Method
Daily Minimum Temperature in July
Both low and high night-time temperatures in winter can limit fruit crop productive potential. Very early flowering stone fruit cultivars can develop chilling injury to buds when temperatures are very low during flowering, while hot nights in this period can potentially damage pollination processes. Both conditions can lead to low fruit set. An extended period of very warm winter nights can interfere with the normal accumulation of chill units and result in trees not reaching the dormant state before spring, as well as triggering early flowering. High night-time temperatures increase respiration rates of emerging leaves and create a carbon deficit in the early growth stage.
The mean monthly night-time minimum temperature (Tmin) in mid-winter (July) was calculated from daily temperature data. More detail is provided in the section Background: Climate Change Modelling.
The modelling for the intermediate future (2050s) was conducted using five different CMIP3 GCMs (Schulze, 2011).
Maps
Map Information
In the following maps, Tmin July (°C) is presented under historical climatic conditions, and as the projected change from the historical climatic conditions to the intermediate future climatic conditions (2050s).
Projected Tmin July by mid-century increases by up to 2.0°C in the western and southern regions, by 2.0-2.2°C in most parts of the Klein and Central Karoo, but by up to 2.5°C in the far north-east (Central Karoo).
The projected increase in winter Tmin holds both positive and negative impacts. Less frost damage could be one positive outcome. Insufficient chill unit accumulation would disrupt dormancy progression and lead to early flowering, especially in already warmer production regions. More hot spells during flowering can impair pollination and fruit set. Many pests and diseases would over-winter in the warmer conditions, thus changing the timing and severity of early season impacts on orchards.