Alicia M. Kinoshita, San Diego State University
Brenton A. Wilder, San Diego State University
Fire frequency and severity in southern California and across the western United States is increasing, posing a concern to the safety and well-being of communities and ecosystems. Increased aridity coupled with water stressed vegetation from prolonged droughts are leading to a higher propensity for larger, more intense fires that impact ecohydrological processes. Accurate characterization of these processes will improve rapid response efforts and long-term resource management to promote resilient communities along the wildland-urban interface. This work investigates prediction tools for small watersheds, where post-fire effects occur at a disproportional rate, by presenting methods to improve rapid predictions of post-fire streamflow and long-term monitoring of ecohydrological recovery.
Key Findings
A commonly used method called Rowe et al. (1949) look-up tables was shown to have poor performance (R2<0.3) for both pre- and post-fire when compared to USGS streamflow data for 33 small watersheds in southern California during the period 1920 to 2019
Relevant topographic and climatic variables were incorporated into an analytical model which showed that the most impactful variables that contributed to improved model accuracy were time elapsed from end of fire to storm, total area of watershed burned, watershed drainage area, watershed perimeter, and peak 1-hour rainfall intensity. These signals are seen clearly when examining box plots of runoff with respect to the variables (Figure 1).
We hypothesize that Rowe et al. (1949) look up table method do not account for these influential parameters, specifically rainfall intensity which is generally regarded today as one of the most influential parameters in moving mass and debris after a fire, as well as watershed size, where we confirmed findings from other studies such as Neary et al. (2005) and Keller et al. (1997) which highlight post-fire peak flow magnitudes are unproportionately higher for smaller watersheds
This work is partially supported by the Joint Fire Science Program Graduate Research Innovation Award
Observed peak streamflow per unit area with respect to peak hourly rainfall intensities (a), watershed size (b), and days after fire containment (c)
