ASSESSMENT OF THE VALUE OF LONG-RANGE WEATHER FORECASTS IN WHEAT HARVEST MANAGEMENT

Quality losses from weather damaged wheat cost the Australian wheat industry on average around $A30 M annually. These losses are higher in the north-eastern region than in other regions of the Australian wheat belt because of spring and summer dominant rainfall coinciding with harvest. If a wet season can be predicted, growers could reduce grain losses by strategies such as early harvesting, contract harvesting, additional grain drying and harvesting at a faster rate. In north-eastern Australia, long-range rainfall forecasting is possible by the analysis of sea surface temperatures and air-pressure differences between Tahiti (17 degrees S 150 degrees W) and Darwin (12 degrees S 131 degrees E) as identified by the Southern Oscillation Index (SOI). Using monthly SOI and rainfall data since 1890, this paper examines the relationship between the SOI and rainfall during the harvest period in north-eastern Australia. A simulation model of wheat harvesting and drying developed earlier was used to investigate the value of seasonal forecasts as a decision aid in harvest management. The results show that in north-eastern Australia, the status of the SOI as early as May gives a reasonable indication of above- or below-average rainfall in the following spring and summer (October-December). This information could enable growers to minimize grain quality damage by altering their management practices according to seasonal variations in rainfall. This could involve harvesting of high-moisture grain and drying it or, the use of contract harvesting when the seasonal outlook for rainfall is high. The value of such information to the producer is predicted to be around $A12 ha(-1) per year through improvements in grain quality and reduced losses. (C) 1995 Silsoe Research Institute