Washington State – Land Use and Land Cover
Overview of Washington State Change Detection
Salmon and steelhead need a variety of habitats for spawning, rearing, and transitioning to and from saltwater. A key question is how much habitat for salmon exists and how much is in good shape. The state’s ability to track development and other land uses, such as farming and logging that affect the waterways where salmon and steelhead live has improved in recent years. The Washington Department of Fish and Wildlife has developed tools that provide information on precise locations of different types of land use, improving over previous years when estimates for entire watersheds were based on a few parameters.
For this report, the Washington Department of Fish and Wildlife analyzed eight Water Resource Inventory Areas, one in each salmon recovery region, to survey different land-use change patterns across the state. After mapping changed locations between 2009 and 2011, the rates of change were compared for areas inside and outside of the city and urban growth areas and within different proximities to fish-bearing streams.
The rate of land changes due to development in and near cities is similar in eastern and western Washington but outside of the cities, the rate of change due to development is more than eight times higher in western Washington. Generally, development seems to have decreased since 2006. Two factors are in play here: first, the population pressure is higher in Puget Sound than in the rest of Washington, and second, the economic downturn has reduced housing construction and development compared to past decades.
Tracking the rate at which land is developed helps determine whether habitat restoration and protection actions are working, or if more habitat is lost than restored.
Washington Department of Fish and Wildlife’s High Resolution Change Detection
One way to monitor land use is through remote sensing, which can provide photographs of entire landscapes from above. Traditionally, analyzing changes in land use was conducted for small projects by manually interpreting photographs or using satellite data, typically Landsat data, which is captured at a single pixel resolution of 30 meters. Advances in digital photography and federal initiatives to monitor agriculture have led to the acquisition of statewide, 1-meter aerial photographs for 2006, 2009, and 2011 (hereafter referred to as the NAIP data).
In 2009, the Salmon Recovery Funding Board provided a grant to the Habitat Science Division of the Washington Department of Fish and Wildlife to use the NAIP data to track major vegetation changes in four Water Resource Inventory Areas. At the time, the primary product for tracking changes in land use and land cover was the Coastal Change Analysis Program, which is a program administered by the National Oceanic and Atmospheric Administration and tasked with providing change data for all U.S. coastal areas.
The image on the left is a LANDSAT composite from 2000 showing a portion of Kitsap County in the center of the Puget Sound region. The image on the right shows changes occurring between 2001 and 2006 as captured by two different methods.
Zooming in to 1:100,000 scale, the differences between different types of changes are more apparent.