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Western Geographic Science Center


Phenology Studies and Research Project

The Phenology Studies Project is concerned with utilizing satellite remote sensing data, coupled with on ground observations to accomplish the following objectives: 1) assess the impact of land use change and climate variability on land surface phenology and related energy and water fluxes; 2) develop methods of characterizing phenology that are appropriate for different environments; 3) serve a leadership role in the National Phenology Network, to assure that data collection and coordination are conducted in a scalable manner, incorporating remote sensing data. The strategy for the Phenology Research project is to expand methods that have been developed over the past several years (e.g., Reed, 2006; Reed and others, 2003) for characterizing phenology and phenological trends and couple this information with studies from other projects in USGS Geography (e.g. Land Cover Status and Trends), build on the methods for characterizing landscapes whose characteristics do not fit the general model, and to participate in national and international phenology for a for two-way communications regarding techniques, results, and applications.

Phenology, the study of the timing of biological events, is increasingly regarded as a key to understanding many phenomena that are related to land cover and land use change, global scale climatic change, and human health. Remote sensing of phenology provides a mechanism to move from plant-specific to regional and continental scale studies of phenology. Given the now-sufficient collection of satellite data to study annual and interannual seasonal characteristics, we have the ability to study aspects of phenology that have previously been difficult, if not impossible to gauge. These aspects include evaluating trends in phenology over the period of satellite record, characterizing phenology for ecosystems that do not fit the standard model (e.g., deserts), and validate these results. Specific tasks that can be achieved include 1) evaluate the variability and trends of vegetation phenology as they relate to land use/land cover change; 2) develop methods for characterizing phenology of difficult, yet important vegetation types, namely desert vegetation, 3) participate in the development of the National Phenology Network.

In the attached movie, created by Brad Reed, we are looking at the desert southwest approximately centered on the Mojave Desert and including parts of California, Nevada, Utah and Arizona. The satellite greenness index measured from the MODIS sensor on the Terra Satellite for the year 2005 has been colored to highlight desert annual vegetation as green, forest vegetation as deep red, and snow as white. 2005 was a year of exceptionally high spring precipitation and very dynamic desert vegetation greenness. As we begin the movie in January, the snow in the higher elevation terrains is gradually disappearing and vegetation in the deserts is becoming more and more abundant, reaching a peak at the end of March. During April, May and June, the desert vegetation senesces (dries out), and the greenness largely disappears. In July, increasing humidity and rain triggers some scattered greenness, with the first evidence of the response to the annual monsoon rains showing up July 28 as green patches in southeastern Arizona. This monsoon greenness rapidly blossoms as a northward-trending front during August. This vegetation in Arizona disappears during the drier conditions in the fall, but more subtle greenup occurs farther west in the Mojave Desert. By the end of December, snow again blankets the higher elevations.

For more information contact: Photo of Peter Ng
Cynthia S.A. Wallace

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