Effects of climatic variability and possible climatic change on reliability of wheat cropping-A modelling approach

Wheat cropping in the northern sector of the Australian wheat belt has been expanding into a region with a more marginal moisture regime and a more variable climate than in the established cropping regions. To provide a sound basis for land use assessment, the likely reliability of cropping in this region was examined. Reliability included the likelihood of planting a wheat crop in any year and the likely yield of planted crops. Simulation studies, using an appropriate model of the cropping system and long-term rainfall records (92-year period), were used to derive yield probability distributions for sites throughout the region. The main features of the cropping system model developed are outlined. The yield probability distributions and associated economic analyses indicated that expansion of wheat cropping in this region was likely. Trends in simulated yield sequences were compared with analyses of factors associated with recent climatic change. Similarities of patterns suggested an association of rainfall and yield trends with climate forcing factors. Implications of this association are discussed. A better understanding of the action of the climate forcing factors is required before possible climatic change can be included in determining reliability of cropping