A changing mosaic of natural vegetation and human land uses has evolved within and around the Flint River Watershed (FRW) in Alabama and Tennessee over the past several decades. To determine the cause of change and linkage between human activities and environmental change can prove problematic. Subsequently, there is a need to produce projections of future environments based on planning instruments and socio-economic parameters. Scenarios of potential future land use land cover (LULC) change are required in order to better manage potential impacts on many environmental issues. This study creates future scenarios for the year 2030 from baseline land use of 2001, relative to three projected land use scenarios which include differences related to conservation, planning, and development. The future growth scenarios were created using the ArcGIS tool, Prescott Spatial Growth Model (PSGM). The model allows users to build different future growth scenarios based on socio-economic projections such as population, employment and other controlling factors. The simulation results indicate that LULC changes associated with future urbanization can increase by ~23% - 43% within the FRW, which will lead to significant environmental issues if not managed properly. The overall analysis and model results demonstrate the ability of future growth scenarios to explore and evaluate options for a future environment. Spatial modeling and analysis tools, such as PSGM, provide a powerful approach to evaluate potential impacts of LULC change in the future and should be used to manage urbanization in areas with more intense development.
Scenarios, as defined by the Intergovernmental Panel on Climate Change [
The PSGM was developed at Prescott College (AZ) in collaboration with National Aeronautics and Space Administration (NASA) and is a dynamic process model with a raster-based structure. The PSGM is an ArcGIS 9.× compatible application that assigns future growth into available land based on user-defined parameters [
One of the input parameters, developable land, is in the form of a binary grid indicating land grid cells suitable for accepting future growth. Growth projection is specified in terms of acres consumed, for each projected year for each developed land use type. The PSGM allocates projected population and employment growth for specific projection years to user-specified land use categories [
The successful function of the PSGM is dependent on the development of rule sets. For each land use class being assessed, a separate rule set is created. The different rules sets are run consecutively letting each rule set allocate land based on available area and priority. There is no limit on the number of rules in a scenario or a rule set [
The PSGM has been previously used to model growth projections for various counties in the Atlanta, Georgia region [
The Flint River watershed (FRW) (Hydrologic Unit Code: 06030002) encompasses approximately 1445 Square km in Madison County, Alabama, and Lincoln County, Tennessee (
The Flint River has a watershed management plan that was developed by the Tennessee Valley Authority, the Madison Soil and Water Conservation District, and the Madison County Watershed Advisory Committee. The plan is based on several years of work by various federal, state, and local organizations and citizens and on currently available data provided by a number of citizens groups [
The growing population is placing heavy and divergent demands on the FRW. For example, the visual interpretation of the National Land Cover Dataset (NLCD) change between 1992 and 2006 (
Knowing where the FRW may develop in the future is significant to create better management practices and ensure that quality water resources are available in the future. While conservation efforts have often focused on maximizing the quantity of land conserved, research efforts in landscape ecology have shown that the spatial pattern of land conversions can have a significant effect on the function of ecological processes [
The three alternative-future scenarios produced by the PSGM are conservation growth, plan trend, and development growth. The conservation growth places greater priority on ecosystem protection and restoration, although still reflecting a plausible balance between ecological, social, and economic considerations. Plan trend assumes existing land use plans are implemented as written, with few exceptions, and recent trends continue. The development growth, which has the least conservation, assumes current land use policies are relaxed and has a greater reliance on land and water use [
