Post-Fire Debris Flows in California: an Atmospheric Perspective
Nina Oakley, Ph.D., WRCC/CNAP/CW3E Jeremy Lancaster, CA Geological Survey ALERT User Group Conference, Ventura, CA April 2018
Atmospheric river influenced post-fire debris flow near Santa Barbara, CA, Jan 20 2017
Western Regional Climate Center What is a post-fire debris flow?
USGS baseline rate: 25 mm h-1 rate for 15 min
2 Factors • Soils/geology • Burn severity • Steepness of terrain • Rainfall intensity • Are there people there? Source: CA Alluvial Fan Task Force Community of Rancho Mirage CA, situated on an alluvial fan Max intensity may not be triggering intensity
Nov 2009, Station Fire burn area (Los Angeles County) Staley et al. 2013, Landslides Outline: CA Post-Fire Debris Flows
1. Climatological study in Transverse Ranges 2. Observations in central/northern California 3. Post-fire debris flows in a future climate
Post-fire debris flow on Springs Fire burn area 12/12/2014, Camarillo, CA Outline: CA Post-Fire Debris Flows
1. Climatological study in Transverse Ranges 2. Observations in central/northern California 3. Post-fire debris flows in a future climate
Post-fire debris flow on Springs Fire burn area 12/12/2014, Camarillo, CA Study Area
You are here Cool Seasons 1980-2014: 19 storm events triggering debris flows on 12 burn areas
Oakley et al. 2017 Natural Hazards7 Atmospheric Rivers
13 of 19 (68%) of events associated with Atmospheric River
Image Source: CIMSS Thanks to Shawn Roj for assembling 8 Conceptual- Synoptic Conditions
Oakley et al. 2017 Natural Hazards9 Conceptual-Cross-Section
Oakley et al. 2017 Natural Hazards10 Old/GrandFire and Flood: Prix Debris Old/Grand Flows, Dec Prix 25 2003 2003
Debris flows from the Old/Grand Prix Fires killed 16 people
Oakley et al. 2017 Natural Hazards Old/Grand Prix Debris Flows, Dec 25 2003
San Gabriel San Bernardino
Radar shows high reflectivity mostly confined to mountains
Image: NCEI radar archive Other Features: Squall line/NCFR
Oakley et al. 2017 Natural Hazards13 Other Features: NCFR
Dec 12 2014: Camarillo Springs Debris Flow
14 Jan 9 2018 Montecito Debris Flow
Thanks to D. Staley for making images into video
Images: CNRFC Summary: Southern CA
• In study: built catalog of PFDF events • ARs present in 13/19 events • Southerly low-level flow • Strong upper level jet with exit over S. CA • Orography plays big role, several cases additionally have NCFR/squall line Damage in Montecito following Jan 9 2018 debris flow
16 Outline: CA Post-Fire Debris Flows
1. Climatological study in Transverse Ranges 2. Observations in central/northern California 3. Post-fire debris flows in a future climate
Post-fire debris flow on Springs Fire burn area 12/12/2014, Camarillo, CA Squall line over Butte Fire burn area March 6, 2016
Mono Lake Angels Camp Stockton
Courtesy Jeremy Lancaster, CGS 12/3/15 (Before) Butte Fire burn area after intense rain March 6, 2016
Rain rates ~1.5 in/h
3/9/16 (After) Debris flow at Hawver Rd, North Fork Calaveras River watershed
Courtesy Jeremy Lancaster, CGS 12/3/15Detwiler (Before) Burn Scar: March 22 2018
Band of intense t-storms
Modesto Mammoth 3/9/16 (After) Turlock
San Jose
Detwiler burn area Madera
Image: CNRFC 12/3/15Detwiler (Before) Burn Scar: March 22 2018
*Preliminary information*
Sediment on roadways, many road closures, damage to several homes Rain rates up to 0.92 inches in 30 minutes observed
Images: K. Mattarochia, NWS Hanford History of debris flows in Big Sur SP Following Basin Complex Fire June 2008
Apr 7, 2009 Precipitation rate 0.84 in/hr (21.3 mm/hr)
Courtesy Jeremy Lancaster, CGS Monitoring Soberanes Burn Area (winter 2016/17)
Possibility of debris flow above 12/29/16 Pfeiffer Falls… 01/10/17
Small debris flows in Palo Colorado Cyn, rate of ~20 mm/h for 15 min Photo: CGS Why no debris flows in Soberanes?
