Synthesis of sediment yields after wildland fire in different rainfall regimes in the western United States

Abstract

Measurements of post-fire sediment erosion, transport, and deposition collected within 2 years of a wildfire were compiled from the published literature (1927–2007) for sites across the western United States. Annual post-fire sediment yields were computed and grouped into four measurement methods (hillslope point and plot measurements, channel measurements of suspended-sediment and sediment erosion or deposition volumes). Post-fire sediment yields for each method were then grouped into eight different rainfall regimes. Mean sediment yield from channels (240 t ha–1) was significantly greater than from hillslopes (82 t ha–1). This indicated that on the time scale of wildfire (10–100 years) channels were the primary sources of available sediment. A lack of correlation of sediment yield with topographic slope and soil erodibility further suggested that sediment availability may be more important than slope or soil erodibility in predicting post-fire sediment yields. The maximum post-fire sediment yields were comparable to long-term sediment yields from major rivers of the world. Based on 80 years of data from the literature, wildfires have been an important geomorphic agent of landscape change when linked with sufficient rainfall. These effects are limited in spatial scale to the immediate burned area and to downstream channel corridors.

Toward a formal definition of water scarcity in natural‐human systems

“…Drought stress increases the forest's vulnerability to changes in the frequency, intensity, and spatial extent of disturbance from fire, insects, and disease. When water availability drops below some threshold level necessary to sustain healthy trees [Coops and Waring, 2011], the measure of water scarcity at this water deficit threshold (the marginal cost to society of slipping below the threshold) must include the compounding and potentially irreversible chain of events of forest loss due to fire, insects, and disease, that in turn, can be followed by other impacts such as landslides, debris flows, floods, or dramatic increases in stream turbidity and sediment transport [Westerling et al, 2006;Moody and Martin, 2009;Allen et al, 2010]. This example represents a case where the value of maintaining forest moisture above a particular biophysical threshold has potentially enormous value to society and thus represents a point below which water scarcity becomes extreme.…”

Reduction of nutrient losses with eroded sediments by post-fire soil stabilisation techniques

“…Post-fire erosion rates are highly variable (reported values range from 1 to 240 Mg ha" ; Robichaud et al 2006;Moody and Martin 2009) and are strongly related to the percentage of bare soil (Vega et al 2005); they generally decrease by an order of magnitude with each year of recovery (Robichaud et al 2000(Robichaud et al , 2006, leading to the greatest nutrient losses in the first 4-12 months after fire (Gimeno-Garcia et al 2000;de Koff et al 2006;Robichaud et al 2006). Therefore, post-fire soil stabilisation techniques (e.g.…”

Post-fire treatment effectiveness for hillslope stabilization

“…Erosion at the plot scale usually is limited to interrill and rill components, while erosion measured at the scale of swales and small catchments includes those two processes as well as channelized flow. Channelized flow-including deposition within the study area rather than at the outlet where the sediment yield is measured-becomes a more dominant process as the contributing area increases (Moody and Martin 2009b;Pietraszek 2006).…”

“…In a study of post-wildfire sediment yields in the western United States, Moody and Martin (2009b) determined that soil availability is a dominant factor in predicting post-fire sediment yields. Soil availability is dependent on soil erodibility, ground cover, and the amount of stored sediment on hillslopes and in channels.…”

“…Observable post-fire ground parameters (for example, amount and condition of ground cover, ash color and depth, soil structure, presence of fine roots, and Table 1. Rainfall regimes, seasonal characteristics, intensity classification, and upper and lower 2-yr, 30-min rainfall intensity limits for each classification as delineated and described by Moody and Martin (2009b) for the western United States (see fig. 4).…”