Incorporating Sea Level Rise Into Flood Maps: Advisory Council’s Interim Report to FEMA

Justin Gundlach
Climate Law Fellow

The Biggert-Waters Flood Insurance Reform Act of 2012 calls for the Federal Emergency Management Agency (FEMA) to incorporate sea level rise into the Flood Insurance Rate Maps (FIRMs) that inform how FEMA and other agencies implement programs related to flood insurance and flood-related disaster mitigation and recovery. The 2013 charter of the Technical Mapping Advisory Council (TMAC) makes TMAC responsible for recommending—based on “the best available climate science”[1]—how to integrate the implications of sea level rise into FIRMs and into guidelines about how to make use of FIRMs. In its October 2015 Future Conditions Risk Assessment and Modeling Report (Interim) Report, TMAC made a number of recommendations to FEMA about how to factor climate change and sea level rise into FIRMs, and how to make the data behind FIRMs available to state and local actors for the purpose of planning for the “short-term” (2 years or less) and “long-term” (more than two years). Three features, discussed below the jump, make those recommendations especially notable.

FEMA is currently reviewing the interim report’s recommendations and is expected to issue its final approval of that report during TMAC’s December 9, 2015 conference call. Another conference call will be held on December 10, during which FEMA’s Flood Mapping Integrated Project Team will brief the TMAC on the status of FEMA’s mapping program. That briefing will kick off another TMAC review and report, this one required by the Homeowner Flood Insurance Affordability Act of 2014 and focused on the mapping that informs FEMA’s National Flood Insurance Program. FEMA is accepting written public comments until December 4 on various issues related to TMAC’s reports and will also accept brief verbal comments at the beginning of the December 9 and 10 conference calls.

First among the interim report’s features mentioned above is this: TMAC considers FEMA a source of scientific information about various flood risks, not just the keeper of FIRMs. Put another way, TMAC’s recommendations highlight that FEMA’s role must change as the scientific understanding of climate change, sea level rise, and related flood risks makes flood mapping into a more dynamic and involved task than just depicting coastlines, waterways, and adjacent 100-year flood elevations.

Second, TMAC recommends that FEMA publish information with potentially significant implications for real estate prices across the country. TMAC does not expressly state that FEMA should seek to influence real estate prices, nor does TMAC acknowledge this potential result of its advice. TMAC merely recommends that “FEMA should develop guidance for how local zoning and land use planning can be used to identify where and how land use will change in the future, and incorporate that into local hazard and risk modeling.” TMAC also recommends that “FEMA should prepare map layers displaying the location and extent of areas subject to long-term erosion and make the information publicly available.”[2]

Third, TMAC’s interim report encourages FEMA to publish “scenario based” approaches to planning in relation to flood risk. That is, rather than just publishing FIRMs that depict how elevations relate to risk of flood damage, TMAC has encouraged FEMA to incorporate key uncertainties about sea level and potential flooding into the information it makes available to state and local governments as part of the National Flood Insurance Program, the Hazard Mitigation program, and other such programmatic efforts to make infrastructure robust to (or safely distant from) flooding. Including scenarios in the information used by local planning authorities reveals not just more information about risks, but also the degree of uncertainty in the current understanding of those risks’ likelihood and magnitude.

[1] TMAC Future Conditions Report—Interim 2 (Oct. 2015).

[2] Id. at 10, 12.

Copied below are the enumerated recommendations and sub-recommendations listed in TMAC’s interim report.

TMAC’s Recommendations and Sub-recommendations

Recommendation 1: Provide future conditions flood risk products, tools, and information for coastal, Great Lakes, and riverine areas. The projected future conditions should use standardized timeframes and methodologies wherever possible to encourage consistency and should be adapted as actionable science evolves.

Recommendation 2: Identify and quantify accuracy and uncertainty of data and analyses used to produce future conditions flood risk products, tools, and information.

Recommendation 3: Provide flood hazard products and information for coastal and Great Lakes areas that include the future effects of long-term erosion and sea/lake level rise. Major elements are:

  • Provide guidance and standards for the development of future conditions coastal flood hazard and risk products.
  • Incorporate local relative sea/lake level rise scenarios and long-term coastal erosion into coastal flood hazard analyses.
  • Consider the range of potential future natural and manmade coastal changes, such as inundation and coastal erosion.

