Assessment of Viticultural Bioclimatic Indices across contrasting microclimates on Madeira Island

Abstract

Viticulture in insular and mountainous environments is particularly sensitive to climate variability due to strong topographic constraints and pronounced microclimatic gradients. Madeira Island represents a paradigmatic case, where altitude, slope orientation and maritime influence generate marked spatial heterogeneity in viticultural conditions. In parallel, recent warming trends may progressively modify the thermal suitability for grapevine cultivation. This study presents a bioclimatic assessment of Madeira Island vineyards based on widely used thermal indices for viticultural zoning, aiming to evaluate current climatic suitability and its recent evolution.

Daily temperature data recorded between 2011 and 2023 at meteorological stations located in Câmara de Lobos (southern slope), Santana, and São Vicente (northern slope) were used to compute the Winkler Index (WI), the Huglin Index (HI), and the Night Freshness Index (NFI). These indices integrate cumulative heat availability and nocturnal thermal conditions during the vegetative period and are key indicators of grapevine development, ripening dynamics and wine style potential (Winkler et al., 1974; Huglin, 1978; Tonietto & Carbonneau, 2004). Spatial contrasts and interannual variability were analysed within the multicriteria climatic classification framework proposed by Tonietto and Carbonneau (2004).

The results reveal a clear spatial differentiation across the island. Câmara de Lobos exhibited significantly higher WI and HI values, corresponding to warm to very warm viticultural classes, reflecting its southern exposure and lower elevation. In contrast, Santana and São Vicente showed lower thermal accumulation and cooler nocturnal conditions, as indicated by higher NFI values, characteristic of temperate to temperate-cool climates. These differences highlight the strong control exerted by altitude and slope orientation on vineyard thermal regimes. Temporally, an increasing tendency in heat accumulation was observed, particularly in the southern municipality, suggesting a gradual shift towards warmer bioclimatic classes over the study period. Despite this tendency, most locations remain within climatic thresholds considered suitable for quality wine production.

Overall, the study confirms that Madeira Island currently maintains moderate to high viticultural suitability, while simultaneously experiencing increasing thermal pressure in warmer areas. The pronounced microclimatic variability emphasises the importance of fine-scale bioclimatic zoning and continuous climatic monitoring to support adaptive vineyard management and long-term planning under climate change.

References

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