Observations of an Extreme Atmospheric River Storm With a Diverse Sensor Network

Hatchett, Benjamin J.; Cao, Qiqi; Dawson, Phillip B.; Ellis, C. J.; Hecht, Chad W.; Kawzenuk, Brian; Lancaster, Jeremy T.; Osborne, Tashiana; Wilson, Anna M.; Anderson, Michael L.; Dettinger, Michael D.; Kalansky, Julie; Kaplan, Michael L.; Lettenmaier, Dennis P.; Oakley, Nina S.; Ralph, F. Martin; Reynolds, David W.; White, Allen B.; Sierks, Michael; Sumargo, Edwin

doi:10.1029/2020ea001129

Cited by 31 publications

(26 citation statements)

References 92 publications

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“…Based on observations and anecdotal reports from the operational meteorology community, NCFRs are relatively common in northern California (e.g., Blier, 2003;Blier et al, 2005;Jorgensen et al, 2003;King et al, 2009;White et al, 2003). Although a catalog of NCFR events has never been compiled (whether causing significant landscape response or not), we can point to another recent and nearby NCFR on 14 February 2019 (Hatchett et al, 2020) as evidence of their occurrence and consequence in the central Sierra region. The 14 February 2019 event also had radar reflectivity in excess of 50 dBZ in a narrow band (Figure 9), and traversed through the two counties (Calaveras and Amador) located northwest of Groveland, producing 10-min rainfall intensities approaching 60 mm/hr (MesoWest, 2019).…”

Section: Broad-scale Ncfr Occurrence and Landscape Responsementioning

confidence: 95%

Linking Mesoscale Meteorology With Extreme Landscape Response: Effects of Narrow Cold Frontal Rainbands (NCFR)

et al. 2020

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Landscapes evolve in response to prolonged and/or intense precipitation resulting from atmospheric processes at various spatial and temporal scales. Whereas synoptic (large-scale) features (e.g., atmospheric rivers and hurricanes) govern regional-scale hydrologic hazards such as widespread flooding, mesoscale features such as thunderstorms or squall lines are more likely to trigger localized geomorphic hazards such as landslides. Thus, to better understand relations between hydrometeorological drivers and landscape response, a knowledge of mesoscale meteorology and its impacts is needed. Here we investigate the extreme geomorphic response associated with one type of mesoscale meteorological feature, the narrow cold frontal rainband (NCFR). Resulting from low-level convergence and shallow convection along a cold front, NCFRs are narrow bands of high-intensity rainfall that occur in midlatitude areas of the world. Our study examines an NCFR impacting the Sierra Nevada foothills (California, USA) that initiated over 500 landslides, mobilized~360,000 metric tons of sediment to the fluvial system (as much as 16 times the local annual sediment yield), and severely damaged local infrastructure and regional water transport facilities. Coupling geomorphological field investigations with meteorological analyses, we demonstrate that precipitation associated with the NCFR was both intense (maximum 15 min intensity of 70 mm/hr) and localized, resulting in a highly concentrated band of shallow landsliding. This meteorological phenomenon likely plays an important role in landscape evolution and hazard initiation. Other types of mesoscale meteorological features also occur globally and offer new avenues for understanding the effects of storms on landscapes. Plain Language Summary Major storms can cause extreme and hazardous landscape disturbances, but links between storm conditions and landscape response such as erosion and landslides remain poorly constrained. This is partly due to the lack of attention generally given to the finer-scale details of storms. We examined one type of atmospheric feature that is common in western North America (as well as in other regions), the narrow cold frontal rainband, and studied its effects on the landscape. In 2018, one such event in the Tuolumne River watershed, California, caused more than 500 landslides in a narrow area, moving more sediment in one day than the river would normally transport in a year. We find that landscape change, including potentially hazardous events such as landslides, can be driven primarily by fine-scale rainfall patterns rather than by the larger-scale storm conditions. More integration between weather and landscape scientists can advance knowledge of how storms influence landscapes and produce hazards, especially during extreme events.

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Section: Broad-scale Ncfr Occurrence and Landscape Responsementioning

confidence: 95%

Linking Mesoscale Meteorology With Extreme Landscape Response: Effects of Narrow Cold Frontal Rainbands (NCFR)

et al. 2020

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“…Observations can be costly, though some expense can be mitigated by leveraging existing networks. For example, California has invested in a diverse sensor network that can be utilized for observing, understanding and forecasting extreme weather events (Hatchett et al., 2020). New observations to expand debris‐flow monitoring in California can leverage infrastructure from this existing network.…”

