Focused review of ‘advance dynamical seasonal forecast system outputs’ for Australian grazing regions

Summary

Followings requests from industry to assess ‘’how well are general circulation models (GCMs) performing over recent years” and “when would have been the best occasions to apply GCMs in an operational environment”, a preliminary time series analysis of seasonal climate forecasting skill for broad grazing regions of Australia for the past 6-7 years has been completed. The time series analysis of forecast skill follows an approach that previously conducted by the Bureau of Meteorology on an SOI-based statistical forecasting system for eastern Australia. The analysis of GCM outputs, that incorporated ‘per cent consistent’ hit rates of forecast skill, was performed on data independent of forecast model development and, thus, is referred to as ‘independent verification if real time’. 
The results suggests generally positive forecast skill results if averaged over the period analysed but with widely varying results if assessed on a year to year or season to season time series basis. Most noticeably is that seasonal forecast skill has only been consistently high over this period if assessed during the onset, duration and cessation of an El Niño or La Niña (ENSO) event but with widely varying results, including very low skill scores, during non-ENSO periods. A further associated comparative analysis also suggests that statistically-based seasonal forecast systems, based on the Southern Oscillation Index (SOI), also possess forecast skill for the regions analysed, especially during ENSO periods, and should not be discarded. It is suggested utilisation of a time-series approach to assessment of seasonal forecast skill be incorporated into any more detailed assessments of seasonal forecast capabilities in the future. 
The results presented in this study are only preliminary and it is recommended that a more comprehensive time series analysis over a much longer time period than 6-7 years be initiated in order to provide a more comprehensive assessment of the periods of most value in the utilisation of seasonal forecasting, especially of GCMs, in Australia and for Australian rural industry needs.