Method
Red Colour
The criteria used to determine conditions conducive to peel red colour development were broadly based on experimental research in South African apple orchards, and modelled for mid- to late-season blushed/bi-colour cultivars for the months March and April. The criteria used were one day of daily minimum temperature below 12°C (for the induction of anthocyanin synthesis), followed by daytime maximum temperatures in the range 20-28°C for three consecutive days (for strong anthocyanin synthesis), conditional upon solar radiation on the qualifying days being at least 60% of those days’ maximum solar radiation potential.
The number of occasions during March and April that the above conditions were met in each of the 1 401 Quinaries were counted for each year of the historical record (1950-1999), the average determined, and the outcome mapped separately for March, April, and the combined March-April period. Using daily outputs from the ECHAM GCM, considered to be a representative GCM for the region, the same criteria were isolated, and the results mapped separately for the intermediate future period of the 2050s. Finally, the differences (in days per month) between the historical and future climate conditions were calculated and mapped for these months.
Maps
Map Information
The first set of maps show the number of days in March on which the climatic criteria are met for red colouring of mid- to late-season blushed or bi-colour apples under historical climatic conditions and into the intermediate future climates. The climatic criteria are met more than 8 times, and in some areas more than 14 times in the pome fruit regions of the west and the Langkloof. In the intermediate future, projections show that much of the region could warm to the extent that climatic criteria for red colouring are met up to 6 times in the warmer southern areas and the western Langkloof, and up to ten times in the cooler northern areas. The greatest reductions (9-15 days less) are seen in the high-lying northern areas and the western Langkloof, and the lowest reductions (0-9 days less) are seen in the coastal south-west.
Conditions for red colouring come into their own in April, when under the historical climatic regime the spatial patterns, although patchy, indicate that the apple production areas meet the red colouring criteria on 10 or more days, and in several areas more than 14 times. However, the April of the intermediate future sees projected reductions in qualifying days to 2-4 days in the south and 2-8 days in the north and western Langkloof. This represents a reduction of up to 15 days in April in apple production regions.
When March and April are combined, the southern production regions have 20-25 days that meet the colouring criteria under historical climate conditions, the western Langkloof has 25-30 days, and the northern regions have at least 25 days and in some areas over 30 suitable days. This decreases significantly into the intermediate future of the 2050s, with the reduction being 9 days or more, and some areas (Koue Bokkeveld, western Langkloof) showing a reduction of more than 15 days.