Report Number: 124
Year: 2009

Watershed Land Cover Change in Guam

Land cover change (LCC) has been a subject of concern for the past century, particularly the past few decades around the world. Although many of the changes have been recorded qualitatively through the use of comparative photography and historical reports, little quantitative information has been available at watershed scale. It is currently possible to detect land cover change and determine trends in ecological and hydrological condition at watershed scale using advanced geo-spatial technologies. Satellite remote sensing, spatial statistics, geographic information systems (GIS), and global positioning system (GPS) can be used to identify LCC of watersheds. These technologies provide the basis for developing landscape composition and pattern indicators as sensitive measures of environmental change and thus, may provide an effective and economical method for evaluating watershed condition related to disturbance from human and natural stresses.

Landsat observations have evolved from an experimental system in the 1970s to a feasible system to ensure our ability to explore, characterize, monitor, manage, and understand changes in the Earth's surface. Land cover has been derived from a multi-date satellite imagery database which incorporates Landsat Multi-Spectral Scanner (MSS) imagery from the early 1970s to early 1990s, Landsat Thematic Mapper (TM) imagery from early 1980s to current, Landsat Enhanced Thematic Mapper Plus (ETM +) from early 1999 to current at local and/or regional scale. Recent surveys indicate that land cover/use changes have a direct and enormous effect on water quality and environmental change. Watershed water quality and ecosystem are threatened constantly by both human impacts such as forest fires and development and also natural phenomena such as storms and droughts. Therefore, it is critical to conduct research on land cover change in watersheds. This study was mainly focused on extraction of land cover information from satellite imagery from early 1970s to 2001, and determination of LCC in watersheds of southern Guam. Remote sensing and GIS were integrated for land cover classification of satellite images.

One scene of Landsat MSS image of November 14, 1973, and one scene of Landsat TM image of March 15, 2001 were utilized to extract land cover information. Different data sources such as digital line graph (DLG), recent IKONOS and QuickBird imagery were used as auxiliary information for land cover classification. Ten (10) meter digital elevation model (DEM) data has been used to delineate the watersheds in Guam. There are 14 watersheds in Southern Guam. The study area focuses on these watersheds in Southern Guam. Land cover change in each watershed, and overall land cover change in the watersheds are presented in this report.

Yuming Wen
Shahram Khosrowpanah
Leroy F. Heitz