Environmental Engineering Reference
In-Depth Information
1. Introduction
Land cover data are used in meteorology, emission, and air quality modeling. In
meteorology modeling land surface exchange processes are based on land cover
categories within each modeling grid (e.g. Xiu and Pleim, 2001). In emission
modeling, land cover data are used to spatially allocate some county-based emission
inventories to modeling grids and to compute biogenic, dust, and fire emissions. In
air quality modeling chemical surface fluxes are modeled based on different land
cover categories (e.g. Pleim et al., 2001). Meteorology, emission, and air quality
models often use land cover data created in the early 1990s. The land cover data
that comes with WRF are USGS Global Land Cover Characteristics (GLCC) 30-s
(~1 km) land use data which were developed from 1 km Advanced Very High
Resolution Radiometer (AVHRR) satellite images obtained in 1992-1993. Currently,
there are two new land cover data sets available for the US and Globe. One is the
2001 National Land Cover Data (NLCD) at 30 m resolution generated from
Landsat 7 and 5 Thematic Mapper (TM) images for the entire U.S. (Homer et al.,
2004) and the other is the 2001 NASA Moderate Resolution Imaging Spectro-
radiometer (MODIS) land cover data at 1 km resolution generated from TERRA
MODIS satellite images for the Globe (Friedl et al., 2001). We have developed
programs to process the 2001 NLCD (for U.S. areas) and MODIS data (for areas
outside U.S.) into fractional coverage of each land category for use in the Weather
Research and Forecast (WRF) and Community Multiscale Air Quality (CMAQ)
models. The gridded land use data are used to specify vegetation and surface related
parameters that are needed by land surface models (LSM), dry deposition models,
and biogenic emission model.
2. Data and Methods
The NLCD data base was developed by a group of federal agencies under the
Multi-Resolution Land Characteristics (MRLC) Consortium since 1992. The
NLCD 2001 data from MRLC includes 21 classes of land cover, tree canopy
percent, and imperviousness percent at each 30-m pixel. NOAA Coastal Services
Center Coastal Change Analysis Program (C-CAP) NLCD data has 30 land cover
classes which includes detailed costal wetland classes in addition to MRLC NLCD
21 classes. NASA MODIS land cover data includes 20 International Geosphere-
Biosphere Programme (IGBP) classes.
Those land cover data are stored in pixel-based format, which is often called
raster data. We developed C++ raster tools using the Geospatial Data Abstraction
Library (GDAL) in the Spatial Allocator (SA, http://www.ie.unc.edu/cempd/
projects/mims/spatial/) to compute gridded land cover information from MRLC
2001 NLCD (including land cover, imperviousness, and canopy), NOAA coastal
2001-2006 NLCD land cover, and NASA 2001 MODIS land cover data (for areas
