Advanced phenology due to climate change is projected to shift precipitation patterns for key cultivar-region combinations in New Zealand

Abstract

Context of the study. Shifts in grapevine phenology driven by temperature increase due to climate change may result in different rainfall profiles between phenological stages. This may lead to extremes of excess or reduced water input at different phenological stages of the grapevine.

Purpose of the study. To evaluate precipitation for phenological periods under future climate change scenarios for key region-cultivar pairings in New Zealand: Sauvignon blanc- Marlborough, Merlot-Hawke’s Bay, and Pinot noir-Central Otago in New Zealand.

Material and methods. Six global circulation models (GCMs) were used to generate daily temperature and rainfall data and averaged across the GCMs for three periods: baseline (1985-2005), mid- (2031-2050) and end-century (2081-2100) using IPPC climate change scenarios RCP4.5 and RCP8.5. The temperature data was used in phenological models simulated budburst to flowering, flowering to veraison, and veraison to target sugar concentration of 200 g/L, and three weeks prior to flowering. Rainfall indices of total precipitation (mm), number of rain days, and rainfall intensity (average precipitation per rain day) were calculated for each phenological phase for each region-cultivar combination.

Results. Rainfall projections increased from budburst to flowering but decreased for the other periods for Sauvignon blanc-Marlborough, and at times was accompanied by increased rainfall intensity due to fewer rain days. However, the total rainfall for the growing season was unchanged.

Merlot in Hawke’s Bay exhibited similar trends for phenophase changes in rainfall, but with fewer rain days, rainfall intensity was unchanged.

For Pinot noir in Central Otago, up to 37 mm more rainfall was projected between budburst and flowering compared to baseline, but conversely deficits of up to –20 mm was projected from veraison to target sugar concentrations by the end of the century.

Significance of study. The projected trends have adaptation management implications such as canopy management to manage vine vigour and disease pressure to manage projected increase rainfall between budburst and flowering for Central Otago-Pinot noir or lower risk of escalating disease in Hawkes-Bay Merlot due to no change in rainfall intensity. The projected differences highlight the importance of combining phenological modelling by cultivar and region, demonstrating a diverse range of potential futures for NZ winegrowing.