Mitigating Future Fire and Flood Hazards in Arid Urban Regions: Initial Analysis of Brush Fire Scars With the new ASTER Instrument

Michael Ramsey 1 and Ramon Arrowsmith 2

1 Department of Geology and Planetary Science, University of Pittsburgh, Pittsburgh, PA 15260, United States;

2 Department of Geological Sciences, Arizona State University, Box 871404, Tempe, AZ 85287, United States;

The summer of 2000 has been the worst fire season in the past 50 years for the western United States. As of early September, over 6.5 million acres have burned and the cost of fighting the fires is expected to top 1 billion US dollars. Much of the damage has been concentrated in the remote, high elevation pine forests of the western states. However, the large Los Alamos, NM fire in May and the numerous smaller fires in the drought-stricken southwestern states, attest to hazards of desert brush fires. Further, these burned regions can facilitate flash flooding and soil erosion during the next several monsoon seasons. The dangers associated with these outbreaks are critical to understand in light of the rapid increase in urbanization and population in cities throughout the southwestern United States and in similar regions around the world. In the next 25 years, for example, estimates place nearly two-thirds of the global population (over 5 billion) in cities. And a vast majority of the fastest growing urban centers are located in semi-arid environments, which are vulnerable to these natural hazards and ecological degradation.

Remote sensing of the urban and surrounding environments of several southwestern US cities reveals the presence of old brush fire scars dating back 30-50 years. Depending on the wavelength region examined, the age and surface properties of the scars can be determined. A pilot study is now underway examining data from the Landsat ETM, SIR-C radar, and airborne thermal infrared scanners of existing brush fire scars surrounding Phoenix, AZ. This stage investigates the linkage between the fire scar age, vegetation type and recovery, soil type and local topography. That information can then be used to model surface response to heavy rainfall and assess the potential for future flood and fire hazards. Once burned, the removal of vegetation may facilitate rapid flood run-off and erosion during intense periods of precipitation. Factors that influence the formation and location of these fire scars are the proximity of human activity, short and long term climate variations and vegetation type and abundance. A multi-frequency, multi-temporal analysis of the areas surrounding Los Angeles, CA, and Las Vegas, NV will commence with new ASTER data.

ASTER data has either been acquired or is scheduled to be gathered over the target locales by the end of 2000. These data will be valuable because of the high spatial resolution (15-90 m/pixel), the multi-spectral coverage (visible - thermal wavelengths), and the ability to generate along-track moderate resolution digital elevation models (DEMs) critical for urban topographic analysis. The ASTER science team also has a dedicated urban monitoring program in place that assures data will be captured twice yearly over 100 of the largest cities. There is an emphasis on those urban areas currently experiencing the fastest growth rates and environmental hazards. The effort will focus on cities in semi-arid environments and will demand dedicated data processing and dissemination to local governments. The primary goal of this effort is to ensure these data are acquired, processed and made available to scientists and local officials working in these cities.

Submitted to: American Geophysical Union Fall Meeting, (H20 Hydrological Applications of Data From NASA's Terra Satellite
), San Francisco, CA, 2000.