Measurement Method Has a Larger Impact Than Spatial Scale For Plot-Scale Field-Saturated Hydraulic Conductivity (Kfs) After Wildfire and Prescribed Fire in Forests

Wildfires raise risks of floods, debris flows, major geomorphologic and sedimentologic change, and water quality and quantity shifts. A principal control on the magnitude of these changes is field-saturated hydraulic conductivity (K_fs), which dictates surface runoff generation and is a key input into numerical models. This work synthesizes 73 K_fs datasets from the literature in the first year following fire at the plot scale (≤ 10 m²). A meta-analysis using a random effects analysis showed significant differences between burned and unburned K_fs. The reductions in K_fs after fire, expressed by the ratio of K_{fs Burned}/K_{fs Unburned}, were 0.46 (95% confidence interval of 0.31-0.70) combining wildfire and prescribed fire and 0.3 (95% confidence interval of 0.13-0.71) for wildfire. No significant differences for K_fs were observed between wildfire and prescribed fire or moderate and high fire severity. Both K_fs magnitude and variability depended more on measurement method than measurement support area at the plot scale, with methods applying head ≥0.5 cm producing larger estimates of K_fs. It is recommended that post-fire efforts to characterize K_fs for modeling or process-based interpretations use methods that reflect the dominant infiltration processes: tension infiltrometers and simulated rainfall methods when soil matrix flow dominates and ponded head methods when macropore flow is critical. Published 2019. This article is a U.S. Government work and is in the public domain in the USA.