Because monitoring the temperature dynamics of all fruits throughout the entire growing season is challenging, models that simulate fruit surface temperature (FST) are developed and applied. One such experimentally based FST model (Li et al., 2014) calculates the maximum temperature of the fruit surface when facing directly to the sun at midday on a sunny day, without any shading of the fruit surface. It then calculates the difference between FST and air temperature, which is on average ~ 12°C. This value which corresponds well with experimentally obtained values in South African and Australian apple orchards.
In this study, we assumed that sunburn browning (FST ≥ 48°C) would occur when daily maximum air temperature (Tmax) was between 34.0 and 38.9°C. Sunburn was thus modelled for the study region using the following scenario:
Number of days with FST ≥48.0°C and daily Tmax 34.0 – 38.9°C
We then analysed the total number of days per month (November to April) where daily Tmax crossed the threshold for potential sunburn damage.
The historical climate risk (days per month meeting the criteria), the projected intermediate future climate risk, and the difference (days per month) between the two were mapped using the average outcomes from four CMIP3 GCMs.