Post-fire temporal trends in soil-physical and -hydraulic properties and simulated runoff generation: Insights from different burn severities in the 2013 Black Forest Fire, CO, USA

Burn severity influences on post-fire recovery of soil-hydraulic properties controlling runoff generation are poorly understood despite the importance for parameterizing infiltration models. We measured soil-hydraulic properties of field-saturated hydraulic conductivity (K-fs), sorptivity (S), and wetting front potential (psi(f)) for four years after the 2013 Black Forest Fire, Colorado, USA, at six sites across a gradient of initial remotely sensed burn severity using the change in the normalized burn ratio (dNBR). These measurements were correlated with soil-physical property measurements of bulk density (rho(b)), loss on ignition (LOI, a measure of soil organic matter), and ground cover composition to provide insight into causal factors for temporal changes in K-fs, S, and psi(f). Modeled infiltration using the Smith-Parlange approach parameterized with measured K-fs, S, and psi(f)-further discerned the role of precipitation intensity on runoff generation. Temporal trends of soil-physical properties and ground cover showed influences from initial bum severity. Trends in soil-hydraulic properties, surprisingly, were not strongly influenced by initial bum severity despite inferred effects of rho b , LOi, and ground cover on trends in K(fs )and S. Calculations of dNBR at the time of sampling showed strong correlations with K-fs and S, demonstrating a new approach for estimating long-unburned K-fs and S values, infiltration model parameters after fire, and assessing the time of return to pre-fire values. Simulated infiltration- excess runoff, in contrast, did depend on initial bum severity. Time series of the ratio S-2/Kfs approximate to psi(f) tended to converge between 1 and 10 mm four years after wildfire, potentially (i) defining a long-unburned forest domain of S-2/K-fs and (Pr from 1 to 10 mm with relatively high K-fs values, and (ii) providing a new post-lire soil-hydraulic property recovery metric (i.e. S-2/K-fs approximate to psi(f) in the range of Ito 10 mm) for sites in the Rocky Mountains of the USA. Published by Elsevier B.V.