No winter, no apples?

Australia’s overlooked threat to temperate fruit production

A warmer winter can feel harmless. But many fruit trees need cold weather before their buds can open normally in spring.

The overlooked risk

Cold during winter is what apples, cherries, pears, and stone fruits need to trigger certain processes. In the event when inadequate chilling occurs, delayed and uneven bud break, flowering, and fruit setting can occur. It is not about the absence of fruit production in any single year. It is about the gradual loss of productivity of the orchards in the current climate conditions.

Visual 1 — The winter signal is changing

The story initially seems like nothing more than climate fluctuation since every orchard area experiences both cold and warm winters.

However, the exact same national level news may hide a different story at the local level. Use the legend below to contrast between warm Applethorpe and cool Huonville.

The scale being used here is Chill Portions, which is determined by taking the daily minima and maxima temperatures and calculating using the Dynamic Model method. This is not fruit production; this is the temperature signal required by fruit trees .

Source: SILO gridded climate data accessed through the weatherOz R package. Chill Portions calculated with chillR. SILO combines Bureau of Meteorology observations with spatial interpolation; results therefore represent gridded estimates rather than a single orchard weather station.

Visual 2 — The national average hides local exposure

First of all, go through the chart horizontally. Those regions that are located to the left side of zero have seen a reduction in their average winter chill.

Now move to the vertical axis. It is possible for a particular region to show a decrease in mean chill, while at the same time having a greater buffer compared to another orchard region that is warmer. This implies that both the current mean chill and the rate of decrease are important.

Bubbles indicate the economic aspect. Larger bubbles mean that the state is more economically affected by climate change due to its higher value in fruit farming .

Use your cursor to hover over any circle and gain information on region, averages, percent changes, and state fruit value. Use the legend for isolating specific states.

Sources: SILO/weatherOz/chillR calculations and Australian Bureau of Statistics, Australian Agriculture: Horticulture, 2023–24. State farm-gate value is included as economic context, not as a forecast of financial loss.

Visual 3 — What does another 1°C, 2°C or 3°C do?

Now consider how the biological signal reacts to warmer temperatures. This graph applies the same warming trend to every day in a typical recent climate.

This is clearly not a forecast, but it is a way of illustrating that the impact of cold winter weather may be nonlinear even though the temperature changes look small.

Select your choice of location from the drop down menu above. Warmer locations can start out with less chill than cooler locations and still lose more of their existing chill.

The future challenge is thus serious, since adaptation is time consuming. New varieties need testing, new plants take time to grow, and a relocation would require suitable land, water, labor, and refrigeration facilities.

Source: sensitivity analysis based on 2016–2025 SILO daily temperature climatologies. Values are modelled temperature responses, not official future climate projections.