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Chill & Thermal Time Calculator |
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This site accesses daily weather station data for the period 1968 to the current year for 600 locations across Australia. This data is used to make calculations for the accumulation of winter chill and growing degree days or hours.
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Chill AccumulationThree methods to calculate chill accumulation are included:
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Growing DegreesTwo methodologies are presented:
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Temperature & RainfallChill and growing degree day calculations are based on weather data from the Long Paddock SILO, therefore the calculations can only be updated when the weather data becomes available. The weather data from yesterday is usually available after about midday (AEST). The Long Paddock SILO uses data form the Bureau of Meterology and patches this to create complete daily data sets. Stations that no longer record temperature data are synthetically in-filled with gridded data derived from statistical analysis. The Long Paddock SILO is available here. |
All calculations are performed using the chillR package of Luedeling et al. (2013) & Luedeling (2017).
- Last updated:
- 13 November 2024
- Last reviewed:
- 30 October 2024
Introduction
This site accesses daily weather station data for the period 1968 to the current year for 600 locatons across Australia. This data is used to make calculations for the accumulation of winter chill and growing degree days/hours.
Because the chill and growing degree day calculations are based on weather data from the Long Paddock SILO, the calculations can only be updated when the weather data becomes available. The weather data from yesterday is usually available after about midday (AEST). The Long Paddock SILO uses data form the Bureau of Meterology and patches this to create complete daily data sets. Stations that no longer record temperature data are synthetically in-filled with gridded data derived from statistical analysis. The Long Paddock SILO is available here.
All calculations are performed using the chillR package of Luedeling et al. (2013) & Luedeling (2017).
Uploading Your Own Data
Datasets downloaded from your weather station need to converted to a uniform format. There are four choices for date and time - select the one that matches your data. Additional columns to the right are OK, they are ignored, but best avoided.
If you get errors you can email the data to me at Dr Neil White, Qld Dept. of Primary Industries
| DateTime | Temperature |
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| 1/5/18 00:00 | 12.1 |
| 1/5/18 01:00 | 12.0 |
| 1/5/18 02:00 | 11.7 |
The names of the header columns are not important, however, the data must be in that order, date and time first column and temperature in the second column. There is very little error checking undertaken at this stage.
Hours can be 0 to 23 or 1 to 24, i.e. midnight can either be hour 0 or hour 24.
Use the checkbox Use This Data Set for Calculations to toggle between your data and the active site.
Note: Your data is not stored on the server and is destroyed when you end the session.Selecting Locations
Locations are selected from the Locations tab by clicking the blue marker for that location on the map. Once a location has been selected, it will appear on the top left hand side of the screen. There are a number of ways to locate the blue marker you are interested in:- Select a growing region and wait for the map to identify the locations available for that region.
- Search for a weather station and select from the list of responses.
- Bencubbin
- Bendigo Airport
- Launceston (Ti Tree Bend)
- Selecting from the list makes this the station of interest
- Benalla VIC 3672
- Bendemeer NSW 2355
- Bendigo VIC 3552
- etc...
- Zoom in or out on the map, and pan the map to select a station.
Searching for a station (1 of the 600) uses a simple searching method that matches the letters entered. "ben" will match
Searching for a locality works by matching Towns that start with the letters enetered. "ben" will match
Results do not show up until the list of possiblties is less than 200 and the selection only moves the map to that locality so that you can search for a station (blue marker)
Storing Location
If the "Remember this station" is ticked when a location marker is clicked, this becomes the default for the next time the web site is used.
The default is overwriten with subsqeuent selections.
Note: This uses a cookie to keep the information between the sessions. This stores only the station number.Viewing the data
Once a location has been selected, simply click on the tabs for Chill, Growing Degrees or Temperature to view the graphs for that location. Once you have clicked on one of these tabs, select the year of data you want to see from the drop down menu at the top of the screen. You can also change the start date and end date by using the drop down calendars. This is particularly useful for chill graphs where you might want to calculate chill from 1 Jun, instead of 1 Mar for example. To close the calendar simply click outside of it. The graphs automatically show the data for the year selected, compared to the long-term historical record (from 1981 to 2010). When you hover your cursor over a particular spot on the graph, the values for that particular date will be flagged.
Chill Accumulation
Chilling can be calculated in either Chill Portions (Erez et al. 1990), Chill Hours (Bennet 1949, Weinberger 1950) or Chill Units (Richardson et al. 1974).
