Global warming has become one of the greatest challenges for winegrowers in recent decades. As temperatures continue to rise, the delicate balance between grapes, soil, and season that defines a region's terroir is shifting, and vineyards across Europe and beyond are feeling the effects of climate change at every stage of production.
In regions long known for their cool-climate wines, such as Champagne, the Mosel, or Burgundy, warmer growing seasons are pushing grapes to ripen faster. While this can enhance sugar levels, it also bears the risk of reducing the acidity and aromatic complexity that define these wines. Meanwhile, southern regions like Spain, Italy, and southern France are facing new extremes: heat stress, water shortages, and even smoke from wildfires. As a result, harvest timings are shifting and also new opportunities for the wine industry are emerging further north or at higher altitudes.
This evolving geography of viticulture calls for new tools and better data to understand how climate change affects vine growth and grape quality. One of the most valuable of these tools is the Huglin Index, a bioclimatic heat indicator that helps winemakers assess the suitability of specific grape varieties for their current and future conditions.
Wine grapes are one of the world’s most valuable horticultural crops.
Measuring heat for wine: What is the Huglin Index?
Developed in the 1970s by French scientist Pierre Huglin, the Huglin Index (HI) is a bioclimatic heat index used to assess how suitable a region's climate is for growing specific grape varieties. It measures the total warmth a vineyard receives during the growing season – from April to September – based on daily average and maximum temperatures above 10°C, the threshold for grape growth. A correction factor accounts for latitude, since longer daylight hours in northern regions can partially offset cooler temperatures.
In practice, the Huglin Index tells winemakers how much heat is available for grape ripening. Each grape variety requires a certain level of accumulated warmth to reach full maturity. Cooler regions with HI values around 1500–1700 are best suited to early-ripening varieties such as Müller-Thurgau, Pinot Blanc, or Gewürztraminer. As the index rises to the 1700–1900 range, conditions become ideal for classic varieties like Riesling, Chardonnay, and Pinot Noir. Warmer areas with HI values above 1900 can successfully produce Cabernet Franc, Merlot, Cabernet Sauvignon, and Syrah. Beyond 2200, typical of southern Mediterranean climates, heat-loving grapes such as Grenache or Carignan thrive.
Each grape variety requires a specific heat sum to be successfully cultivated in a given area over an extended period.
Global warming and the northward shift of vineyards
As global temperatures rise, the Huglin Index has increased across Europe. Areas once too cold for viticulture, such as southern England and parts of Denmark and Poland, now observe HI values that make grape cultivation feasible. Conversely, traditional wine regions in southern Europe are already surpassing the optimal heat thresholds for many of their typical varieties.
This northward shift in wine-growing zones is already visible on Huglin Index maps derived from decades of reanalysis data. Between 1981 and 2020, regions classified as "moderately warm" expanded significantly, allowing new areas to produce high-quality wines. At the same time, established vineyards in warmer zones are rethinking their varietal mix, irrigation strategies, and harvest timing to adapt to the increasing heat.
Spatial distribution of the Huglin Index (HI) has changed in Europe over the decades from 1981 to 2020 (meteoblue.com).
In addition to changes in temperature, climate change also brings greater variability: late frosts, prolonged droughts, intense heatwaves, and shifting rainfall patterns. These extremes complicate vineyard management and make data-driven adaptation more important than ever.
Planning ahead: Using the Huglin Index in climate projections
The Huglin Index not only helps to analyse current suitability but also allows for future scenario planning. By combining the index with climate projections under different greenhouse gas emission pathways (RCP scenarios), viticulturists can estimate how their local conditions might evolve by 2050 or 2100.
For example, projections show that a region currently suited to Riesling or Pinot Noir (HI around 1800) could, by mid-century, reach heat levels better suited to Cabernet or Syrah. For winemakers, these insights are critical for long-term decisions such as replanting, varietal selection, or investing in new vineyard sites. These changes usually take decades to accomplish, so early adaptation is essential for maintaining both quality and economic viability.
Map showing an emergence of new regions suitable for viticulture, and shifts in existing wine-producing regions, where varieties with higher heat requirements can be cultivated in the future (meteoblue.com).
It is, however, important to note that local microclimates, slope orientation, and altitude can create variations in heat accumulation. South-facing slopes, for instance, can have significantly higher HI values than the regional average. This is why site-specific modelling remains crucial.
Wine-production supported by smart tools and data
Modern viticulture increasingly relies on data to adapt to shifting climates. With advanced weather and climate modelling, winegrowers can now calculate the Huglin Index for any location for the past, the present and the future, and use it to guide planting decisions and anticipate long-term risks.
meteoblue offers this capability within its climate+ services package, which provides access to detailed historical weather data and climate projections. These insights make it possible to compare different decades, identify emerging trends, and plan for future growing conditions. By understanding how heat accumulation and regional climates evolve, producers can choose grape varieties best suited for tomorrow's vineyards while protecting the quality and character of their wines.
In the face of today's environmental challenges, the modern wine-making industry can benefit greatly from smart tools like the Huglin Index and keep great wines thriving for generations to come.
The maps and meteoblue web content in this article were created within the EU-funded Horizon 2020 project STARGATE (Grant Agreement 818187).
