Flood Mapping in California: The Good, the Bad, and the Ugly

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Figure 1. The first FEMA flood maps were based on modeling run on mainframe computers (Maeder, 2015). Flood modeling has evolved far, but many FEMA maps remain based on early methods.

by Kathleen Schaefer and Nicholas Pinter

FEMA flood insurance rate maps (FIRMs) are the principle tool for managing the National Flood Insurance Program (NFIP).  They identify properties whose owners may be required to purchase flood insurance and help set flood insurance premiums across the US.

FEMA is required to assess FIRMs at least every five years, with revisions when necessary.  However, for almost half of California’s communities, the engineering studies supporting FIRMs are over 20 years old.  Less than 30,000 miles of the State’s 180,000 stream miles have been mapped by NFIP and less than 23% of the flood mapped river miles are designated as ‘Valid’.  A 2013 California Department of Water Resources (DWR) assessment, funded by FEMA, estimated the cost to bring California FIRMs into ‘Valid’ status using current methods to be over $406 million.  Most California communities are unlikely to ever get a new FEMA study.

History of US Flood Mapping

The first US FIRMs used topographic information collected by surveyors using measuring rod and surveying level, a time-consuming and sometimes dangerous process.  Water-surface elevations and floodplain boundaries were hand-drafted onto topographic base maps.  Starting in the 1980s, computer modeling improved the process, but FEMA map production remained an expensive and time-consuming.

In California, from 1973 to 1983, FEMA issued new FIRMs to 376 communities.  But it became apparent that FEMA would not meet Congressionally mandated deadlines to provide all flood-prone communities with detailed flood information.  In 1985, FEMA initiated a new method to reduce the cost and time required for new flood studies.  From 1983 to 1993, FEMA issued new FIRMs to 103 California communities using this revised method.

Beginning in 1986, Congress required NFIP to pay program expenses from insurance premiums.  Without outside federal appropriations, new flood studies lagged, and existing paper maps across the US continued to age (FEMA 2006).  For the past 20 years, an average of just 7-8 new flood studies have been completed each year in California.

By 2015, California flood maps were translated into a seamless digital flood layer.  This meant that anyone could pull up a map and determine if their home touched the floodplain boundary.  By making digital maps readily available to the public, Map Mod transformed many 40-year old, hand-drafted mapping into a digital product perceived to be accurate to within inches.

Age of California Flood Maps

The Community Status Book (FEMA 2018a) lists, by political jurisdiction, the dates of the first map and the date of current effective map.  If a single map panel is updated for any reason, the effective date for that community is updated.  For example, the current effective date for the City of Los Angeles is December 21, 2018, meaning that at least one map panel in Los Angeles was updated then.

FIRM ages

Figure 1.  Number of 532 California communities with a river study by year.  New Flood Insurance Studies (FISs) peaked in the late 1980s and early 1990s.  For the past decade, an average of 7-8 communities per year have received new studies.

On January 1, 2019, the Community Status Book listed 2012 as the average year of the current effective map for California’s 532 jurisdictions.  Most of these updates were small alterations, not formal re-analyses.  This information gives the perception that the modeling that supports the maps average just 6 years old.  The actual average date of the most recent FEMA modeling study underlying California FIRMs is 1993.

Flood-Risk Mapping Today

In 2009, FEMA developed a new plan to manage its inventory of flood maps, entitled Risk Mapping, Assessment, and Planning (Risk MAP).  The Risk MAP vision is for FEMA’s flood mapping program to become database-driven.  Additional meetings and mapping products mandated by the Risk MAP program add cost and time to complete a new study.  Since 2015 at least five new Risk MAP projects have not yet led to a final product (E. Curtis, written comm., May 4 2019).  What will it cost to upgrade the maps using the Risk MAP process?

In 2013, FEMA asked DWR to assist in developing a Mapping Master Plan (DWR 2013) to: (1) assess funding needs for Risk MAP, and (2) provide a road map for meeting the Risk MAP NVUE and deployment metrics.  The plan found that producing a Risk MAP product for each of California’s 532 communities would cost an estimated $445 million (inflation adjusted to 2019).  The Plan also showed that some communities in California may never again receive a new flood map funded by FEMA.

How does flood map age affect NFIP claims?

Over time, economic development and natural processes including climate change alter the hydrology and hydraulics of rivers and watersheds, changing flood risk.  Almost half of the FIRMs in California are based on studies over 20 years old.  This observation leads to several questions:

  • Do older flood maps lead to more flood damages and a greater proportion of flood insurance claims?
  • Do aging flood maps allow development or perhaps deter mitigation in ways that impact flood claims?

