FORECASTING WHEAT YIELD IN A MEDITERRANEAN-TYPE ENVIRONMENT FROM THE NOAA SATELLITE

This paper reports the relationship between the spatial variation in m ean wheat yield/ha of 50 Local Government Areas in Western Australia a nd satellite measures of the Normalized Difference Vegetation Index (N DVI). Yield/ha was based on estimates of the area harvested and actual grain received by the Cooperative Bulk Handling Ltd. The study area c overed 16.3 million ha, in which 2.9 million ha of wheat were sown and 4.66 million tonnes of grain harvested. This was 78% of the total Wes tern Australian wheat crop. Spatial variations in NDVI in early July, at around stem elongation, accounted for 46% of the spatial variation in final yield. This increased to 56% of yield variance around the ons et of anthesis at the end of August. It remained high until early Nove mber (48%) when crops were senescing or senescent. A combination of ND VI from late August and early November accounted for 70% of the yield variance. In comparison, total rainfall during the 1992 growing season from April to October, the main determinant of yield variations, acco unted for 28% of the yield variation. The significant correlation of N DVI with final yield by the middle of the growing season 3 to 5 months before harvest indicates the feasibility of making useful yield forec asts from this time onwards. In addition, the NDVI could provide usefu l spatial information on the significance of the yield/canopy developm ent/water use relationship which underlies this correlation.