GSA 2020 Connects Online

Paper No. 147-12
Presentation Time: 5:00 PM


PARFAIT, Devon N. and COX, Rónadh, Geosciences Department, Williams College, 947 Main St, Williamstown, MA 01267-2606

Louisiana's land loss—famously estimated to be about a football field an hour—is increasingly well documented, but less attention is paid to rate variability, and how that intersects with issues of social justice. Native Americans, socially and physically marginalized in the southernmost wetlands, are disproportionately affected. The scale of the difference, however, is unquantified. We used GIS to measure changes over a 33-year period (1987-2020), to evaluate differences between regional land loss and land loss in tribal lands. We focused on three state-recognized tribes—the Isle de Jean Charles (IdjC), and Grand Caillou/Dulac (GCD) Bands of Biloxi Chitimacha Choctaw, and the Pointe-Au-Chien Tribe (PaC).

Unsupervised classifications of 1987 Landsat 5 and 2020 Sentinel 5 data (using bands 2, 6 and 11 for 2020, and bands 4 and 5 for 1987) were effective in distinguishing land from water. Heavily turbid bayous and wetlands are notoriously difficult to classify in GIS, so we also defined a "mixed water" category. The control area, from which we determined average regional land loss, was approximately 3272 km2 of southeastern Terrebonne Parish, and included the three tribal areas.

For the control area, land decreased from 64% to 50% over the 33 years: a 14% overall loss, or 0.4% per year on average. The tribal areas, in contrast, all showed higher rates. The GCD area lost 31% of the land to open water, PaC lost 17%, and IdJC lost 25%. These correspond to annual land-loss rates of 0.6% to 1.0% per year. In particular, GCD and IdJC have lost land at rates more than twice the regional background.

The roots of this problem lie in 19th century removals that drove indigenous peoples to vulnerable lands at the southern limits of the delta. Now, in the 21st century, these peoples suffer disproportionate impacts from ongoing subsidence and sea-level rise. The land-loss-forced resettlement of the IdJC community, considered America's first climate refugees, is a particularly strong example. And futures of Louisiana's other tribal communities in the southern delta are similarly unsafe. Ongoing work will include these groups, and will also generate more detailed land-loss rate profiles for each tribal area. Ultimately we aim to provide data that will help these marginalized peoples as they struggle to have their plight recognized.