VineTrack

Research / GDD study / Varieties

VARIETY MATURITY-SCREEN

Grape varieties

Each variety has one master GDD maturity-screening range. Regional Raw GDD and Hambrook Pressure-Adjusted Growing Degree Days (HP-GDD) are both tested against that same range.

Research and HP-GDD framework: Jonathan Hambrook
Variety maturity ranges: VineTrack master variety framework

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Variety matches are maturity-screening results based on the master GDD range. They do not replace local evidence on rainfall, frost, heat, soils, aspect, water, disease pressure, wine style or observed vineyard performance.

The current master variety maturity-anchor dataset has an upper observed GDD anchor of approximately 1925. Above-window regions require additional warm-climate calibration and should not be interpreted as unsuitable for wine grapes.

RANGE METHODOLOGY

How the variety GDD ranges were developed

These are climate-maturity screening ranges, not absolute biological limits or planting recommendations. Published grapevine research does not provide one universally standardised GDD minimum and maximum for every cultivar.

One comparable framework

Sources may report conventional GDD, biological effective degree days (BEDD), the Huglin Index, budburst-to-harvest or pruning-to-harvest thermal time, maturity groups, growing-season mean temperature, or established regional performance.

VineTrack therefore does not automatically copy a published degree-day number into the master range. Source evidence is assessed for methodological compatibility, then represented within the study's common base-10 C GDD framework so varieties can be compared consistently.

RAW GDD FRAMEWORKDaily GDD = max(0, ((Tmax + Tmin) / 2) - 10)

The climate study applies this daily calculation across its defined 1 October to 30 April growing-season window.

A master GDD maturity-screening range describes the climatic maturity window used in this study. Vineyards can perform outside it depending on site, elevation, aspect, soils, water availability, rootstock, clone, yield, management and intended wine style.

EVIDENCE HIERARCHY

How evidence informs the framework

  1. 1

    Direct thermal evidence

    Published cultivar-specific GDD or directly comparable thermal accumulation.

  2. 2

    Published maturity framework

    Recognised variety maturity or climate classifications used to anchor the range where exact comparable GDD is unavailable.

  3. 3

    Benchmark-region evidence

    Established regions where the variety has a strong history of commercial production, used to validate or inform climatic placement.

  4. 4

    Analogue / inferred evidence

    Used cautiously where cultivar-specific thermal evidence is limited and treated as lower-certainty until stronger evidence is found.

COMPARABILITY

Why you may find different GDD numbers elsewhere

Values can differ because studies use different base temperatures, start and end dates, hemisphere or season windows, budburst, pruning or harvest endpoints, upper temperature caps, BEDD, Huglin or other adjusted indices, and local weather stations rather than gridded climate data.

A published thermal-time value is therefore evidence, not automatically the VineTrack master GDD value.

SOURCE FRAMEWORK

Primary source framework

  • VineTrack master variety framework / publication Table A.1 — the immediate authority for the currently published master ranges.
  • Jones climate–maturity framework — part of the study's climate and maturity source basis.
  • Amerine/Winkler heat-summation concept — methodological background for base-10 GDD, not a source of cultivar-specific ranges.

Individual cultivar-level provenance is being progressively audited and expanded. Where the database records only the master framework, the site says so rather than claiming a more specific citation.