Rainfall and Precipitation Timing

Rainfall varies widely between wine regions. Wine Australia's regional snapshot puts average annual rainfall in the Riverland, Australia's largest winegrape region by tonnage, at 254mm for 2006 to 2025, with 148mm of that falling in the October to April growing season. Mendoza, Argentina's most important wine province by productivity, is a desert with around 200mm of rain a year, Roberto de la Mota noted in a Decanter feature. At the wet end, Decanter reports rainfall of 1,600 to 1,800mm per year across Rías Baixas, which sits right on the Atlantic.

A yearly total says little about when water reaches the vine or how much the vine needs. The International Organisation of Vine and Wine (OIV) names the main drivers of vineyard water demand as solar radiation, air temperature, humidity and wind speed, working together with the canopy and the vineyard floor. Demand is also uneven through the season. A water management guide hosted by Wine Australia estimates that the stage from fruit set to veraison uses about 35% of the vine's annual water, while veraison to harvest, when sugars accumulate in the berries, uses about 36%. It also notes that flowering and berry set are very sensitive to water stress. Winter and spring rain matter because they stock the soil before the season starts: the same guide advises checking soil moisture two weeks before budburst, leaving time to fill the soil profile if winter or spring rain has fallen short. Rain at the wrong moment works against quality. Decanter notes that too much rain just before harvest can make grapes swell, risking dilution or berries bursting on the vine and opening them to disease. A Wine Australia botrytis factsheet adds that rain which splits berries often leads to direct infection of ripening fruit, and that high soil water during ripening may increase botrytis growth. Drainage is covered in its own WineWiki article.

• Vine water demand follows sun, heat, humidity and wind, not rainfall alone
• Winter and spring rain refill the soil before budburst

The Riverland shows the dry, irrigated model. Wine Australia credits its low relative humidity with little or no disease pressure, and a Wine Australia benchmarking project reviewed the irrigation practices of over 40 growers across the Riverland, Sunraysia and Riverina regions. Research there has measured Shiraz and Chardonnay water use to inform irrigation practice. That water-use study also notes that higher growing season temperatures in South Australian regions have led to water scarcities for irrigators. Mendoza gets its roughly 200mm through some summer storms, and de la Mota calls it "a really healthy viticulture." In the same feature, Daniel Pi explained that Mendoza's oases have water for farming thanks to the Mendoza, Tunuyán, Atuel and Diamante rivers. Rías Baixas shows the wet extreme. WSET notes that Albariño was traditionally trained on pergolas, and Decanter describes high pergolas that keep the grapes well away from the damp ground, and WSET adds that raising vines improves airflow to cut humidity and fungal disease risk, that the region's stony, relatively infertile soils drain well, and that Albariño's thicker skins give the grapes some resistance to fungal disease.

• Dry: Riverland (irrigated) and Mendoza (river-fed oases)
• Wet and ventilated: Rías Baixas

Where rain falls short, irrigation fills the gap. The Wine Australia-hosted water guide says irrigation is required when rainfall or existing soil moisture cannot meet the vine's water requirements. The OIV advises growers to check whether rainfall is adequate and consistent enough to support a profitable non-irrigated vineyard, and notes that in dry climates, soils with high or medium water reserves may support vines with little or no irrigation. Where dry farming stops being viable, it recommends drip irrigation, regulated deficit irrigation (RDI) and monitoring the plot's water status. RDI means restricting water for a set period, most commonly after fruit set, to control shoot vigour and berry size, which can benefit fruit quality. The guide names the amount of water in the soil at the start of the season as the biggest limitation on RDI. In wet sites the tools shift to drainage, vineyard floor management and airflow, though the botrytis factsheet notes drainage may be difficult in years with high and frequent rainfall. Slashing mid-row grasses can help draw water out of the soil.

• Dry regions: irrigation, ideally drip and RDI
• Wet regions: drainage, floor management and airflow

Primary sources: https://www.wineaustralia.com/market-insights/regions-and-varieties/south-australia-wines/riverland, https://www.wineaustralia.com/getmedia/4c434a71-6284-44d6-8e23-07e0e629ac0a/MI_Riverland-Region-Snapshot-2025-26.pdf, https://www.decanter.com/features/r-as-baixas-grows-up-245821/, https://www.wsetglobal.com/knowledge-centre/blog/2026/why-albari%C3%B1o-is-more-than-a-refreshing-summer-wine, https://www.decanter.com/wine/wine-regions/mendoza/mendoza-world-wine-capital-30632/, https://www.wineaustralia.com/getmedia/0d28f6c3-49f8-4865-8304-26d2f64bf977/Water-management-for-wine-grapes-in-a-drying-environment.pdf, https://www.oiv.int/node/3132, https://www.decanter.com/learn/how-to-understand-vintage-54305/, https://www.wineaustralia.com/getmedia/b78baaea-d1de-469f-a8aa-1aec30d4d756/201307-Botrytis-QA?ext=.pdf, https://www.wineaustralia.com/research_and_innovation/projects/incubator-initiative-how-does-phenological-stage-i, https://www.wineaustralia.com/research_and_innovation/projects/irrigation-benchmarking-in-the-murray-darling-basin. Last verified 2026-09-24