Growing Degrees
Growing Degree Hours (GDH) (Anderson et al 1974) or Growing Degree Days (GDD) are calculated when the user selects the "Growing Degrees" tab. GDH are calculated using the methodology of Anderson et al. (1986) that uses four thresholds to calculate the accumulation of yield. GDD are calculated by subtracting 10oC (or which ever base temperature is used) from the average daily temperature. Only positive values are accumulated, i.e. temperatures greater than 10oC. These can be accumulated from 1 January (default) or set at a later date using the date selector box. To close the calendar simply click outside of it.
Interaction with the Graph
The data presented in each of the graphical tabs, Chill, Growing Degrees and Temperature, show the average and a shaded area that represents the highest 10% and lowest 10% of years. If this is too much information click on the thick bar object that is pointing to the left. This will change from compare mode to show only the closest value. The closest value is the default in the Temperature graphs.
In the screen capture below the the graph is in compare mode, i.e. the two bars pointing left are highlighted
© State of Queensland, Department of Primary Industries and Horticulture Innovation Australia Ltd, 2024.
Why are there different methods for calculating winter chill?
Many models of winter chill have been developed using the observed effects of temperature on dormancy breaking. The Chill Hours model (Weinberger, 1950) was the first to be developed and estimates winter chill based on hourly temperatures between 0 & 7.2°C. The Chill Units model (Richardson et al., 1974) is slightly more complicated. It incorporates the understanding that temperatures vary in how much they contribute to winter chill and that high temperatures can have an adverse effect. In this model, temperatures below 1.4°C do not contribute to chill accumulation, temperatures between 2.4 and 9.1°C make the greatest contribution and temperatures above 15.9°C have a negative impact.
Knowledge of temperature effects on winter chill has since expanded and the Dynamic chill model (Erez et al. 1990) is the current best practice model, especially in warmer climates. It calculates chill in Chill Portions, based on hourly temperatures. The Dynamic model has many features that capture known temperature-winter chill relationships that are lacking in other models including the Chill Hours model.
The Dynamic model uses a two-step process. In the first step, an intermediate product is created following a bell-shape response function to temperature with an optimum at 6°C, tapering to zero at -2 and 14°C. This intermediate product can then be destroyed by subsequent warm temperatures. The second step is where the intermediate product is banked as a chill portion once a threshold is reached. A chill portion cannot be destroyed regardless of subsequent temperatures. Summing chill portions over autumn and winter provides an estimate of accumulated winter chill.
What are the chilling requirements of apple and pear cultivars?
Knowing how much winter chill different crops and cultivars need for healthy flowering and strong yields is essential for growers when deciding what to plant in their region. Failure to suitably match the chilling requirement of a crop or cultivar with the local winter chill will result in reduced productivity. And yet chilling requirements are unknown for many cultivars of apples and pears.
Cultivars are generally ranked in broad groups of 'high', 'medium' and 'low' chill often based on observations of flowering time in the climate in which they have been grown. Gala apple and Williams' pear are generally considered 'high' chill, Cripps Pink apple and Packham's pear 'medium' chill and tropical apple cultivars such as Anna are in the 'low' chill category. Gaps in understanding of the physiological processes involved in dormancy breaking and a lack of necessary research means that putting actual numbers on these chilling requirements remains difficult.
Some reported chilling requirements include:
- 34 chill portions for Cripps Pink (Darbyshire et al. 2016)
- 50 chill portions for Golden Delicious Document showing chill portion requirements
- 1041 chill units for Granny Smith and 1115 chill units for Gala.
How will climate change impact winter chill?
Warmer temperatures in future years are likely to mean less winter chill for most growing regions of Australia.
Summary of mean values in chill portions (1 March 31 August) for 2030 and 2050 using a moderate (RCP4.5) to worst case scenario (RCP8.5) modelling approach
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Average Chill Portions |
Present |
2030
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2050
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RCP4.5 |
RCP8.5 |
RCP4.5 |
RCP8.5 |
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Applethorpe |
72 (62-83) |
63 (48-75) |
60 (44-73) |
56 (41-69) |
51 (36-65) |
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Shepparton |
84 (73-93) |
75 (63-85) |
74 (62-86) |
71 (57-81) |
67 (56-79) |
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Manjimup |
67 (55-82) |
57 (43-76) |
55 (42-75) |
50 (36-72) |
47 (33-68) |
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Huonville |
105 (94-113) |
98 (81-112) |
97 (78-110) |
93 (74-105) |
90 (71-104) |
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Orange |
100 (90-110) |
94 (85-104) |
93 (82-101) |
90 (81-99) |
87 (78-94) |
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Mount Barker |
84 (67-93) |
74 (55-88) |
73 (53-88) |
70 (53-84) |
65 (47-80) |
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What are the symptoms of inadequate winter chill?
