Land Cover Data for Global-Scale Applications

Recently developed, global land cover data products are presented. These data, assembled from standard data products, derived from satellite observations by MODIS sensors on NASA's Terra and Aqua spacecraft, are well-suited to use with Earth system and climate change integrated assessment models as well as in a variety of applications addressing questions at global scales. Participating in NASA's Advancing Collaborative Connections for Earth System Science (ACCESS) program, we developed global mosaics of the standard MODIS data products representing 'Land Cover Type Yearly' and 'Vegetation Continuous Fields Yearly' for each year of available data. The combination of these data products at global scale provides additional insight into changes in the fraction of tree cover within land units designated as forest or savannah over the decade of observations. Land cover attributes are specified within many global change applications, and satellite remote sensing measurements are widely used to estimate such attributes. The standard MODIS data products provide one of the highest-quality representations of land cover attributes globally over a relatively long time period, 2001-2011. But although the 500 m and 250 m spatial resolutions of these data are well-suited to many regional and local analyses, most global models represent land surface characteristics at significantly coarser resolutions. Additionally, models and many global-scale applications typically require global coverage by a single data set with variables projected in geographic coordinates of latitude and longitude. To facilitate use of the standard MODIS products with global models and to address questions in a global context, we re-projected the data for land cover type and vegetation continuous fields into geographic coordinates and created global mosaics of these data for each year of available data. We aggregated the 500 m resolution land cover type and 250 m resolution vegetation continuous fields to two coarser resolutions in common use with Earth system and climate change integrated assessment models: (1) 0.5 degrees latitude x 0.5 degrees longitude, and (2) 5' latitude x 5' longitude. The Global Land Cover Facility distributes these data in both GeoTIFF and ESRI ASCII grid file formats. Overlaying vegetation continuous fields data onto land cover type at global scale is straightforward within this data structure using operations similar to those used to incorporate such data into global models. On doing so, we identify geospatial patterns in global trends of the fraction of tree cover within land units assigned to land cover types corresponding to forests and savannah.