Abstract
In many fire-prone watersheds, wildfire threatens surface drinking water sources with eroded contaminants. We evaluated the potential to mitigate the risk of degraded water quality by limiting fire sizes and contaminant loads with a containment network of manager-developed Potential fire Operational Delineations (PODs) using wildfire risk transmission methods to partition the effects of stochastically simulated wildfires to within and out of POD burning. We assessed water impacts with two metrics—total sediment load and frequency of exceeding turbidity limits for treatment—using a linked fire-erosion-sediment transport model. We found that improved fire containment could reduce wildfire risk to the water source by 13.0 to 55.3% depending on impact measure and post-fire rainfall. Containment based on PODs had greater potential in our study system to reduce total sediment load than it did to avoid degraded water quality. After containment, most turbidity exceedances originated from less than 20% of the PODs, suggesting strategic investments to further compartmentalize these areas could improve the effectiveness of the containment network. Similarly, risk transmission varied across the POD boundaries, indicating that efforts to increase containment probability with fuels reduction would have a disproportionate effect if prioritized along high transmission boundaries.
Highlights
Improved wildfire containment is an attractive strategy to mitigate the risk of degrading water quality beyond limits for treatment because of the potential to limit fire sizes and impacts to tolerable levels without the need to completely exclude fire from the landscape
The avoided area burned and modeled are similar to the impact metrics used to value the benefit of containment in previous studies, sediment load measures we modeled are similar to the impact metrics used to value the benefit of but our evaluation of water quality degradation provided a unique opportunity to evaluate whether containment in previous studies, but our evaluation of water quality degradation provided a unique the size and spatial arrangement of the Potential fire Operational Delineations (PODs) are appropriate to mitigate a scale-dependent risk
Approximately 75% of fires intersected potential control features and, if these fires were contained within their POD of origin, watershed area burned would be reduced by 58.7%, total sediment load to the diversion would be reduced between
Summary
Improved wildfire containment is an attractive strategy to mitigate the risk of degrading water quality beyond limits for treatment because of the potential to limit fire sizes and impacts to tolerable levels without the need to completely exclude fire from the landscape. Beyond the inherent value of engaging managers in the process to identify and critique potential control features, the resulting POD areas become relevant spatial units for pre-fire analysis of endogenous and transmitted wildfire risk to inform response strategies that are appropriate for the predicted direction and magnitude of fire effects to water supplies and other natural resources and human assets [2]. Previous efforts to account for fire effects on watersheds and water supplies account for some of these factors [18,19], but the use of relative fire effects measures makes it difficult to evaluate whether a given fire will degrade water quality This shortcoming has been addressed in recent years with increasing use of spatially explicit erosion and sediment transport models to make quantitative predictions of sediment yield from modeled wildfires (e.g., [20,21,22,23,24]). Sediment yield models have been widely used to examine the risk mitigation effectiveness of area-wide fuel treatments meant to reduce burn severity [23,24,25,26]
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