Winter dormancy, although an effective protective measure, can pose production challenges during mild winters when fruit trees do not accumulate sufficient winter chill to meet chilling requirements. Light and variable flowering and a protracted flowering period may result from insufficient accumulation of winter chill. These conditions can markedly affect fruit yield and quality through poor pollination, increased risk of frost damage or by increasing the variability in fruit maturity, making picking more difficult and extending the length of harvest.
References
Anderson, J., Richardson, E., & Kesner, C. (1986). Validation of chill unit and flower bud phenology models for 'Montmorency' sour cherry. Acta Horticulturae, 184, 74-78. Bennett JP (1949) Temperature and bud rest period. Calif Agric 3 (11), 9-12 Darbyshire, R., K. Pope and I. Goodwin (2016). An evaluation of the chill overlap model to predict flowering time in apple tree. Scientia Horticulturae 198: 142-149. Erez A, Fishman S, Linsley-Noakes GC, Allan P (1990). The dynamic model for rest completion in peach buds. Acta Hortic 276, 165-174 Ghariani, K. and R. L. Stebbins (1994). Chilling requirements of apple and pear cultivars. Fruit Varieties Journal 48: 215. Luedeling E, Kunz A and Blanke M, 2013. Identification of chilling and heat requirements of cherry trees - a statistical approach. International Journal of Biometeorology 57,679-689. Luedeling, E., 2017. chillR: Statistical methods for phenology analysis in temperate fruit trees. R package version 0.66, URL http://cran.r-project.org/web/packages/chillR/. Richardson EA, Seeley SD, Walker DR (1974) A model for estimating the completion of rest for Redhaven and Elberta peach trees. HortScience 9(4), 331-332 Weinberger JH (1950) Chilling requirements of peach varieties. Proc Am Soc Hortic Sci 56, 122-128About This Site
This site is being developed to deliver up-to-date and historical information on the accumulation of chill and growing degree days. This work was undertaken for the project AP12029 Understanding apple and pear production systems in a changing climate funded by Horticulture Innovation Australia Limited using the Apple and Pear Industry levy and funds from the Australian Government. Additional financial support was contributed by Department of Agriculture and Fisheries (Qld), Department of Economic Development, Jobs, Transport and Resources (Vic), Department of Agriculture and Food Western Australia and Pomewest (WA). Based on or contains data provided by the State of Queensland (Department of Science, Information Technology and Innovation) [2016]. In consideration of the State permitting use of this data you acknowledge and agree that the State gives no warranty in relation to the data (including accuracy, reliability, completeness, currency or suitability) and accepts no liability (including without limitation, liability in negligence) for any loss, damage or costs (including consequential damage) relating to any use of the data. Data must not be used in breach of the privacy laws.If you would like further information please contact: Dr Heidi Parkes, Qld Dept. of Primary Industries For Technical issues: Dr Neil White, Qld Dept. of Primary Industries
© State of Queensland, Department of Primary Industries and Horticulture Innovation Australia Ltd, 2024
Site News
13 November 2024 Improved WCAG Compliance
23 July 2019 API change required change
3 July 2019 - Some big fixes and speed up of code, perhaps?
1 July 2019 - Changes required as API is in state of flux. Also tried to resolve problems with Dropbox.
7 May 2019 - Changed in progress notification
5 April 2018 - Added 7-day forecast to GDD and added Alstonille
15 June 2018 - Added ability to use a 7 Day forecast for chill only at this stage
30 May 2018 - Added the ability to load grower data from orchard weather stations etc. See the Upload tab and the Instructions tab for instructions.
17 Apr 2018 - Issues with data connections have been sorted out. Rainfall added to output. Uses a single site for calculations to make it faster to load.
1 February 2018 - added a feature to allow user to keep location stored for future use.
7 September 2017 - squashed a couple of bugs. Please let me know if you get any errors.
24 August 2017- added this page and caught a small bug that was affecting some calculations when the SILO data was out of sync.
23 August 2017 - Nambour DPI has been added a station. At this point this is interpolated data from nearby stations including the new Nambour DAF station. At this stage the new station has not been added to the list of stations that are currenly servived by SILO.