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GEOPHYSICAL RESEARCH LETTERS, VOL. 32, L04705, doi:10.1029/2004GL021961, 2005

A global framework for monitoring phenological responses to climate change

Michael A. White

Department of Aquatic, Watershed, and Earth Resources, Utah State University, Logan, Utah, USA


Forrest Hoffman

Computer Science and Mathematics, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA


William W. Hargrove

Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA


Ramakrishna R. Nemani

NASA Ames Research Center, Moffett Field, California, USA


Abstract

Remote sensing of vegetation phenology is an important method with which to monitor terrestrial responses to climate change, but most approaches include signals from multiple forcings, such as mixed phenological signals from multiple biomes, urbanization, political changes, shifts in agricultural practices, and disturbances. Consequently, it is difficult to extract a clear signal from the usually assumed forcing: climate change. Here, using global 8 km 1982 to 1999 Normalized Difference Vegetation Index (NDVI) data and an eight-element monthly climatology, we identified pixels whose wavelet power spectrum was consistently dominated by annual cycles and then created phenologically and climatically self-similar clusters, which we term phenoregions. We then ranked and screened each phenoregion as a function of landcover homogeneity and consistency, evidence of human impacts, and political diversity. Remaining phenoregions represented areas with a minimized probability of non-climatic forcings and form elemental units for long-term phenological monitoring.

Received 10 November 2004; accepted 21 January 2005; published 18 February 2005.

Index Terms: 0414 Biogeosciences: Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912); 0426 Biogeosciences: Biosphere/atmosphere interactions (0315); 0429 Biogeosciences: Climate dynamics (1620); 0438 Biogeosciences: Diel, seasonal, and annual cycles (4227); 0480 Biogeosciences: Remote sensing.

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Citation: White, M. A., F. Hoffman, W. W. Hargrove, and R. R. Nemani (2005), A global framework for monitoring phenological responses to climate change, Geophys. Res. Lett., 32, L04705, doi:10.1029/2004GL021961.