Subtask 3.3: Late 20^th Century Landcover Change in the Northern Gulf Coast

Subtask Leader: John Barras - USGS National Wetlands Research Center

Subtask 3.3 Aim:

Spatial analysis of Landsat data from 1970s to today will reveal the landscape-level impacts of hurricanes on coastal vegetation, from both short-term damages to long-term marsh loss and recovery. [enlargement]

Land cover provides baseline information when measuring the impacts of urbanization, wetland loss, climate change, sea-level rise, or other environmental stressors on the resilience of communities. Using satellite-derived land cover data, we can examine multi-decade evolution of landscape change using consistent methodology and contiguous data. In addition, a closer look at wetland trends in high temporal detail will further elucidate the affect of environmental factors on wetland loss in the northern Gulf of Mexico.

The applications of land cover data for NGOM scientific endeavors are numerous, from landscape spatial modeling in Subtask 4.3 to land-loss time series analysis in Subtask 3.5. These data will provide a significant baseline data set for decadal landscape evolution for the entire NGOM study area and marsh loss studies for coastal Louisiana. A second, coupled study focusing on land cover changes and wetland impacts due to historic hurricanes will complement these analyses and will further support NGOM research in Task 4, particularly subtasks dealing with catastrophic disturbances and landscape modeling.

The goal of this subtask is to identify and document land-cover changes within the NGOM project area by acquiring and classifying historical Landsat satellite imagery using a standardized project classification scheme on a decadal basis from the 1970s to the present.  Annual to biannual classified Landsat TM land-water data sets will be used to refine trend timing and variance over the NGOM landscape. In addition, Landsat data and other remotely-sensed data sets will be examined to understand the impact of hurricane-induced landscape changes as well as changes from other episodic events.  The use of “wet” marsh as a potential stress or loss indicator will be investigated for selected areas.

Subtask 3.3 Activities:

Specific objectives of this subtask include:

• Building on existing data sets to develop land cover data spanning 1970s to present using Landsat TM and MSS and conduct land cover change analyses.
• Expand the spatial and temporal frequency of wetland loss studies and examine the variance in wetland area calculations under varying meteorlogical, riverine, and tidal conditions.
• Examine wetland loss and recovery following hurricanes and tropical storms.

Water level has a direct affect on wetland area calculations, as demonstrated by a comparison of total water area, derived from classified landsat imagery, and water level averages. Water area (converse is wetland area) follows similar trends as water level height for the same region.

Publications:

Barras, J.A., 2007, Satellite images and aerial photographs of the effects of Hurricanes Katrina and Rita on coastal Louisiana: U.S. Geological Survey Data Series 281, (Online only).