3-2 FEMA should use future risk assessments to take into account the likelihood of events occurring and their impacts, as well as the associated uncertainties surrounding these estimates.

3-3 FEMA should frame future risk messages for future conditions data and information such that individuals will pay attention to the future flood risk. Messages may be tailored to different stakeholders as a function of their needs and concerns.

3-4 FEMA should define a future population metric that uses a standard future population database along with various budget scenarios for keeping the data current to predict the percent of the population covered at various points in the future.

3-5 FEMA should take into account future development (excluding proposed flood control structures for the base condition/scenario) for future conditions mapping. An additional scenario can be generated that does include future flood control structures.

3-6 FEMA should use population growth as an indicator of areas with increased potential flood risk.

3-7 FEMA should publish multiple future conditions flood elevation layers that incorporate uncertainty so as to provide a basis for building designs that lower flood risk.

Recommendation 4: Provide future conditions flood risk products and information for riverine areas that include the impacts of: future development, land use change, erosion, and climate change, as actionable science becomes available. Major elements are:

  • Provide guidance and standards for the development of future conditions riverine flood risk products.
  • Future land use change impacts on hydrology and hydraulics can and should be modeled with land use plans and projections, using current science and build upon existing model study methods where data are available and possible.
  • Future land use should assume built-out floodplain fringe and take into account the decrease of storage and increase in discharge.
  • No actionable science exists at the current time to address climate change impacts to watershed hydrology and hydraulics. If undertaken, interim efforts to incorporate climate change impacts in flood risk products and information should be based on existing methods, informed by historical trends, and incorporate uncertainty based upon sensitivity analyses.
  • Where sufficient data and knowledge exist, incorporate future riverine erosion (channel migration) into flood risk products and information.

4-1 FEMA should use a scenario approach when considering shoreline location for the estimation of future conditions flood hazards. At least two scenarios should be evaluated, one in which the shoreline is held at its present location, and another in which the shoreline is eroded according to the best available shoreline erosion data.

4-2 FEMA should support expanded research innovation for water data collection, for example using Doppler radar.

4-3 FEMA should use a scenario approach to evaluate the impacts of future flood control projects on future conditions flood hazards.

4-4 FEMA should develop guidance for how local zoning and land use planning can be used to identify where and how land use will change in the future, and incorporate that into local hazard and risk modeling.

4-5 FEMA should support research on future conditions land use effects on future conditions hydrology and hydraulics.

4-6 FEMA should develop guidance for incorporating future conditions into coastal inundation and wave analyses.

4-8 FEMA should evaluate previously-issued guidance for future conditions land use and hydrology to incorporate best practices and lessons learned from communities that have implemented the guidance since 2001.

4-9 FEMA should determine long-term riverine erosion hazard areas for areas subject to high erosion and provided to the public in a digital layer.

4-10 FEMA should utilize a national standard for riverine erosion zone delineations that reflects geographic variability.

4-11 FEMA should develop a policy and standards on how to consider and determine erosion zones that are outside of the [Special Flood Hazard Area (SFHA)] as they ultimately affect flooding and environmental conditions within the SFHA.

4-12 FEMA should develop guidance for evaluating locally developed data from States and communities to determine if it is an improvement over similarly-available National data sets and could be used for future condition flood hazard analyses.

4-13 FEMA should develop better flood risk assessment tools to evaluate future risk, both population-driven and climate-driven. Improve integration of hazard and loss estimation models (such as HAZUS) with land use planning software designed to analyze and visualize development alternatives, scenarios, and potential impacts to increase use in local land use planning.

Recommendation 5: Generate future conditions data and information such that it may frame and communicate flood risk messages to more accurately reflect the future hazard in ways that are meaningful to and understandable by stakeholders. This should enable users to make better- informed decisions about reducing future flood-related losses.

5-1 Future flood hazard calculation and mapping methods and standards should be updated periodically as we learn more through observations and modeling of land surface and climate change, and as actionable science evolves.

5-2 FEMA should use a scenario approach for future conditions flood hazards calculation and mapping that will allow users to evaluate the robustness of proposed solutions to a range of plausible future conditions including uncertain land use and climate change impacts.

