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ARS Home » Pacific West Area » Boise, Idaho » Northwest Watershed Research Center » Research » Publications at this Location » Publication #307930

Title: Assessment of fire impacts on hydrology and erosion using field experiments and the Rangeland Hydrology and Erosion Model

item Williams, Christopher - Jason
item Pierson Jr, Frederick
item ROBICHAUD, PETER - Us Forest Service (FS)
item BOLL, JAN - University Of Idaho
item AL-HAMDAN, OSAMA - University Of Idaho

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 8/22/2014
Publication Date: 4/19/2015
Citation: Williams, C.J., Pierson, F.B., Robichaud, P.R., Boll, J. 2015. Assessment of fire impacts on hydrology and erosion using field experiments and the Rangeland Hydrology and Erosion Model [abstract]. Accepted by the SEDHYD 2015 joint 10th Federal Interagency Sedimentation Conference and 5th Federal Interagency Hydrology Modeling Conference, April 19-23, 2015, Reno, NV.

Interpretive Summary:

Technical Abstract: High-intensity and large-volume rainfall events on burned and fragmented landscapes commonly generate substantial runoff and erosion and pose risks to natural resources, property, and human life. Hillslope and watershed responses to rainfall input are a function of process connectivity. Knowledge regarding the influence of cross-scale process connectivity on burned and degraded lands remains limited due to the individual plot-scale nature of most research. This study quantified surface susceptibility and runoff and erosion across point- to hillslope-scales at unburned and burned pinyon and juniper woodlands using a suite of high-intensity rainfall simulation, overland flow experiments, and hydrologic modeling. At both sites, runoff and sediment generated in bare patches at the fine (0.5 m2) spatial scale were sources for overland flow and sediment discharge at the patch scale (13 m2). High levels of runoff (31-47 mm) and erosion (154-1893 g m-2) were measured at the patch scale associated with accumulation of fine-scale runoff and sediment sources and formation of high velocity (0.10-0.26 m s-1) concentrated flow through contiguous bare areas (64-85% bare ground). Burning increased the continuity of runoff sources and sediment availability through removal of vegetation and ground cover. For unburned and burned conditions, cumulative runoff was generally consistent across plot-scales while erosion increased with increasing plot-area up to the patch scale. The cross-scale increase in erosion was attributed to the enhanced sediment detachment and transport in well-defined concentrated flow paths at the patch scale. At the hillslope scale, predicted runoff and erosion rates reflected the measured patch-scale runoff and erosion trends and the connectivity of hydrologic and erosion processes and sediment availability. For similar rainfall (~75 mm) across unburned conditions, predicted hillslope runoff (19-35 mm) was slightly less than or equal to measured patch-scale runoff (27-37 mm), and predicted erosion (100-413 g m-2) was greater than or equal to patch-scale measured erosion (124-311 g m-2). For burned conditions, predicted hillslope runoff (36-41 mm) was greater than or equal to patch-scale runoff (28-34 mm), and predicted hillslope erosion (314-516 g m-2) was either constant or decreased relative to patch-scale measures (274-884 g m-2). The decline in simulated hillslope-scale erosion relative to measured patch-scale erosion for burned conditions was attributed to more limited sediment availability at the hillslope scale. Predicted annual runoff and sediment yield at the hillslope scale were 2-6-fold and 2-8-fold greater for burned (11-15 mm and 91-171 g m-2) versus unburned (2-7 mm and 11-72 g m-2) conditions. On average, predicted event runoff and sediment yield were 2-3-fold and 2-5-fold greater for burned versus unburned conditions. The cross-scale experiments and simulations in this study clearly demonstrate that the magnitude of hillslope response is governed by the degree of connectivity in surface susceptibility, connectivity of runoff and erosion processes, sediment availability, and rate or volume of rainfall input.