RECOGNISING THE IMPACT OF CLIMATE ON CCS OF SUGARCANE ACROSS TROPICAL AND SUB-TROPICAL REGIONS OF THE AUSTRALIAN SUGAR INDUSTRY

CCS decline in the wet tropics has been associated with the GCTB harvest system, extraneous matter, suckers, lodging and pest damage, yet there has been no integrated analysis of any underlying impact of climate on CCS. Such an analysis is presented in this paper through development of statistical models to estimate weekly CCS from climate variables and date of harvest for Condong, Moreton, Babinda and Mourilyan mills from 1987–1999. Three models were developed: a regional model for each of the geographic regions and a global model for the combined data. Average difference between actual weekly CCS and that estimated from relevant regional models was within 5% to 8% of weekly mill average CCS for 72% and 93% of years, respectively. Similarly, average CCS residuals for the global model were within the above categories for 65% and 91% of years, respectively. The models were most suited to estimation of CCS prior to calendar weeks 43–47 (late October to late November), after which CCS was overestimated in years where there was a rapid decline in actual CCS. The otherwise satisfactory performance of the global model demonstrates the underlying impact of climate on CCS across regions. Regional and global models were validated against weekly CCS for each mill in the 2000 season, where there was good agreement between actual and estimated CCS (r2 = 0.86–0.94). The declining trend in radiation and diurnal temperature range during the 1990s and an increase in rainfall during the harvest had a negative impact on CCS.