VineTrack

GDD STUDY - CLIMATE DATA

How the regional climate dataset was built

This page explains how daily weather data were sampled, calculated and aggregated for all 64 official Wine Australia regions and the five Orange analytical altitude bands.

Research and HP-GDD framework: Jonathan Hambrook

DATASET AT A GLANCE

Data sourceSILO DataDrill daily climate data
Study period1976-77 to 2025-26
Growing seasons50
Official regions64
Reporting units69, including five Orange altitude bands
Climate datapointsApproximately 108 million

The national dataset was regenerated from scratch in March 2026.

REGIONAL SAMPLING

How a region was sampled

  1. 1

    Wine Australia GI boundaries define each official region reporting polygon.

  2. 2

    A 0.05000 degree SILO-style grid (approximately 5 km x 5 km) was placed across the GI polygons.

  3. 3

    Sample points falling inside each relevant region polygon were used as the climate-sampling locations.

  4. 4

    Daily SILO data were collected for the grid locations.

  5. 5

    Each grid point was calculated by season.

  6. 6

    Regional season values are the mean of valid point-season values within the region.

Study provenance. 16,900 base GI sample points were used across the 64 official regions. No fallback representative points were required.

The grid cells are methodological climate-sampling units and are not legal GI boundary definitions.

RAW GDD CALCULATION

One consistent growing season

The growing season runs from 1 October to 30 April. Season labels use the season-start year, such as 1976-77.

Daily GDD = max(0, ((Tmax + Tmin) / 2) - 10)
  • Base temperature: 10 C
  • Negative daily values are clipped at zero
  • No upper daily temperature cap was applied

HP-GDD INPUT WINDOWS

Climate-pressure windows

Heat metricsOct 1-Apr 30
Harvest rainfallFeb 1-Apr 30
Spring frostSep 1-Nov 30, assigned to the same season-start year
Ripening diurnal rangeJan 1-Apr 30
Ripening solar radiationJan 1-Apr 30

Solar radiation is used as a light/exposure proxy, not as a direct UV measurement.

ORANGE ALTITUDE ANALYSIS

One GI, five analytical bands

Orange whole GI remained a normal official region reporting unit. Its grid points were also classified by SILO-derived elevation into five analytical bands:

  • 600-700 m = 650 m band
  • 700-800 m = 750 m band
  • 800-900 m = 850 m band
  • 900-1000 m = 950 m band
  • >=1000 m = 1050 m band

The below-600 m review group contained only two points and was excluded from the final 69-unit reporting model. These bands are analytical subdivisions, not official GI subregions.

MISSING-DATA TRANSPARENCY

The Tasmania edge case

Five Tasmania coastal or ocean-edge SILO sample cells returned metadata or header information but no daily climate rows. They were retained in the processing audit and excluded from point-season and region-season summaries.

99.83%2,975 valid daily-data cells from 2,980 polygon sample cells

Important interpretation. SILO provides a consistent gridded daily climate series for regional comparison. SILO itself cautions that its data are not intended for formal climate-change detection because small long-term movements can be affected by changes in instruments, station locations and the observing network. This study therefore uses SILO to examine regional GDD movement and viticultural climate screening; it should not be read as formal causal climate attribution.

MAP GALLERY

SILO sampling maps for every reporting unit

These maps document the climate-sampling method. They are sampling illustrations, not legal GI maps. Wine Australia also cautions that mapped boundaries are representations; the textual GI description remains the legal definition.

Sampling map gallery is being loaded from the audited study assets.

SOURCES

Primary references

Wine Australia maps are representations only. The textual description of a geographical indication remains its legal definition.