Hypotheses: • Rainfall not intense enough • All sediment flushed out by 2009 event • Soil burn severity may not have been high enough (low-moderate) Ash movement on Palo Colorado Rd late Oct 2016. Photo: CGS North Bay: No significant debris flows this winter. Why not?
Atlas Fire Nuns Fire
landslides.usgs.gov/hazards/postfire_debrisflow/ Hypotheses: • Low to moderate severity burn • Rainfall intensities not high enough? (little known about area) Summary: Central/Northern CA
• Much less known about triggering rates • Generally higher than southern CA • Isolated thunderstorms, squall lines appear to dominate • Limited populations on alluvial fans; smaller fans Atlas Fire burns hills east of Napa on 9 Oct than S. CA 2017. Photo: M. Short, SF Chronicle
26 Outline: CA Post-Fire Debris Flows
1. Climatological study in Transverse Ranges 2. Observations in central/northern California 3. Post-fire debris flows in a future climate
Post-fire debris flow on Springs Fire burn area 12/12/2014, Camarillo, CA California Fire in the Future
• Length of fire season, size of fires likely to increase • Forested areas prone to more intense fires • Southern CA remains “ignition limited” • Population growth a big factor in fire frequency/impacts Thomas Fire smoke over 101 Freeway near • No consensus on Carpinteria. Photo: S. Palley/Washington Post lightning activity
28 Future Hourly Precipitation Extremes
For Dec-Jan-Feb
Change in exceedance probability of the top 0.05% highest hourly precipitation rates observed in control period (Jan 2001-Sept 2013) 2-3x more likely to exceed top 0.05% hourly rainfall in Based on RCP 8.5 (high warmer climate in emissions) scenario CA in DJF
Prein et al. 2017, Nature Climate Change Take-home messages: Post-fire debris flows in California
• Antecedent rainfall not needed for debris flow in burn area • Do not need “big storm” • High intensity rainfall key • Atmospheric rivers present, mesoscale features play key role • Extended fire season likely in future • Hourly precipitation extremes more frequent in future climate • ALERT observations critical to post-fire debris flow research! Looking down on Thomas burn area, Feb 2018 Future Work
• Establish sub-daily records for CA! • Process data, increase monitoring in northern/central CA • Improve understanding of NCFR/squall lines in CA • Evaluate weather model performance Thomas Fire Photo: Ventura OES • Assess changes (historic, future) in high intensity, short duration precipitation
31 Research supported by: Thank you!
Nina Oakley [email protected] @WRCCclimate @CnapRisa @CW3E_Scripps WRCC
NASA astronaut Randy Bresnik photographed the Southern California plumes of smoke on 5 Dec 2017 aboard the ISS
Western Regional Climate Center EXTRA SLIDES
Post-fire debris flow on Springs Fire burn area 12/12/2014, Camarillo, CA
Western Regional Climate Center Providing climate services since 1986 Atmospheric Rivers
Source: AMS Glossary 34 Event Case Studies
Data Sources:
• NARR (32 km) • SSM/I • radar • wind profilers • precipitation gauges
35 Sample case study: 18 Jan 2010 Determining Event Timing
wildlife camera Laser stage gauge pressure + rain triggered transducer camera Precipitation Observations
ALERT research gauges
RAWS gauges radar
15 min or better real-time observations most valuable! CW3E Probability of AR Conditions
Western Regional Climate Center Providing climate services since 1986 USGS Debris Flow Hazard Assessment
The area above Montecito was evaluated as having a high likelihood of debris flow with the design storm (peak 15 min intensity of 24 mm/h rate)
Western Regional Climate Center Providing climate services since landslides.usgs.gov/hazards/postfire_debrisflow/ 1986 CNRFC Radar Archive http://www.cnrfc.noaa.gov/radarArchive.php
Western Regional Climate Center Providing climate services since 1986 Jan 9 2018 Montecito: Low-level winds
Source: CANSAC WRF Future Hourly Precipitation Extremes
Prein et al. 2017, Nature Climate Change Decrease in Number of Precipitation Days
Future period: 2060-2069 Baseline period: 1985-1994
Pierce et al. 2013, J. Climate Increase in daily precipitation totals
Discrepancies on wetter/drier trend in future depends largely on changes in frequency of largest (>60 mm/day) events
Change in days per year exceeding thresholds (2060-2069 minus 1985-1994) Pierce et al. 2013, J. Climate