Esperance (Figure 1). Monthly rainfall is already above average for much of the central grainbelt, parts of the south-west and Esperance coast.

Map of Western Australia showing rainfall totals in millimetres for 1 to 21 August 2018
Figure 1 Western Australian rainfall totals (in millimetres) for 1–21 August 2018 (source: Bureau of Meteorology, www.bom.gov.au/climate/)

Monthly rainfall to date is available from the DPIRD weather stations and radar page (select Month to Date from the drop-down menu).

Seasonal rainfall

Good rain in July and most of August has advanced much of the northern and central grainbelt to be close to or above median seasonal rain to date (Figure 2). South-eastern parts of the grainbelt remain well below normal seasonal rain to date, with much of the south coast still at decile 2. Note Figure 2 uses the years 1975-2017 as reference period for derivation of deciles. This period is drier than the baseline used by the Bureau of Meteorology (1961-1990).

Map of Western Australia showing rainfall as deciles for 1 April to 19 August 2018
Figure 2 Rainfall deciles from 1 April to 19 August 2018 (data source: Patched Point Database)

For graphs of rainfall at individual locations, see DPIRD’s Rainfall to date tool.

Soil moisture

Figure 3 shows relative root zone soil water storage to 20 August 2018 from the Bureau of Meteorology’s Landscape Water Balance model. Rain in early August has improved soil water storage for much of the grainbelt and parts of the south coast. A region along the south coast east of Albany remains with relatively low levels of soil water storage for this time of year.

For soil water estimates at individual locations with and without crop water use, see DPIRD’s Soil water tool .

Map of Western Australia showing relative root zone soil water at 20 August 2018
Figure 3 Estimated relative root zone soil water at 20 August 2018 from the Bureau of Meteorology’s Landscape Water Balance model

Potential yield

Potential crop yield is estimated using the French-Schultz relation, and uses seasonal rainfall from 1 April to date. Rainfall for the rest of the growing season (to 30 September) is assumed to be decile 5. This model does not account for crop diseases or soil constraints.

Map of Western Australia showing potential crop yield in tonnes per hectare at 20 August 2018
Figure 4 Potential crop yield based on seasonal rainfall to date, and assuming an average finish to the season

To estimate yields at individual locations refer to the Potential yield tool.

Rainfall forecast for the next two weeks

Rainfall forecast for the next week shows continuing rain for the lower west coast and south west of WA (Figure 5). Rain along the south coast appears to be confined to coastal parts.

Beyond next week, the US NCEP model indicates rain, although lighter falls, continuing into early September (Figure 6).

Map of Australia showing forecast rainfall 21 to 28 August 2018
Figure 5 Bureau of Meteorology forecast rain in millimetres for 21-28 August 2018 (source: www.bom.gov.au/jsp/watl/rainfall/pme.jsp)

 

Map of Australia showing forecast rainfall from the NCEP model for 28 August to 6 September  2018
Figure 6 Rainfall predicted for the next two weeks from the US NCEP model, to 6 September 2018 (source: http://wxmaps.org/pix/prec7)

In this Issue

Seasons