Land Area Change in Coastal Louisiana: A Multidecadal Perspective (from 1956 to 2006)

The USGS analyzed changes in land-area in coastal Louisiana from 1956 to 2006 using a series of 14 sequential datasets. These datasets provide a spatially and temporally consistent source of land area information for coastal Louisiana and by physiographic province. Land-area changes were interpreted using spatial analysis and linear regression. The spatial analysis quantified and mapped land-area changes for five time periods. These changes are spatially depicted on the map. The linear regression analysis provided an estimate of recent land-area change from 1985 to 2004, before the 2005 landfalls or Hurricanes Katrina and Rita, and from 1985 to 2006.

Total land loss for coastal Louisiana from 1956 to 2006 was 3,493.9 km2. Annual land-loss rates were highest from 1956 to 1978 at 101.7 km2 /yr and accounted for 64% of land loss. The 1978 to 2004 period accounted for 21% of land loss. The 512.8 km2 potential loss from the 2005 hurricanes accounts for 14.7% loss from 1956 to 2006 and for 40.7% of the loss from 1978 to 2006. The linear regression based annual loss rate, declined to 30.7 ± 5.7 km2/yr from 1985 to 2004.

The majority of land loss from 1985 to 2004 occurred in the Deltaic Plain. The Marginal Deltaic Plain experienced slight gains while the Chenier Plain was stable. The rapid decrease in land loss rates after the 1970s confirms findings of past studies although rates observed in this study are lower. Initial observations suggest that large hurricanes can contribute significantly to coastal land loss and may alter time-averaged trends of landscape change. Prior trend assessments may lack the temporal resolution to identify the loss contributions of past episodic events. Trend projections based on extrapolation of annual loss rates may not account for potential future episodic events.