Info

Note: NS = nonsignificant result; in RAINMAN a result with probability less than 90 percent; * = 95 percent probability of effect being real; ** = 99.9 percent probability of effect being real.

above +5. Therefore, the most appropriate values for this year are in the scenario "SOI above +5." This indicates a 63 percent chance of rainfall exceeding 200 mm in the coming October to December period. In other words, the odds favor an above-average rainfall in the coming season.

2. It is autumn in Walgett, New South Wales. To obtain the maximum yield, a farmer wants to sow his wheat crop at the first available opportunity. He wants to know the likely date of the first rain in the season so that he can be ready to complete the sowing operation in one go.

The information the Walgett farmer needs can be easily obtained from Australian RAINMAN. RAINMAN has historical rainfall records for Walgett and thousands of other locations.

Procedure. Open Walgett in RAINMAN, and choose "Daily Forecasts" from the "Selector" dropdown window; the "Daily Forecasts" window opens. Click on "Setting"; the "Critical Rainfall Event Setting" window opens. Select:

Rainfall period start date as May 1 and end date as October 30 SOI start month March and end month April

Minimum rain in a rainfall event as 25 mm and maximum duration of rain event as three days

Close the "Critical Rainfall Event Setting" window and return to the "Daily Forecasts" window. Select:

SOI phases from the "Methods of Daily Analysis" (Any one of the four methods can be chosen.)

A table (Table 8.4) is generated (can be a graph also) that gives the information about the rainfall event at Walgett during the coming season under alternative scenarios.

Time of occurrence of the first effective rainfall event at Walgett is highly variable from season to season. From historical records it is established that, like any other place in eastern Australia, the first effective rainfall event and overall rainfall in a particular season is normally influenced by the SOI phase during the two months prior to the commencement of a season.

The average date of the first rainfall event (rain > 25 mm in three consecutive days) at Walgett is July 15. This year, SOI value in March was -7.8 and in April -8.6. These values represent a negative SOI phase in March and April. Therefore, the most appropriate forecast for the coming season is in

TABLE 8.4. Chance of first rainfall event of the May to October season at Walgett, using SOI phases in March-April (Event = 25 mm in three days; rainfall period: May 1 to October 31)

SOI phases

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