The resource concern modeling strategy was mostly dictated by the NRCS national directives with some modifications allowing for the use of available local data, input from the collective experiences of the NRCS conservation partners and preliminary research and analysis completed during 2010. The Arkansas SRA project team was fortunate to have begun research and data collection during 2010 and during the first phase of the Arkansas SRA effort meetings were held with NRCS Conservation Partners to discuss possible methods and datasets that would benefit this assessment. Information related to project goals and proposed modeling strategies were disseminated through meetings and presentations to these partners as well as through the project website.
In order to model each of the 29 resource concerns relevant within Arkansas, existing GIS data and weighting suggestions were collected from the project partners and each raster input layer was prepared and submitted to NRCS for review and approval prior to inclusion into each of the twenty-nine models. These input data layers were selected due to their applicability, availability, and because they were the datasets recommended by State resource concern experts or directly specified within the NRCS National Directives. The Arkansas NRCS Office coordinated with numerous NRCS technical committees responsible for reviewing all datasets identified by project team members. A weighted sum overlay (raster) modeling method was developed within the ArcGIS software environment, and it became a template for how each natural resource concern model would be executed (and later distributed to partners) for the purposes of identifying the extent of each resource concern’s at-risk acreages within Arkansas. The weighted sum overlay methodology was chosen so that model results could be repeated and consistent for addressing all resource concerns required by the NRCS national directives, while also producing a ‘relative risk’ map that would encourage conversation and critics from Arkansas’ resource managers. The resulting output raster maps represented the ‘relative risks’ for each resource concern within all of the NRCS service areas, so these products helped our technical committees to review and analyze the results of their proposed input data and assigned layer weights. This was an iterative process with each review from our experts resulting in further refinements to each GIS model until each technical committee was satisfied that our weighted sum output raster maps were representative of their collective expert opinions for the ‘At-Risk’ areas within Arkansas.
These overlay models were created so that the NRCS land use designations, specified within the national directives and developed through a reclassification from the 2006 National Land Cover Dataset, were used as a weighted multiplier to the collection of simple additive input binary or classified raster layers selected for each natural resource concern. For example, a model could be summarized this way: each binary and classified input raster layer (30-meter resolution) was summed for each individual natural resource concern; the summation of those input raster layers resulted in one additive sum raster layer that was then multiplied by the weight-specific NRCS land use designation raster layer as specified for each individual natural resource concern. If any NLCD land use category was valued zero; those areas would result in a value of zero being assigned to all land areas of that NLCD category within the individual natural resource concern model output. Therefore any land areas covered by a NLCD weighted reclass of zero would result in those land areas being removed from the total potential at-risk area for the natural resource concern being modeled
Upon the completion of this raster calculation, the federal lands mask (all federals lands; plus a 300-foot buffer, Map 2) was applied. This multiplication mask essentially extracted or removed those land areas from the final resource concern model result map because it was simply a reclassification of those land areas within the federal lands mask as zero. Since NRCS conservation programs are primarily applied to private lands, the federal lands of Arkansas were excluded from consideration for this analysis. Land use weights are detailed for each natural resource concern model in the Results and GIS Layer Specifications section.
The base layer weight for the water land use designation received a weight of zero (0) for all models, except for Soil Erosion – Excessive Bank Erosion from Streams, Shorelines or Water conveyance Channels. The Federal Lands mask (all federal lands; plus a 300-foot buffer, Map 2) accounts for approximately 13% of all land use designations in Arkansas. Those areas were considered unserviceable or as already receiving conservation treatments from other federal agencies so it was decided that those land areas would be excluded from the At-Risk Area estimates within Arkansas since NRCS conservation programs are primarily focused on private lands.