A landsat-based assessment of Mobile Bay land use and land cover change from 1974 to 2008

Abstract

This paper discusses results of a Gulf of Mexico Application Pilot project conducted in 2008 to quantify and assess land use land cover (LULC) change from 1974 to 2008. Led by NASA Stennis Space Center, this project involved multiple Gulf of Mexico Alliance (GOMA) partners, including the Mobile Bay National Estuary Program (NEP), the U.S. Army Corps of Engineers, the National Oceanic and Atmospheric Administration's (NOAA's) National Coastal Data Development Center (NCDDC), and the NOAA Coastal Services Center. The Mobile Bay region provides great economic and ecologie benefits to the Nation, including important coastal habitat for a broad diversity of fisheries and wildlife. The Mobile Bay region has experienced considerable LULC change since the latter half of the 20th century. Accompanying this change has been urban expansion and a reduction of rural land uses. Much of this LULC change (largely urbanization) has reportedly occurred since the landfall of Hurricane Frederic in 1979. Regional urbanization threatens the estuary's water quality and aquatic-habitat dependent biota, including commercial fisheries and avian wildlife. Coastal conservation and urban land use planners require additional information on historical LULC change to support coastal habitat restoration and resiliency management efforts. This project quantified and assessed LULC change across the 34-year time frame and at decadal and mid-decadal scales. Nine Landsat images were employed to compute LULC products because of their availability and suitability for the application. The project also used Landsat-based national LULC products, including coastal LULC products from NOAA's Coastal Change & Analysis Program (C-CAP), available at 5-year intervals since 1995. Our study was initiated in part because C-CAP LULC products were not available to assess the region's urbanization prior to 1995 and subsequent to post-Hurricane Katrina in 2006. The study area included the majority of Mobile and Baldwin counties that encompass Mobile Bay. Each date of Landsat data was classified using an end-user defined modified Anderson level 1 classification scheme. LULC classifications were refined using a decision rule approach in conjunction with available C-CAP products. Individual dates of LULC classifications were validated by image interpretation of stratified random locations on raw Landsat color composite imagery in combination with higher resolution remote sensing and in situ reference data. Overall classification accuracies for five separate single-date products ranged from 83% to 89%. The results of the LULC change analysis indicate that during the 34-year study period, urban areas increased from 96,688 to 150,227 acres, representing a 55.37% increase, or 1.63% per annum. Most of the identified urban expansion regarded the conversion of rural forest and agriculture to urban cover types. Final LULC mapping and metadata products were produced for the entire study area as well as for multiple watersheds of concern within the study area. The final project products, including LULC trend information, were incorporated into the Mobile Bay NEP State of the Bay report. Products and metadata were also transferred to NOAA NCDDC to allow free online accessibility and use by GOMA partners and by the public.