Diurnal range is the difference between the highest and lowest temperatures recorded over a 24-hour period, usually referring to daytime and nighttime temperatures. In viticulture, a large diurnal range means warm days are followed by relatively cool nights. The effect on grape ripening depends on the timing of the season, water availability, sunlight and the grape variety.
Warm daytime temperatures support photosynthesis and sugar accumulation when water and vine function are adequate. Cooler nighttime conditions can slow respiration and may help preserve acidity, particularly malic acid. However, a large diurnal range does not automatically produce better grapes or guarantee high acidity; overall seasonal temperature and vine health remain important.
Altitude, distance from the ocean, continentality, valley shape, air drainage, cloud cover and humidity all influence the difference between daytime and nighttime temperatures. High-altitude and inland vineyards may experience substantial temperature swings, while maritime sites often have more moderate daily variation.
Example: some vineyards in Mendoza, the Okanagan and elevated sites in California experience warm days and cool nights, which can help maintain freshness in ripe fruit.
Diurnal range describes temperature variation within one day. Continentality describes the broader influence of distance from large bodies of water on seasonal and annual temperature patterns. The terms refer to different climate characteristics.
Chef’s note: diurnal range is one part of vineyard climate. Use it as context, not as a direct predictor of wine quality or flavour.
This term is one of hundreds covered in depth across OCS courses, learning paths, and 1-on-1 coaching with Chef Eric.
