Post-Fire Debris Flows in California: an Atmospheric Perspective
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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.