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AERSURFACE User's Guide
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EPA-454/B-08-001
January 2008
AERSURFACE User's Guide
U. S. Environmental Protection Agency
Office of Air Quality Planning and Standards
Air Quality Assessment Division
Air Quality Modeling Group
Research Triangle Park, North Carolina
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PREFACE
This document provides a technical description and user instructions for the AERSURFACE
tool, designed to aid in obtaining realistic and reproducible surface characteristic values for
AERMET, the meteorological processor for AERMOD.
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ACKNOWLEDGMENTS
The AERSURFACE User's Guide has been developed by the Air Quality Modeling Group
within EPA's Office of Air Quality Planning and Standards, with input from the AERMOD
Implementation Workgroup. The AERSURFACE code has been developed by MACTEC
Federal Programs, Inc., under U.S. EPA Contract No. EP-D-05-096, with Karen Wesson as
Work Assignment Manager. The efforts of all contributors are gratefully acknowledged.
in
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CONTENTS
PREFACE ii
ACKNOWLEDGMENTS iii
FIGURES v
TABLES vi
1.0 INTRODUCTION 1
2.0 TECHNICAL DESCRIPTION OF AERSURFACE 2
2.1 DESCRIPTION OF USGS LAND COVER DATA 2
2.2 ASSIGNMENT OF SURFACE CHARACTERISTICS BY LAND COVER CATEGORY 4
2.3 AERSURFACE CALCULATION METHODS 6
3.0 AERSURFACE USER INSTRUCTIONS 8
3.1 RUNNING AERSURFACE 8
3.2 INTERACTIVE USER PROMPTS 8
3.3 AERSURFACE ERROR HANDLING 13
3.4 FILE DESCRIPTIONS 13
3.5 EXAMPLE TEST CASE 14
4.0 REFERENCES 18
APPENDIX A. SURFACE CHARACTERISTICS TABLES A-l
APPENDIX B. DESCRIPTIONS OF NLCD92 LAND COVER CATEGORIES B-l
IV
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FIGURES
Figure Page
3-1. Contents of rdu_seamless.dat File for RDU Seamless Test Case 15
3-2. Diagram of User-specified Radius and Sector Definitions Overlaid on Land Cover Grid Cells... 15
3-3. Contents of rdu_seamless.out File for RDU Seamless Test Case 16
3-4. NLCD Map for RDU Seamless Test Case, Showing Albedo/Bowen Ratio Domain, and
Surface Roughness Domain and Sectors 17
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TABLES
Table Page
2-1. USGS NLCD92 Land Cover Categories 2
2-2. Seasonal Category Descriptions 5
A-1. Seasonal Values of Albedo for the NLCD92 21 -Land Cover Classification System ... A-2
A-2. Seasonal Values of Bowen Ratio for the NLCD92 21-Land Cover Classification
System A-3
A-3. Seasonal Values of Surface Roughness (m) for the NLCD92 21-Land Cover
Classification System A-5
VI
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1.0 INTRODUCTION
When applying the AERMET meteorological processor (EPA, 2004a) to process meteorological
data for the AERMOD model (EPA, 2004b), the user must determine appropriate values for
three surface characteristics: surface roughness length {z0}, albedo {r}, and Bowen ratio {B0}.
The surface roughness length is related to the height of obstacles to the wind flow and is, in
principle, the height at which the mean horizontal wind speed is zero based on a logarithmic
profile. The surface roughness length influences the surface shear stress and is an important
factor in determining the magnitude of mechanical turbulence and the stability of the boundary
layer. The albedo is the fraction of total incident solar radiation reflected by the surface back to
space without absorption. The daytime Bowen ratio, an indicator of surface moisture, is the ratio
of sensible heat flux to latent heat flux and, together with albedo and other meteorological
observations, is used for determining planetary boundary layer parameters for convective
conditions driven by the surface sensible heat flux. Further details regarding the AERMOD
model formulations and their dependence on surface characteristics are provided in Cimorelli, et
al. (2004).
The AERSURFACE tool has been developed to aid users in obtaining realistic and reproducible
surface characteristic values, including albedo, Bowen ratio, and surface roughness length, for
input to AERMET. The tool uses publicly available national land cover datasets and look-up
tables of surface characteristics that vary by land cover type and season. This user's guide
provides a technical description of the AERSURFACE tool, including information on the data
used by AERSURFACE to provide these surface characteristics for AERMET. Detailed user
instructions for application of AERSURFACE are also provided.
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2.0 TECHNICAL DESCRIPTION OF AERSURFACE
2.1 DESCRIPTION OF USGS LAND COVER DATA
AERSURFACE requires the input of land cover data from the U.S. Geological Survey (USGS)
National Land Cover Data 1992 archives (NLCD92), which it uses to determine the land cover
types for the user-specified location. AERSURFACE matches the NLCD92 land cover
categories to seasonal values of albedo, Bowen ratio, and surface roughness. Values of surface
characteristics are calculated based on the land cover data for the study area and output in a
format for input into AERMET Stage 3.
The USGS NLCD92 data utilized by AERSURFACE provide land cover data at a spatial
resolution of 30 meters, mapped using an Albers Conic Equal Area projection, and based on a
21-category classification scheme applied over the continental U.S. A list of the 21 land cover
categories in NLCD92 is shown in Table 2-1. More information on this data can be found at the
USGS Land Cover Institute (LCI) website: http://landcover.usgs.gov/natllandcover.php. The
NLCD92 data can be downloaded in two different forms: 1) complete files by state; and 2) files
for a user-specified domain of arbitrary size and location from a "seamless data server."
AERSURFACE supports both forms of the NLCD92 data.
Table 2-1: USGS NLCD92 Land Cover Categories
Classification
Water
Developed
Barren
Forested Upland
Shrubland
Non-natural Woody
Herbaceous Upland
Herbaceous
Planted/Cultivated
Wetlands
Class
Number
11
12
21
22
23
31
32
33
41
42
43
51
61
71
81
82
83
84
85
91
92
Land Cover Category
Open Water
Perennial Ice/Snow
Low Intensity Residential
High Intensity Residential
Commercial/Industrial/Transportation
Bare Rock/Sand/Clay
Quarries/Strip Mines/Gravel Pits
Transitional
Deciduous Forest
Evergreen Forest
Mixed Forest
Shrubland
Orchards/Vineyards/Other
Grasslands/Herbaceous
Pasture/Hay
Row Crops
Small Grains
Fallow
Urban/Recreational Grasses
Woody Wetlands
Emergent Herbaceous Wetlands
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The state NLCD92 data files can be accessed through the following website, which includes two
formats for each state (TIP and BIN), as well as an NLCD92 legend and other user files:
http://edcftp.cr.usgs.gov/pub/data/landcover/states/. The state NLCD filenames are of the form
"statename.nlcd.tif.gz" for the "TIP format", more accurately referred to as the GeoTIFF format,
and "statename.nlcd.bin.gz" for the BIN format. The ".gz" extension on the filenames indicates
that the files are in compressed form (due to their large size). The state files must be
uncompressed, using public domain or commercial software that supports the "gzip"
compression format. These two formats for state NLCD data are essentially equivalent.
