Location: Water Management and Systems ResearchTitle: Simulating hydrologic effects of wildfire on a small sub-alpine watershed in New Mexico, U.S.
|MOESER, CHARLES - Us Geological Survey (USGS)|
Submitted to: International Journal of Wildland Fire
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/12/2020
Publication Date: 2/10/2021
Citation: Moeser, C.D., Douglas-Mankin, K.R. 2021. Simulating hydrologic effects of wildfire on a small sub-alpine watershed in New Mexico, U.S. International Journal of Wildland Fire. 64(1):137-150. https://doi.org/10.13031/trans.13938.
Interpretive Summary: Wildfire causes major changes to the hydrology of a landscape. Hydrologic simulation models can help scientists and land managers understand the complex, site-specific effects of fire on plant canopies, soils, and surfaces, but rarely are data available from both before and after a fire to calibrate these models. This study is one of the first to calibrate a watershed model for both prefire and postfire conditions in a burned watershed. We used streamflow data to calibrate the Precipitation-Runoff Modeling System (PRMS) before and after the 2012 Little Bear Fire in New Mexico, which burned 44,200 acres, including all of the 3,400-acre mixed-conifer sub-alpine forest North Fork Eagle Creek watershed. Before the fire, streamflow was driven by more-steady shallow subsurface flow (baseflow). After the fire, streamflow was dominated by more-flashy surface runoff. Although the prefire watershed only generated surface runoff for the wettest soil conditions, the postfire watershed generated runoff across both dry and wet soil conditions. This suggests that after a fire, flooding could occur more frequently, even on days with drier soils that would not have been a concern before the fire.
Technical Abstract: Streamflow records available before and after wildfire in a small, mixed-conifer, sub-alpine watershed in the southwestern U.S. provided a unique opportunity to calibrate a watershed model (PRMS) for prefire and postfire conditions. Hydrologic variables within the calibrated models exhibited substantial annual variation. Postfire surface runoff was greater than prefire for the 29-year simulation period. The relationship between precipitation and streamflow changed dramatically after wildfire, largely as a function of antecedent soil moisture (ASM). For higher ASM, prefire and postfire streamflow was similarly variable. But for moderate and lower ASM, postfire streamflow often exhibited a linear increase with precipitation whereas prefire streamflow showed little to no response. Over low to moderate ASM, postfire streamflow efficiency also increased with soil moisture, demonstrating a large sensitivity to ASM not present in prefire conditions. Overall, streamflow increased and shifted from baseflow-dominated to surface-runoff-dominated after wildfire, and postfire conditions allowed runoff to occur across all ASM. This result indicates substantial increases in runoff efficiency (20% or more of precipitation volume) can occur across a range of ASM postfire, which may have severe consequences for flooding. This also suggests monitoring soil moisture would enhance raingage networks providing early flood warning.