California Nevada Applications Program / California Climate Change Center


CNAP/CCCC researcher Mike Dettinger has led coordination of the meteorological aspects and formulation for a USGS/NOAA team which has examined California's preparedness for a cataclysmic flood. The name for this scenario is ARk Storm and it ran during April 2011. CNAP/CCCC researchers Dan Cayan and Kelly Redmond were also part of this effort.

Please click here for a summary of the ARkStorm project: California's Other "Big One"
Understanding the Impacts of Massive Winter Storms

Last update: 10 August 2011

A couple of years ago, some CNAP researchers were asked by the USGS MultiHazards Demonstration Project to develop and provide considerable detail for a scenario that would help emergency managers to plan and prepare for the something like the worst winter storm you can think of for California. In fact, the scientists working on the scenario decided that they would just be asking for dissent if they went for a worst-case storm, and so they just tried to take lessons from the past (along with recent advances in our understanding of California's worst storms) and come up with something that they were pretty sure was worse than any other 20th century storm. The result was a scenario that has been labelled the "ARkStorm" (with help from the media experts at the Pasadena Arts College of Design).
A paper describing the process and resulting scenario has come out in the journal Natural Hazards:
Dettinger, M.D., F.M. Ralph, M. Hughes, T. Das, P. Neiman, D. Cox, G. Estes, D. Reynolds, R. Hartman, D. Cayan and L. Jones, 2011: Design and quantification of an extreme winter storm scenario for emergency preparedness and planning exercises in California. Natural Hazards, 27 p., doi:10.1007/s11069-011-9894-5.
(Please click here or here for a personal use copy)

Figure 1 from article:
Composite SSM/I satellite image of vertically integrated water vapor (g cm-2; color bar at bottom) constructed from polar-orbiting swaths in the 12 h prior to 10 am UTC 14 October 2009. The atmospheric river indicated here channeled water vapor from a decaying typhoon over the western North Pacific, across nearly the entire width of the ocean basin, to deposit copious rains over the central coast of California
A more recent general audience paper has been published in EOS Transactions, AGU:
Ralph, F.M., and M.D. Dettinger, 2011: Storms, floods and the science of atmospheric rivers. EOS, Transactions, AGU, 92(32), 265-66.
(Please click here for a personal-use copy)

Figure 1 from article:
Analysis of an atmospheric river (AR) that hit California on 13-14 October 2009. (a) A Special Sensor Microwave Imager (SSM/I) satellite image from 13-14 October showing the AR hitting the California coast; color bar shows, in centimeters, the amount of water vapor present throughout the air column at any given point if all the water vapor were condensed into one layer of liquid (vertically integrated water vapor). (b) Rain gage data for 12:00 UTC on 14 October 2009 showing the total amount of precipitation (in inches) that occurred over the previous 24 hours. (c) Discharge for Nacimiento River (site indicated by red triangles in other panels); data are from U.S. Geological Survey stream gage 11148900. (d) Statewide streamflow historical ranking of 14 October 2009, compared to discharges on the same day of the year recorded by gages with more than 30 years of data.
This scenario was presented to a dozen expert panels and was worked thru with about 80 experts in disaster and resource management to work out its likely impacts and reasonable preparations that could be made, as described at

Cover of USGS report
Last winter, an ARkStorm workshop was held with about 350 participants. This workshop attracted a lot of public attention and discussion (see article from the UK Daily Mail; right). Even now, researchers continue to pursue various elements of the scenario, fleshing them out or developing new uses and responses. A number of agencies including the Navy are exploring its implications for their people and facilities. But it all sort of started with the efforts described in the paper linked to above.

