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geographic_data_for_wrf-fire

Installing additional geographic data for WRF-Fire

WRF/WPS comes with a standard distribution of geogrid input data. The data is available globally at a resolution of at most 30 arc seconds (a little less than 1 km in NS-direction). For WRF-Fire, however, two additional variables at higher resolution are needed: ZSF for terrain elevation and NFUEL_CAT for the categories of the fuel model, by default the 13 categories of the Anderson model. The source data for these variables needs to be manually downloaded, converted and added to the geogrid configuration. The description here is based on the notes on the WRF-Fire User Guide on the OpenWFM Community Wiki.

Downloading elevation and fuel data

The additional input data should be available on a resolution as close as possible to that of the fire grid (5-10m, typically). 1” data is acceptable (30 m in NS-direction), 1/3” data is better. (1” latitude corresponds to approx. 30 m, but 1” longitude in Interior Alaska is reduced by a factor of the cosine of the latitude, to approx. 13 m.) In the following, NS-extensions will be indicated.

ZFS: high-resolution elevation data

The USGS maintains a list of freely available elevation data (US and globally) including links to download tools and sites.

For Alaska, the options are:

  • Global Multi-resolution Terrain Elevation Data 2010 (GMTED2010): this data set is easily retrieved via EarthExplorer (registration required), but only available in a 7.5” resolution (250 m).
  • National Elevation Dataset (NED): In the lower 48, the NED is available at a resolution of 1/3” (10m), which is the recommended data source as per the WRF-Fire User Manual. Selected areas are available at 1/9” (3m). However, in Alaska, the best available resolution is only 1” or 2”. Downloading this data via the National Map Viewer and Download Platform is somewhat convoluted: follow the instructions to the letter, or maybe try the web services. The USGS Seamless platform was retired in July 2012, but some of the web services may still be available. There is a direct download tool, but it offers only ArcGrid and GridFloat formats.
  • ASTER DEM: the Gina/SDMI Alaska Mapped browse and download tools provides tiles at 1” resolution that appear to cover interior Alaska nearly completely. Download in GeoTIFF format of 1'x1' tiles is straightforward for registered users.

Unfortunately, the otherwise interesting Shuttle Radar Topography Mission (SRTM) 1” data is not available above the 60th degree latitude.

The ASTER DEM option appears to be the easiest to use. The 1” NED should integrate the same data (as it is a product composed of the best available data), and downloading GeoTIFF files from the National Map site turns out to be not always straightforward: even when the option is offered, sometimes GridFloat files are provided.

NFUEL_CAT: high resolution

1” fuel category data for the entire US (including Alaska) are available from the USGS Landfire data distribution site. The steps to download are:

  1. Zoom to the approximate area of interest (first hidden dropdown menu)
  2. “Download Data” (second hidden dropdown menu)
  3. Select “LF2008” > “Fuel” and check “ak_110 13 Anderson Fire Behavior Fuel Model”
  4. Select the download area with the tools at the top of the download tool box, either by marking a rectangle or by entering lat/long using the keyboard icon
  5. “Modify Data Requets”, scroll down to the requested dataset and change the Data Format dropdown to “GeoTIFF” (the default is “ArcGRID”)
  6. “Download”

Other than the Anderson model, the 40 categories from the Scott and Burgan model are available as well.

Converting GeoTIFF data

At this stage, the potentially multiple GeoTIFF source files for the ZSF and NFUEL_CAT variables need to be converted into the intermediate format used by WPS/geogrid.exe. Fortunately, the authors of WRF-Fire have provided a utility program for this purpose, with high-level and detailed instructions how to install and use it.

Before it can be used, however, it is necessary to combine the downloaded GeoTIFF files of each dataset into a single file. The easiest way to do this is via the free gdal_merge.py utility from the Geospatial Data Abstraction Library (GDAL). On Mac OS X, GDAL can be installed via Homebrew. Using the Python utilities requires setting the PYTHONPATH variable – pay close attention to the installation script outputs (or brew info gdal).

