THE VALUE OF SKILL IN SEASONAL CLIMATE FORECASTING TO WHEAT CROP MANAGEMENT IN A REGION WITH HIGH CLIMATIC VARIABILITY

In Australia, and particularly in the northern part of the grain belt, wheat is grown in an extremely variable climate. The wheat crop manag er in this region is faced with complex decisions on choice of plantin g time, varietal development pattern, and fertiliser strategy. A skilf ul seasonal forecast would provide an opportunity for the manager to t ailor crop management decisions more appropriately to the season. Rece nt developments in climate research have led to the development of a n umber of seasonal climate forecasting systems. The objectives of this study were to determine the value of the capability in seasonal foreca sting to wheat crop management, to compare the value of the existing f orecast methodologies, and to consider the potential value of improved forecast quality. We examined decisions on nitrogen (N) fertiliser an d cultivar maturity using simulation analyses of specific production s cenarios at a representative location (Goondiwindi) using long-term da ily weather data (1894-1989). The average profit and risk of making a loss were calculated for the possible range of fixed (i.e. the same ev ery year) and tactical (i.e. varying depending on seasonal forecast) s trategies. Significant increase in profit (up to 20%) and/or reduction in risk (up to 35%) were associated with tactical adjustment of crop management of N fertiliser or cultivar maturity. The forecasting syste m giving greatest value was the Southern Oscillation Index (SOI) phase system of Stone and Auliciems (1992), which classifies seasons into 5 phases depending on the value and rate of change in the SOI. The sign ificant skill in this system for forecasting both seasonal rainfall an d frost timing generated the value found in tactical management of N f ertiliser and cultivar maturity. Possible impediments to adoption of t actical management, associated with uncertainties in forecasting indiv idual years, are discussed. The scope for improving forecast quality a nd the means to achieve it are considered by comparing the value of ta ctical management based on SOI phases with the outcome given perfect p rior knowledge of the season. While the analyses presented considered only one decision at a time, used specific scenarios, and made a numbe r of simplifying assumptions, they have demonstrated that the current skill in seasonal forecasting is sufficient to justify use in tactical management of crops. More comprehensive studies to examine sensitivit ies to location, antecedent conditions, and price structure, and to as sumptions made in this analysis, are now warranted. We have examined d ecisions related only to management of wheat. It would be appropriate to pursue similar analyses in relation to management decisions for oth er crops, cropping sequences, and the whole farm enterprise mix.