A New Scheme for Predicting Leaf Onset in Summer-Green Vegetation in the Northern Hemisphere

Abstract

A modified thermal time model (MTM) was developed to reproduce the leaf onset for summer-green vegetation in the Northern Hemisphere. The model adopts the basic concept of a thermal time model (TM) in that leaf onset is primarily triggered by growing degree days (GDD). Based on global phenology data derived from satellite observations, a new parameterization for the critical model parameter T_b (i.e., baseline temperature for GDD calculation) has been introduced, and the spatial distribution of T_b was calculated. Simulations of leaf onset during 1982–2000 in the range 30–90°N showed a significant improvement of MTM over the standard TM model with constant T_b. The mean error and mean absolute error of the climatological simulation were 1.11 and 6.8 days, respectively, and 90% of the model error (5th and 95th percentiles) was between −12.4 and 13.7 days.

Keywords:

• leaf onset
• baseline temperature
• growing degree days
• Global Land Surface Satellite (GLASS) dataset