The graphs are produced using daily rainfall data from the Patched point data set and data from DAFWA's automatic weather stations (AWS). When data for an AWS is unavailable, data from the geographically closest Patched Point station are used. For example, many of the AWS only began recording data recently, so historical data from the closest Patched Point station is used to create pseudo rainfall deciles.
Rainfall to date tool
Rainfall to date graphs show the amount of rainfall accumulated from the start of the grain growing season and can be used as a tool in the seasonal decision-making process.
The amount of summer rainfall provides an indication of the amount of stored soil water at the start of the growing season.
Rainfall deciles are generated using data from 1975 to the year prior to the current year (inclusive) for each location.
While rainfall to date graphs can help create a narrative for the progress of a given crop and aid key in-season decision-making, other key factors also need to be considered for any given crop to arrive at an accurate picture. These include:
- soil status and characteristics including stored soil moisture, soil water-holding capacity and any barriers to infiltration
- stored nitrogen and other nutrient availabilities
- factors such as non-wetting, water-logging through topography or impermeable layers, leaching or dispersible clays in the soil.
The timing and event intensity of rain during the growing season can also greatly influence the conversion of rainfall to biomass and yield.
How to use the tool
To use the tool, first select a weather station from the drop-down list below.
Next, select the summer start date. Usually, the start of summer is set to 1 November of the year prior to the current growing season. This can be changed, for example if a large rainfall event occurred in early November that is unlikely to affect the soil moisture status at the end of summer then you may set the summer start date to exclude that event. The start of summer must be before the start of the growing season. The end of summer will be automatically set as the day before the growing season starts.
Now select the growing season start and end dates. Usually, the growing season is set to be from 1 May to 31 October. However, some growers may find 1 April to 30 September to be more appropriate, depending on their location. The growing season start and end dates must be within the same calendar year.
Cumulative rainfall for the current growing season is shown up to and including the forecast date. After the forecast date, projected decile finishes are shown. During the growing season, the forecast date is usually set to the current date.
Graphs can be downloaded and saved by clicking on the three horizontal lines to the right of the graph title.
How to interpret the graphs
The figure below shows how the deciles and current rainfall are displayed in the graphs for each location. Note that deciles will look different depending on location. For example, decile 1 in a high rainfall zone will look very different in terms of rainfall received to decile 1 in a low rainfall zone.
The top solid green line is decile 9, which means that 90% of years in the historical data (1975 onwards) have recorded less rainfall than this and 10% recorded more.
The middle solid green line is decile 5, which means that 50% of years in the historical data have recorded less rainfall than this and 50% recorded more.
The bottom solid green line is decile 1, which means that 10% of years in the historical data have recorded less rainfall than this and 90% recorded more.
The solid purple line is the current amount of rainfall received for the current growing season.
Graphing these lines enables a comparison between current rainfall received and the historical records and provides some context to the current season and how it's tracking.
Throughout the growing season, the solid purple line will show current rainfall received. Extending out from the solid purple line are three blue dashed lines which represent the historical finishes to a season from the current date onwards.
The top blue dashed line is a decile 9 finish, which means that 90% of years in the historical data finished with less rainfall than this and 10% finished with more.
The middle blue dashed line is a decile 5 finish, which means that 50% of years in the historical data finished with less rainfall than this and 50% finished with more.
The bottom blue dashed line is a decile 1 finish, which means that 10% of years in the historical data finished with less rainfall than this and 90% finished with more.
What is average rainfall?
Use the deciles to interpret where current rainfall sits in a historical sense.
Deciles are generated using data from 1975 to 2014 (inclusive) for each location.
Rainfall deciles are calculated by ordering data from smallest to largest and then seperating into 10 groups of equal size.
When speaking about deciles, we can refer to them as "well below average", "below average", "average", "above average" and "well above average".
Decile 1 is the lowest 10% of years on the historical record and is considered well below average.
Deciles 2 and 3 are the lowest 20-30% of years on the historical record and are considered below average.
Deciles 4 to 7 are the middle 40% of years on the historical record and are considered average. Decile 5 is the median (middle).
Deciles 8 and 9 are the top 20-30% of years on the historical record and are considered above average.
Decile 10 is the top 10% of years on the historical record and is considered well above average.
Extent of range
Lowest 10% of records
Well below average
Second and third lowest 10% of records
Middle 40% of records
Second and third highest 10% of records
Highest 10% of records
Well above average