Theme for 2010:
ARkStorm: Examining a Potential California Flood Disaster

June 23, 2010
University of California, Davis
On this page:

Why this theme?

The ARkStorm is an emergency planning scenario hypothesizing the occurrence of a series of severe winter storms caused by atmospheric rivers striking California. The hypothetical storm event is like the one that flooded the Central Valley and much of Los Angeles and Orange County in the winter of 1861-1862. This large, but scientifically plausible, flood scenario is followed by expert analysis of the secondary hazards, and the physical, social, and economic consequences. ARkStorm is a successor to the Southern California ShakeOut scenario of a hypothetical, but plausible, magnitude 7.8 earthquake on the San Andreas Fault. Both scenarios were developed by the U.S. Geological Survey's Multi-Hazards Demonstration Project to use hazards science to improve communities' resiliency to natural disasters.

Special Recognition Award

The 2010 Special Recognition Award was presented to Don Neudeck. See the award language, biographical information, and hear the presentation on the Symposium's Don Neudeck award page.

Speaker Presentations

ARkStorm: A West Coast Storm Scenario

Dale Alan Cox
Project Manager
Multi-Hazards Demonstration Project
U.S. Geological Survey
Sacramento, CA


The United States Geological Survey (USGS) Multi-Hazards Demonstration Project (MHDP) is preparing a new emergency-preparedness scenario, called ARkStorm, to address massive U.S. West Coast storms analogous to those that devastated California in 1861-62. Storms of this magnitude are projected to become more frequent and intense as a result of climate change.

Experts at federal, state, and regional levels have been assembled to design the large, but scientifically plausible, hypothetical storm scenario that would provide emergency responders, resource managers, and the public a realistic assessment of what is historically possible.

The ARkStorm is patterned after the 1861-1862 historical events but uses modern modeling methods and data from large storms in 1969 and 1986. The ARkStorm draws heat and moisture from the tropical Pacific, forming Atmospheric Rivers (ARs) that grow in size, gain speed, and, with a ferocity equal to hurricanes, slam into the U.S. West Coast for several weeks. Using sophisticated weather models and expert analysis, precipitation, snowlines, wind, and pressure data the modelers will characterize the resulting floods, landslides, and coastal erosion and inundation. These hazards will then be translated into the infrastructural, environmental, agricultural, social, and economic impacts. Consideration will be given to catastrophic disruptions to water supplies resulting from impacts on groundwater pumping, seawater intrusion, water supply degradation, and land subsidence. Possible climate-change forces that could exacerbate the problems will also be evaluated.

Scheduled for completion in 2010, ARkStorm will be the basis of a statewide emergency response drill, Golden Guardian, led by the California Emergency Management Agency in 2011.

Flooding Emergency Response Exercise

James Woodward
Senior Exercise Planner
California Emergency Management Agency
Mather, CA


California is all too familiar with catastrophic events: earthquakes, floods, drought, and devastating fires. Local, regional, and state agencies plan and prepare for the next great event. How do you know if your emergency manager and agency is ready for the task when the event happens? California has been training and exercising just for those events since 2004 with the Governor's Statewide Golden Guardian Full Scale Exercises. I intend to guide you through how the California Emergency Management Agency looks at exercise planning. I will then discuss what is involved in the planning and development of a major full-scale exercise, making sure we test and evaluate those risks, gaps, or issues that have been identified. Finally, reviewing the next Governor's Statewide Golden Guardian Full Scale Exercise, Golden Guardian 2011 will be based on a flood theme.

Formulating the ARkStorm Meteorology

Michael D. Dettinger, Ph.D.
Research Hydrologist
U.S. Geological Survey
Scripps Institution of Oceanography
La Jolla, CA


The USGS Multi-Hazards Demonstration Project is working with numerous agencies and experts to evaluate hazards that would be associated with a scientifically plausible series of extreme winter storms in California. The scenario consists of a storm sequence that impacts both Southern and Northern California in rapid succession, and that is more severe overall than any single 20th century storm, but that may rival the extreme storms of 1861-62. The atmospheric and hydrological characteristics of the storms are quantified to provide the basis for other teams to estimate human, infrastructure, economic, and environmental impacts. The scenario will be used to design emergency preparedness and flood planning exercises by federal, state and local agencies.

Recent storm episodes were "stitched" together to describe a rapid sequence of several major storms over the state, yielding precipitation totals and runoff rates beyond any that occurred during the individual (unstitched) historical events. This stitching approach is a new strategy that allowed the scenario-design team to avoid arbitrary scalings to achieve much greater-than-historical storm and flood totals, by instead allowing for the very real occasions when storms stall over parts of the state and when extreme storms have followed each other into the state over short periods of time. The scenario — called the ARkStorm — is quantified by a dynamical (regional weather-model) downscaling of historical observations of extreme winter storms of January 1969 and February 1986 to 6-km and 2-km grids over California. The weather model outputs were used to force a hydrologic model to estimate runoff, for comparison with historical runoff. The methods used to build this scenario, and key results, could also be applied to other, nonemergency or non-California applications.

