| This research investigates the impact of wildfires on watershed flow regimes throughout the western United States, specifically focusing on evaluation of fire events within specified subregions and determination of the impact of climate and geophysical variables in post-fire flow response. Fire events were collected through federal and state-level databases and streamflow data were collected from U.S. Geological Survey stream gages. 82 watersheds were identified with at least 10 years of continuous pre-fire daily streamflow records and 5 years of continuous post-fire daily flow records. For each watershed, percent changes in annual runoff ratio (RO), low-flows (LF), high-flows (HF), peak flows (PF), number of zero flow days (Nzeros), baseflow index (BFI), and Richards-Baker flashiness index (RB) were calculated from pre- to post-fire. Numerous independent variables were identified for each watershed and fire event, including topographic, vegetation, climate, burn severity, and soils data. The national watersheds were divided into five regions through k-means clustering and LASSO linear regression models were calculated for each region. Regression models were also produced for watersheds grouped by total area burned. The coefficient of determination (R2) was used to determine the accuracy of the resulting models. Model accuracy was highly variable, both by group and by response variable. Resulting coefficient values demonstrate that, of the watershed parameters applied in this study as explanatory variables, watershed area and burn severity parameters explain the greatest amount of the post-fire flow change variability. Burn area slope and soil erodibility factor (Kfact) also contribute significantly to post-fire response. Watershed area and Kfact are generally negatively correlated with response variables, while slope and percent moderate burn severity (BS_M) are positively correlated. |
