Post‐fire runoff and erosion from simulated rainfall on small plots, Colorado Front Range

Abstract

Abstract:Wildfires in the Colorado Front Range can trigger dramatic increases in runoff and erosion. A better understanding of the causes of these increases is needed to predict the effects of future wildfires, estimate runoff and erosion risks from prescribed fires, and design effective post-fire rehabilitation treatments. The objective of this project was to determine whether runoff and sediment yields were significantly related to the site variables of burn severity, percent cover, soil water repellency, soil moisture, time since burning, and slope. To eliminate the variability due to natural rainfall events, we applied an artificial storm of approximately 80 mm h 1 on 26 1 m 2 plots in the summer and fall of 2000. The plots were distributed among a June 2000 wildfire, a November 1999 prescribed fire, and a July 1994 wildfire.For 23 of the 26 plots the ratio of runoff to rainfall exceeded 50%. Nearly all sites exhibited strong natural or fire-induced water repellency, so the runoff ratios were only 15-30% larger for the high-severity plots in the two more recent fires than for the unburned or low-severity plots. The two high-severity plots in the 1994 wildfire had very low runoff ratios, and this probably was due to the high soil moisture conditions at the time of the simulated rainfall and the resulting reduction in the natural water repellency. Sediment yields from the high-severity sites in the two more recent fires were 10-26 times greater than the unburned and low-severity plots. The plots burned at high severity in 1994 yielded only slightly more sediment than the unburned plots. Percent ground cover explained 81% of the variability in sediment yields, and the sediment yields from the plots in the 1994 wildfire are consistent with the observed recovery in percent ground cover.

Climate change, forests, fire, water, and fish: Building resilient landscapes, streams, and managers

“…Many have studied the formation of water repellency after fire (see, for example, Shakesby and Doerr 2006 for review). Surface sealing has been suggested as another mechanism for increased runoff after fire (Rowe 1948;Benavides-Solorio and MacDonald 2001;.…”

“…Hillslope and steep channel processes, such as surface erosion and mass wasting, receive the greatest attention (e.g., Benavides-Solorio and MacDonald 2001;Cannon and others 2001;Miller and others 2003;Pierce and others 2004;Robichaud and others 2009b), while the disposition of channels with aquatic habitat is comparatively poorly discussed, despite more direct connections to aquatic ecology (Benda and others 2003a;Lisle 2008). Most post-fire erosion studies focus on relatively short-term and small-scale processes, because they are acute and intense, with relevance to human life and property as well as aquatic ecology.…”

The effects of bushfires on hydrological processes using a paired-catchment analysis

“…The classic method of exploring fire effects on hydrological processes is to perform laboratory experiments (Aston and Gill, 1976) and field experiments on runoff (Dobrowoski et al, 1992;Robichaud and Waldrop, 1994;Cerda et al, 1995;Keller et al, 1997;Nelson et al, 1999;Morales et al, 2000;Murakami et al, 2000;Robichaud, 2000;Benavides-Solorio and MacDonald, 2001;Veenhuid, 2001) and fire-induced soil water repellency (DeBano, 2000;Scott, 2000;Letey, 2001) with rainfall simulators. However, pairedcatchment analysis becomes more appropriate when the research scale is extended from small plots to catchment scale.…”

Index for Characterizing Post-Fire Soil Environments in Temperate Coniferous Forests

“…The next threshold (categories 2.0 and 3.0) is for areas that have between 0% and 85% surface organic material. Literature on post-fire erosion and hydrophobic soils identifies thresholds across a range of surface organic material percentages (30%, [50]; 40%, [51]; 45%, [54]; 50%, [52]) from which we selected the median (40%) to divide the categories where 2.0 is 40-85% and 3.0 is less than 40%. We further categorized them by mineral soil char color using a decimal.…”

“…Common soil physical properties influenced by fire include water repellency, structure stability, texture, color, post-fire surface temperatures, and abundance of surface organic material [48] (Table 3). Typically erosion only occurs when organic cover is less than 40-50% after a fire [50][51][52]54]. Therefore, if slopes are steep and coarse textured soils are present, post-fire soil erosion is likely to occur in areas with PFI categories of 3.0 to 4.0.…”