growingdegreeday

Growing degree day is a metric used in agriculture to estimate plant and pest development by measuring heat accumulation over time. It relies on daily temperatures and a crop-specific base temperature, below which growth is assumed not to occur. The most common calculation for daily growing degree days (GDD) is: GDD = max(0, [(T_max + T_min)/2 − T_base]), where T_max and T_min are the day’s high and low temperatures and T_base is the base temperature for the crop. Some approaches cap the daily mean with an upper threshold to account for heat stress, giving GDD = max(0, min(T_upper, (T_max + T_min)/2) − T_base). The growing degree day accumulation for a period is the sum of daily GDD values.

Base temperatures vary by crop and growth stage; common examples include 0, 5, and 10 degrees Celsius. For instance, with a base of 10°C and a day where T_min = 12°C and T_max = 26°C, the daily GDD would be 9. GDD is not only used for crops but also for tracking the development of certain pests whose life cycles depend on heat units.

Applications of GDD include timing of planting and harvest, predicting flowering or fruiting stages, scheduling irrigation, and forecasting pest emergence. Data are typically drawn from weather stations or local climate records that provide daily minimum and maximum temperatures. Limitations include its simplifications: it ignores soil temperature, radiation, moisture, and chilling requirements; it assumes a constant base temperature and does not account for cultivar-specific responses or microclimates. Nevertheless, GDD remains a widely used, practical tool for planning and risk assessment in agriculture.