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‘Slow’ Hillside Vegetation Regrowth in Thomas Fire Burn Area Raises Concerns for Future Debris Flows

‘Slow’ Hillside Vegetation Regrowth in Thomas Fire Burn Area Raises Concerns for Future Debris Flows


Vegetation in the Thomas Fire burn area is recovering more slowly than expected, according to experts from the U.S. Forest Service and CAL FIRE.  They reported this latest information at a community meeting held Tuesday night following a report to the County Board of Supervisors earlier in the day. The conditions raise the risk of additional flooding and debris flows in the 2018-2019 rainy season.

The latest research and field observations show that hillside regrowth in the Thomas Fire burn area is progressing slowly, said Kevin Cooper, U.S. Forest Service biologist and Burn Area Emergency Response (BAER) team leader. Vegetation growth is critical to stabilizing burned hillsides.

The U.S.F.S. and CAL FIRE partner to examine wildfire impacts on the national forest/public lands as well as on privately held land, respectively.

Because the Thomas Fire occurred near the end of a dry winter and was followed by debris flows that removed large amounts of topsoil, the hillside plant life has been slow to bounce back, Cooper said. Plant regrowth is at about 5 to 10 percent, he said, far less than the 50 to 60 percent of coverage that would be more typical at this stage of a fire recovery. Cooper said he does not expect to see significant additional growth during the dry summer months, but the teams will re-evaluate the vegetation in August.

Scientists and fire experts with the CAL FIRE’s Watershed Emergency Response Team (WERT) concurred that the slow regrowth could increase the risk of flooding or debris flows in the next rainy season.

The BAER and WERT teams have examined the Thomas Fire’s impacts on soils and soil erosion, sediment flow, flooding, rockfall, debris, roads, hiking trails, cultural resources, and fish and wildlife. In other highlights from the BAER and WERT presentations, officials discussed:

  • Updated hazard maps that can be used to help predict a general risk of future debris flow during heavy rains
  • The probability that a significant amount of material remains on the hillsides, despite the massive volume of debris that flowed on Jan. 9
  • How specific paths of future floods and debris flow are extremely difficult to predict, given the complex and evolving hillside conditions
  • That debris flows may occur several times in watersheds below the same burned areas

Debris flow “remains a continued risk,” said Drew Coe, a CAL FIRE hydrogeologist and WERT lead. The County has experienced 63 fires since 1913, he said, and many have resulted in flooding and debris flow, though not as extreme as the recent Montecito disaster.

The reports underscore the need for residents to remain vigilant, County officials said.

“While it’s disappointing that the hillside vegetation isn’t where we’d like it to be, we have known that this recovery will take time,” said Rob Lewin, director of the Santa Barbara County Office of Emergency Management. “Our residents will need to be mindful of the ongoing risks during wet weather and prepare accordingly,” concluded.

The public is invited to read the BAER Team and WERT reports here. Presentation slides shown at the meeting can be found here.

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