5-3 FEMA should conduct future conditions mapping pilots to continue to refine a process and methods for mapping and calculating future flood hazards and capture and document best practices and lessons learned for each.

5-4 FEMA should use Parris et. al, 2012, or similar global mean sea level scenarios, adjusted to reflect local conditions, including any regional effects (Local Relative Sea Level) to determine future coastal flood hazard estimates. Communities should be consulted to determine which scenarios and time horizons to map based on risk tolerance and criticality.

5-5 FEMA should work with other Federal agencies (ex. NOAA, USACE, USGS), the U.S. Global Change Research Program (USGCRP), and the National Ocean Council to provide a set of regional sea-level rise scenarios, based on the Parris et al, 2012 scenarios, for the coastal regions of the U.S. out to the year 2100 that can be used for future coastal flood hazard estimation.

5-7 FEMA should prepare map layers displaying the location and extent of areas subject to long-term erosion and make the information publicly available. Elements include:

  • Establishing the minimum standards for long-term erosion mapping that will be used by FEMA that must be met by partners / communities if it is to be incorporated into the FEMA products.
  • Working with Federal, State, and local stakeholders to develop these minimum standards via pilot studies.
  • Securing funding that can support sustained long-term erosion monitoring and mapping by allowing for periodic updates.

5-9 FEMA should support additional research to characterize how a changing climate will result in changes in Great Lakes and ocean wave conditions, especially along the Pacific Coast. The relative importance of waves on this coast makes this an important consideration.

5-10 For the Great Lakes, the addition or subtraction of future lake level elevations associated with a changing climate is not recommended at this time due to current uncertainty in projections of future lake levels.

5-11 FEMA should build upon the existing current conditions flood hazard analyses prepared by FEMA for the NFIP to determine future coastal flood hazards.

5-12 FEMA should incorporate local Relative Sea Level Rise scenarios into the existing FEMA coastal flood insurance study process in one of the following ways:

  • Direct Analysis – Incorporate sea level rise directly into process modeling (ex. surge, wave setup, wave runup, overtopping, and erosion) for regions where additional sea level is determined to impact the BFE non-linearly (ex. 1FT SLR = 2FT or more BFE increase).
  • Linear Superposition – Add sea level to the final calculated total water level and redefine base flood elevation for regions where additional sea level is determined to impact the BFE linearly (ex. 1FT SLR = 1FT BFE increase).

Wave effects should be calculated based on the higher Stillwater including sea level rise.

5-13 Maps displaying the location and extent of areas subject to long-term coastal erosion and future sea level rise scenarios should be advisory (non-regulatory) for Federal purposes. Individuals and jurisdictions can use the information for decision-making and regulatory purposes if they deem appropriate.

5-14 FEMA should support research for future conditions coastal hazard mapping pilots and case studies using the latest published methods to determine the best means to balance the costs and benefits of increasing accuracy and decreasing uncertainty.

5-15 FEMA should use observed riverine trends to help estimate what future conditions might look like. In watersheds where floods of interest may decrease in magnitude and frequency then use existing riverine study results as the basis for flood hazard mapping. In watersheds where floods exhibit increase in magnitude or frequency then use best available science to determine future hydrology and flood hazards.

5-16 FEMA should work with other Federal agencies via the Advisory Committee on Water Information sub-committee on hydrology to produce a new method to estimate future riverine flood flow frequencies. This method should contain ways to consistently estimate future climate-impacted riverine floods and address the appropriate range of flood frequencies needed by the NFIP.

5-17 FEMA should produce, and should encourage communities to adopt, future conditions products to reduce flood risk.

Recommendation 6: Perform demonstration projects to develop future conditions data for representative coastal and riverine areas across the nation to evaluate the costs and benefits of different methodologies or identify/address methodological gaps that affect the creation of future conditions data.

Recommendation 7: Data and analysis used for future conditions flood risk information and products should be consistent with standardized data and analysis used to determine existing conditions flood risk, but also should include additional future conditions data, such as climate data, sea level rise information, long-term erosion data; and develop scenarios that consider land use plans, planned restoration projects, and planned civil works projects, as appropriate, that would impact future flood risk.

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