However, as discussed in Section 3.0, the TIP format requires less user input when running the
AERSUKFACE program, and can also be visualized through various public domain and
commercial software products. The USGS provides a free data viewer, called "dlgv32 PRO",
which can be downloaded from the following website:
http://mcmcweb.er.usgs.gov/drc/dlgv32pro/.
The NLCD92 data can also be downloaded from the USGS Seamless Data Server (SDS) through
the following website: http://seamless.usgs.gov/. AERSURFACE supports the default format for
seamless NLCD files, which is the GeoTIFF format. The seamless data downloaded from the
server is a compressed file (with a ".zip" file extension) that contains several data files. The only
file needed to run AERSURFACE is the file with the ".tif' file extension. The SDS offers the
advantage that the user can download only the data needed for a particular application, and thus
the file sizes will be considerably smaller than the state NLCD data. For sites located near state
boundaries, the use of seamless NLCD data may be the only option for successfully applying
AERSURFACE. The SDS also allows the user to the visualize the land cover data, which can be
overlaid with other geographic information for reference purposes, such as state and county
boundaries, roadways and waterways, as well as topographic information.
Users should note that the SDS also offers access to several types of data other than the NLCD92
data, including topographic data and a newer land cover data base referred to as 2001 NLCD
data. AERSURFACE currently does not support the 2001 NLCD data. Users should take care
to ensure that they are downloading the correct type of data for use with AERSURFACE, which
is labeled as "NLCD 1992 Land Cover."
The USGS SDS website offers a Tutorial, Frequently Asked Questions, and other user support
information. Several options are available regarding types of data to display, as well as types of
data to download. Users should become familiar with the options available for navigating the
data server and extracting the data needed for AERSURFACE. In addition to navigating and
accessing the correct type of data for the desired domain, the user may also need to make
adjustments to their web browser settings in order to successfully download the data. This may
include disabling "pop-up blockers," as well as modifying other settings. Users experiencing
difficulties with accessing NLCD92 data through the SDS are encouraged to review the user
support information available through the USGS SDS website or request assistance through their
own computer user support group.
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2.2 ASSIGNMENT OF SURFACE CHARACTERISTICS BY LAND COVER
CATEGORY
Each of the 21 land cover categories in the NLCD92 archive is linked within AERSUKFACE to
a set of seasonal surface characteristics. These values of seasonal surface characteristics are
provided in Appendix A. Table A-l provides the seasonal albedo values, Table A-2 has the
seasonal Bowen ratio values for three categories of surface moisture (average, dry and wet), and
Table A-3 lists the seasonal surface roughness values. These values are based on data reported
in the literature and the tables include information and references regarding their derivation. A
more detailed explanation of the NLCD92 21 land cover categories is presented in Appendix B
to provide a better understanding of the surface types included within each category.
The values of seasonal surface characteristics by land cover category were developed for the
continental U.S. for the five seasonal categories listed in Table 2-2. These seasonal categories
are the same as those used by the AERMOD model (EPA, 2004b) for the gas deposition
algorithms (GDSEASON keyword). The user is given the option of choosing which months
belong to which seasonal category for their specific location if they choose to output monthly or
annual surface characteristics for AERMET. This option will allow a more state-specific
estimate, and in many cases be more reflective of the true nature of the site. Otherwise, the user
can select to use the program's default setting which assigns the months of March, April, and
May to seasonal category 5 ("Transitional spring with partial green coverage or short annuals");
June, July, and August to seasonal category 1 ("Midsummer with lush vegetation"); and
September, October, and November to seasonal category 2 ("Autumn with unharvested
cropland"). The user will also be asked whether the location experiences continuous snow cover
in the winter. If the area does experience continuous snow cover, then the default seasonal
category 4 ("Winter with continuous snow on ground") will include the months of December,
January, and February. If the area does not experience continuous snow cover, then the months
of December, January, and February will be paired with surface characteristic values listed with
seasonal category 3 ("Late autumn after frost and harvest, or winter with no snow").
Some locations may never experience significant periods of continuous snow cover, while other
locations may experience continuous snow cover for a period of one or more months during the
year. AERSURFACE will prompt the user regarding whether the study area experiences
continuous snow cover for at least one month during the year to allow for an appropriate
designation of seasonal categories 3 and 4 for the specific application. Further details regarding
these user options are provided in Section 3.0.
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Table 2-2: Seasonal Category Descriptions
Seasonal
Category
1
2
O
4
5
Season Description
Midsummer with lush vegetation
Autumn with unharvested cropland
Late autumn after frost and harvest, or winter with no snow
Winter with continuous snow on ground
Transitional spring with partial green coverage or short annuals
Default Month
Assignments
Jun, Jul, Aug
Sep, Oct, Nov
Dec, Jan, Feb
Dec, Jan, Feb
Mar, Apr, May
Because the 21 land cover classification system of NLCD92 was applied across the continental
U.S., there are instances where the surface characteristic values for two areas of the U.S. may
differ, although the land cover type is the same. There are also categories that cover several
surface types for which albedo, roughness, and/or Bowen ratio may be quite different. To
address these issues, Land Cover Classes 23, 31, and 51 are each split into two separate
categories in Tables A-l, A-2, and A-3, and the values used for each of these categories are
determined by the user's responses to questions about the location. These questions and how the
user response will affect the output are explained below:
"Is this site at an airport? "
The answer to this question will affect the Commercial/Industrial/Transportation
category (Class 23) which covers both transportation land cover (e.g. roadways and
airport runways) and commercial and industrial areas (e.g. industrial parks). If the site is
at an airport, AERSURFACE will use surface characteristics that reflect an area more
dominated by transportation land cover. If the user answers "No" to the above question,
AERSURFACE will choose higher surface roughness values that are more representative
of an area dominated by buildings associated with commercial and industrial land cover.
To represent this split, the Commercial/Industrial/Transportation category is broken out
into two categories in Tables A-l, A-2, and A-3: "site at airport" and "not at airport".
"Is this site in an arid region? "
The answer to this question will affect the Shrubland (Class 51) and the Bare Rock/
Sand/Clay (Class 31) categories. These two categories may appear in the NLCD92 data
in both desert and non-arid regions of the U.S., two climatologically different areas
which will have quite different surface characteristic values. If the user answers "Yes,"
AERSURFACE will use the seasonal surface characteristics for the Shrubland and Bare
Rock/Sand/Clay categories that are more representative of a desert area. Therefore, in
general, the albedo and Bowen ratio will be higher and the surface roughness lower.
