• Assess vineyard suitability with precise Huglin Index predictions customised to your region's climate
• Enhance long-term viticulture planning by identifying optimal grape varieties for future climate conditions
• Save time and resources by adopting consolidated grape varieties in climates similar to your region's future conditions

Understanding the Huglin Index (HI)

The Huglin Index is a crucial metric for viticulturists and winemakers to assess the climatic suitability of a location for cultivating specific grape varieties. For a successful harvest with sustained yields at a specific location, each variety needs a certain amount of heat to mature and develop as desired. The index represents the heat sum of air temperatures above 10° C during the critical growing season from 1 April to 30 September. Additionally, the HI incorporates a K-factor, which adjusts the index to account for the length of the day at different latitudes.

Why the Huglin Index matters

• Suitability for grape varieties:
  The HI allows for the classification of regions based on their suitability for growing various grape varieties.
• Climate change impact:
  By analysing the Huglin Index over time, it is possible to observe how climate change may affect the suitability of different wine-growing regions. By projecting future changes in the HI, decision makers can identify potential risks to current grape varieties and take proactive steps.
  It is crucial to act early, as the transition to cultivating more climate-resilient grape varieties at a profit can take decades. Early planning and adaptation ensure that vineyards remain productive and sustainable in the face of evolving climate conditions.

Interpretation of the Huglin Index

The HI values can be categorised into the following ranges, each associated with specific grape varieties, e.g:

Huglin-Index (HI)	Grape variety
1500 ≤ HI < 1600	Müller-Thurgau, Blauer Portugieser
1600 ≤ HI < 1700	Pinot blanc, Grauer Burgunder, Aligoté, Gamay noir, Gewürztraminer
1700 ≤ HI < 1800	Riesling, Chardonnay, Silvaner, Sauvignon blanc, Pinot noir, Grüner Veltliner
1800 ≤ HI < 1900	Cabernet Franc
1900 ≤ HI < 2000	Chenin blanc, Cabernet Sauvignon, Merlot, Sémillon, Welschriesling
2000 ≤ HI < 2100	Ugni blanc
2100 ≤ HI < 2200	Grenache, Syrah, Cinsaut
2200 ≤ HI < 2300	Carignan
2300 ≤ HI < 2400	Aramon

The following maps show how the spatial distribution of the averaged HI changes over the decades from 1981 to 2020 in Europe. It can be seen very clearly that the pattern is shifting northwards, indicating a trend towards the emergence of new regions suitable for viticulture and locations where varieties with higher heat requirements can be grown. On the other hand, the trend leads to a scenario where the HI exceeds the range required for the established varieties.

The analysis was carried out using gridded reanalysis data with limited spatial resolution. The map may therefore miss some regions with well-established vineyards, or show an average HI for the region, which may be different on local hills.

Location-specific Huglin Index prediction until 2100

Using climate prediction data, the HI can be calculated for the future based on the four RCP emission scenarios at any location on Earth.

The following graph shows the past and simulated future development of HI from 1981 to 2100, averaged over each decade. The varieties shown in the graph are examples of the most common crops in the HI ranges.

To adjust the HI values to the local microclimate and to match the historical simulations with local observations, an offset can be applied. This value is added to the temperature time series on which the HI is based.

The following example shows how big the difference can be when adding 1.2 K, which results in an increase in HI of approximately 200 at this specific location in Basel.

Important considerations

• Microclimate variations:
  Local factors like slope orientation and microclimate can cause actual HI values to differ. For instance, higher HI values may be observed on south-facing slopes.
• Uncertainties in climate predictions:
  See general remarks and limitations of the meteoblue climate+ service.