VineTrack

VINETRACK RESEARCH - GDD STUDY

What are we trying to understand?

Growing Degree Days (GDD) add up the useful heat a vine receives across a season. It is a valuable thermal baseline - but two regions with similar accumulated heat can have very different ripening environments because of frost, late-season rainfall, heat spikes, diurnal range and radiation. I wanted to understand how much these pressures change the way a region behaves relative to its accumulated heat - and that question led to the development of Hambrook Pressure-Adjusted Growing Degree Days (HP-GDD).

Research and HP-GDD framework: Jonathan Hambrook

THE PROBLEM

Why Raw GDD is not enough

Two regions that both record 1,600 Raw GDD look identical on heat. Look at the pressures around that heat and the picture changes.

Region A

Hypothetical
Raw GDD1,600
  • Diurnal rangeWide
  • Harvest rainfallLow
  • Heat spikesFew
  • Spring frostRare
  • RadiationHigh

Region B

Hypothetical
Raw GDD1,600
  • Diurnal rangeNarrow
  • Harvest rainfallHigh
  • Heat spikesFrequent
  • Spring frostCommon
  • RadiationLow

Explanatory illustration only - these are not measured regions.

NATIONAL REFERENCE

50 seasons of GDD & HP-GDD climate class across Australian wine regions

Switch between Raw GDD and Hambrook Pressure-Adjusted Growing Degree Days (HP-GDD) to see how the same 50 seasons are classified under each view. Raw GDD is the thermal baseline before HP-GDD is applied; rows are the study reporting units, and Orange's analytical altitude bands are grouped at the end and are not official GIs.

This national GDD dataset was regenerated from scratch in March 2026 using SILO climate data. Across the study, approximately 108 million datapoints were processed to rebuild the regional climate series.

Loading heatmap…

Web reproduction of the study's annual climate-class heatmap (01_wine_gi_regions_annual_climate_class_heatmap_with_range_key).

MAP

Current decade across the country

Explore all regions

THE FRAMEWORK

Introducing HP-GDD

Hambrook Pressure-Adjusted Growing Degree Days (HP-GDD) keeps Raw GDD visible and adds a transparent interpretation layer made of five climate pressure components. It is a prototype screening and interpretation framework that requires calibration. It does not replace GDD and is not a planting recommendation.

HP-GDD = Raw GDD + clamp(AD + ARain + AHeat + AFrost + ARad, -180, +180)
AD

Diurnal range

The Jan-Apr gap between day and night temperatures, measured against a neutral reference.

ARain

Feb-Apr harvest rainfall

Late-season rain above a reference amount, which can constrain the ripening environment.

AHeat

Heat exposure

Days at or above 35, 38 and 40 C, plus multi-day heatwave events.

AFrost

Spring frost

Sep-Nov frost days above a reference count, which can set the season back.

ARad

Jan-Apr radiation

Mean solar radiation during ripening relative to a neutral reference.

Positive components lift the pressure-adjusted maturity signal; negative components reduce or constrain it. Neither direction means good or bad.

See the full method

WHY THIS MATTERS

Heat is the start of the conversation, not the end.

Variety choice, block planning and season expectations are often screened against GDD. Showing the pressures beside the heat makes those comparisons more honest - and shows which climate factor is driving any difference.

Orange, NSW is the first live worked example, drawn from 50 seasons of data.

View Orange

Loading Orange example…