Otherwise, AERSURFACE will use the seasonal surface characteristics for the non-arid
area. In Tables A-l, A-2, and A-3, these categories are broken out and labeled "arid
region" and "non-arid region". (Note: If the user specifies that the location experiences
continuous snow cover for at least one month during the year, the program assumes that
the area is non-arid and will not offer this prompt.)
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"Characterize the surface moisture condition at the site relative to climatological
normals, to be applied for all periods. Enter 'A'for Average, 'W for Wet, or 'D'for
Dry."
The answer to this question will dictate the value of the Bowen ratio. If the user answers
average, the average Bowen ratio values will be used; if the user answers wet, the wet
Bowen ratio values will be used; and, if the user answers dry, the dry Bowen ratio values
will be used for each land cover category. The surface moisture condition for the site
may vary depending on the meteorological data period for which the surface
characteristics will be applied. The current version of AERSUKFACE applies the
surface moisture condition for the entire data period. Therefore, if the surface moisture
condition varies significantly across the data period, then AERSURFACE may need to be
applied multiple times to account for those variations. The surface moisture condition
can be determined by comparing precipitation for the period of data to be processed to
the 30-year climatological record, selecting "wet" conditions if precipitation is in the
upper 30th-percentile, "dry" conditions if precipitation is in the lower SO^-percentile, and
"average" conditions if precipitation is in the middle 40th-percentile.
2.3 AERSURFACE CALCULATION METHODS
Determining effective surface characteristics for the purpose of processing meteorological data
for use with the AERMOD model presents many challenges. AERMOD is a steady-state plume
model which assumes spatially uniform meteorological conditions across the modeling domain
for each hour of meteorology, while land cover across the domain is typically very
heterogeneous. A sound understanding of the important physical processes represented in the
AERMOD model algorithms (Cimorelli, et a/., 2004) and the sensitivity of those algorithms to
surface characteristics is needed in order to properly interpret the available data and make an
appropriate determination.
The recommendations for determining surface characteristics presented in Section 3.1 of the
AERMOD Implementation Guide (EPA, 2008) have been incorporated into AERSURFACE.
These recommendations are briefly summarized below:
1. The determination of the surface roughness length should be based on an inverse-
distance weighted geometric mean for a default upwind distance of 1 kilometer relative to
the measurement site. Surface roughness length may be varied by sector to account for
variations in land cover near the measurement site; however, the sector widths should be
no smaller than 30 degrees.
2. The determination of the Bowen ratio should be based on a simple unweighted
geometric mean (i.e., no direction or distance dependency) for a representative domain,
with a default domain defined by a 10km by 10km region centered on the measurement
site.
3. The determination of the albedo should be based on a simple unweighted arithmetic
mean (i.e., no direction or distance dependency) for the same representative domain as
defined for Bowen ratio, with a default domain defined by a 10km by 10km region
centered on the measurement site.
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While the AERSUKFACE tool is not currently considered to be part of the AERMOD regulatory
modeling system, i.e. the use of AERSURFACE is not required for regulatory applications of
AERMOD, the recommended methodology described above should be followed unless case-by-
case justification can be provided for an alternative method.
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3.0 AERSURFACE USER INSTRUCTIONS
3.1 RUNNING AERSURFACE
The AERSURFACE program was written in Fortran and can be run interactively from the
command prompt. The program can be executed by navigating to the folder containing the
AERSURFACE executable (aersurface.exe), and typing "aersurface" (without the quotes) at the
command prompt. The program can also be executed from Windows Explorer by double-
clicking on the aersurface.exe file. In the interactive mode, the user responds to a series of
prompts to identify the input and output filenames and specify options for processing the land
cover data.
Alternatively, the AERSURFACE program can be run by redirecting the responses to prompts
from a separate text file. Running AERSURFACE using an input file through redirection is
accomplished by typing "aersurface
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since the NLCD92 provides multiple land cover data files to cover these states. Note that
filenames are case-sensitive for Linux systems.
"Enter name of OUTPUT file for the surface characteristics formatted for AERMET
Stage 3 input. AERSURFACE.DAT and '*.LOG' are not accepted output filenames.
Enclose with quotes if the path or filename contains spaces. Linux users include quotes
to accommodate forward slash in path.
(132 character limit)."
AERSUKFACE will output a file with this user-specified name which will contain
surface characteristics values in a format for use in AERMET Stage 3. AERSURFACE
will not give this file an extension, although the user may specify an extension when
naming the file at the prompt. However, the extension ".log" will not be allowed since
AERSURFACE will automatically output another file with the same prefix as the user-
specified output file and the extension ".log", which will document the user's response to
the program's prompts and other details of the program's calculations. This is discussed
in more detail in Section 3.4.
"Enter the type of coordinate used to define the center of the study area.
'UTM' for Universal Transverse Mercator coordinates;
' LATLON' for Latitude and Longitude coordinates.
(Note: User responses are not case-sensitive.) "
This prompt asks the user to enter the type of coordinates to be used for the site center.
The coordinates input to AERSURFACE should be based on the location of the
meteorological tower (measurement site) for the meteorological data to be processed with
the output surface characteristics. AERSURFACE uses these coordinates to extract land
cover data for the area of interest from the NLCD92 data file. If the user enters "UTM",
the user will be asked to enter the UTM Easting and Northing coordinates (in meters) and
the UTM zone. If the user chooses "LATLON", the user will be prompted to enter the
latitude and the longitude (in decimal degrees), using a negative number for west
longitude. The user must also specify the horizontal reference datum (NAD83 or
NAD27) for the input coordinates for either UTM or LATLON coordinates. The
NLCD92 data are based on the NAD83 horizontal datum, and AERSURFACE will
convert the input coordinates to NAD83 if needed. The NAD Grid conversion files
(conus.las and conus.los) must be included in the local folder for NAD27 conversions.
Coordinates for airport locations are generally provided in the NAD83 datum.
NOTE: Significant discrepancies have been identified between station coordinates
reported by the National Climatic Data Center (NCDC) and the actual location of
the meteorological instrument tower for National Weather Service (NWS) sites.
Discrepancies of several hundred meters up to a few kilometers are common, which
could significantly compromise the representativeness of AERSURFACE
calculations, especially for surface roughness. Users are encouraged to verify the
coordinates of the meteorological tower before applying AERSURFACE.
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"Enter the radius (in km) of the study area used for surface roughness (0.1 5.0 km).
The recommended default value is 1 km. "
The user should enter the distance from the center of the site location that will be used in
calculating the effective surface roughness length. The current recommended default is
1km. If a radius other than the recommended default value of 1km is used, it is
recommended that this choice be documented and justified in a modeling protocol prior
to conducting the modeling. AERSURFACE will not accept values outside of the range
from 0.1 to 5.0 km, inclusive. AERSURFACE uses this information, along with the
coordinates of the center of the study area, to extract a subsection of land cover data from
the NLCD92 data file.
