PT  - JOURNAL ARTICLE
AU  - Previtali, Pietro
AU  - Giorgini, Filippo
AU  - Sanchez, Luis A.
AU  - Dokoozlian, Nick K.
TI  - Long-term Weather Observations Reveal the Impact of Heatwaves on the Yield and Fruit Composition of Cabernet Sauvignon
AID  - 10.5344/ajev.2025.25017
DP  - 2026 Jan 01
TA  - American Journal of Enology and Viticulture
PG  - 0770001
VI  - 77
IP  - 1
4099  - http://www.ajevonline.org/content/77/1/0770001.short
4100  - http://www.ajevonline.org/content/77/1/0770001.full
SO  - Am J Enol Vitic.2026 Jan 01; 77
AB  - Background and goals Warming trends observed globally have fostered research to understand the effects of increasing temperatures on the yield and fruit composition of winegrapes. However, the impact of extreme heat events at the commercial scale remains unsubstantiated. The present study represents the first attempt to combine available long-term spatiotemporal climate data with historical yield and quality metrics to investigate the impact of heatwaves (two or more days with maximum temperature ≥ 38 °C) on commercial winegrape production.Methods and key findings Historical weather data (1981 to 2023) for five sites in California were modeled using clustering analysis, separating three clusters: cool seasons, seasons with preveraison heat, and seasons with postveraison heat. Actual or temperature-based phenological stages were used to discriminate heatwave timing. Historical records of fruit composition, yield, and harvest date were then analyzed to determine differences between years experiencing extreme heat events and cool seasons. Yield and harvest date were affected by the intensity and distribution of heat in the growing season. Preveraison heat led to an advancement of harvest and substantial yield losses—on average, 13 days and −30%, respectively. Postveraison heat resulted in lower yield losses (−22%) and even earlier harvest dates (−17 days). Fruit quality parameters most affected by heatwaves were sugar, malic acid, pH, color, and phenolic compounds. Early- versus late-season heat resulted in unique effects on individual quality markers.Conclusions and significance By linking climate observations with grape yield and quality metrics at harvest, this study provides measured effects of heatwaves for the grapegrowing industry at a regional scale and points to the need for specific mitigation strategies.