2. Model configuration and methodology

a. Land-use data

Fig. 2. Grid configurations for the RAMS domain used in this study. [larger image]

A Geographic Information System (GIS) was employed by the USGS to combine a variety of data sources to develop the updated land-cover datasets. Early vegetation maps, historical analyses, and paleodata studies were the primary inputs for the pre-1900 dataset. The reconstructed natural vegetation for the Everglades (south of the Kissimmee River watershed) was derived mainly from a GIS analysis of the Davis (1943) South Florida Natural Vegetation Map, as adapted by McVoy (1996), McVoy et al. (2003), and Willard et al. (2001). McVoy (1996) analyzed historical documents and early photographs to reconstruct the distribution of saw grass and slough/bogs/marshes in the Everglades prior to conversion to agriculture and the diversion of surface water flow by the construction of surface hydrology controls [a historical review of water resource engineering activities is provided by Light and Dineen (1994)]. Subsequently, Willard et al. (2001) presented evidence based on paleostudies of pollen data extracted from core samples within the Everglades to support the analysis of McVoy. Given these historical and paleovegetation studies, the pre-1900 land-cover dataset is believed to closely approximate the vegetation patterns that existed in the Everglades prior to large-scale human disturbance activities. The predisturbance land-cover data constructed by Costanza (1975, 1979) was used for the Kissimmee River watershed. The Kuchler (1964) potential natural vegetation dataset was used as the primary source of pre-1900 data for the remainder of Florida and the southeastern United States, with two modifications. First, the southern mixed forest class was modified to a predominantly evergreen needle leaf forest, which represents the extensive areas of longleaf pine and Florida slash pine in fire-prone areas (Landers and Boyer 1999). Second, the data were modified to account for the freshwater marsh areas of the southern St. Johns River basin (note the axis of marsh over the east-central peninsula shown in Fig. 1, just inland of Cape Kennedy, southward to the latitude of the north shore of Lake Okeechobee).

The 1993 land-cover datasets were derived from the USGS 30-m National Land Cover Data dataset (NLCD; Vogelmann et al. 1998, 2001) and the 30-m Florida Gap Analysis Project (GAP) dataset (Pearlstine et al. 2002). The USGS NLCD, which was developed for the conterminous United States based on 1992-93 Landsat Thematic Mapper (TM) data, was used for the RAMS outer grid within the southeastern United States. The 1993 land-cover data for the model inner grid was derived by combining the NLCD for Florida with the GAP data. The GAP land-cover product was developed by the USGS (Biological Resources Discipline), the Florida State Cooperative Fish and Wildlife Research Unit, and the University of Florida using Landsat TM scenes from the 1992-94 time frame. Urban, residential, mixed agriculture, and other standard classes were selected from the NLCD, while wetlands, forests, and dry prairies were selected from the GAP data.

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