The time steps for these future growth scenarios are 2000 to 2007 and 2007 to 2030, building off Census data for 2000. Projections for 2007 were created in order to validate the model. County-level data obtained from the U.S. Census report was used to create population and employment tables. Population and employment data for 2000, 2007 and 2030 for each county and area in acres of commercial and residential land was used to determine the input parameters for the model. The 2007 population and employment data was collected from the American Community Survey. Input for residential land use data includes Dwelling Units per Acre (DUAC) for each county and Persons per Housing Unit (PPHU). DUAC values were set as 2.75, 2.5 and 2.25 for Lincoln County (TN) and 3.25, 3 and 2.75 for Madison County (AL) in the conservation, plan and development growth scenarios respectively. The PPHU value was 2.0 for both counties in each of the three scenarios. Commercial land use data included Gross Square Footage per employee (GSF) and Floor Area Ratio (FAR) for each county in the study area. The GSF of commercial land was generalized in this analysis to be 250 for Lincoln County and 350 for Madison County. For both counties FAR values were calculated from jobs per acre and were 0.9, 0.6 and 0.3 in the conservation, plan and development scenarios respectively. The model uses a spreadsheet-like interface to calculate acres consumed of future commercial and residential land from inserted values of DUAC, PPHU, GSF, FAR, population and employment for each time step (
The NLCD serves as the definitive Landsat-based, 30 meter resolution, and land cover database for the Nation [
Time Step | County | Job Increase | Consumed Conservation (Acre) | Consumed Plan (Acre) | Consumed Development (Acre) |
---|---|---|---|---|---|
2000-2007 | Lincoln | 1067 | 6 | 10 | 20 |
2000-2007 | Lincoln | 3992 | 25 | 38 | 76 |
2000-2007 | Madison | 23,594 | 210 | 315 | 631 |
2007-2030 | Madison | 99,484 | 888 | 1332 | 2664 |
Time Step | County | Job Increase | Consumed Conservation (Acre) | Consumed Plan (Acre) | Consumed Development (Acre) |
---|---|---|---|---|---|
2000-2007 | Lincoln | 1393 | 253 | 278 | 309 |
2000-2007 | Lincoln | 2730 | 496 | 546 | 606 |
2000-2007 | Madison | 37,096 | 5707 | 6182 | 6744 |
2007-2030 | Madison | 75,358 | 11,593 | 12,559 | 13,701 |
nership of Federal agencies led by the USGS. The 2001 NLCD for both counties within the FRW was used as the land use input grid for projected growth. The 2001 land use distinguishes 16 different classes but in the study area the perennial ice/snow land use was excluded leaving the following land use classes; open water, developed open space, developed low intensity, developed medium intensity, developed high intensity, barren land, deciduous forest, evergreen forest, mixed forest, grassland, shrub, pasture/hay, cultivated crops, woody wetlands and emergent wetlands [
The developable land grid, which contained valid values for cells that represent land use areas suitable for accepting future growth, was created from the 2001 NLCD layer. The developable land grid was different for all three scenarios but in no scenario contained areas classified as urban, developed open space or open water. The conservation scenario had a 50 foot buffer around the classified wetland areas that was excluded from the available land layer, thus conserving land within 50 ft of wetlands. The developable land grid contained the forest, shrub, pasture, and agriculture land use classes for the conservation scenario and for the plan trend scenario the grid included these classes plus barren and grassland classes. For the development scenario the land available for development included all the land use classes except urban, developed open space and open water therefore, future growth could be allocated in many land use areas, including wetlands making this scenario have the least conserved land.
The suitability rules are defined in PSGM to guide the allocation of projected growth for residential and commercial land use. Each of the rules is used to create an individual suitability grid; when there is more than one rule the individual grids are added to create a composite suitability grid for that land use category [
Rule Theme | Commercial Distance (Miles) | Weight | Residential Distance (Miles) | Weight |
---|---|---|---|---|
In County―develop land in respective county first | 10 | 7 | 10 | 7 |
Near roads―Within x miles of road network | 0.1 | 5 | 0.5 | 1 |
Within x miles of existing development of same type (commercial or residential) | 1 | 5 | 1 | 5 |
Random―allows spontaneous development in available land layer | Not used | 1 | Not used | 1 |
PSGM’s growth allocation module assigns growth (in acres) to the composite suitability grid. As land use is allocated, it is removed from consideration by the model in the allocation of other land use needs. The output grids of the model were merged by land use type and year of growth to display the complete LULC data for assessment for each county and time step. The 2007 projected land use was only used to validate the performance of the model.
Using the PSGM parameter inputs and rule sets described in the previous sections, the conservation, plan and development growth simulations were performed starting from the same NLCD 2001 observed data to predict land use in the year 2030. The initial land use output was for the entirety of Lincoln County, Tennessee and Madison County, Alabama (
