Georgia Land Use Trends (GLUT) Project data is produced using LANDSAT satellite imagery data and can be downloaded from the Georgia GIS Clearinghouse. Land cover maps have been created on a somewhat regular basis since 1974. Land cover maps describe the physical landscape and the classes for GLUT include open water, low intensity urban, high intensity urban, deciduous forest, evergreen forest, row crops/pasture, etc. You can read more about GLUT here.
I took the land class data for 1974 and 2015 and used QGIS to work with the data. I clipped the statewide data down to just Hall County to define my project area then used the landscape statistics function of the LecoS plugin to generate the land area covered by the classifications as well as other interesting statisics like proportion, mean patch area, greatest patch area, and the number of patches. I then took all that information and made a map composition within QGIS. The class land cover area came through in meters and I converted that over to acres and square miles then added the square miles to the composition. Do you know how many square miles make up Hall County? 429.
Here's the 1974 GLUT land cover map for Hall County:
The 2015 GLUT land cover map for Hall County:
The 1974 data used 60 m cell sizes and the 2015 data used 30 m cell sizes.
I then downloaded the NLCD data from the USGS and took the 2001 and 2016 imagery through the same process. The classifications in the NLCD data are a little different and seems a little more accurate based on my own familarity with actual county land cover.
2001 NLCD Hall County Land Cover:
2016 NLCD Hall County Land Cover
The statistics from LecoS can be exported out to a spreadsheet software so I used LibreOffice Calc to do a little more ciphering.
NLCD - 2016
Average patch area forest – 10 acres
NLCD - 2001
Average patch area forest- 11.28 acres
If we subtract the land area classified as forest in the 2001 NLCD imagery (151,986.42 acres) from the 2016 NLCD imagery (142,531.08 acres) we find a loss of 9,455.34 acres, or a decrease of just over 6% of the forested land in Hall County over the 15 years between 2001 and 2016.
100,391.26 acres were classified as urban and agriculture development in 2016 while 92,208.68 acres were classified as such in 2001, a 8.9% increase of 8,182.58 acres.
5,968.41 acres were classified as medium and high intensity urban development in 2001 and 10,150.10 acres were classified as such in 2016, an interesting increase of 70%.
42,760.30 acres were classified as agriculture in 2001 and 38,390.91 acres were classified as such in 2016, a decrease of 10.2%.
1,171.35 acres were classified as wetlands in 2001 and 1,203.82 acres were classified as such in 2016, an intriguing increase of 32.47 acres or 2.8%.
GLUT - 1974
Average patch area forest – 17.07 acres
GLUT - 2015
Average patch area forest – 10.36 acres
If we subtract the land area classified as forest in the 1974 GLUT imagery (174,778.33 acres) from the 2015 GLUT imagery (125,343.29 acres) we find a loss of 49,435.04 acres, or a decrease of just over 28% of the forested land in Hall County over the 41 years between 1974 and 2015.
116,014.49 acres were classified as urban and agriculture development in 2015 while 67,556.44 acres were classified as such in 1974, a 71.7% increase of 48,458 acres.
21,969.05 acres were classified as urban development in 1974 and 67,490.83 acres were classified as such in 2015, an increase of 207%.
45,587.38 acres were classified as agriculture in 1974 and 48,523.66 acres were classified as such in 2015, a small increase of 6.4%.
2,029.13 acres were classified as forested wetland in 1974 and 1,720 acres were classified as such in 2015, a loss of 309.13 acres, or a loss of about 15%.
I found that the USGS had another geospatial product on their website called Conterminous United States Land Cover Projections - 1992 to 2100. Please check out that page, and I'll summarize a TL;DR anyway. They developed a model to make land-use and land-cover projections for the US. They modelled four scenarios based off four storylines from the Intergovernmental Panel on Climate Change. Three of the scenarios were similar with expanding human land use, with the B2 scenario having a more stable balance of natural land cover and fragmentation.
I took the B1 and B2 scenarios and got snapshots of what they project for Hall County in 2040 and 2100, then got a shot of the region under B1 at 2100 for the "wow" factor, and included a reference to Hall County at the 2016 NLCD data.
There's also an impervious surface product from the USGS. Here are the impervious surfaces in Hall County in 2001 and 2016.
You can see an increasing amount of impervious in South Hall, and you can see Gwnnett's impervious expanding north. You can see Gainesville expanding further north.
Tree Canopy Data from the USFS Tree Canopy Cover Mapping Service. I added the question marks as a reminder to interpret the imagery and data carefully. We are looking at the cumulative area of actual tree canopy, not ground area. That 259 square miles of tree canopy in 2016 shows us that 60% of Hall County total is covered with tree canopy, and 65% of Hall County land has tree canopy.
It's interesting to see how tree-less Gainesville proper is. There is a significant opportunity to plant trees throughout Gainesville. If you look to the southeast of Gainesville you can see the Allen Creek area in vibrant green, which is now planned to be turned into an industrial park. Look to the north at the large area that could have been and could at some point turn into Glades Farm Reservoir and associated development. Additionally, consider the impact of further development along the 365 corridor.
The above map shows change- anything you see within the Hall County boundary represents an area that was changed.
Rather late into this project I realized that there is an NLCD Land Cover Change Index that shows land cover change with an accompanying index. It represents any change that occured from 2001 to 2016. Note the minimap at the bottom right, the pink radiating out from Atlanta represents change to or from Urban class. Meanwhile the area in and immedately around Atlanta shows little change.
The 2016 NCLD data was not released until 2019. Professor Miller at the University of North Georgia had suggested using this data to observe land use changes in Hall County and I'm glad he did.
The next round of this data will include many changes. There are several residential, commercial, and industrial areas that have been and are currently planned to be developed. How much interest is there in protecting natural areas, focusing on smart development, and creating and enforcing strong tree ordinances and zoning rules? These are steps that could help keep Hall County sustainable and livable.
If you want to see a project that was done with higher quality remote sensing data and is a well put-together analysis of urban tree canopy, check this out: http://www.ci.minneapolis.mn.us/www/groups/public/@citycoordinator/documents/webcontent/convert_261908.pdf
We have this sort of data available for Hall County, so a next step will be to do that Minneapolis project here.
This has been a fun rain day project that I've been looking forward to for some time now.