Understanding and Forecasting Atmospheric Rivers

David W. Reynolds
Weather Forecast Office — San Francisco Bay Area
NOAA/National Weather Service
Monterey, CA


Over the past decade, special observations have been made within northern California, monitoring the strength and location of land-falling Atmospheric Rivers (AR). Atmospheric Rivers are rather narrow plumes (< 400 kilometers width) of high moisture content air that can extend thousands of kilometers across the Pacific Ocean with origins in the subtropics. It is believed these are generated by circulations associated with a strong and extended East Asian jet stream that at times creates a nearly continuous AR across the entire Pacific Basin.

Research, done by NOAA scientist in Boulder, CO, have shown that these strong and sustained land-falling AR's are associated with many if not a majority of floods in California. This presentation will review AR's and discuss how current NWS forecast offices can recognize and attempt to forecast these phenomena well in advance of landfall. The Columbus Day 2009 event will be used as an example. In addition, the idea of developing an AR threat index or intensity category will be presented. Finally the paper discusses how this knowledge of AR's could be used to prepare state and local officials for a hypothetical, but very believable catastrophic flood event being proposed as part of a statewide emergency response drill in 2011 called ARkStorm.

The Psychology of Uncertainty: Challenges to Communicating Risk

Elke U. Weber, Ph.D.
Graduate School of Business
Columbia University
New York, NY


A better understanding of what uncertainty means to human decision makers and how they process information about possible outcomes in uncertain environments helps with the design of more effective risk communication. My presentation will provide an overview of the psychology of judgment and choice under uncertainty, including models to modify and improve rational-economic formalizations, which often do not describe human behavior. My examples will focus on small probability events, relevant to extreme precipitation forecasts.

Potential Flooding from ARkStorm

Kathleen Schaefer, P.E. CFM
Regional Engineer
Mitigation Division, Region IX
Federal Emergency Management Agency
Oakland, CA


A state-of-the-art meteorological model was created by the ARkStorm atmospherics team to estimate pressures, wind speeds, temperatures, and precipitation time series in nested grid with resolution up to 2 km. The wind speed time series are being used directly for ARkStorm damage modeling, but it was impractical to input the precipitation time series into a statewide hydrological and hydraulic model to produce flood maps. Instead, ARkStorm is using FEMA's digital Flood Insurance Rate Maps, and the associated National Flood Hazard Layer, as a representation of areas vulnerable to flooding under the ARkStorm scenario.

As a part of the Map Modernization Program, FEMA created a seamless, digital National Flood Hazard Layer. Building on the success of Map Modernization, FEMA is transitioning to a new program entitled RiskMAP. RiskMAP's vision is to collaborate with State, local, and tribal entities to deliver quality flood hazard data that increases public awareness and leads to mitigation actions that reduce risks to life and property. An overview of how the seamless National Flood Hazard Layer was used to support the goals of both RiskMAP and ARkStorm, in this innovative pilot project, will be presented.

Potential Landslide Impacts from ARkStorm

Christopher Wills
Supervising Engineering Geologist
California Geological Survey
Sacramento, CA


ARkStorm is a statewide emergency planning scenario hypothesizing severe storms that entrain huge amounts of moisture from the tropical Pacific and dump it on California over a few days. The storm is projected to be similar to, but more intense than recent historic storms that have struck California in recent decades, and approach the massive storms of 1861-1862 in total rainfall. A meteorological model for the ARkStorm has been developed from records of the 1969 and 1986 storms, both of which caused widespread and severe landslides in California.

Estimating the numbers and impact of landslides from the ARkStorm requires models relating rainfall to the numbers and distribution of landslides and detailed records of the impact of landslides in past storms. Neither of these basic data sets exists. Models that estimate the areas with the greatest susceptibility to landsliding do exist, however, and can be combined with the detailed maps of small areas showing the numbers of landslides triggered in individual storms. We have extrapolated the distribution of landslides mapped in past storms to areas where no such maps exist using the landslide susceptibility maps. Similarly, we have extrapolated the incomplete records of damage from landslides in past storms to the ARkStorm using the susceptibility maps. We anticipate that the ARkStorm would trigger thousands of landslides causing hundreds of millions of dollars in direct repair costs.

