Improved building-specific flood risk assessment and implications of depth-damage function selection

Average annual loss (AAL) is traditionally used as the basis of assessing flood risk and evaluating risk mitigation measures. This research presents an improved implementation to estimate building-specific AAL, with the flood hazard of a building represented by the Gumbel extreme value distribution. AAL is then calculated by integrating the area under the overall loss-exceedance probability curve using trapezoidal Riemann sums. This implementation is compared with existing AAL estimations from flood risk assessment. A sensitivity analysis is conducted to examine the variability in AAL results based on depth-damage function (DDF) choice. To demonstrate the methodology, a one-story single-family residence is selected to assess the financial benefits of freeboard (i.e., increasing lowest floor elevations). Results show that 1 ft. of freeboard results in annual flood risk reduction of over $1,000, while 4 ft of freeboard results in annual flood risk reduction of nearly$2,000. The sensitivity result suggests that the DDF selection is critical, as a large proportion of flood loss is counted below the top of the first floor. The findings of this paper will enhance DDF selection, improve flood loss estimates, encourage homeowners and communities to invest in flood mitigation, and provide government decision-makers with improved information when considering building code changes

Freeboard life-cycle benefit-cost analysis of a rental single-family residence for landlord, tenant, and insurer

Flood risk to single-family rental housing remains poorly understood, leaving a large and increasing population underinformed to protect themselves, including regarding insurance. This research introduces a life-cycle benefit-cost analysis for the landlord, tenant, and insurer [i.e., (U.S.) National Flood Insurance Program (NFIP)] to optimize freeboard [i.e., additional first-floor height above the base flood elevation (BFE)] selection for a rental single-family home. Flood insurance premium; apportioned flood risk among the landlord, tenant, and NFIP by insurance coverage and deductible; rental loss; moving and displacement costs; freeboard construction cost; and rent increase upon freeboard implementation are considered in estimating net benefit (NB) by freeboard. For a 2,500 square-foot case study home in Metairie, Louisiana, a two-foot freeboard optimizes the combined savings for landlord and tenant, with joint life-cycle NB of $23,658 and$14,978, for a 3% and 7% real discount rate, respectively. Any freeboard up to 2.5 feet benefits the tenant and NFIP, while the landlord benefits for freeboards up to 4.0 feet. Collectively, results suggest that at the time of construction, even minimal freeboard provides substantial savings for the landlord, tenant, and NFIP. The research provides actionable information, supporting the decision-making process for landlords, tenants, and others, thereby enhancing investment and occupation decisions

Single-Family Residential Flood Loss Reduction through Freeboard

The lack of flood loss estimation methods conducted on a micro-scale level that consider the full loss‐exceedance probabilities curve poses a significant problem in flood risk assessment. Also, the lack of robust benefit-cost analysis (BCA) that quantifies benefits at the micro-scale level leads to sub-optimal results, and therefore sub-optimal decisions when determining the optimal freeboard. Further, flood loss assessments focus on owner-occupied housing and neglect rental housing. These loss assessment deficiencies underscore the need for a robust assessment that quantifies the life-cycle benefits for all stakeholders and provides actionable information to enable informed decisions. This research presents a comprehensive methodology such that the life-cycle benefits of adding freeboard for homeowners, landlords, and tenants are evaluated at the single-residence building level using life-cycle BCA. The expected average annual loss (AAL) from flooding is determined through the numerical integration of the full loss-exceedance probabilities curve. The optimal freeboard is determined through a micro-scale BCA with life-cycle benefits disaggregated and allocated to the proper parties. The results show that while the construction cost of adding freeboard is modest, the life-cycle benefits of avoided losses and savings are substantial. Results highlight the need to assess flood risk at the micro-scale level for a more localized and accurate assessment, where it can be upscaled in a “bottom-up” approach for a higher degree of accuracy. The results also highlight the need to include rental housing and underscore the need for a robust life-cycle BCA that provides actionable recommendations to landlords and tenants. The numerical integration AAL estimation method introduced in this research is fundamental, with only few parameters required to reduce the increased prediction uncertainty associated with more complex models requiring more input parameters. Further, this research provides a robust, generalized methodology to evaluate the benefits of adding freeboard through a micro-scale life-cycle BCA. Moreover, this work provides a novel framework for quantifying life-cycle benefits of freeboard for landlord and tenant in a single-family rental housing. All methodologies introduced in this research are developed generally and can be adapted for new data, loss functions, and other input

Table_1_Freeboard life-cycle benefit-cost analysis of a rental single-family residence for landlord, tenant, and insurer.docx

Flood risk to single-family rental housing remains poorly understood, leaving a large and increasing population underinformed to protect themselves, including regarding insurance. This research introduces a life-cycle benefit-cost analysis for the landlord, tenant, and insurer [i.e., (U.S.) National Flood Insurance Program (NFIP)] to optimize freeboard [i.e., additional first-floor height above the base flood elevation (BFE)] selection for a rental single-family home. Flood insurance premium; apportioned flood risk among the landlord, tenant, and NFIP by insurance coverage and deductible; rental loss; moving and displacement costs; freeboard construction cost; and rent increase upon freeboard implementation are considered in estimating net benefit (NB) by freeboard. For a 2,500 square-foot case study home in Metairie, Louisiana, a two-foot freeboard optimizes the combined savings for landlord and tenant, with joint life-cycle NB of $23,658 and$14,978, for a 3% and 7% real discount rate, respectively. Any freeboard up to 2.5 feet benefits the tenant and NFIP, while the landlord benefits for freeboards up to 4.0 feet. Collectively, results suggest that at the time of construction, even minimal freeboard provides substantial savings for the landlord, tenant, and NFIP. The research provides actionable information, supporting the decision-making process for landlords, tenants, and others, thereby enhancing investment and occupation decisions.</p