Hydrologic recovery after wildfire: A framework of approaches, metrics, criteria, trajectories, and timescales

Abstract

Deviations in hydrologic processes due to wildfire can alter streamflows across the hydrograph, spanning peak flows to low flows. Fire-enhanced changes in hydrologic processes, including infiltration, interception, and evapotranspiration, and the resulting streamflow responses can affect water supplies, through effects on the quantity, quality, and timing of water availability. Post-fire shifts in hydrologic processes can also alter the timing and magnitude of floods and debris flows. The duration of hydrologic deviations from a pre-fire condition or function, sometimes termed hydrologic recovery, is a critical concern for land, water, and emergency managers. We reviewed and summarized terminology and approaches for defining and assessing hydrologic recovery after wildfire, focusing on statistical and functional definitions. We critically examined advantages and drawbacks of current recovery assessment methods, outline challenges to determining recovery, and call attention to selected opportunities for advancement of post-fire hydrologic recovery assessment. Selected challenges included hydroclimatic variability, post-fire land management, and spatial and temporal variability. The most promising opportunities for advancing assessment of hydrologic recovery include: (1) combining statistical and functional recovery approaches, (2) using a greater diversity of post-fire observations complemented with hydrologic modeling, and (3) defining optimal assemblages of recovery metrics and criteria for common hydrologic concerns and regions.

How Long Do Runoff‐Generated Debris‐Flow Hazards Persist After Wildfire?

“…Recovery processes are complexly inter‐related (Ebel et al., 2022). For example, vegetation recovery tends to influence soil hydrology in several ways, including: (a) increasing canopy development, leading to increased rainfall interception (Hoch et al., 2021) and reduced raindrop impacts (Cerdà, 1998); (b) developing roots, leading to increased macropore flow (Hubbert & Oriol, 2005); and (c) promoting increased hydrologic roughness (Liu et al., 2021), which contributes to lower runoff velocity (Rengers et al., 2016) and reduced erosion and overland flow (Cerdà & Doerr, 2005).…”

“…The likelihood of runoff‐generated debris flows following fire is thought to scale inversely with vegetation and soil‐hydraulic recovery of the burned area (Thomas et al., 2021). Recovery parameters return to prefire conditions over various timescales (Ebel et al., 2022; Santi & Rengers, 2022). For example, sediment yields from burned catchments can return to background rates within 3–4 years, whereas stream discharge or tree regrowth may take decades (Santi & Rengers, 2022).…”

“…Commonly used indices include Normalized Differenced Vegetation Index (Cuevas‐Gonzàles et al., 2009; Kurbanov et al., 2022; Walker & Soulard, 2019), Enhanced Vegetation Index (Jin et al., 2012) or National Aeronautical and Space Administration Moderate Resolution Imaging Spectroradiometer (MODIS) leaf area index (LAI) (Ebel, 2020; Myneni et al., 2002). Recovery rates and trajectories are highly variable (Ebel et al., 2022), depending on factors including vegetation type, burn severity, aspect, and climatic conditions in the years after fire (Kinoshita & Hogue, 2011; Vanderhoof et al., 2018; Viana‐Soto et al., 2020).…”

Introduction to the special issue on fire impacts on hydrological processes

“…This special issue presents research on the impact of fire on the Earth System. Most of the special issue (Caltabellotta et al, 2022;Ebel et al, 2022;Godoy et al, 2022;Li et al, 2022;Lucas-Borja et al, 2022;Sanin et al, 2022) is devoted to the impact of wildfire or prescribed fire on hydrological processes. The remaining articles are devoted to the heat-induced changes in soil properties (Fajković et al, 2022;Hološ et al, 2022) and the impact of biochar (produced by pyrolysis/heating biomass in the total or partial absence of oxygen) amendment on soil organic molecular markers (Atanassova et al, 2022).…”

“…The results confirmed that wildfire can induce destruction of an SWR layer that naturally occurs at the surface of forest soils, and can create a shallow hydrophobic layer that may increase overland flow and erosion risk. Ebel et al (2022) reviewed and summarized the existing terminology and approaches for defining and assessing hydrologic recovery after wildfires. The work also critically examined the advantages and drawbacks of current recovery assessment methods, outlined challenges to determining recovery, and highlighted opportunities for advancing post-fire hydrologic recovery assessment.…”