Using remote sensing to examine changes of closed-basin surface water area in Interior Alaska from 1950-2002

Abstract

Over the past fifty years Alaska has experienced an increase in mean annual temperature. This warming may be causing significant changes in hydrology and permafrost dynamics. In recent decades, Native Americans and land managers have reported losses of water bodies and surface water area in interior Alaska. We conducted a study to determine the degree to which these informal observations were representative of a regional trend in surface water area loss. This study examines closed-basin water bodies in nine regions across Alaska: 1) Copper River Basin, 2) Talkeetna, 3) Tetlin National Wildlife Refuge, 4) Denali National Park, 5) Innoko Flats National Wildlife Refuge, 6) Minto Flats State Game Refuge, 7) Stevens Village, 8) Yukon Flats National Wildlife Refuge, and 9) Prudhoe Bay/Arctic Coastal Plain. The study included approximately 850,000 hectares and over 40,000 water bodies. To conduct such a large-scale study, GIS and Remote Sensing techniques were applied. Water body change detection was conducted over a fifty-year time period. A minimum of three time periods were used for each area. Imagery included black and white aerial photography (1950 -1957), color infrared aerial photography (1978 -1982), Landsat TM (1986 - 1995), and Landsat ETM+ (1999 - 2002). Based on these images, water body polygons were digitized for each time period. Area was calculated for each polygon and compared to corresponding ponds from images at later times. Of the nine regions, six showed substantial reductions in surface water area: Copper River Basin, Minto Flats, Innoko Flats, Yukon Flats, Stevens Village, and Denali National Park. The Innoko Flats and Copper River Basin regions showed the most loss at 31% and 28% respectively. There are several mechanisms possible for reductions of surface water in a warming climate including increased formation of taliks, increased soil water holding capacity, increased evapotranspiration, and terrestrialization.