Growing degree days (GDD) are calculated as: GDD = T_mean − T_base (if T_mean > T_base; otherwise GDD = 0). The base temperature depends on the crop: 10 °C for maize, 5 °C for wheat. GDD accumulation predicts phenological stages (germination, flowering, ripening).
Applications
In viticulture, the thermal integral (season's GDD sum) classifies wine regions and predicts harvest dates. In entomology, GDD predict pest emergence. Climate change is increasing annual GDD, advancing harvests, shifting crop distributions, and moving wine regions northward.