"Do you want to define the surface roughness length for multiple sectors? "
The user is given the option of defining the surface roughness length for multiple sectors,
up to a maximum of 12. If the user opts to use multiple sectors, AERSURFACE will
prompt for the number of sectors to be used to characterize the area, and the starting
direction (in whole degrees) of each sector. An input of 0° will correspond with true
North. The minimum sector width allowed by AERSURFACE is 30 degrees. If the user
selects the maximum of 12 sectors, AERSURFACE will automatically define 30-degree
sectors starting with 0° (North).
Define the temporal resolution of surface characteristic
outputs (ANNUAL, SEASONAL or MONTHLY) .
***************************************************
The reference surface characteristics used in AERSURFACE
are stored as seasonal values for each land cover category
based on the following seasonal categories:
Late autumn after frost and harvest, or winter with no snow
Winter with continuous snow on the ground
Transitional spring (partial green coverage, short annuals)
Midsummer with lush vegetation
Autumn with unharvested cropland
SEASONAL surface characteristics output implies the
following seasonal definitions based on AERMET:
Dec, Jan, Febfor Winter (snow-covered or no snow)
Mar, Apr, May for Spring
Jun, Jul, Augfor Summer
Sep, Oct, Nov for Fall
Months can be reassigned to different seasonal
categories for ANNUAL or MONTHLY output, including
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the option to specify continuous snow cover for one
or more months.
Months cannot be reassigned for SEASONAL output, and
Winter will assume either continuous snow cover or
no snow cover for all three months, depending on the
user response to the subsequent prompt.
Enter 'A'for ANNUAL, 'S'for SEASONAL, or 'M'for MONTHLY:
This prompt allows the user to specify the temporal resolution of the surface
characteristic outputs, based on the options supported by AERMET.
Does the site experience continuous snow cover for at
least one month? {for ANNUAL or MONTHLY outputs}
or
Does the site experience continuous snow cover for most
of the winter? {for SEASONAL outputs}
Enter T for Yes or 'N'for No
Because the surface characteristics are affected by snow cover, this question is asked of
the user to determine whether surface characteristics for continuous snow cover should
be used. The wording of this prompt will vary as shown depending on the temporal
resolution for outputs specified by the user. For the ANNUAL or MONTHLY output
options, the user may specify which months are assumed to experience continuous snow
cover. For SEASONAL output, continuous snow cover will be assumed for all winter
months if the user answers Yes to this prompt.
The default month-to-season associations inAERSURFACE
will be as follows (where l=Jan, 2=Feb, 3=Mar, etc.):
Winter with continuous snow on the ground: 12, 1, 2
or, {depending on response to snow cover prompt}
Late autumn after frost and harvest, or winter with no snow: 12, 1, 2
Transitional spring (partial green coverage, short annuals): 3, 4, 5
Midsummer with lush vegetation: 6, 7, 8
Autumn with unharvested cropland: 9, 10, 11
**************************************************
Would you like to reassign the months to different seasons?
Enter '₯' to reassign or 'N' to use the default assignments.
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This prompt is only offered if MONTHLY or ANNUAL output has been selected. If the
user opts to reassign the months to different seasons, the user will be prompted to enter
the months for each of the applicable seasonal categories in Table 2-2. If the user
indicates that continuous snow cover occurs, the prompts will include all five seasonal
categories, otherwise the "Winter with continuous snow on the ground" category will be
omitted. If the user opts to not reassign the months to different seasons, or if the user
chooses the SEASONAL output option at the previous prompt, the default
AERSURFACE month-to-season associations will be used.
The following prompt is provided if the user elects to reassign months:
Assign months to seasons by entering a space or
comma-delimited list, e.g., to assign Nov, Dec, and
Jan, enter "11 12 1" (without the quotes).
To skip a season enter "0" (no quotes).
Enter "-9" to restart month-season assignments.
You will be prompted for the following seasonal categories:
Late autumn after frost and harvest, or winter with no snow
Winter with continuous snow on the ground
Transitional spring (partial green coverage, short annuals)
Midsummer with lush vegetation
Autumn with unharvested cropland
****************************************************
"Is this site at an airport? "
See discussion in Section 2.2.
"Is this site in an arid region? "
See discussion in Section 2.2. (Note: If the user specifies that the location experiences
continuous snow cover for at least one month during the year, the program assumes that
the area is not arid and will skip this prompt.)
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"Characterize the surface moisture condition at the site relative to climatological
normals, to be applied for all periods. Enter 'A'for Average, 'W for Wet, or 'D'for
Dry."
See discussion in Section 2.2.
3.3 AERSURFACE ERROR HANDLING
When performing the surface characteristic calculations, if AERSURFACE determines that more
than 10% of the land cover in any one sector for surface roughness or within the entire domain
for albedo and Bowen ratio falls within the "Transitional" land cover category, a warning will be
issued to the user. This is because the "Transitional" land cover category represents an area that
is dynamically changing from one land cover to another, and since the NLCD92 data were
collected between 199land 1992, the current land cover for that area will most likely differ (see
Appendix B.) If this warning message is generated, it is recommended that the user take a closer
look at the land cover in the area to determine whether the land cover data can be supplemented
with more current land cover data. To assist in this, the warning message will include the
percentage of the area in the "Transitional" category, and also the sector in which this occurs in
the case of surface roughness.
AERSURFACE will also issue a warning if more than 10% of the land cover in any one sector
for surface roughness or the entire domain for albedo and Bowen ratio is labeled as "Missing" or
"Outside Boundary." When this occurs for more than 90% of the area in any one sector,
AERSURFACE will not continue with its calculations and the program will end. If this occurs,
the user may want to investigate the land cover data, and decide if they are able to supplement
the missing data with current land cover data. However, this problem can also occur if the user
specified site is too close to the state boundary for a state NLCD file or the edge of the data
domain for seamless data. If the application site is too close to the boundary of a state file, then
the user should acquire seamless data for the proper domain. If the application site is too close
to the edge of the seamless data file, then a larger domain of seamless data should be acquired.
3.4 FILE DESCRIPTIONS
As mentioned in Section 3.1, AERSURFACE will always create a text file called
"AERSURFACE.DAT" that contains the annotated user responses to the program prompts. The
AERSURFACE.DAT file can be renamed and/or modified for use in rerunning AERSURFACE
with redirected input. In modifying the input file, users should be aware that modifications to
certain prompts may alter the input requirements for AERSURFACE.
Based on the name specified by the user, AERSURFACE outputs two files. The user-specified
output filename will contain the surface characteristics formatted for input into AERMET Stage
3. The other file, which will have the same prefix as the user-specified output file with an
extension of ".log", will contain the following information: a summary of the user's responses to
the AERSURFACE prompts; an extraction of land cover data from the user specified location
for both the albedo/Bowen ratio domain and the surface roughness domain; and a tally of the
number of land cover grid cells for each of the 21 land cover categories for the albedo/Bowen
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ratio domain, and for each of the sectors for the surface roughness domain. This file is supplied
to aid the user in better understanding the data being used by AERSUKFACE and to help quality
assure the program's outputs.
