Diurnal Temperature Variation

Diurnal range is the difference between day and night temperatures in the vineyard: the gap between the hottest temperature and the coolest. It should not be confused with continentality, which covers the difference between the hottest and coolest month in a growing season. Diurnal temperatures during ripening are one of the individual weather and climate factors affecting grape growth, production and wine quality, alongside solar radiation, average temperatures, temperature extremes, heat accumulation, wind, precipitation, humidity and soil-water balance. The two most common measures of the ripening-period day-night temperature pattern are the diurnal temperature range and the average nighttime temperature during the last month of the vintage.

• Diurnal range: the difference between day and night temperatures in the vineyard
• Continentality: the difference between the hottest and coolest month in a growing season, a separate measure
• Two common ripening-period measures: the diurnal temperature range and the average nighttime temperature during the last month of the vintage
• The ripening period runs from véraison to harvest, averaging 40-60 days for most cultivars and wine regions

'Diurnal temperature variation has major implications for wine quality, structure and balance,' in the words of Sarah Ahmed, regional chair for Portugal at the Decanter World Wine Awards. A large diurnal range can help grapes ripen in a more balanced way: warmer daytime temperatures help foster sugar development, while cool nights can help preserve aromas, freshness and acidity. This is one reason vineyards in hot climates may still produce fresh, aromatic wines. Acidity follows the same pattern: warmer climates often produce wines with lower levels of acidity, but high altitude and cool night temperatures can preserve their freshness. Research points to the last 30 days of ripening as the period when the majority of the polyphenols, color, flavor and aroma compounds develop. Climatologist Gregory Jones adds a caveat: most cooler-climate cultivars achieve greater typicity with higher diurnal temperature ranges, whereas many warmer-climate cultivars typically require warmer nighttime temperatures to ripen more fully and to metabolize compounds considered detrimental to quality.

• Warm days foster sugar development; cool nights can help preserve aromas, freshness and acidity
• High altitude and cool night temperatures can preserve freshness in warmer climates
• Cooler-climate cultivars: greater typicity with higher diurnal ranges, where nighttime temperatures slow respiration and metabolism
• Warmer-climate cultivars: many typically require warmer nights to ripen more fully

The Valle de Uco in Mendoza has rigorous winters and warm summers, with mild days and very cold nights that produce a daily thermal amplitude of approximately 15°C. Argentina's official regional profile links this with a high color index and tannin production in red grapes. Altitude runs from 900 metres above sea level at the city of Tunuyán to 1,250 metres at Tupungato. The Washington State Wine Commission puts the state's daily temperature fluctuations among the most dramatic of any wine region in the world, with a diurnal shift of 35 to as much as 47 degrees Fahrenheit between daytime high and nighttime low. Columbia Valley temperatures also cool down rapidly during harvest. In Central Otago, New Zealand's southernmost wine region, Bendigo's plantings capture hot summer sun and cold clear nights, and New Zealand Winegrowers credits the marked daily climatic variations in Alexandra, right up to harvest, with vividly varietal, aromatic, finely structured wines. Ribera del Duero in Spain has a diurnal temperature swing of 20-22°C, conditions that help preserve acidity and concentrate aromas. Sarah Ahmed points to the Douro in Portugal and Rutherglen in Australia as fortified regions that depend on diurnal variation; in Rutherglen, temperatures during March and April can range from 5°C at night to 35°C during the day.

• Valle de Uco, Mendoza: daily thermal amplitude of approximately 15°C; altitude 900 m at Tunuyán to 1,250 m at Tupungato
• Washington State: diurnal shift of 35 to as much as 47°F, with rapid cooling at harvest in the Columbia Valley
• Central Otago, New Zealand: hot summer sun and cold clear nights in Bendigo; marked daily climatic variations up to harvest in Alexandra
• Ribera del Duero: 20-22°C diurnal swing; Rutherglen: 5°C at night to 35°C by day in March and April

