Evaluation of Analytical Techniques for Production of a Sea Level Rise Advisory Mapping Layer for the NFIP Jerry W. Sparks, P.E., CFM ASFPM Annual National Conference Louisville, KY May 17, 2011

Overview  Background  SLR Advisory Map Concept  Study Purpose and Results  Next Steps

Background  FEMA & Climate Change  Projected Impact of RSLR on NFIP  GAO recommended FEMA analyze impacts of climate change on NFIP o FEMA National Climate Change Study  SLR Advisory Feasibility Study  Risk MAP  Significant investment into updating coastal studies

TRB Special Report 290 “ FEMA should reevaluate the effectiveness of the National Flood Insurance Program in risk reduction…At a minimum, updated FIRMs that account for sea level rise…should be a priority in coastal areas”

SLR Advisory Layer Concept  Non-regulatory (advisory)  Low incremental production cost  Develop as add-on to Risk MAP studies  Leverage models/data produced by FIS  Convey future changes to coastal flood hazard  Guide long-term planning & adaptation  Develop for pro-active states & communities

Proof of Concept Study  Scope:  Evaluate analytical techniques for suitability to produce a Sea Level Rise Advisory Layer  Consider approaches across the range accuracy and level of effort  Evaluate trade-offs  Provide mock-ups of cartographic products for advisory layer  Recommendations and considerations for follow-on pilot studies

Study Area Puerto Rico  Selection based on ready availability of baseline framework o Ability to cost effectively re-run FIS analysis o Accessible data o Modern study* o Diversity of coast type

Sea Level Rise Scenario Definition for This Study  Methodology  Review latest literature  Evaluate observations  USACE procedure (EC )  Validate selection  Scenario:  Limited to 1  0.4 m ( Adapted from Vermeer & Rahmstorf, 2009, and USACE, 2009

Establish Baseline Evaluate Proposed Combinations Compare Results Methodologies Wave WHAFIS HAZUS FIT Wave Equations Surge ADCIRC Baseline SLOSH X Linear Superposition X X X Process: Methods:

Storm Surge Modeling - ADCIRC  ADCIRC Simulations  Approach o Re-use FIS model, input files, storm suite o Impose SLR condition at boundaries, wait & save o Run storms on new condition, same setting as FIS  Issues o New instabilities

Storm Surge Modeling - SLOSH  SLOSH Simulations  Approach o Leverage National Hurricane Center Basin (2010) o Re-use FIS storm data, surge stations o MSL, then set SLR condition as tide level  Issues o Weather generated, rather than input o FIS surge stations too dense, req. adjustment

Comparison – ADCIRC & SLOSH At coast: SLOSH: 0.5 mi (2580 ft) ADCIRC: ft

ADCIRC Compared to SLOSH (FIS Case – 0 ft MSL) SLOSH > FIS (ADCIRC) Median: 1.7 ft Range: 6.4 ft 23% Error Trend: Difference ↑ w/ return period. (1.3 ft spread from 10 to 500 yr) ADCIRC higher SLOSH higher

ADCIRC Compared to SLOSH (SLR Case – 1.4 ft MSL) SLOSH > ADCIRC Median: 0.6 ft Range: 6.6 ft Error: 10% Previous Trend: Difference ↑ w/ return period – Not evident in this case

ADCIRC Compared to Linear Superposition (SLR Case ft MSL) ADCIRC SLR ≈ Simple + Median: 0 ft Range: 0.8 ft Error: 1% Trend: Difference ↑ w/ return period – (0.1)

Comparison of Surge Methodologies MethodProsCons External Data Requirements Required Expertise Duration ADCIRC Accurate, consistent with FIS ExpensiveNone*High2-5 Months** SLOSH Quick, physics based Did not compare well to FIS elevations (Baseline = +23% error; SLR = +10% error) Some preparation required depending on study High2 Weeks Linear Superposition Simple and efficient, compared well to ADCIRC solution Does not directly consider physical process, applicability to other locations uncertain (1% error) NoneLow1 Hour *Assumes ADCIRC application for FIS study **Represents computational production requirements for typical JPM storm suites

