Exurban Change Detection in Fire-Prone Areas with Nighttime Satellite Imagery

Fire-prone landscapes are increasingly being settled. Monitoring this development is an emerging need, and a low-cost method would benefit emergency managers. Existing changedetection methods can be expensive and time consuming when applied to low-density urban change in large, vegetated areas. Nighttime satellite imagery is explored as means for addressing this problem, and a case study is presented for Colorado. The results indicate that from 1992–2000, Grand County had the greatest absolute increase in ambient sprawl into fire-prone areas (215 km), but Teller County had the greatest percentage increase (7.3 percent). In 2000, La Plata County had the most ambient development in fire-prone areas (909 km), but Jefferson County had the greatest percentage (42 percent). The paper concludes with a discussion of the prospects and problems of the approach. Introduction Fire-prone landscapes are increasingly being settled (GAO, 1999). Densely vegetated areas with panoramic views and proximal outdoor recreation offer an appealing alternative to urban and suburban living (McGranahan, 1999). Furthermore, advances in telecommunication technology are allowing people to live further from cities. This is impacting development rates in many fire-prone, exurban areas. In most locales, this growth is gradual, while in others it is very rapid with near year-round construction. New residents typically have little to no knowledge of fire recurrence intervals and are generally not accepting of the notion that they are building a home between large fires. Thus, emergency managers must plan for the next large event in the face of a steadily growing at-risk population and housing stock. Monitoring urban change in hazardous areas is a critical input into the emergency management process (Radke, et al., 2000). It is particularly important in risk assessment, loss estimation, mitigation, and evacuation planning (Cova and Church, 1997; Cova, 1999; Cova and Johnson, 2002). Urban change-detection is an inherently geographic enterprise because development rates vary spatially. Unfortunately, changing settlement patterns are not well-monitored in most fireprone areas. Simple questions like the amount of development in a defined area for a given time period are costly and inconvenient to answer at scales larger than a city or county. This is Exurban Change Detection in Fire-Prone Areas with Nighttime Satellite Imagery Thomas J. Cova, Paul C. Sutton, and David M. Theobald important because fire protection and emergency services may be declining relative to population growth in some fireprone areas, as local and state governments cannot keep pace with the change. For this reason, a simple, low-cost means for monitoring development in fire-prone regions could help agencies allocate emergency resources and coordinate adjacent jurisdictions. A number of remote-sensing techniques exist for urban change detection that have been applied to core urban areas and the urban-rural fringe (Jensen and Toll, 1982; Gong and Howarth, 1990; Jensen, 1996; Ridd and Liu, 1998; Ward, et al., 2000; Ryzner and Wagner, 2001; Zhang, 2001; Zhang, et al., 2002; Civco, et al., 2002; Herold, et al., 2002). Large vegetated exurban areas complicate the urban change-detection process because it can be expensive and time-consuming to translate spectral signals from roads, rooftops and patios into housing densities, population counts, and ultimately human vulnerability. One approach to this problem is to define the change in terms of emitted light rather than subtle changes in land-cover type. Nighttime satellite imagery provided by the Defense Meteorological Satellite Program’s Operational Linescan System (DMSP-OLS) has been used to map and monitor fires, estimate population densities, delineate urban land cover, identify land-use conflicts, map greenhouse gas emissions, and characterize housing distributions in wildlands (Elvidge, et al., 1997; Imhoff, et al., 1997a; Imhoff, et al., 1997b; Doll, et al., 2000; Sutton, et al., 2001; Elvidge, et al., 2001a; Lo, 2002; Schimdt, et al., 2002). It also holds potential to be a low-cost means for detecting urban change in fire-prone areas. In this paper, we present a method and case study in using nighttime satellite imagery for urban-change detection in fire-prone areas. The paper begins with background on fire hazard mapping and urban change detection. Data and methodological issues are discussed, and the results of a study are presented for Colorado. We conclude with a discussion of the results and areas for further research.