Infrastructure and Physical Damages Estimated for ARkStorm

Keith A. Porter, Ph.D.
Associate Research Professor
Civil, Environmental, and Architectural Engineering
College of Engineering & Applied Science
University of Colorado at Boulder
Boulder, CO


An event like the ARkStorm scenario would impose severe flooding and hurricane-force winds on large areas of California, potentially damaging buildings, contents, and infrastructure such as roads, bridges, electric power system, etc. We estimated physical damages in the ARkStorm scenario by three approaches. To produce a realistic outcome at the aggregate societal level, we employed the data and methods of FEMA's flagship emergency-planning software HAZUS-MH, although the calculations had to be done outside of HAZUS-MH. To examine the effects of the ARkStorm on lifelines such as the highway network, electric power, etc., a series of 12 panel discussions were held with engineers, operators, and emergency planners from the various lifelines at risk. The panel participants were presented with the meteorological and flooding inputs, and they offered their judgments about the resulting damage and restoration efforts that they would undertake if ARkStorm were to occur. In three cases, special studies were performed by individual experts. These were of demand surge (sudden temporary increases in costs resulting from the need to repair widespread damage), telecommunications, and insurance impacts.

Between the three approaches, it is deemed realistic that an event like the ARkStorm would result in property damage costing $310 to $330 billion to repair, of which approximately $200 billion is from building damage from flooding, $100 billion from content damage from flooding, $5 billion from wind damage to buildings, and the balance from infrastructure damage. Demand surge could potentially increase this amount by 20%. Some highways in steep terrain could be heavily damaged by multiple landslides, in some cases taking months or more to repair. Electric power would be unavailable for up to 2 weeks in most places, but in some places with very high winds such as the southern Sierras, commercial electric power could take months to restore. Sewer systems in heavily flooded areas are subject to damage, with some counties having half their wastewater treatment plans flooded, damaging the electrical equipment, and requiring a month or more to restore. Water service is severely impacted in some places, especially where well pumps are flooded and contaminated with untreated wastewater, in some places taking several months to restore. Lifeline service providers are being given a second opportunity to review and offer revisions to these findings.

Economic Consequences of the ARkStorm Scenario

Anne Wein, Ph.D.
Operations Research Analyst
Western Geographic Science Center
U.S. Geological Survey
Menlo Park, CA


We contribute an economic perspective on the ARkStorm winter storm scenario and resiliency to natural hazards. The economic consequences of the ARkStorm scenario emanate from the physical, agricultural, and environmental damages resulting from precipitation, runoff, wind, flooding, landslides, and coastal processes. The economic impacts are also determined by both the workings of individual businesses and the macroeconomy.

The ARkStorm damages are transformed into sources of business interruption including evacuation, loss of building use and output, lifeline service (power, water, waste water) outages, reduced highway capacities, agricultural losses, and environmental damages. These business interruptions are described spatially and temporally to estimate effects on various economic sectors. The interdependencies among the sectors in the California economy are captured in a computable general equilibrium model to produce estimates of direct and indirect (ripple effects) economic impacts to sector activity over a two-year period.

Dr. Snell's Precipitation Measurements of December 1861-January 1862 are Valid

Leon Hunsaker
Chief Meteorologist, 1966-1968
Pacific Gas & Electric Co.
TV & Radio Broadcast Meteorologist, 1968-2009
Grants Pass, OR


Validation of Dr. Snell's rainfall measurements changes the way we look at flood history on the American River watershed. It indicates that the amount of precipitation which fell on the American River watershed in January 1862 has been significantly underestimated — by as much as 20%. A repeat of the December 1861-January 1862 Flood Series would challenge the now approved levee modifications designed to protect Sacramento and would exceed any other flood which has been experienced on the American River since 1861-62.

Panel Discussion: Flood Modeling Uncertainties


David Ford, Ph.D., P.E., D.WRE
David Ford Consulting Engineers, Inc.
Sacramento, CA


Joe Countryman, P.E., D.WRE
MBK Engineers
Sacramento, CA
Michael D. Dettinger, Ph.D.
Research Hydrologist
U.S. Geological Survey
Scripps Institution of Oceanography
La Jolla, CA
Justin Ferris, Ph.D., P.H.
U.S. Geological Survey
Sacramento, CA
Michael Mierzwa, P.E.
River Forecasting Section
California Department of Water Resources
Sacramento, CA
Kathleen Schaefer, P.E. CFM
Regional Engineer
Mitigation Division, Region IX
Federal Emergency Management Agency
Oakland, CA
Ron Stork
Senior Policy Advocate
Friends of the River
Sacramento, CA

2010 Sponsors

USGS Multi-Hazards Demonstration Project
Sacramento Area Flood Control Agency
Center for Watershed Sciences
MBK Engineers
David Ford Consulting Engineers
Balance Hydrologics, Inc.
WEST Consultants, Inc.
Sierra College Natural History Museum
American River Watershed Institute