Influence of El Nino-Southern Oscillation and the Indian Ocean Dipole on winegrape maturity in Australia

Seasonal timing of winegrape maturity is influenced by weather conditions. Significant changes to day-of-year of-maturity (DOYM), both earlier and later than average, causes logistical problems during harvest, impacting on grape and wine quality. Shifts in climate circulation patterns resulting from atmospheric teleconnections to changes in sea surface temperature (SST) anomalies associated with El Nino-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) events can alter seasonal weather across Australia. Events tend to peak in the austral spring (IOD) and summer (ENSO), when vine and berry development is susceptible to anomalous weather. To investigate the impacts of ENSO and IOD on the Australian winegrape growing sector, SST data and annual grape maturity data from a variety of wine growing regions were collected and analysed. Mean DOYM values during IOD events were significantly (P < 0.05) different for the largest number of vineyard blocks, with IOD positive (IOD +) events linked to earliest mean DOYM and IOD negative (IOD -) events linked to latest mean DOYM. ENSO and IOD combined events (ENSOIOD) had the largest difference between earliest mean DOYM and latest mean DOYM (42 days). Results for ENSO only grouped events were mixed, with no clear pattern emerging. This finding suggests that the IOD had more impact on DOYM than ENSO and that the IOD superseded the ENSO signal in combined events for the regions included in this study. The results indicate that improved seasonal forecasting of IOD, ENSO, and combined events would allow the Australian winegrape sector to better plan for changes to timing of grape maturity and associated impacts on grape and wine quality, vineyard management, and harvest logistics.