Methodology

Topic coverage

This tool covers the same 27 California counties covered in NOAA's Coastal County Snapshots tool. As with that tool, 23 counties come from the original Economics: National Ocean Watch (ENOW) dataset, which expands on NOAA's definition of "coastal shoreline counties" by dropping "shore-adjacent counties with no relevant economic activity" and adding inland ones with "significant levels of ocean- and Great Lakes-dependent economic activity". Four counties were added because FEMA flood data is available. Additional sea level rise data was used to add Sea Level Rise topics to the three Delta counties.

Coverage tiers

Full 20 counties

All four topics. Alameda, Contra Costa, Del Norte, Humboldt, Los Angeles, Marin, Mendocino, Monterey, Napa, Orange, San Diego, San Francisco, San Luis Obispo, San Mateo, Santa Barbara, Santa Clara, Santa Cruz, Solano, Sonoma, Ventura.

Delta 3 counties

Flood hazard, sea level rise and marine economy. No total economy: these counties are on ENOW's list but outside its shore-adjacent definition. Their sea level rise comes from NOAA's Delta inundation file. Sacramento, San Joaquin, Yolo.

Flood only 4 counties

Flood hazard only. Lake, San Benito, Sutter, Trinity.

For a coverage matrix and details about why a certain topic is excluded, see the topic matrix on the Data page.

Sea Level Rise Guidance

This tool follows the published Ocean Protection Council (OPC) 2024 California Sea Level Rise Guidance. As per the guidance (pp. 7-8), this tool includes the Intermediate, Intermediate-High, and High scenarios relative to a year 2000 baseline. Broadly speaking, at a "High" scenario at the 2050 and 2100 years in the OPC guidance, the state on average will see 1.2 feet and 6.6 feet respectively of sea level rise. However, the average sea level rise hits 2.0 feet at the "High" scenario in 2060, so I feel a 2 foot minimum matching the NOAA Coastal County Snapshots is still relevant as a "near term (2020-2050)" planning tool, especially considering combined impacts such as El Niño impacts and storm events (for more on this, see "Combined Impacts of Sea Level Rise and Other Coastal Hazards" on pp. 38-52).

"Average" doesn't paint the county-level picture; as the OPC guidance states, local site conditions will impact the specific sea level scenario at each tide gauge (p. 55). The tide-gauge-specific sea level rise scenarios in Appendix 2 (pp. 85-92) were used for Sea Level Rise topics in this tool; simple linear interpolation was used between decades to determine year-specific height projections. To simplify the tool, I made an editorial decision to pick one tide gauge per county; some were "obvious" and had a nearby gauge, while others were judgement calls based on what I thought was relevant to the selected county. The county profile and the linked gauges are listed below. For project planning, OPC guidance suggests either finding the nearest tide gauge, or to average two if equidistant (p. 56). Tide gauge locations along with heights at specific scenarios and years are visible as a layer on the CASCA Map tool.

Crescent City

Del Norte

North Spit

Humboldt

Arena Cove

Mendocino

Point Reyes

Marin, Sonoma

San Francisco

San Francisco

Alameda

Alameda, San Mateo, Santa Clara

Port Chicago

Contra Costa, Napa, Sacramento, San Joaquin, Solano, Yolo

Monterey

Monterey, Santa Cruz

Port San Luis

San Luis Obispo

Santa Barbara

Santa Barbara, Ventura

Los Angeles

Los Angeles, Orange

San Diego

San Diego

Exposure calculations

NOAA did not publish exactly how it calculated exposure in its Coastal County Snapshots tool. This tool calculates exposure by intersecting the floodplain and sea level rise extents with Census block level data, which is the smallest geography available. Census LODES provides jobs at the per-block level. Census ACS provides population and poverty at the block group level, and is distributed to blocks based on 2020 Census distribution. This allows for splitting of exposure based on partial overlap; for example, if a block is 30% inside of a floodplain, 30% of people and jobs are counted.

Facilities are a simple count of plotted points inside the mapped area. Flood insurance claims are not mapped, and are totalled per county.

Connected and low-lying sea level rise exposure

NOAA's Coastal County Snapshots seemed to only tabulate direct exposure to sea level rise in some counties, when the OPC guidance recommends considering all low-lying areas which are also exposed to risk, for example from groundwater intrusion (p. 48) or coastal storms (p. 52). This tool includes exposure to these areas indicated differently (dashed bars). This data is built on areas identified by NOAA in the Sea Level Rise Viewer method description; as noted however, this doesn't account for infrastructure like storm drains and ditches, so the impact is less certain but nonetheless still a risk. In some places, the difference is small. In others, however, the difference is stark: for example, compare San Mateo's CASCA County Profile to NOAA's Coastal County Snapshot.

Land cover

The natural-features sections use NOAA's 1996 and 2021 C-CAP regional land cover data at 30 meters, which uses the latest update (NOAA's tool was using 2016 C-CAP data). Wetland is the palustrine and estuarine wetland and aquatic-bed classes; upland is grassland, forest, scrub and shrub; other is developed, cultivated, pasture, bare and shore land. Open water is not counted as land. "Development added" is the difference between undeveloped land in 1996 and developed land in 2021. Inside and outside the floodplain, and inside each sea level rise extent, are pixel counts against the same hazard polygons as every other section.

View on map links

The original NOAA tool generated and cached inset maps for each topic. This feature is removed in favor of a link to the CASCA map tool with the relevant layers enabled; the table below lists the details. Because the CASCA map data is loaded live instead of being cached on the server, adding another layer of caching and processing while also supporting snapshotting for this tool seemed time and storage intensive. Map links are omitted for some sections for which data is available but is not built into the map tool, like the FEMA NFIP community layer. Dated snapshots explicitly note the map data is current, implying there may be some drift.

Note that the map does not exactly reproduce the County Profile topic because the data behind County Profiles do not always have a 1:1 mapping layer, and in some cases the map layer presents a different source entirely. Consider the map a separate way to assess the same hazard instead of an extension of the County Profiles tool.

Limitations