Land Area Changes in Coastal Louisiana after the 2005 Hurricanes: A Historical Perspective

The U.S. Geological Survey (USGS) compared short term 2004 to 2005 land and water area changes caused by the landfalls of Hurricanes Katrina and Rita (Aug. 29 and Sept. 24, 2005, respectively) to historical 1956 to 2004 land and water area changes in coastal Louisiana. All data sets were clipped to a common boundary to provide a standardized comparison area.

The depiction of land-water changes on the map is based on three data points representing two time periods: 1956 to 2004 (historical) and 2004 to 2005 (before and after the hurricanes). Intervening land-water changes, during the 1956 to 2004 period, such as those caused by prior hurricanes or other events, are not specifically identified. The 2004 to 2005 period represents land-water changes occurring over a period of approximately one year rather than decades and primarily analyzes the immediate impacts of the two hurricanes. The 1956 to 2004 comparison showed a net increase in water area of 2,976 km². The net increase in water area from 2004 to 2005 was 764 km². This latter measurement, however, includes 200 km² of flooded lands consisting of flooded burned marsh and flooded agricultural and developed areas occurring after the hurricanes. Adjusting for these flooded lands, the estimated increase in water area from 2004 to 2005 is 564 km².

The distribution of new water areas after Hurricanes Katrina and Rita varied coast wide but followed a similar pattern in the southeastern and southwestern portions of Louisiana. Shears were often located in marshes fringing historical land loss areas but they also occurred in historically stable areas as well such as in the upper Breton Sound basin. Estimation of permanent losses cannot be made until several growing seasons have passed and the transitory impacts of the hurricanes are minimized.