Forest management and climate change effects on Wildfire in a Western Washington Watershed

Abstract:

Climate change has altered wildfire regimes in the Western United States in the past few decades. Fire season is becoming longer and burned area in the Western Cascades is projected to increase 200-400% above contemporary levels by the end of the century. Such changes in fire regimes can have cascading consequences for human and natural systems, including degradation of downstream water quality. Understanding the potential consequences of an altered fire regime will be necessary for managing forested watersheds to protect highly valued resources, especially high-quality drinking water, from the threat of wildfire. In this study, we apply the ecohydrologic model RHESSys, coupled with the fire spread model WMFire and a fire effects model, to investigate how climate change and the forest management technique of stand thinning can affect wildfire regimes in the Cedar River Watershed in western Washington, which provides drinking water for people in the greater Seattle area. We ran multiple simulations with different forest management and climate change scenarios to assess future changes in fire activity to assess the efficacy of management practices in reducing fire severity. Both forest management and climate change alter the fire regime in the Cedar River watershed. With climate change, this basin becomes progressively more fuel-limited. Climate scenarios that featured increased warm-season aridification caused forest stand thinning to become an effective method for managing wildfire in specific areas of the basin. Thus, thinning may be a viable management tool in western Washington under certain climate conditions and in targeted locations but more research is needed to explore this.