Vegetation phenology examines life cycle events such as bud burst, flowering, and leaf senescence. The phenology of terrestrial ecosystems reflects response of the biosphere to proximal climatic factors (e.g. temperature and rainfall). Thus phenology can be used to identify and describe different vegetation types and to monitor vegetation responses to changes in these climatic determinants. Vegetation phenology has already shown clear changes in the northern hemisphere during the past 20 years, with growing season length increasing by up to a month.