Flood risk assessment for residences at the neighborhood scale by owner/occupant type and first-floor height

Abstract

Evaluating flood risk is an essential component of understanding and increasing community resilience. A robust approach for quantifying flood risk in terms of average annual loss (AAL) in dollars across multiple homes is needed to provide valuable information for stakeholder decision-making. This research develops a computational framework to evaluate AAL at the neighborhood level by owner/occupant type (i.e., homeowner, landlord, and tenant) for increasing first-floor height (FFH). The AAL values were calculated here by numerically integrating loss-exceedance probability distributions to represent economic annual flood risk to the building, contents, and use. A simple case study for a census block in Jefferson Parish, Louisiana, revealed that homeowners bear a mean AAL of $4,390 at the 100-year flood elevation (E100), compared with $2,960, and $1,590 for landlords and tenants, respectively, because the homeowner incurs losses to building, contents, and use, rather than only two of the three, as for the landlord and tenant. The results of this case study showed that increasing FFH reduces AAL proportionately for each owner/occupant type, and that two feet of additional elevation above E100 may provide the most economically advantageous benefit. The modeled results suggested that Hazus Multi-Hazard (Hazus-MH) output underestimates the AAL by 11% for building and 15% for contents. Application of this technique while partitioning the owner/occupant types will improve planning for improved resilience and assessment of impacts attributable to the costly flood hazard.

Cost-effectiveness of federal CDBG-DR Road Home Program mitigation assistance in Jefferson Parish, Louisiana

“…The calculation begins by utilizing the computational framework developed by Al Assi et al (2023) for determining the annual flood risk, considering both home attributes and flood data. The framework developed by Al Assi et al (2023) was chosen because it offers several advantages for the analysis of AAL across multiple homes. First, it utilizes a refined numerical integration method that allows for a more mathematically elegant calculation of AAL.…”

“…Third, the damage initiation point according to the selected DDF affects risk assessment. For example, Al Assi et al (2023) showed that considering the damage initiation point at depths less than zero increases the AAL substantially. Therefore, future research should focus on the accuracy of the flood maps, DDFs, and the damage initiation point.…”

“…The most common among these approaches uses only the flood AAL resulting from floods at return periods for which available data exist for estimating annual exceedance probabilities (AEPs), but because flood losses also occur from floods at extremely short and very long return periods for which return period data are unavailable, the losses are often underestimated (Oliver et al 2019). Therefore, applying a refined numerical integration method that covers the full losses across the range of exceedance probabilities addresses this drawback (Al Assi et al 2023;Gnan et al 2022a;Mostafiz et al 2022a). The Gumbel extreme value distribution (GEVD; Gumbel 1941) is considered one of the most widely accepted probability functions for predicting flood peak (Patel 2020;Parhi 2018) and analyzing flood frequency for calculating return periods (Singh et al 2018;Mostafiz et al 2022b;Mostafiz, 2022c).…”

“…Gnan et al (2022c) employed a lifecycle benefit-cost analysis (LCBCA) approach to optimize freeboard height for a hypothetical case study home and found that adding two feet of freeboard yields the highest NB; however, the greatest NBCR occurs with one foot of freeboard. After defining the most effective FFH as the one that yields the most reduction in flood risk for building, contents, and use, Al Assi et al (2023) found that increasing the FFH by one foot above the 100-year flood elevation results in approximately 90% flood risk reduction, but increasing the FFH by two feet above the 100-year flood elevation may provide the most effective benefit at a nearly 99% flood risk reduction.…”

Homeowner flood risk and risk reduction from home elevation between the limits of the 100- and 500-year floodplains

“…Flood risk is assessed as the product of flood occurrence probability and the associated consequences (Šugareková & Zeleňáková, 2021). Average annual loss (AAL) has been used in past research to represent flood risk (Hallegatte et al, 2013;Armal et al, 2020;Rahim et al, 2021;Mostafiz et al, 2022a;Bowers et al, 2022;Wing et al, 2022;Yildirim & Demir, 2022;Al Assi et al, 2023b;Friedland et al, 2023) in terms of costs associated with direct building loss, direct contents loss, and indirect losses such as use loss while the building is being renovated (Al Assi et al, 2023a). AAL is calculated as the integral of flood loss as a known function of the flood probability (or flood return period), and the Gumbel distribution function is one of the most widely accepted probability functions (Singh et al, 2018;Patel, 2020).…”