Northern Gulf of Mexico (NGOM) Ecosystem Change and Hazard Susceptibility

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Subtask: Landscape and Hazard Forecast for the Mississippi-Alabama Coastal Zone (MACZ)

Aim

The overarching goal of U.S. Geological Survey Gulf Coast science in the post-Hurricane Katrina environment is to provide the scientific knowledge and tools required to make optimal decisions about land resource use, management practices, and future development in the northern Gulf of Mexico coastal zone and adjacent watersheds. A goal of the NGOM Project is to understand and predict landscape change and the associated storm hazard vulnerability of northern Gulf Coast region over the coming decades. This Task seeks to realize these goals within the Mississippi-Alabama coastal zone (MACZ), a developed portion of the northern Gulf Coast that is highly vulnerable to storm surge inundation. Following the storm surge devastation wrought by Hurricane Katrina across the MACZ in late summer 2005, it is apparent that a better understanding of the northern Gulf of Mexico coast hazard vulnerability and its interactions with human activities is necessary for sustainable restoration, redevelopment, and sound natural resource management strategies.

Several intersecting trends will likely worsen the already severe vulnerability of the northern Gulf Coast. Global climate projections that suggest more intense Atlantic hurricanes will occur over the next several decades provide further justification for investigations of the hazard vulnerability of the northern Gulf Coast. Most scientists agree that the global climate is changing, and model results and theoretical considerations support the idea that ocean warming will affect tropical storm characteristics. Knowledge of rates of relative sea-level rise in the region will impact restoration and storm protection plans, but the extent to which sea-level projections can be incorporated is contingent on a better understanding of climate change.

Barrier island chains in the northern Gulf of Mexico extending from Mobile Bay, Alabama to Atchafalaya Bay, Louisiana that may offer a degree of protection are disintegrating rapidly as a result of combined physical processes involving limited sediment availability, alteration of alongshore sediment transport, and rising absolute sea level. Such extreme change to the northern Gulf Coast landscapes that has diminished protection from severe storms has coincided with a general shift of the U.S. population to the nation's coasts over the last several decades. Since 1900, population density has sharply increased in all sixteen coastal counties along the Louisiana, Mississippi, and Alabama Gulf of Mexico coastline. Across the eastern portion of this coastal reach, population density has typically increased by more than 50 people per mi2, and in the area south of New Orleans, such increases have exceeded hundreds of people per square mile (U.S. Census Bureau, 2006).

This probability map displays the probability of urbanization (between the years 2008 and 2040) of 30-meter x 30-meter pixels (or cells) across the more than 40 million pixels of this Coastal Mississippi and Alabama study area.
This probability map displays the probability of urbanization (between the years 2008 and 2040) of 30-meter x 30-meter pixels (or cells) across the more than 40 million pixels of this Coastal Mississippi and Alabama study area. Probability classes were determined by a prediction run of the SLEUTH-3r urban-growth model with parameters selected by earlier calibration runs. This prediction run was based on parameters indicating high resistance to urban growth on slopes, relatively low attraction of growth by major roads, and very low tendencies for spontaneous exurban growth or spreading of existing urban or road-related urban areas.
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Approach

Objectives:

Develop a forecast model that admits the effects of offshore sediment dynamics, land cover change and sea level rise inundation to predict the future MACZ shelf and terrestrial landscape, and apply that model to create spatial predictions of the MACZ landscape (land cover, shoreline and topobathymetric geomorphology) over the coming half century at decadal increments.

Create hazard predictions by conducting storm surge simulations across the predicted MACZ landscapes using various hurricane climate scenarios that may prevail over the next 50 years.

Develop a conceptual model that will provide a framework for the NGOM project, allow us to test hypotheses and describe our understanding of the northern Gulf Coast, and be a tool for synthesizing data and scientific interpretation.

Methodology:

The steps required in the development of a MACZ landscape forecast model are outlined below:

  • Preparation or compilation of base layers that represent the present MACZ landscape
  • Forecast future MACZ geomorphologies
  • Forecast future distributions of MACZ land cover
  • Apply sea level rise inundation modeling to predicted MACZ landscapes
  • Apply a storm surge model to predicted MACZ landscapes impacted by sea level rise
These map images show the map of urban pixels in year 2008 contrasted with a map of 32 land-use/land-cover classes.
Modeling and forecasting urban growth in Coastal Mississippi and Alabama with the SLEUTH-3r model required the preparation of urban inputs and the use of land-use/land-cover classifications for the region. These map images show the map of urban pixels in year 2008 contrasted with a map of 32 land-use/land-cover classes.
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