Estimating Trends in Phenology

Data Science Team

Natural resource managers in the Northeastern US would like ready access to maps that indicate when, on average, various growing degree day (GDD) thresholds are met. These GDD thresholds can indicate phenological events such as the emergence of an insect pest or when leaves turn colors in the fall. Using high resolution temperature data from 1981–2023 we can estimate the number of GDD on each day of year (DOY), and then estimate the DOY that various GDD thresholds are reached each year.  Trends in the DOY a GDD threshold is reached can tell us whether these phenological events are happening earlier or later over time as the climate changes and if particular regions are experiencing greater changes in phenology.