In addition to the AERMET Stage 3 output and the log file, AERSURFACE creates two text
files containing the extracted land cover data for the albedo/Bowen ratio and surface roughness
domains, respectively. These files are named "albedo_bowen_domain.txt" and
"roughness_domain.txt". These domain files contain the same extracted land cover data that is
included in the log file, but also include several records at the top of the file containing the
Albers coordinates for the lower left corner of the domain and horizontal resolution of the data.
These domain files can be imported into mapping software, such as ArcGIS, to visualize the
extracted land cover data to further assist with interpretation and quality assurance of the data.
3.5 EXAMPLE TEST CASE
An example AERSURFACE test case was run for the Raleigh/Durham (RDU) airport located in
North Carolina. The input and output files for this test case are packaged with the
AERSURFACE code. Figure 3-1 shows the input data file associated with this test case, called
"rdu_seamless.dat". The center of study area was located at the NWS meteorological station
tower at the airport (latitude in decimal degrees: 35.89194; longitude in decimal degrees:
-78.78194). The test case uses the SEASONAL output option with the default month
assignments and no continuous snow cover. An average surface moisture condition was
assumed, with non-arid conditions. The option to vary surface roughness outputs by sector was
selected with three sectors defined. Figure 3-2 shows the sectors selected for this tests case.
Sector 1 was selected to start at 0°, Sector 2 at 90°, and Sector 3 at 225°. Figure 3-3 shows the
output appearing in the file "rdu_seamless.out", formatted for input into Stage 3 of AERMET.
The extracted albedo/Bowen ratio and surface roughness domains and sectors are also shown in
Figure 3-4, overlaid on the seamless NLCD data file. The airport runways, terminals and other
structures are clearly visible on this figure as NLCD category 23, Commercial/Industrial/
Transportation. The large open areas surrounding the airport runways and terminals show up as
category 85, Urban Recreational Grasses.
14
-------
"rdu_seamless.tif"
"rdu_seamless.out"
LATLON
35.891940
-78.781940
NAD83
1
0
90
225
0
Land use data file
Output file with sfc values for AERMET Stage 3
Coordinate type (UTM, LATLON)
Latitude
Longitude
Datum
Study radius for surface roughness (km)
Vary by sector? (Y/N)
Number of sectors
Start of sector 1
Start of sector 2
Start of sector 3
Temporal resolution (A=ANNUAL, M=MONTHLY, S=SEASONAL)
Continuous snow cover most of the winter? (Y/N)
Airport? (Y/N)
Arid region? (Y/N)
Surface Moisture (A=Average, W=Wet, D=Dry)
Figure 3-1. Contents ofrdu_seamless.dat File for RDU Seamless Test Case
\Z
ctor
Sector <
Figure 3-2. Diagram of User-specified Radius and Sector
Definitions Overlaid on Land Cover Grid Cells
15
-------
** Generated by AERSURFACE, dated 08009
** Center Latitude (decimal degrees): 35
** Center Longitude (decimal degrees) : -78
** Datum: NAD83
** Study radius (km) for surface roughness:
** Airport? Y, Continuous snow cover? N
** Surface moisture? Average, Arid region? N
** Month/Season assignments? Default
891940
781940
1.0
** Late autumn after frost and harvest, or winter with no snow: 12 1 2
** Winter with continuous snow on the ground
0
** Transitional spring (partial green coverage, short annuals): 345
** Midsummer with lush vegetation: 678
** Autumn with unharvested cropland: 9 10 11
* *
FREQ SECT SEASONAL 3
SECTOR 1 0 90
SECTOR 2 90 225
SECTOR 3 225 360
** Season Sect Alb Bo
SITE CHAR 1 1 0.15 0.85
SITE CHAR 1 2 0.15 0.85
SITE CHAR 1 3 0.15 0.85
SITE CHAR 2 1 0.14 0.63
SITE CHAR 2 2 0.14 0.63
SITE CHAR 2 3 0.14 0.63
SITE CHAR 3 1 0.15 0.36
SITE CHAR 3 2 0.15 0.36
SITE CHAR 3 3 0.15 0.36
SITE CHAR 4 1 0.15 0.84
SITE CHAR 4 2 0.15 0.84
SITE CHAR 4 3 0.15 0.84
Zo
0.028
0.029
0.169
0.039
0.037
0.209
0.048
0.044
0.243
0.039
0.037
0.218
Figure 3-3. Contents of rdu_seamless.out File for RDU Seamless Test Case
16
-------
Figure 3-4. NLCD Plot for the RDU Seamless Test Case, Showing Albedo/Bowen Ratio
Domain, and Surface Roughness Domain and Sectors
17
-------
4.0 REFERENCES
Cimorelli, A. 1, S. G. Perry, A. Venkatram, J. C. Weil, R. J. Paine, R. B. Wilson, R. F. Lee, W.
D. Peters, R. W. Erode, and J. O. Paumier, 2004. AERMOD: Description of Model Formulation,
EPA-454/R-03-004. U.S. Environmental Protection Agency, Research Triangle Park, NC.
EPA, 2004a: User's Guide for the AERMOD Meteorological Preprocessor (AERMET).
EPA-454/B-03-002. U.S. Environmental Protection Agency, Research Triangle Park, NC.
EPA, 2004b: User's Guide for the AMS/EPA Regulatory Model - AERMOD. EPA-454/B-03-
001. U.S. Environmental Protection Agency, Research Triangle Park, NC.
EPA, 2008. AERMOD Implementation Guide. U.S. Environmental Protection Agency,
Research Triangle Park, NC (Available @ www.epa.gov/scram001/)
Garratt, J. R., 1992: The Atmospheric Boundary Layer. Cambridge University Press, New York,
New York, 334pp.
Oke, T. R., 1978: Boundary Layer Climates. John Wiley and Sons, New York, New York,
372pp.
Randerson, D., 1984, "Atmospheric Boundary Layer," in Atmospheric Science and Power
Production, ed., D. Randerson. Technical Information Center, Office of Science and Technical
Information, U.S. Department of Energy, Springfield, VA, 850pp.
Slade, D.H. (ed.), 1968. Meteorology and Atomic Energy. Division of Technical Information,
U.S. Atomic Energy Commission. Oak Ridge, TN, 445pp.
Stull, R. B., 1988. An Introduction to Boundary Layer Meteorology. Kluwer Academic
Publishers, The Netherlands, 666pp.
18
-------
APPENDIX A. SURFACE CHARACTERISTICS TABLES
Tables A-l through A-3 provide the values of albedo, Bowen ratio, and surface roughness,
respectively, based on the NLCD92 land cover categories. Each table includes a column
containing references used in estimating the values for each surface characteristic parameter and
each land cover category. As explained in Section 2.0, more than one value of surface
characteristics may be listed for certain land cover categories depending on user responses to
specific prompts regarding the site location.
