The probability of unprecedented high rainfall in wine regions of northern Portugal

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Climate is arguably one of the most important factors determining the quality of wine from any given grapevine variety. This study focuses on three wine-growing regions in northern Portugal: Vinho Verde, Trás-os-Montes and Douro, the latter coinciding with Porto. High rainfall during late spring (April to June) can promote growth of the vines but increases the risk of fungal disease. High rainfall during harvest time (August to October) also bears the potential for severe operational disruption and heavy economic losses. The probability of unprecedented rainfall totals in spring and the harvest season over wine-growing regions of northern Portugal has been assessed. A large ensemble of initialised climate model simulations is analysed, and the probability of unprecedented rainfall in each season is quantified. Seasonal rainfall totals considerably higher than any observed are possible in the current climate. An unprecedented rainfall event in either season could occur with a probability between 0.01 and 0.05 in the present climate. Extreme value analysis was applied to rainfall totals from observations and the model ensemble, and the return periods of known extreme rainfall events are calculated. Similar probabilities for unprecedented rainfall totals were calculated. A year similar to 1993, when both seasons were exceptionally wet, would be expected to occur, on average, just once in the next 70–80 years in the current climate. These results could inform the requirements for improved vineyard management and resilience, such as design of drainage channels, access roads and terraces.