Section: Monitoring Is Key For Expansion Of Decision Support Tools Tomentioning

confidence: 99%

A Warming Climate Adds Complexity to Post‐Fire Hydrologic Hazard Planning

Oakley

2021

Earth's Future

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Wildfire removes vegetation and weakens root strength, making burned areas more susceptible to erosion. Wildfire can also alter the physical and chemical characteristics of soil, creating a hydrophobic layer which increases runoff and may lead to damaging floods and debris flows in steep terrain. For example, following the 2017 Thomas Fire in Southern California, the devastating 9 January 2018 debris flows in the community of Montecito resulted in 23 deaths and nearly $1B in damages (Lancaster et al., 2021). In a meeting following the event, a Santa Barbara County resource manager made a plea to researchers: "I need to know how frequently I can expect post-fire debris flows of this magnitude in this area." Managers in other susceptible areas have expressed similar concerns for events in their area of responsibility.Impactful post-fire debris flows are not new to southern California, though the penultimate fatality event occurred in 2003 when 16 people died in debris flows emanating from the Old/Grand Prix burn areas in the San Bernardino Mountains (Oakley et al., 2017). The Montecito event renewed focus on post-fire debris-flow preparedness, with understanding the recurrence intervals of these events in the current and future climate as key concerns in planning efforts. Southern California's well-documented history of impactful post-fire debris flows compared to other susceptible regions makes it an excellent "laboratory" for research and development of decision support tools. Kean and Staley (2021) utilize Southern California's data to provide the first known framework to estimate recurrence intervals for minor and major post-fire debris flows in the region. This tool allows for evaluation of recurrence intervals in both a stationary and warming climate. Emerging research from disciplines relevant to post-fire hazards (e.g., soil, wildfire, and climate science) can be readily integrated into this framework. While regionally focused, this tool is applicable to other locations susceptible to post-wildfire debris flows provided the requisite data on rainfall triggering thresholds, burn severity, and wildfire recurrence can be collected. Debris Flow Recurrence Interval as a Pre-Fire Decision Support ToolThe time between wildfire and precipitation events is decidedly brief in California, such that pre-fire planning presents significant advantages. For example, the 2018 Montecito debris flow occurred before the Thomas Fire was 100% contained (Lancaster et al., 2021). Observations over the past 60 years demonstrate a delayed onset of the rainy season in California (Lukovic et al., 2021). This allows dry conditions to extend into the autumn/winter offshore wind season (Abatzoglou et al., 2021;Swain, 2021), amplifying wildfire risk (Goss et al., 2020). Climate model projections suggest further "sharpening" of the precipitation Abstract Climate change will likely increase the frequency of damaging post-wildfire floods and debris flows, amplifying the threat to life, property, and infrastructure situated in susceptible are...

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“…In regions located near climatological expected rain-snow transition elevations (Jennings et al, 2018), such as the Sierra Nevada, individual storms can produce dramatically different responses in snowpack spatial variability and magnitude. ARs are a common type of storm event yielding variable snowpack and hydrologic responses as a result of heavy precipitation with high snow line elevations (Hatchett et al, 2017;Hatchett, 2018;Henn et al, 2020) or with snow line elevations that vary widely over the duration of the storm (Lundquist et al, 2008;Hatchett et al, 2020).…”

Section: Snow Drought Variation In Time and Spacementioning

confidence: 99%

Monitoring the Daily Evolution and Extent of Snow Drought

Hatchett

Rhoades

McEvoy

2021

Preprint

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Abstract. Snow droughts are commonly defined as below average snowpack at a point in time, typically 1 April in the western United States (wUS). This definition is valuable for interpreting the state of the snowpack but obscures the temporal evolution of snow drought. Borrowing from dynamical systems theory, we applied phase diagrams to visually examine the evolution of snow water equivalent (SWE) and accumulated precipitation conditions in maritime, intermountain, and continental snow climates in the wUS using station observations as well as spatially distributed estimates of SWE and precipitation. Using a percentile-based drought definition phase diagrams of daily observed SWE and precipitation highlighted decision-relevant aspects of snow drought such as onset, evolution, and termination. The phase diagram approach can be used in tandem with spatially distributed estimates of daily SWE and precipitation to reveal variability in snow drought type and extent. When combined streamflow or other data, phase diagrams and spatial estimates of snow drought conditions can help inform drought monitoring and early warning and help link snow drought type and evolution impacts on ecosystems, water resources, and recreation. A web tool is introduced allowing users to create real-time or historic snow drought phase diagrams.

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Observations of an Extreme Atmospheric River Storm With a Diverse Sensor Network

Cited by 31 publications

References 92 publications

Linking Mesoscale Meteorology With Extreme Landscape Response: Effects of Narrow Cold Frontal Rainbands (NCFR)

Linking Mesoscale Meteorology With Extreme Landscape Response: Effects of Narrow Cold Frontal Rainbands (NCFR)

A Warming Climate Adds Complexity to Post‐Fire Hydrologic Hazard Planning

Monitoring the Daily Evolution and Extent of Snow Drought

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