A-l
-------
Table A-1. Seasonal Values of Albedo for the NLCD92 21-Land Cover Classification System
Class
Number
11
12
21
22
23
31
32
33
41
42
43
51
61
71
81
82
83
84
85
91
92
Class Name
Open Water
Perennial Ice/Snow
Low Intensity Residential
High Intensity Residential
Commercial/lndustrial/Transp (Site at Airport)
Commercial/lndustrial/Transp (Not at Airport)
Bare Rock/Sand/Clay (Arid Region)
Bare Rock/Sand/Clay (Non-arid Region)
Quarries/Strip Mines/Gravel
Transitional
Deciduous Forest
Evergreen Forest
Mixed Forest
Shrubland (Arid Region)
Shrubland (Non-arid Region)
Orchards/Vineyards/Other
Grasslands/Herbaceous
Pasture/Hay
Row Crops
Small Grains
Fallow
Urban/Recreational Grasses
Woody Wetlands
Emergent Herbaceous Wetlands
Seasonal Albedo Values1
1
0.1
0.6
0.16
0.18
0.18
0.18
0.2
0.2
0.2
0.18
0.16
0.12
0.14
0.25
0.18
0.18
0.18
0.2
0.2
0.2
0.18
0.15
0.14
0.14
2
0.1
0.6
0.16
0.18
0.18
0.18
0.2
0.2
0.2
0.18
0.16
0.12
0.14
0.25
0.18
0.18
0.18
0.2
0.2
0.2
0.18
0.15
0.14
0.14
3
0.1
0.7
0.18
0.18
0.18
0.18
0.2
0.2
0.2
0.18
0.17
0.12
0.14
0.25
0.18
0.18
0.2
0.18
0.18
0.18
0.18
0.18
0.14
0.14
4
0.1
0.7
0.45
0.35
0.35
0.35
NA
0.6
0.6
0.45
0.5
0.35
0.42
NA
0.5
0.5
0.6
0.6
0.6
0.6
0.6
0.6
0.3
0.3
5
0.1
0.6
0.16
0.18
0.18
0.18
0.2
0.2
0.2
0.18
0.16
0.12
0.14
0.25
0.18
0.14
0.18
0.14
0.14
0.14
0.18
0.15
0.14
0.14
Reference
AERMET2'3
Stull & Garratt4
(22+43+85)/35
Stull6 & AERMET7
Stull6 & AERMET7
Stull6 & AERMET7
Garratt8
Garratt8 & AERMET7
Garratt8 & AERMET7
same as 849
Stull6 & AERMET7
Stull6 & AERMET7
(41+42)/210
Stull6
Estimate11&AERMET7
Estimate12
AERMET2
AERMET2'13
AERMET2'13
AERMET2'13
Garratt8
Estimate14
Stull6 & AERMET7
Stull6 & AERMET7
10
11
12
13
14
Values are listed for the following seasonal categories: 1 - Midsummer with lush vegetation; 2 - Autumn with unharvested
cropland; 3 - Late autumn after frost and harvest; or winter with no snow; 4 - Winter with continuous snow on ground; 5 -
Transitional spring with partial green coverage or short annuals
Estimate based on AERMET User's Guide, Table 4-1.
We assume no freeze of the water and no seasonal changes in albedo.
Estimate based on Stull, Table C-7 and Garratt, Table A8. Assume fresher snow and more ice in seasonal categories 3 & 4 and
older snow in seasonal categories 1, 2, & 5.
Assume an equal mix of three classes: "High Intensity Residential", "Mixed Forest", and "Urban/Recreational Grasses."
Estimate based on Stull, Table C-7.
Estimate based on AERMET User's Guide, Table 4-1 albedo value for winter with continuous snow cover.
Estimate based on Garratt, Table A8.
Assume "Transitional" is similar to Class 84: "Fallow". A warning will be issues to the user if this category appears in more than
10% of the land cover data.
Estimate based on the average of Classes 41 and 42.
Estimate based on the non-arid shrubland having more vegetation that the arid-region shrubland.
Estimate based Class 51: "Shrubland (non-arid region)" for seasonal categories 1,2 & 4 and AERMET User's Guide ("Cultivated
Land") for seasonal categories 3 & 5.
Estimate based on AERMET User's Guide; assume more vegetation in summer and soil being wetter in spring than in fall.
Estimate based on AERMET User's Guide ("Cultivated Land") for seasonal category 3 & 4, and Garratt, Table A8 for seasonal
categories 1, 2 & 5.
A-2
-------
Table A-2. Seasonal Values of Bowen Ratio for the NLCD92 21-Land Cover Classification System
Class
Number
11
12
21
22
23
31
32
33
41
42
43
51
61
71
81
82
83
84
85
91
92
Class Name
Open Water
Perennial Ice/Snow
Low Intensity Residential
High Intensity Residential
Commercial/lndustrial/Transp
(Site at Airport)
Commercial/lndustrial/Transp
(Not at Airport)
Bare Rock/Sand/Clay (Arid
Region)
Bare Rock/Sand/Clay (Non-arid
Region)
Quarries/Strip Mines/Gravel
Transitional
Deciduous Forest
Evergreen Forest
Mixed Forest
Shrubland (Arid Region)
Shrubland (Non-arid Region)
Orchards/Vineyards/Other
Grasslands/Herbaceous
Pasture/Hay
Row Crops
Small Grains
Fallow
Urban/Recreational Grasses
Woody Wetlands
Emergent Herbaceous Wetlands
Seasonal Bowen Ratio1 -
Average
1
0.1
0.5
0.8
1.5
1.5
1.5
4
1.5
1.5
1
0.3
0.3
0.3
4
1
0.5
0.8
0.5
0.5
0.5
0.5
0.5
0.2
0.1
2
0.1
0.5
1
1.5
1.5
1.5
6
1.5
1.5
1
1
0.8
0.9
6
1.5
0.7
1
0.7
0.7
0.7
0.7
0.7
0.2
0.1
3
0.1
0.5
1
1.5
1.5
1.5
6
1.5
1.5
1
1
0.8
0.9
6
1.5
0.7
1
0.7
0.7
0.7
0.7
0.7
0.3
0.1
42
0.1
0.5
0.5
0.5
0.5
0.5
NA
0.5
0.5
0.5
0.5
0.5
0.5
NA
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
5
0.1
0.5
0.8
1.5
1.5
1.5
3
1.5
1.5
1
0.7
0.7
0.7
3
1
0.3
0.4
0.3
0.3
0.3
0.3
0.3
0.2
0.1
Seasonal Bowen Ratio1 - Wet
1
0.1
0.5
0.6
1
1
1
1.5
1
1
0.7
0.2
0.2
0.2
1.5
0.8
0.3
0.4
0.3
0.3
0.3
0.3
0.3
0.1
0.1
2
0.1
0.5
0.6
1
1
1
2
1
1
0.7
0.4
0.3
0.35
2
1
0.4
0.5
0.4
0.4
0.4
0.4
0.4
0.1
0.1
3
0.1
0.5
0.6
1
1
1
2
1
1
0.7
0.4
0.3
0.35
2
1
0.4
0.5
