CoSMoS 1.0: Southern California

Science Center Objects

CoSMoS was initially developed and tested for the Southern California coast in collaboration with Deltares.

Map illustrated to show locations of islands and cities, and outlines of counties, in southern California.

Southern California study area.

CoSMoS was initially developed and tested for the Southern California coast in collaboration with Deltares. The Southern California study area extends 470 kilometers from Pt. Conception, California (USA), south to the Mexican border and includes microtidal basins but has few significant inlets or narrow straits that would focus tidal currents in the nearshore. The coastline is highly variable in terms of its orientation (west to south facing), morphology (rocky to wide, flat beaches), structures (seawalls, jetties, groins, breakwaters, and so on), exposure (open to significant island sheltering), and backbeach development (for example, rural coast to urban beach front).

CoSMoS has been used to assess coastal vulnerability within Southern California for the three following scenarios:

Map of a city area with an airport, on the coast, with a narrow barrier island, and lines drawn to show potential change.

Map shows flooding and shoreline change projections in the Imperial Beach area of southern San Diego County, CA, from the ARkStorm scenario.





Initial evaluations of the CoSMoS model were performed as part of the USGS Multihazards Demonstration Project (Porter and others, 2011). A team of atmospheric scientists with expertise in west coast storms used information from two powerful west coast storms in 1969 and 1986 to simulate an extreme storm event with a recurrence interval of at least 100 years (Dettinger and others, 2011). This extreme winter scenario, entitled “ARkStorm,” provided a time-series of wind and atmospheric pressure fields that served as boundary conditions for the CoSMoS model.

[Download Southern California model projections]


Map of a coastal city with a harbor with colored areas drawn on top to show potential flooding extent under different scenarios.

Example of flooding hazards predicted from the CoSMoS hindcast of the January 2010 storm, with and without sea-level rise (SLR) scenarios, in the region of Venice and Marina del Rey, CA.




January 2010 El Niño and Sea-Level Rise Scenarios

The El Niño-fueled storm of January 18–25, 2010, produced large waves (offshore deep-water waves up to 9 meters high) that remained elevated for a week, producing some of the most extreme coastal erosion observed for several decades throughout California (Barnard and others, 2011). This event provided numerous observations both for model forcing and validation, and provided managers with data from a known severe storm, thus serving as an optimal extreme-storm test case for CoSMoS. In addition to running a hindcast of this event with CoSMoS, future (2050 and 2100) sea-level rise (SLR) scenarios were also applied using the upper-end values from Rahmstorf (2007) (0.5 meter and 1.4 meter, respectively). These water levels were added to the tidal forcing for the January 2010 storm to estimate the potential for increased flooding that could result from various SLR scenarios combined with a recent, well-documented coastal storm.

[Download Southern California model projections]


Map of a coastal city with a harbor with colored areas drawn on top to show differences between observed vs. modeled flooding.

Flooding hazards projected by CoSMoS versus ground-truthed flooding extents from the January 2005 extreme tide event in Newport Harbor, CA. The tendency for CoSMoS version 1.0 to over-predict the level of flooding in protected embayments has been addressed through model enhancements in CoSMoS version 2.0.


January 2005 Newport Harbor Flood

An extreme high-tide event (king tide) coupled with an atmospheric low-pressure system caused significant flooding in Newport Beach on January 10, 2005. Newport Beach officials were deployed to manage the flood, and city personnel documented the flooded areas on Balboa Peninsula and Balboa Island with digital photographs. These data were interpreted and the flood extent was manually delineated using ArcGIS (Gallien and others, 2012). This represents the only known event and location where coastal flooding has been quantitatively determined along the entire U.S. west coast. 

CoSMoS was run for this scenario and flood-hazard projections were compared with ground-truthed flood extents produced from city photos (see Newport Harbor figure) for model validation and to support local flood-prediction improvements.

Download Model Projections

Download a zip file containing an essential readme.txt file and model projections of two Southern California flooding hazard scenarios: ARkStorm, and January 2010 El Niño and SLR.

Southern California flooding hazard scenarios (zip, 3.6 MB)

Suggested Citation: Barnard, P.L., van Ormondt, M., Erikson, L.H., Eshleman, J., Hapke, C., Ruggiero, P., Adams, P. N., and Foxgrover, A. 2014. Coastal Storm Modeling System: CoSMoS. Southern California 1.0, projected flooding hazards, doi: 10.5066/F74B2ZB4


Inundated areas shown should not be used for navigation, regulatory, permitting, or other legal purposes. The U.S. Geological Survey provides these data “as is” for a quick reference, emergency planning tool but assumes no legal liability or responsibility resulting from the use of this information.

The suggestions and illustrations included in these images are intended to improve coastal-flood awareness and preparedness; however, they do not guarantee the safety of an individual or structure. The contributors and sponsors of this product do not assume liability for any injury, death, property damage, or other effects of coastal flooding.

Use of trade names in this report is for identification purposes only and does not constitute endorsement by the U.S. Geological Survey.