ARkStorm attendees
Summit attendees
Mike Dettinger giving presentation
Dr. Michael Dettinger, of USGS and Scripps Institution of Oceanography, describes details of the meteorological foundations of the ARkStorm at the Summit.
February 4, 2011

ARkStorm Summit Uses HMT Findings to Define A Major Emergency Preparedness Scenario

The ARkStorm Summit held 13-14 January 2011, and hosted by the U. S. Geological Survey (USGS)'s Multi Hazards Demonstration Project, involved 250 scientists, engineers, emergency preparedness professionals, and public officials. The project and resultant report was a collaborative effort of the USGS, NOAA and a number of other federal and state agencies, and universities. The intent was to define a large, scientifically realistic heavy precipitation event, subsequent flooding, the physical damages to the built environment, and social and economic consequences. The hypothetical storm strikes southern and central California and might rival the intense California winter storms of 1861 and 1862 that left much of southern California and the Central Valley of California impassible. The storm is estimated to produce precipitation that in many places exceeds levels only experienced on average once every 500 to 1,000 years. Given the storm's wide extent, extensive flooding would likely result across the state, potentially overwhelming flood protection dams and levees. Extensive property damages and related economic impacts are estimated to exceed $400 billion dollars; these losses would exceed those associated with a severe earthquake having similar likelihood, and would exceed those of Hurricane Katrina.

A significant outcome of the Summit was acknowledgment of the scientific realism and likelihood of the ARkStorm event. Definition of the event was led by Dr. Michael Dettinger of the USGS and Scripps Institution of Oceanography and Dr. Marty Ralph of NOAA's Earth System Research Laboratory. Provision of scenario details was based on simulations by modern weather forecasting and land-hydrologic models. The storm sequence at the core of the ARkStorm scenario is designed around a sustained sequence of landfalling atmospheric rivers (ARs), which are the primary historical cause of heavy precipitation along California's Pacific Coast. A similar sequence of storms may have been the cause of the rains and floods of 1862. A focused NOAA/ESRL/Physical Sciences Division research program during the past 10 years, including a major role in HMT, has led to better understanding of AR meteorology, frequency and strength. Continuing research is directed to developing better tools for forecasting ARs so that increased lead times and accuracies can be provided to facilitate emergency preparedness efforts. Implementation of permanent AR-focused 21st Century Observations and Modeling techniques is underway as part of the HMT-West Legacy project with California's Department of water Resources.

The products of the ARkStorm are intended for use by emergency planners, utility operators, policymakers, and others to inform preparedness plans and to enhance resiliency. A summary review of the ARkStorm Summit was carried by the New York Times, and a detailed overview of all facets of the study can be downloaded from a USGS web site.

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