Accurate and up-to-date maps are needed to guide wise development on floodplains.

Conclusions and Recommendations

Several observations stand out from this analysis.

  • Less than 30,000 miles of California’s estimated 180,000 stream miles have been mapped by the National Flood Insurance Program (NFIP).
  • Less than 23% of California’s 30,000 NFIP mapped stream miles are designated as ‘Valid’ in FEMA’s asset management system.
  • Of the 22,138 California flood mapped stream miles not characterized as ‘Valid,’ FEMA currently has plans to study only a small fraction.
  • Most of California’s FIRMs are based on studies from the 1970s and early 1980s, when mapping and computing technology was significantly less accurate.
  • The conversion of paper FIRMs to digital format can give the public and policy makers false perceptions of map accuracy and flood risk.
  • The cost of updating all of California’s outdated FIRMs using the Risk MAP process ($445 million dollars) would be almost $2000 per current California NFIP policyholder (inflation adjusted to 2019).
  • Many California communities may never again receive a new flood study funded by FEMA.

The original mandate of NFIP was to update flood maps at least every five years.  In actuality, map updates are unusual and the nation’s inventory of flood maps has become “out-of-date, using poor quality data or methods and not taking account of changed conditions” (Horn 2018).

Flood maps continue to age faster than they are updated.  New mapping and map updates have become more expensive and time-consuming.  NFIP has run up a $36 billion structural deficit.  California can lead in using new technologies to quantify and communicate flood risk.  Several private companies already market models that assess flood risk throughout the US.  These models are arguably less accurate than a detailed site-specific model, but they calculate flood hazard as a continuous parameter, not just in or out of a 100-year line.  These risk-based models can better quantify and incorporate uncertainty.  Risk-based modeling also can easily and quickly be updated to reflect changing hydrologic, hydraulic, and climatic conditions over time.

California should consider making improvements to how flood risks are assessed, mapped, and updated.

Further Readings

California Department of Water Resources (DWR), 2013.  California Deployment and Mapping Master Plan (Draft). Prepared under Mapping Activity No. 3 executed in 2010 by Atkins.  Sacramento, CA: CA Department of Water Resources.

Congressional Budget Office (CBO), 2017.  “The National Flood Insurance Program: Financial Soundness and Affordability. Congressional Budget Office Report.  Washington D.C.: Congressional Budget Office.  https://www.cbo.gov//system//files//115th-congress-2017-2018//reports//53028-nfipreport2.pdf..

FEMA, 2018a.  Community Status Book, FEMA Database.  The National Flood Insurance Program Community Status Book.  2018.  https://www.fema.gov/national-flood-insurance-program-community-status-book.

Horn, D.P.,  2018.  “National Flood Insurance Program: Selected Issues and Legislation in the 115th Congress. Report to Congress R45099.  Washington DC: Congressional Research Service.  https://fas.org/sgp/crs/homesec/R45099.pdf.

Kelly, J.V.  2017.  FEMA Needs to Improve Management of Its Flood Mapping Programs. OIG Report OIG-17-110.  Washington D.C.: Office of the Inspector General, Department of Homeland Security.  https://www.oig.dhs.gov/sites/default/files/assets/2017/OIG-17-110-Sep17.pdf.

Kathleen Schaefer is a PhD student in Civil Engineering at the University of California, Davis and a former FEMA administrator.  Nicholas Pinter is a Professor at the UC Davis Department of Earth and Planetary Sciences.


About jaylund

Professor of Civil and Environmental Engineering Director, Center for Watershed Sciences University of California - Davis
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2 Responses to Flood Mapping in California: The Good, the Bad, and the Ugly

  1. Tom Orvis says:

    No worries – it’s all good

    *Tom Orvis*

    *Stanislaus County Farm Bureau*

    *(209) 522-7278*

    *TomO@stanfarmbureau.org *

    *“Every once in awhile we need to howl with the coyotes instead of just bark with the dogs.” – theorvii*

    *From:* California WaterBlog [mailto:comment-reply@wordpress.com] *Sent:* Sunday, June 16, 2019 5:27 PM *To:* tomo@stanfarmbureau.org *Subject:* [New post] Flood Mapping in California: The Good, the Bad, and the Ugly

    jaylund posted: ” by Kathleen Schaefer and Nicholas Pinter FEMA flood insurance rate maps (FIRMs) are the principle tool for managing the National Flood Insurance Program (NFIP). They identify properties whose owners may be required to purchase flood insurance and help”

  2. Pingback: Risk Rating 2.0: A first look at FEMA’s new flood insurance system | California WaterBlog

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