Projections of future state cannot be validated, but the accuracy of the model can be evaluated in hind-cast mode, in which projections are made from some past starting point, and results compared with observed LULC data at the simulation end time [
Land Cover | Percent Total Area and Percent Change | |||
---|---|---|---|---|
2001 Baseline | Smart | Plan | Sprawl | |
Water | 0.51 | 0.51 (0.0) | 0.51 (0.0) | 0.51 (0.0) |
Urban/residential | 7.0 | 9.81 (+40.14) | 10.01 (+43.00) | 11.43 (+63.29) |
Forest | 31.23 | 29.99 (−3.97) | 29.95 (−4.10) | 29.76 (−4.71) |
Range | 4.79 | 4.71 (−1.67) | 4.68 (−2.3) | 4.6 (3.97) |
Pasture | 27.65 | 26.8 (−3.08) | 26.73 (−3.35) | 26.09 (−5.65) |
Cultivated crops | 25.18 | 24.54 (−2.55) | 24.48 (−2.78) | 24.02 (−4.63) |
Wetland | 3.65 | 3.65 (0) | 3.65 (0) | 3.59 (−1.64) |
Land Use Class | NLCD 2006 (ha) | Basin % | Conservation 2007 (ha) | Basin % | Plan 2007 (ha) | Basin % | Development 2007 (ha) | Basin % | |
---|---|---|---|---|---|---|---|---|---|
Open water | 708.12 | 0.49 | 741.87 | 0.51 | 741.87 | 0.51 | 741.87 | 0.51 | |
Developed open space | 8724.96 | 5.99 | 8302.68 | 5.70 | 8302.68 | 5.70 | 8302.68 | 5.70 | |
Residential | 3791.61 | 2.60 | 4453.65 | 3.06 | 4588.47 | 3.15 | 4696.74 | 3.23 | |
Commercial | 137.52 | 0.09 | 150.03 | 0.10 | 162.18 | 0.11 | 202.77 | 0.14 | |
Barren land | 43.47 | 0.03 | 45.18 | 0.03 | 44.73 | 0.03 | 44.91 | 0.03 | |
Deciduous forest | 39538 | 27.16 | 39,500 | 27.13 | 39466 | 27.11 | 39460 | 27.10 | |
Evergreen forest | 1901.88 | 1.31 | 1941.75 | 1.33 | 1938.33 | 1.33 | 1934.91 | 1.33 | |
Mixed forest | 2393.82 | 1.64 | 2423.34 | 1.66 | 2421.54 | 1.66 | 2421.18 | 1.66 | |
Shrub | 5191.83 | 3.57 | 5173.11 | 3.55 | 5168.70 | 3.55 | 5160.15 | 3.54 | |
Grassland | 2066.85 | 1.42 | 1742.67 | 1.20 | 1725.75 | 1.19 | 1723.86 | 1.18 | |
Pasture | 39796.92 | 27.34 | 39614.31 | 27.21 | 39549.60 | 27.17 | 39494.79 | 27.13 | |
Cultivated crops | 35970.57 | 24.71 | 36187.29 | 24.86 | 36166.05 | 24.84 | 36114.66 | 24.81 | |
Woody wetlands | 5283.81 | 3.63 | 5276.43 | 3.62 | 5276.43 | 3.62 | 5254.02 | 3.61 | |
Emergent wetlands | 33.12 | 0.02 | 30.24 | 0.02 | 30.24 | 0.02 | 30.06 | 0.02 | |
Total | 145582.2 | 100 | 145582.2 | 100 | 145582.2 | 100 | 145582.2 | 100 |
narios, but is slightly higher than the 708.12 ha classified in the 2006 NLCD. Similarly, there are minor differences in the Emergent Wetlands class.
Specifically, the assessment suggests that an approximate 23% increase in urbanized area in the conservation scenario will occur by 2030 within the FRW. Within the conservation scenario, the areas with the largest increase in development were located near the developing cities of Moores Mill and Meridianville Alabama. For the plan scenario, urbanized area increased by ~25%, and areas with the largest increase in development were the same as the conservation scenario. The development scenario had the largest increase in urban land use of ~43%, with the largest increase in development near the Huntsville City Limits and developing cities adjacent to major roads. The simulation results indicate that LULC changes associated with future urbanization can increase by ~23% - 43% within the FRW which will lead to significant environmental issues if not managed properly.
The analysis reveals that the PSGM is an effective tool in forecasting scenario based land use change over a 30-year period and can be run with readily available data. The validation results indicate that with accurate input parameters and reasonable population and employment forecasts, land use change can be projected into the future with acceptable accuracy. The uncertainties in estimating PSGM parameters such as dwelling units per acre and jobs per acre and errors in population and employment forecasts have a substantial impact on the ability of the model to simulate urban land use changes. The overall analysis and model results demonstrate the ability of future growth scenarios from baseline digital land use data to explore and evaluate options for a future environment. Spatial modeling and analysis tools such as PSGM provide a powerful approach to evaluate potential impact to LULC change in the future and can be used to manage development in areas with more intense urbanization
The authors gratefully acknowledge Drs. David Mays and Dawn Lemke for thorough review of this manuscript. We also thank Heather Howell, Allison Bohlman, Helen Czech, Dr. Raghavan Srinivasan, Mr. Hoyt Johnson and Mr. Howard Ward for their endless support of information pertaining to the research. Also, the United States Department of Agriculture, National Institute of Food and Agriculture Award No. 2008-51130-04899 and National Aeronautics and Space Administration Graduate Student Research Program Fellowship for their financial support to complete this work.
WubishetTadesse,StephanieWhitaker,WilliamCrosson,ConstanceWilson, (2015) Future Land-Use Land-Cover Scenarios for the Flint River Watershed in Northern Alabama Using the Prescott Spatial Growth Model. Journal of Geographic Information System,07,319-327. doi: 10.4236/jgis.2015.74025