Productivity performance of climatological sub-regions within the Tully Mill area

Inter-annual climate variability has a significant impact on productivity in the Wet Tropics region. Climate also varies spatially, yet the impact on productivity is less well known. Two distinct climatological sub-regions (northern and southern) have been identified within the Tully mill area based on total annual rainfall and annual average daily radiation. The wetter northern sub-region is characterised by lower radiation, lower temperatures and higher rainfall than in the drier southern sub-region. Mean cane and sugar yields were analysed for the two climate sub-regions using block productivity data obtained from Tully Sugar Limited for 2000 to 2017. After excluding 2011 (Tropical Cyclone Yasi), only farms with 15 or more years of data were included. The impact of spring-summer (SONDJF) rainfall and El Niño Southern Oscillation (ENSO) phases on cane and sugar yields in the two climate sub-regions was also analysed. On average, the northern, wetter climate sub-region yielded less cane and sugar yield than the southern, drier sub-region. There were significant differences between SONDJF rainfall terciles (dry, normal and wet) and ENSO phases (El Niño, Neutral and La Niña) for cane and sugar yields in the two climate sub-regions. Cane and sugar yields were significantly lower in years experiencing high SONDJF rainfall or in the La Niña phase. This analysis validates the results of the analyses used to derive the two climatological sub-regions in Tully. Improved knowledge of how climatic conditions influence sub-regional productivity performance will assist industry extension programs and on-farm management decisions. Key words Climate, productivity, extension, Tully