0.4
0.4
0.4
0.4
0.4
0.1
0.1
42
0.1
0.5
0.5
0.5
0.5
0.5
NA
0.5
0.5
0.5
0.5
0.5
0.5
NA
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
5
0.1
0.5
0.6
1
1
1
1
1
1
0.7
0.3
0.3
0.3
1
0.8
0.2
0.3
0.2
0.2
0.2
0.2
0.2
0.1
0.1
Seasonal Bowen Ratio1 -
Dry
1
0.1
0.5
2
3
3
3
6
3
3
2
0.6
0.6
0.6
6
2.5
1.5
2
1.5
1.5
1.5
1.5
1.5
0.2
0.2
2
0.1
0.5
2.5
3
3
3
10
3
3
2
2
1.5
1.75
10
3
2
2
2
2
2
2
2
0.2
0.2
3
0.1
0.5
2.5
3
3
3
10
3
3
2
2
1.5
1.75
10
3
2
2
2
2
2
2
2
0.2
0.2
42
0.1
0.5
0.5
0.5
0.5
0.5
NA
0.5
0.5
0.5
0.5
0.5
0.5
NA
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
5
0.1
0.5
2
3
3
3
5
3
3
2
1.5
1.5
1.5
5
2.5
1
1
1
1
1
1
1
0.2
0.2
Reference
AERMET&Oke3
AERMET&Oke3
Estimate4
AERMET&Oke3
AERMET&Oke3
AERMET&Oke3
AERMET&Oke3
AERMET&Oke3
AERMET&Oke3
Estimate5
AERMET&Oke3
AERMET&Oke3
(41+42)/26
AERMET&Oke3
Estimate7
AERMET&Oke3
AERMET&Oke3
AERMET&Oke3
AERMET&Oke3
AERMET&Oke3
AERMET&Oke3
AERMET&Oke3
Estimate7
AERMET&Oke3
Values are listed for the following seasonal categories: 1 - Midsummer with lush vegetation; 2 - Autumn with unharvested cropland; 3 - Late autumn after frost and harvest; or winter with
no snow; 4 - Winter with continuous snow on ground; 5 - Transitional spring with partial green coverage or short annuals.
i
Values for seasonal category 4 are based on the AERMET User's Guide (EPA, 2004a) and Oke (1978), Tables 4-2a-c, Bowen ratio values for winter with continuous snow cover, except for
class 11 with the assumption the water does not freeze.
Values for seasonal categories 1, 2, 3 & 5 are based on AERMET User's Guide (EPA, 2004a), Tables 4-2a-c and Oke (1978).
Estimate based on composition being an equal mix of three classes: "High Intensity Residential", "Mixed Forest", and "Urban/Recreational Grasses."
A-3
-------
Estimate based on the Bowen ratio of "Transitional" being between the Bowen ratio of Classes 31 and 71.
Assume "Mixed Forest" is composed of equal parts of "Deciduous Forest" and "Evergreen Forest."
Estimate based on comparison to Bowen ratio for other classes.
A-4
-------
Table A-3. Seasonal Values of Surface Roughness (m) for the NLCD92 21-Land Cover Classification System
Class
Number
11
12
21
22
23
31
32
33
41
42
43
51
61
71
81
82
83
84
85
91
92
Class Name
Open Water
Perennial Ice/Snow
Low Intensity Residential
High Intensity Residential
Commercial/lndustrial/Transp (Site at Airport)
Commercial/lndustrial/Transp (Not at Airport)
Bare Rock/Sand/Clay (Arid Region)
Bare Rock/Sand/Clay (Non-arid Region)
Quarries/Strip Mines/Gravel
Transitional
Deciduous Forest
Evergreen Forest
Mixed Forest
Shrubland (Arid Region)
Shrubland (Non-arid Region)
Orchards/Vineyards/Other
Grasslands/Herbaceous
Pasture/Hay
Row Crops
Small Grains
Fallow
Urban/Recreational Grasses
Woody Wetlands
Emergent Herbaceous Wetlands
Seasonal Surface Roughness1 (m)
1
0.001
0.002
0.54
1
0.1
0.8
0.05
0.05
0.3
0.2
1.3
1.3
1.3
0.15
0.3
0.3
0.1
0.15
0.2
0.15
0.05
0.02
0.7
0.2
2
0.001
0.002
0.54
1
0.1
0.8
0.05
0.05
0.3
0.2
1.3
1.3
1.3
0.15
0.3
0.3
0.1
0.15
0.2
0.15
0.05
0.015
0.7
0.2
3
0.001
0.002
0.50
1
0.1
0.8
0.05
0.05
0.3
0.2
0.6
1.3
0.95
0.15
0.3
0.1
0.01
0.02
0.02
0.02
0.02
0.01
0.6
0.2
4
0.001
0.002
0.50
1
0.1
0.8
NA
0.05
0.3
0.2
0.5
1.3
0.9
NA
0.15
0.05
0.005
0.01
0.01
0.01
0.01
0.005
0.5
0.1
5
0.001
0.002
0.52
1
0.1
0.8
0.05
0.05
0.3
0.2
1
1.3
1.15
0.15
0.3
0.2
0.05
0.03
0.03
0.03
0.02
0.015
0.7
0.2
Reference
Stull2
Stull2
40% 22 + 50% 43+
10% 853
AERMET4
5%:22&95%:315
80%:22&20%:315
Slade6
Slade6
Estimate7
Estimate8
AERMET4
AERMET4
(41+42)/29
50% 51 (Non-Arid)10
AERMET4
Garratt11
AERMET4
Garratt11 & Slade12
Garratt11 & Slade12
Garratt11 & Slade12
31 &81,82,8313
Randerson14
(43+92)/215
AERMET4
10
11
12
13
Values are listed for the following seasonal categories: 1 -Midsummer with lush vegetation; 2 -Autumn with unharvested cropland; 3 -Late
autumn after frost and harvest; or -winter with no snow; 4 - Winter -with continuous snow on ground; 5 - Transitional spring -with partial
green coverage or short annuals
Estimate based on Stull, Fig 9.6. We have specified a larger roughness than the AERMET "calm open sea" roughness value because we
have assumed that most of the water is closer to land and will experience waves and be closer to the shoreline, increasing roughness.
Assume a mix of three classes: 40% "High Intensity Residential", 10% "Mixed Forest", and 50% "Urban/Recreational Grasses."
Based on the AERMET User's Guide (EPA, 2004a), Table 4-3.
If the site is near the airport, we assume 95% of the land cover is "Transportation" and has similar roughness to Class 31 (Bare
Rock/Sand/Clay) and 5% is "Commercial/Industrial" with similar roughness to Class 22 (High Intensity Residential). If the site is not
near the airport, then we assume 20% of the land cover is "Transportation" and 80% is "Commercial/mdustrial".
