Science Background - Phenology and Climate
Phenology Climate Science
Science of the Phenology and Climate project
The following are key science questions about phenology and climate that scientists are interested in answering. These big picture questions should be considered during participation in the Phenology and Climate Project and when conducting related research investigations of your own:
- What are the best indicators to define the onset and end of the growing season?
- How well do satellite-based measurements of ground-based plants (such as the Normalized Difference Vegetation Index or NDVI) compare with ground-based observations of green-up or green-down?
- How much do phenology measurements vary from year-to-year? (You can address this science question if you have been collecting GLOBE phenology on a regular basis for several years or by using data from a school or network with a long history of phenology data)
- What is the relationship between spring budburst and atmospheric/soil measurements among GLOBE schools within a biome or by latitude?
Phenology is the study of recurring biological cycles and their connection to climate. Examples of phenological events include leaf and flower openings, butterfly, bird and other animal migrations, insect emergence and fish spawning. Plant and animal life cycle phases respond to environmental changes, seasonal variations in temperature and precipitation driven by weather and climate. Each phenophase or life cycle event, gives a measure of the environment from the perspective of the associated organism. Thus, timings of biological events are ideal indicators of local and global changes in weather and climate on Earth's biosphere.
GLOBE phenology investigates the timing and length of the plant growing season: leaf-out, expansion and senescence (plant aging). These basic GLOBE phenology protocols are Budburst, Green-up and Green-down. The plant growing season is the period between green-up and green-down. Monitoring the length of the plant growing season is important for society because plant growing season length has a direct effect on food and fiber production, and thus on society's ability to support itself. Changes in the length of the growing season are among the climate change indicators that the Environmental Protection Agency has identified.
While variations in climate influence phenology, the reverse is also true. Plant phenology affects the partitioning of radiant energy into latent and sensible heat. In the presence of plants, more energy is used in latent heat thereby reducing sensible heat. As plant green-up begins, leaf chlorophyll absorbs sunlight for photosynthesis which fixes carbon dioxide from the atmosphere. Plants also begin to transpire water from the soil to the atmosphere, which affects air temperature, humidity and soil moisture. Processes occurring at the leaf level strongly influence global processes.
Green-up and senescence can be used to study carbon cycling, examine global vegetation patterns, inter-annual variation, and response to climate change. Timing of green-up together with weather parameters can be used to predict vulnerability of forests to fires. Across the world many spring events like budburst and bird migrations are happening earlier (see example described in the GLOBE Scientists' Blog) and autumn events occurring later. However not all species are changing at the same rate, and the difference in the rates and timings of response of different plant and animal species alter interactions and processes in ecosystems. Ground observations and measurements by students are very helpful not only in validating satellite data measurements (affected by age of sensors, angle to the surface of the Earth, and atmospheric conditions), but also in understanding the impact of changing phenology on ecosystems and people.