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Website shows winter chill data for your region

Industry Best Practice

A new website ( is providing access to accurate local winter chill data for Australian apple and pear growers, with benefits for in-season orchard management and long-term orchard business planning.

A new website  helps growers to access and interpret local winter chill data to help with crop management for the current season, as well as historically and under future climates.

Apple and pear trees need winter chill to break dormancy and promote healthy flowering in the spring. Failure to get enough chill results in delayed and uneven bud burst and flowering, with negative consequences for yield and quality. For this reason, the amount of chill accumulated in a region each year largely determines the crops and cultivars that can be commercially grown.

Despite its importance, there are differences across the industry when it comes to understanding winter chill: How is it measured? What’s the difference between chill hours, units and portions? When does it start accumulating? How much chill have we had this year? A big part of the problem is that access to accurate local winter chill data for Australian growers has been limited.

To address this issue, we developed a website to enable growers and industry more broadly to access and interpret local winter chill data for the current season, as well as historically and under future climates. While the website was developed for the apple and pear industry, the winter chill data can be used across all Australian temperate fruit and nut industries.

Real-time chill data for 600 locations

The website provides winter chill data for 600 locations across Australia and has a number of useful features.

View in any unit of measurement

Chill can be viewed in portions, units or hours. Different models of winter chill have been developed over the years to describe how autumn and winter temperatures affect dormancy breaking. The Dynamic model which calculates chill in portions is the current best-practice model, especially in warmer climates.

Get real-time and historic data

The chill accumulation curve for any year selected is compared with the local range in the historical chill record. Users can access real-time in-season chill data or choose to view data from a previous year.

Choose your time period

The period of chill accumulation can be specified by the user – that is, you can choose when to start and stop accumulating chill. For example, you might start on a calendar date such as 1 March or a date based on a physiological measure such as 50 per cent leaf-fall.

How the website works

After the location has been chosen, the website obtains daily maximum and minimum temperature data from the SILO database and calculates chill using the selected model. SILO is an enhancedclimate database provided by the Queensland Department of Science, Information Technology and Innovation, using raw data from the Bureau of Meteorology. Of the many thousands of weather stations available we have selected those where temperature is currently recorded, or has been recorded for a substantial period.

Why winter chill data is useful

Local historical and in-season winter chill data can be used for in-season decision-making in the orchard, as well as for longer-term strategic planning, particularly for milder winter growing regions where the amount of chill can vary considerably from season to season.

By recording accurate winter chill data alongside bud burst and flowering dates you can build up a picture of how chill varies from year to year in your region and its relationship with full bloom dates and length of flowering in different orchard blocks and cultivars. This can be used to make more informed predictions about the timing of bud burst for the coming season by comparing progress of the current season’s chill accumulation with that of previous seasons.

It can also be used to assess the climate suitability of different crops and cultivars. Identification of delayed and uneven flowering in a particular cultivar every time there is a lower chill year indicates problems with inadequate chilling, and it can help you make better-informed decisions on the use and timing of dormancy-breaking sprays.

Winter chill in a changing climate

This winter chill website came out of a larger research project looking at the effects of climate change on the apple and pear industry. As part of this work we developed climate projections for 2030 and 2050 for pome fruit regions across Australia; we plan to publish an article on this in an upcoming edition of Australian Fruitgrower. We found that all regions could expect to experience declines in winter chill over this time period.

The increased frequency of low-chill years in milder-winter growing regions will likely result in symptoms of inadequate chill in some cultivars. Recording of winter chill alongside bud burst and flowering dates can provide early indication of cultivars affected by inadequate chill, and therefore assist management decisions regarding varietal choice for new plantings and future orchard adaptation planning.

Access to accurate winter chill data enables the preparation of an orchard management strategy that can be enacted in low-chill years – for instance, through the effective application of dormancy-breaking chemicals – to reduce climate-change-related risk.

A novel feature of the website is that it can be used to look at orchard data retrospectively. If you have records of bud burst and/or flowering going back a number of years, you can use the website to access the winter chill for each of those years, and assess what affect any lower-chill years may have had, if any, to give you a better idea of what to expect in the orchard in the future.

Bonus features and future work

As well as providing winter chill for specific sites, the website can compare locations, calculate growing degree days and hours, and show minimum and maximum temperatures. In the future we hope to add in-season forecasts of winter chill so that in early June, for example, you can forecast how much chill will be received and determine whether an intervention with dormancy-breakers might be needed.

Chill accumulation graph for Manjimup, Western Australia, for 2017 (up to 4 June). Chill is shown as portions. The boxed section of the graph is expanded to show comparison of chill in 2017 with the historical chill range from the highest 10 per cent of years to the lowest 10 per cent of years, as at 25 May.

Predicted changes in chill to 2050

This table shows the average chill portions (1 Mar to 31 Aug) using two greenhouse gas emission scenarios: Low (a minimum to medium increase in greenhouse gases) and High (worst-case scenario increase in greenhouse gases).

Average chill portionsPresent20302050
Applethorpe72 (62-83)63 (48-75)60 (44-73)56 (41-69)51 (36-65)
Shepparton84 (73-93)75 (63-85)74 (62-86)71 (58-81)67 (57-79)
Manjimup67 (55-82)57 (43-76)55 (42-75)50 (36-72)47 (33-68)
Huonville105 (94-113)98 (81-112)97 (78-110)93 (74-105)90 (71-104)
Orange100 (90-110)94 (85-104)93 (82-101)90 (81-99)87 (78-94)
Mount Barker84 (67-93)74 (55-88)73 (53-88)70 (53-84)65 (47-80)

About the authors

Dr Heidi Parkes and Neil White work with Queensland’s Department of Agriculture and Fisheries, and Rebecca Darbyshire is with the NSW Department of Primary Industries.


This project is a strategic levy investment under the Hort Innovation Apple and Pear Fund. It is funded by Hort Innovation using the apple and pear levy and funds from the Australian Government. Additional financial support was contributed by the Department of Agriculture and Fisheries (Qld); the Department of Economic Development, Jobs, Transport and Resources (Vic); the Department of Agriculture and Food Western Australia; and Pomewest (WA).

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