Understanding the Role of Burn Scars in Post-Wildfire Flooding

In the aftermath of wildfires, Oregon communities are increasingly encountering a secondary hazard: elevated flood and debris flow risks associated with burn scars. These post-fire conditions can significantly alter how landscapes respond to rainfall, particularly in areas with steep terrain or limited vegetation recovery.

What Are Burn Scars?

A burn scar refers to the area of land affected by wildfire, where vegetation has been removed and soil properties may have changed. In many cases, the heat from a wildfire can create a hydrophobic layer in the soil, reducing its ability to absorb water. This can lead to increased surface runoff during rain events.

Without vegetation to slow and absorb rainfall, water can move more quickly across the landscape, potentially leading to flash flooding or debris flows-fast-moving mixtures of water, soil, ash, and rock.

Oregon-Specific Examples

Several regions in Oregon have experienced post-wildfire flooding or debris flow concerns in recent years:

• Santiam Canyon: Following the Beachie Creek and Lionshead fires, the area has remained vulnerable to post-wildfire flooding. In early 2021, debris flows occurred near Mill City and Gates, and the risk persists during heavy rain events.
• McKenzie River Corridor: After the 2020 Holiday Farm Fire, the watershed has experienced increased runoff and sedimentation. Monitoring continues during storm events due to altered hydrology.
• Harney County: Flooding along the Silvies River impacted the city of Burns and surrounding areas. Snowmelt and rainfall over the 2024 Falls Fire burn scar contributed to rapid runoff. Infrastructure, including levees, was overwhelmed, and nearly 950 homes were affected.
• Douglas County: Heavy rainfall from March 14-18, 2025, led to significant flooding in areas previously burned by wildfires. The Deer Creek at Roseburg reached a historic crest of 15.91 feet. Burn scars in the Umpqua National Forest likely contributed to increased runoff and sediment transport.
• Josephine County: Similar to Douglas County, areas with recent fire history experienced elevated runoff and localized flooding. The Illinois River and its tributaries rose rapidly during the March storms.
• Curry and Coos Counties: These coastal counties experienced flooding and landslides during the March 2025 atmospheric river event. Burn scars from smaller 2022-2024 fires in the Rogue River-Siskiyou National Forest may have contributed to slope instability and debris movement.
• Jackson and Klamath Counties: These counties saw moderate flooding and wind damage. Areas affected by the 2021 and 2022 wildfire seasons were monitored for debris flow potential during the March storms.

Why Flood Risk Increases

Post-wildfire landscapes often exhibit reduced infiltration capacity and increased erosion potential. According to the Oregon Department of Emergency Management (OEM), these conditions can persist for several years, depending on the severity of the fire and the pace of vegetation regrowth.

Oregon's Emergency Operations Plan - Incident Annex 03 Flood-Volume III of the Comprehensive Emergency Management Plan-outlines how even moderate rainfall can result in significant runoff in burn-scarred areas, especially on steep slopes or near waterways, as well as how the state will respond.

Risk Mitigation and Preparedness

State and federal agencies, including the OEM, Oregon Department of Geology and Mineral Industries (DOGAMI), the Oregon Department of Land Conservation (DLCD), United States Geological Survey (USGS), and U.S. Army Corps of Engineers (USACE), are working with local jurisdictions to assess and model post-fire flood risks. Tools such as debris flow hazard maps and hydrologic models help identify vulnerable areas and inform emergency planning.

Residents near recent burn scars are encouraged to:

• Stay informed by signing up for ORAlert.gov and making sure Wireless Emergency Alerts are enabled on their cell phones
• Monitor weather forecasts during the rainy season
• Follow evacuation guidance when issued
• Know your local flood risk
• Understand the landslide risk in a particular area
• Avoid camping, hiking, or driving in burn-scarred areas during or immediately after rainfall
• Ensure you have adequate flood insurance coverage, as most standard homeowners and renters' insurance policies do not include flood protection, and FEMA will not pay to replace your home.

Looking Ahead

As wildfire activity continues to affect Oregon's landscapes, understanding the connection between burn scars and flooding is essential for community safety and resilience. Ongoing collaboration between scientists, emergency managers, and local governments will be key to addressing these evolving challenges.

Learn more about how burns scars contributed to the March 2025 flooding in Oregon on the Oregon Department of Emergency Managements March 2025 Story Map.