Study Reaches  Reach Selection (Total of 10 miles)  Two reaches selected to test methods over a variety of conditions  Selection factors: o Floodplain Extent o Flooding Type o Land Cover / Urbanization o Geomorphology

WHAFIS Evaluation  Concept:  Serve as a baseline case  Approach:  Leverage FIS study data  Re-run as FIS application  Re-map flood zones using FIS as guide  Comparison to:  HAZUS Flood Information Tool  Geospatial application of wave equations

Application of Wave Equations  Apply depth-limiting wave criterion to assess changes in flood elevation  Shows that wave effects can increase flood elevation beyond sea level change Parameter, all units in feet Baseline Case SLR Scenarios 1 ft2 ft3 ft Total Stillwater Ground Elevation5 555 Water Depth Wave above SWEL Wave Crest Elevation BFE Difference, SLR-Baseline 135

Summary of Wave Hazard Methods MethodProsCons External Data Requirements Required Expertise Duration WHAFIS Spatially variable, considers dune failure, obstructions and wave regeneration Relatively expensive NoneHigh2-6 Weeks* HAZUS Flood Information Tool Existing application, seamless implementation Did not work (tools not implemented) NoneMedium- Wave Equations Informative, effective given uncertainties No obstructions, not spatially variable NoneLow1 Hour *Duration dependent on size and complexity of study area

Example Cartographic Products FIS-style mapping  Familiar  Specific Uncertainty bands  Clear uncertainty  Distinct  Difficult to define

Example Cartographic Products Color-shifted uncertainty  Highly visual  May present complexities if too highly resolved Flooding changes  Can be presented alone  Can be superimposed on any other method

Data Serving Concepts  Increment Driven  Scenario Driven

Findings and Recommendations  Further examination of linear superposition needed  FIS approach provides only accurate description of changes to flood zone boundaries  Analysis best undertaken at the time or shortly after FIS studies  Both changes in surge elevation and wave height should be considered  Linear superposition combined with wave equations may provide effective estimate at low production cost  Implement through Community Rating System and Coastal Construction Manual

Next Steps Programmatic Consideration Engage PartnersReview Methods Identify and Select Study Areas Apply and Evaluate Results Stakeholder Feedback Lessons Learned Production Recommendations Program Implementation  Proposed plan for phased approach over FY10-12

Evaluation of Analytical Techniques for Production of a Sea Level Rise Advisory Mapping Layer for the NFIP QUESTIONS?

Overview  Background  Vision  Study Purpose and Results  Next Steps  Conceptual Mapping Products

Risk MAP and Coastal Updates  Risk MAP Program  Address hazard gaps  Increase awareness  Translate to mitigation  Enhance digital products  Coastal Updates  Large investment into coastal mapping  100% of pop. coast to have modern studies

Programmatic Considerations  How will development of this data affect program perception?  What are the potential benefits and drawbacks to the NFIP?  How much does FEMA want to invest in producing SLR advisory information?  Should FEMA enter into being a provider of SLR scenarios, or should FEMA direct users to other sources?  Should long-term erosion and/or changes in storminess be taken into account? If so, how?  Are there potential impacts to insurance rates, both for the NFIP and private insurers?  What is the level of expected community participation?  What type of public outreach would be needed to implement the program?  Should risk related to SLR changes be communicated (rather than just hazards)?  How should the concept and data be presented and delivered to best communicate the advisory intention and not engender initial fears that it will become a mandatory program element?  Is there future potential or desire for incorporating the advisory layers into floodplain regulations, and if so, what are the implications to the initial efforts?  How should SLR advisory information be tied into mitigation planning and risk reduction?

Graphical User Interface— Scenario Approach  User selects scenario and time  Graph and map display selection ProCon Scenario InformationFuture relevance limited to scenario accuracy Less computationally intensive Requires selection of specific scenarios; does FEMA want to be in position of establishing SLR scenarios?

Graphical User Interface— Incremental Approach  User selects level (e.g., whole foot increments)  Map displays selection; graph display times of selection ProCon Does not require scenarioLess informative Easy standardization of method; consistent with approach used by CSC Sea Level Rise Viewer Slightly more computationally intensive Covers a wide range of possible SLRs