Is a 10-day rainfall forecast of value in dry-land wheat cropping?

Grain yields vary widely between seasons in rain-fed agriculture. The yield variability is strongly influenced by rainfall variability and a number of related crop management decisions. This is well recognised in the literature through the use of seasonal rainfall forecasts applied to the main cropping decisions. However, the value of short-term 10-day rainfall forecasts for management decisions in cropping has not yet been quantified. Here we report on the potential benefits of a hypothetical, always-correct 10-day rainfall (greater than 10 mm in three days) forecast used to determine early and late in-season crop management decisions.

Most of the analysed applications of short-term rainfall forecasts show a significant increase in cropping profitability depending on rainfall region and soil type. Using a 10-day rainfall forecast to dry-sow prior to the traditional start of sowing at the first autumn rainfall can yield an extra A$20,000 to A$200,000 for a typical farm (i.e. A$10 to A$100/ha for a 2000 ha cropping programme). The same forecast type can be used to determine late in-season decisions on N fertiliser, and fungicide applications to control rust at the end-of-ear growth stage. In the one-third of seasons with late rainfall, the increased yield or decreased fungal damage can lead to benefits of A$10 to A$160/ha. When 10-day rainfall forecasts are applied together within a season, the extra benefits from correct short-term forecasts can be cumulative.

Fine-tuning the forecast length, rainfall thresholds and exploring other possible crop decisions could lead to further increased returns in cropping from short-term rainfall forecasts. Ultimately, using hindcasts of short-term rainfall forecasts to measure the forecast skill and the implication of occasional non-correct forecasts will determine the actual value of such forecasts.