Water Resources Professional Project Reports

Document Type

Report

Publication Date

Fall 2019

Abstract

Beginning in the mid-1980s, the number of fires and acres burned by wildfire in the United States has grown at an explosive rate. Several factors, anthropogenic and natural, have converged to create a new era of high frequency, high intensity fires, which is predicted to continue until at least mid-century. Investigations into wildfire impacts have largely focused on post-fire impacts on terrestrial systems, while effects on aquatic ecosystems have been underrepresented. The growing threat of fire to streams has accelerated the need for germane information regarding the spatial extent of fire impacts on watersheds and post-fire impacts to aquatic systems. To understand the consequence of wildfire on streams, the first task is to understand the geography and scale of streams being burnt by fire. This research describes changes in geographic location of wildfire within ecoregions of the western United States, quantifies stream length directly burned, and describes trends in burn severity along streams by ecoregion. Public geospatial datasets were utilized to produce a dataset that includes streams within wildfire burn boundaries, year burned, number of kilometers of burned stream reaches, and burn severity for each stream reach. This research demonstrates that from 1984 to 2014, study area experienced wildfires that burned 307,955 stream kilometers. Additionally, eight of nine EPA Level 2 Ecoregions exhibited an increase in stream length burned over the study period. Few ecoregions demonstrated temporal trends in burn severity; for example, the Mediterranean California ecoregion experienced a significant increase in the proportion of stream length burned by medium severity fire. Furthermore, burn severity was typically reduced in stream reaches that burned more than once.

Keywords

water, wildfire, terrestrial systems, ecosystems, watersheds, aquatic systems

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