Article from the Daily Mail: Click here for article
In July 2011, Navy Regional Operations Center in San Diego conducted a full-scale response exercise using the ARkStorm scenario dubbed "Citadel Rumble". Dale Cox (USGS) oversaw the operation and reports ".. the exercise did more than move ships and jets. They were rescuing and moving families, day care centers, and pets; clearing sewage; and putting out fires." The photo below shows organizers of the exercise (Dale Cox is second from left). To the right is an approved photo that Dale took during the exercise. Note this scenario has been used and is going to be used for similar exercises by groups such as:
  • Stockholm Environmental Institute with American Rivers (focusing on the San Joaquin River)
  • NASA (focusing on JPL, AMES and Edwards)
  • San Joaquin County with FEMA support
  • Contra Costa County Public Works

Navy operations center, San Diego

January 2011

The ARkStorm Summit will inform participants of the real potential for a massive storm and its consequences -- and will elicit a plan-of-action to address these new findings.

The two-day ARkStorm Summit serves as venue for the offical release of the ARkStorm Scenario. 250 invited guests from the public and private sector will join together to to take action as a result of the scenario’s findings. Emergency managers, regulatory and scientific agencies, policymakers, business leaders, and other experts from the public and private sector will come to Sacramento on January 13 & 14, 2011 for a full day of sessions. The USGS, FEMA, and CalEMA are presenting this two-day event to engage stakeholders from across California to take action as a result of the scenario’s findings, which will be officially released at the Summit. Leaders from across the country will help to share the multidisciplinary scientific findings of the USGS ARkStorm Scenario, which has been developed over the last two years by over 100 scientists and experts. Taking place at California State University, Sacramento, the ARkStorm Summit will not only inform the participants of the real potential for a massive storm and its consequences, but it also intends to elicit a plan-of-action to address these new findings.

CNAP/CCCC researcher Mike Dettinger recently presented results at the 2010 California Extreme Precipitation Symposium (American River Watershed Institute (ARWI) lead sponsor). The theme for this year's symposium was "ARkStorm: Examining a Potential California Flood Disaster". Proceedings can be found on the ARWI Proceedings web page.

Update July 2011
The ARkStorm presentation as given by Mike at the 2010 California Extremem Precipitation Symposium has been presented at numerous venues including:

From an abstract presented by Marty Ralph at the 2009 Extreme Precipitation Symposium:
A Winter Storm Scenario for USGS Multihazards Demonstration Project
F.M. Ralph, M. Dettinger, D. Cox, and L. Jones

In 2008, the USGS Multihazards Demonstration Project (MHDP) brought together over 300 experts to create "ShakeOut" the most comprehensive earthquake scenario and the largest earthquake drill ever.

The MHDP is now preparing for its next major public project, "ARkStorm," a scenario to address massive West Coast storms that rival those that severely impacted California in December 1861 and January 1862. The MHDP has assembled experts from National Oceanic and Atmospheric Administration (MOAA), US Geological Survey (USGS), Scripps Institution of Oceanography (Scripps), the State of California, and many other organizations to design a large, but scientifically plausible, hypothetical storm. The storm will originate near the equator, resulting in an Atmospheric River (AR) of moisture that will grow large, gain speed, and slam into the US West Coast with intense winds and rains for a prolonged period of several weeks. The task of ARkStorm is to elevate the visibility of the very real threats to human life, property, and ecosystems posed by extreme winter storms on the US West Coast. The ARkStorm scenario will provide emergency responders, resource managers, and the public a reality check on what is historically possible.

To help prepare, experts will examine in detail the possibility, cost and consequences of floods, landslides, coastal erosion and inundation, debris flows, environmental consequences like pollution and extirpation of endangered species, and physical damage possibilities like bridge scour, road closures, dam failure, property loss, and levee system collapse. Consideration will be given to catastrophic disruption to the water supply to California; the resulting impacts on groundwater pumping, seawater intrusion, water supply degradation, and land subsidence; and a detailed examination of climatic change forces that could exacerbate the problems.

Experts from the California Nevada Applications Program are providing leadership in the design and production of the detailed description of the extreme storm conditions at the core of this exercise, and with overall planning of the broader program.

Recent news articles about ARkStorm

Please click here for a YouTube video describing the ARkStorm Scenario