Now the single GeoTIFF file can be converted to the geogrid intermediate format as described on the OpenWFM WRF-Fire User Guide, for example:

~/util/convert_geotiff.x -c 13 -w 1 -u "fuel category" -d "Anderson 13 fuel categories" myfuelcats.tiff

The output will be a set of directories containing binary files and a file called index containing the metadata. The index file should be checked to compare to the one in the WRF-Fire User Guide.

Setting up WPS/geogrid for additional data

The elevation and fuel data are then copied each to its own directory, and the location has to be provided to geogrid.exe together with instructions for how to generate the variables. As an example setup, the default geog data, met data (narr) and additional geog data can be placed in directories off the same level as one's WRF installations (if several versions are used). Here, high resolution data for separate domains are placed each in its own directory and the currently used data set is linked symbolically:

pacman9:wrf_fire waigl$ ls -lAF
total 44
drwxrwxr-x 4 waigl uafsmoke  4096 Oct 10 17:26 geog/
lrwxrwxrwx 1 waigl uafsmoke    19 Oct 30 21:41 geog-extra -> geog-wrffire-alaska/
drwxrwxr-x 2 waigl uafsmoke  4096 Oct 19 13:49 geog-wrffire-alaska/
drwxrwxr-x 5 waigl uafsmoke  4096 Oct 30 21:41 geog-wrffire-testcase/
drwxrwxr-x 2 waigl uafsmoke 12288 Oct  2 17:47 narr/
drwxr-xr-x 8 waigl uafsmoke  4096 Oct  6 13:09 WRFF-GH-20121006/
drwxr-xr-x 4 waigl uafsmoke  4096 Sep 25 17:09 WRFV3.3.1/
drwxrwxr-x 4 waigl uafsmoke  4096 Oct 10 16:51 WRFV34/
drwxrwxr-x 3 waigl uafsmoke  4096 Oct 10 15:42 WRFV341/
pacman9:wrf_fire waigl$ ls -lAF geog-extra/
total 0
lrwxrwxrwx 2 waigl uafsmoke 25 Oct  6 13:08 dem_data/
lrwxrwxrwx 2 waigl uafsmoke 30 Oct  6 13:08 landfire_data/
lrwxrwxrwx 1 waigl uafsmoke 25 Oct 19 13:18 ned_data -> dem_data/

Within the WPS/ directory, namelist.wps sets geog_data_path = ../../geog/. And the GEOGRID.TBL is edited to add the additional variables on the fire subgrid as follows:

===============================
name=NFUEL_CAT
    priority = 1
    dest_type = categorical
    dominant_only = NFUEL_CAT
    z_dim_name=fuel_cat
    fill_missing = 14.0
    interp_option = default:nearest_neighbor
    abs_path=../../geog-extra/landfire_data
    subgrid=yes
==============================
name=ZSF
    priority = 1
    dest_type = continuous
    df_dx=DZDXF
    df_dy=DZDYF
    smooth_option = smth-desmth_special; smooth_passes=1
    interp_option = default:average_gcell(4.0)+four_pt+average_4pt
    abs_path=../../geog-extra/ned_data
    subgrid=yes
==============================

Note in particular the NFUEL_CAT settings fill_missing = 14.0 and interp_option = default:nearest_neighbor: The fuel data will have missing values in locations where there is no fuel, in particular for rivers and other water surfaces. With more sophisticated interpolation schemes, bogus data may be created in these cells. It is better to fill those cells with a pre-selected missing value (14, when using the 13 Anderson fuel behavior model categories) than to interpolate or let WPS set its default value (10^20).

Example: Elevation data

Examples of elevation data for a 30×30 km domain around the 2012 Dry Creek fire south-east of Fairbanks:

Low resolution -- variable HGT_M

Variable HGT_M (low resolution)

High resolution -- variable ZFS

Variable ZFS (high resolution)

High resolution -- variable NFUEL_CAT

Variable NFUEL_CAT (high resolution)

geographic_data_for_wrf-fire.txt · Last modified: 2012/11/01 15:17 by chris