Grape ripening runs on four clocks at once, each at a different rate: sugar accumulation, acid respiration, phenolic ripeness and fruit character. As temperatures rise during the ripening period, the vine metabolises malic acid, which can leave warmer regions and warmer vintages with lower-acid wines. In cooler-climate cultivars with higher diurnal ranges, daytime temperatures are high enough to facilitate ripening while nighttime temperatures slow respiration and metabolism, bringing the more delicate aromas associated with cool to intermediate climate cultivars. Regions with lower diurnal temperatures or higher nighttime temperatures tend to allow greater metabolism of the methoxypyrazines behind the green, herbaceous aromas of under-ripe Cabernet Sauvignon, while high concentrations of rotundone, the compound behind Syrah's peppery character, typically result from a cooler climate with higher diurnal ranges. Not enough research has been done to adequately define the region and cultivar limits and diurnal temperature ranges for quality wine production.

• Four ripeness clocks: sugar accumulation, acid respiration, phenolic ripeness and fruit character
• As temperatures rise during ripening, the vine metabolises malic acid, which can leave warmer regions with lower-acid wines
• Lower diurnal ranges or warmer nights tend to allow greater metabolism of green-tasting methoxypyrazines in Cabernet Sauvignon
• Higher diurnal ranges in cooler climates typically give high rotundone, the peppery compound in Syrah

Cooler nights can come from an inland location or high elevation, as in the Douro's mountainous terroir. Temperature drops by approximately 0.6°C for every 100 metres climbed above sea level. Humidity matters too: Bordeaux has relatively low daytime and high nighttime temperatures due to higher humidity, while the Napa Valley has much higher daytime and much lower nighttime temperatures due to lower humidity. The contrast between morning and afternoon relative humidity is smallest along coasts and greatest inland. Washington's Columbia Valley is protected from wet weather systems by the Olympic and Cascade ranges, and eastern Washington is an arid and semi-arid desert with hot summer days and cool nights that help lock in acidity. On nights when radiation inversions form, a warmer thermal belt develops upslope, generally 30-300 metres off the valley floor, and inversions occur most frequently on long, calm, cloud-free nights. Insolation, soil composition and color, local topography, slope aspect and drainage can all be major factors in a vineyard's temperature structure, especially at night.

• Inland location or high elevation can bring cooler nights
• Altitude: approximately 0.6°C cooler for every 100 metres above sea level
• Lower humidity: Napa's lower nighttime temperatures versus Bordeaux's higher ones
• Cold-air inversions on long, calm, cloud-free nights, with a warmer thermal belt 30-300 m upslope

Generally, the less day-to-day temperature variability leading up to harvest, the better the wine quality. In Jones's reading, the majority of the most renowned and established vineyards are in regions with the most equitable day-to-day climates. In an ideal season, vines ripen into the early fall, when shortening day lengths bring about changes in diurnal temperature ranges and a balance of the four ripeness clocks. Observed warming over the last hundred years has been asymmetric, with the greatest warming during winter and spring and at night. Many regions are also seeing much earlier ripening in a hotter period of the summer, with trends of higher sugar levels and lower acidity in grapes and higher alcohol levels in wines.

• Less day-to-day temperature variability leading up to harvest generally means better wine quality
• Shortening day lengths in early fall bring changes in diurnal temperature ranges
• Observed warming has been greatest in winter and spring and at night
• Many regions see much earlier ripening in a hotter part of summer; trends of higher sugar and lower acidity in grapes have been observed

Primary sources: https://www.wsetglobal.com/knowledge-centre/blog/2025/from-ancient-vines-to-modern-wines-in-ribera-del-duero, https://www.wsetglobal.com/knowledge-centre/blog/2026/understanding-acidity-in-wine, https://www.wsetglobal.com/knowledge-centre/blog/2021/august/24/how-does-geography-affect-a-wine-s-style, https://www.argentina.gob.ar/sites/default/files/2018/10/valle_de_uco_0.pdf, https://www.nzwine.com/en/regions/central-otago/, https://www.washingtonwine.org/grapes-soil-sun/. Secondary sources: https://www.guildsomm.com/public_content/features/articles/b/gregory_jones/posts/climate-grapes-and-wine, https://www.decanter.com/learn/what-is-diurnal-range-ask-decanter-413231/. Last verified 2026-10-04