1. Study of the temporal aspects of recurrent natural phenomena, and their relation to weather and climate.
2. The scientific study of cyclical biological events; such as, flowering, breeding, and migration, in relation to climatic conditions.
3. The recording and study of periodic biotic events, as flowering, breeding, migrations, etc., in relation to climatic and other factors.

Phenological records of the dates on which seasonal phenomena occur and which provide important information on how climate change affects ecosystems over time.