A Regional-Scale Estimate of Annual Streamflow Response to Fire in California

Abstract:

Understanding the effect of fire on annual streamflow is important for management of water supply, water quality and the environment. Unfortunately, annual streamflow response to fire is highly variable, making predictions of post-fire streamflow change for a given watershed or for a given period challenging. For this study, the regional effect of fire on annual streamflow was calculated for parts of central and southern California. Synthesizing data from 12 paired-watershed studies, a mixed modeling statistical approach was used to account for the hierarchical structure of the combined dataset. Hierarchical structures occur when data are organized at more than one level, such as when annual streamflow data is grouped by watershed. Post-fire effects were best represented in the model by a fire variable that accounted for both differences in watershed area burnt and post-fire vegetation recovery. At a regional scale, post-fire annual streamflow increased 145% (86% to 310%) during the first post-fire year for watersheds that were 100% burnt. This response was sensitive to annual wetness conditions, with the greatest increase in post-fire annual streamflow observed during moderately wet years. These results provide a baseline estimate of post-fire streamflow response for both gauged and ungauged California watersheds.