Increase in Solar Radiation (6% and 8% per 1000 m of Altitude) and Effect on the Red Color of the Apple

The red color of apple skin is due to anthocyanins, compounds that accumulate in response to sunlight during ripening. Studies indicate solar radiation increases between 6% and 8% for every 1000 m of Altitude. Apples grown at higher elevations show better quality, with greater red pigmentation resulting from increased anthocyanin biosynthesis.

Source: Gómez Sierra, L. A. (2019). Influence of UV-B radiation on the biosynthesis of anthocyanins in apple fruits (Malus domestica Borkh) CV." ANNA" for high tropical conditions in Boyacá, Colombia.