Estimate based on Slade, Table 3-1, assuming the surface is not completely level due to inclusion of some larger rocks.
Estimate reflecting "significant surface expression"
Estimate reflecting significant mix of different land cover classes. A warning will be issued to the user if this category appears in more
than 10% of the land cover data.
Assume "Mixed Forest" is composed of equal parts of "Deciduous Forest" and "Evergreen Forest."
Assume arid region would have approximately 50% less vegetation than a non-arid region.
Estimate based on Garratt, Table A6.
Estimate based on Slade, Table 3-1
Based on class 31 ("Bare Rock/Sand/Clay") for seasonal categories 1 &2 and 81, 82, 83 ("Pasture/Hay", "Row Crops" & "Small
Grains") for seasonal categories 3, 4, & 5, with seasonal category 5 having a more similar amount of vegetation to seasonal category 3
and, therefore, the same roughness.
Estimate based on Randerson, Table 5.4
Assume land cover similar in composition to 50% of Class 43 (Mixed Forest) and 50% of Class 92 (Emergent Herbaceous Wetlands)
A-5
-------
-------
APPENDIX B. DESCRIPTIONS OF NLCD92 LAND COVER CATEGORIES
The following information, taken from the USGS documentation on the NLCD92, provides more
detailed descriptions of the 21 land cover categories in NLCD92.
Water
All areas of open water or permanent ice/snow cover.
Open Water - All areas of open water; typically 25 percent or greater cover of water (per pixel).
Perennial Ice/Snow - All areas characterized by year-long cover of ice and/or snow.
Developed
Areas characterized by a high percentage (30 percent or greater) of constructed materials (e.g. asphalt, concrete,
buildings, etc).
Low Intensity Residential - Includes areas with a mixture of constructed materials and vegetation. Constructed
materials account for 30-80 percent of the cover. Vegetation may account for 20 to 70 percent of the cover. These
areas most commonly include single-family housing units. Population densities will be lower than in high intensity
residential areas.
High Intensity Residential - Includes highly developed areas where people reside in high numbers. Examples
include apartment complexes and row houses. Vegetation accounts for less than 20 percent of the cover.
Constructed materials account for 80 to 100 percent of the cover.
Commercial/Industrial/Transportation - Includes infrastructure (e.g. roads, railroads, etc.) and all highly developed
areas not classified as High Intensity Residential.
Barren
Areas characterized by bare rock, gravel, sand, silt, clay, or other earthen material, with little or no "green"
vegetation present regardless of its inherent ability to support life. Vegetation, if present, is more widely spaced and
scrubby than that in the "green" vegetated categories; lichen cover may be extensive.
Bare Rock/Sand/Clay - Perennially barren areas of bedrock, desert pavement, scarps, talus, slides, volcanic material,
glacial debris, beaches, and other accumulations of earthen material.
Quarries/Strip Mines/Gravel Pits - Areas of extractive mining activities with significant surface expression.
Transitional - Areas of sparse vegetative cover (less than 25 percent of cover) that are dynamically changing from
one land cover to another, often because of land use activities. Examples include forest clearcuts, a transition phase
between forest and agricultural land, the temporary clearing of vegetation, and changes due to natural causes (e.g.
fire, flood, etc.).
Forested Upland
Areas characterized by tree cover (natural or semi-natural woody vegetation, generally greater than 6 meters tall);
tree canopy accounts for 25-100 percent of the cover.
Deciduous Forest - Areas dominated by trees where 75 percent or more of the tree species shed foliage
simultaneously in response to seasonal change.
Evergreen Forest - Areas dominated by trees where 75 percent or more of the tree species maintain their leaves all
year. Canopy is never without green foliage.
Mixed Forest - Areas dominated by trees where neither deciduous nor evergreen species represent more than 75
percent of the cover present.
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Shrubland
Areas characterized by natural or semi-natural woody vegetation with aerial stems, generally less than 6 meters tall,
with individuals or clumps not touching to interlocking. Both evergreen and deciduous species of true shrubs,
young trees, and trees or shrubs that are small or stunted because of environmental conditions are included.
Shrubland - Areas dominated by shrubs; shrub canopy accounts for 25-100 percent of the cover. Shrub cover is
generally greater than 25 percent when tree cover is less than 25 percent. Shrub cover may be less than 25 percent in
cases when the cover of other life forms (e.g. herbaceous or tree) is less than 25 percent and shrubs cover exceeds
the cover of the other life forms.
Non-natural Woody
Areas dominated by non-natural woody vegetation; non-natural woody vegetative canopy accounts for 25-100
percent of the cover. The non-natural woody classification is subject to the availability of sufficient ancillary data
to differentiate non-natural woody vegetation from natural woody vegetation.
Orchards/Vineyards/Other - Orchards, vineyards, and other areas planted or maintained for the production of fruits,
nuts, berries, or ornamentals.
Herbaceous Upland
Upland areas characterized by natural or semi-natural herbaceous vegetation; herbaceous vegetation accounts for 75-
100 percent of the cover.
Grasslands/Herbaceous - Areas dominated by upland grasses and forbs. In rare cases, herbaceous cover is less than
25 percent, but exceeds the combined cover of the woody species present. These areas are not subject to intensive
management, but they are often utilized for grazing.
Planted/Cultivated
Areas characterized by herbaceous vegetation that has been planted or is intensively managed for the production of
food, feed, or fiber; or is maintained in developed settings for specific purposes. Herbaceous vegetation accounts for
75-100 percent of the cover.
Pasture/Hay - Areas of grasses, legumes, or grass-legume mixtures planted for livestock grazing or the production of
seed or hay crops.
Row Crops - Areas used for the production of crops, such as corn, soybeans, vegetables, tobacco, and cotton.
Small Grains - Areas used for the production of graminoid crops such as wheat, barley, oats, and rice.
Fallow - Areas used for the production of crops that are temporarily barren or with sparse vegetative cover as a
result of being tilled in a management practice that incorporates prescribed alternation between cropping and tillage.
Urban/Recreational Grasses - Vegetation (primarily grasses) planted in developed settings for recreation, erosion
control, or aesthetic purposes. Examples include parks, lawns, golf courses, airport grasses, and industrial site
grasses.
Wetlands
Areas where the soil or substrate is periodically saturated with or covered with water as defined by Cowardin et al.
Woody Wetlands - Areas where forest or shrubland vegetation accounts for 25-100 percent of the cover and the soil
or substrate is periodically saturated with or covered with water.
Emergent Herbaceous Wetlands - Areas where perennial herbaceous vegetation accounts for 75-100 percent of the
cover and the soil or substrate is periodically saturated with or covered with water.
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United States Office of Air Quality Planning and Standards Publication No. EPA-454/B-08-001
Environmental Protection Air Quality Assessment Division January 2008
Agency Research Triangle Park, NC
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