Among-station Analysis of Thermal and Solar-thermal Phonological Models for Flowering of Syringa vulgaris

Abstract

The within-station performance of the most accurate phenological model in each of three classes of hourly models was compared for the ability to predict flowering dates of common purple lilac (Syringa vulgaris L.). For the three model classes used, day-only, solar thermal unit (STU), and 24-hour interpolations were made between three threshold temperatures and five effective temperature exponents. The most accurate within-station model for each of the three model classes, all having a threshold temperature of 5C, were: (T - 5) 1.54 day-only, (T - 5) 1.26 R 0.5 STU, and (T - 5) 1.70 24-hour, where T = temperature and R = solar radiation. These three models and the corresponding three linear temperature exponent models were then compared for among-station performance using 10 sites in the western United States. The most accurate model for the among-station analyses was the (T - 5) 1.0 day-only model. The two STU models did not perform as well as the two day-only and the two 24-hour models.