Huglin Index
The Huglin Index (HI) helps viticulturists assess the climatic suitability of regions for specific grape varieties by measuring heat accumulation during the growing season (April 1 – September 30). The HI adjusts for latitude differences using a K-factor and provides insights into how climate change may impact grape production. By projecting future HI values, stakeholders can plan for climate-resilient grape varieties.
HI values are categorized by grape varieties:
1500–1600: Müller-Thurgau, Blauer Portugieser
1600–1700: Pinot blanc, Gamay noir, Gewürztraminer
1700–1800: Riesling, Chardonnay, Sauvignon blanc
1800–1900: Cabernet Franc
1900–2000: Chenin Blanc, Cabernet Sauvignon
2000–2100: Ugni Blanc
2100–2200: Grenache, Syrah, Cinsaut
2200–2300: Carignan
2300–2400: Aramon
The STARGATE platform provides a settings panel to input field names, elevation, and calculate the future HI based on climate predictions and four RCP emission scenarios.
Users, if they want to generate the following table, must select their location and the ASL.
How the Huglin Index Works:
The Huglin Index measures heat accumulation over the growing season (April 1 – September 30 in the Northern Hemisphere) and takes into account:
Daily Mean Temperature – Average of maximum and minimum temperatures.
Daily Maximum Temperature – Helps account for extreme heat.
Latitude Adjustment Factor – Corrects for the longer daylight hours at higher latitudes.
Formula:
HI=∑(Tmean+Tmax2−10)×kHI = \sum \left( \frac{T_{\text{mean}} + T_{\text{max}}}{2} - 10 \right) \times kHI=∑(2Tmean+Tmax−10)×k
TmeanT_{\text{mean}}Tmean = Daily mean temperature
TmaxT_{\text{max}}Tmax = Daily maximum temperature
10°C = Base temperature (below which grapevines do not grow)
kkk = Latitude correction factor (varies from 1.02 at 40° latitude to 1.06 at 50° latitude)
Huglin Index Classification:
HI (°C degree-days)
Climate Type
< 1500
Very Cool
1500 – 1800
Cool
1800 – 2100
Temperate
2100 – 2400
Warm
> 2400
Very Warm/Hot
Using climate prediction data, the Huglin Index (HI) can be calculated for the future based on the four Representative Concentration Pathways (RCPs) emission scenarios. RCPs project future greenhouse gas concentrations, adopted by the IPCC, to describe different climate change scenarios depending on GHG emissions. The four RCPs (RCP2.6, RCP4.5, RCP6, RCP8.5) reflect expected radiative forcing changes from 1750 to 2100. An example shows the past and projected HI development from 1981 to 2100, averaged by decade, with common grape varieties displayed in each HI range.
Last updated