Reevaluating Flood Risks: Beyond Federal Maps

If your home is outside a federally designated flood zone, flooding may appear irrelevant to you. You aren’t required to buy flood insurance, and maps suggest safety. However, this assumption could be misleading.

Evidence shows 6 million more homes are at risk of flooding than FEMA’s maps indicate—totaling around 14.6 million properties. These maps are often outdated, sometimes by decades. They typically use historical flood data, ignoring future risks. Yet, updating maps won’t fix everything. FEMA maps only assess if water may reach a neighborhood, not individual homes’ risks or flood impact.

Comprehensive data is needed to gauge home risks, including probable flood depth, building age and quality, and insurance coverage. These factors show that flood risk is more complex than maps suggest. Data reveals two houses on the same street can have different flood risks. One might be newer, well-maintained, and insured, while another could be older, poorly maintained, and uninsured. The same storm affects them differently, with distinct recovery paths. Averages obscure which homes face severe hits, making understanding individual risks crucial for residents and officials focusing flood-protection funding.

Our research team, including Aaron Flores from Arizona State University and Sara Meerow from the University of Colorado Boulder, has developed a detailed flood risk score for nearly one million Houston homes. Findings appear in a recent Applied Geography study.

Our previous research revealed over half of Houston’s 100,000 flood-prone buildings fall outside official flood zones. Those overlooked structures are likelier to be in poor condition and uninsured. The new research assists communities in identifying these homes.

Factors Making Homes Vulnerable

To better understand household vulnerability, we analyzed four home-related factors:

• Water: Estimated flood depth at the home in a 100-year flood event (1% yearly occurrence chance) was recorded using a national flood model’s parcel-level flood depth map in Harris County.
• Building: Home age, construction quality, and maintenance. Older, poorer quality homes suffer more flood damage. County appraisal records by assessors offer crucial information.
• Mobility: Traffic levels on nearby roads, measured within a half-mile and three miles. Busier roads mean greater flood disruption to work, school, and healthcare access, complicating first responders’ actions.
• Finances: Home repair costs and nearby flood insurance coverage. These factors reflect recovery costs post-flooding.

We selected these criteria as flood research consistently highlights them, but other measures can apply based on data availability.

Research Findings

Homes in the same neighborhood show varying flood vulnerability scores. Scores differ more between houses in a region than between neighborhoods. Thus, a neighborhood’s flood risk doesn’t predict an individual home’s impact during a flood.

Many neighborhoods appear safe on average but may house risky properties. Conversely, secure homes might exist amid generally risky neighborhoods. Problem roots lie at the building scale, not neighborhoods or postal zones.

Actions for Residents and Communities

Homeowners can identify risks by asking neighbors about past flooding, checking the home’s age and condition in property records, and evaluating routes to work and school for flood susceptibility. Ensure you have flood insurance as most policies don’t cover flood damage.

Communities applying our approach with local data can locate vulnerable homes masked by neighborhood averages, utilizing address-level flood scores and local building, road, and insurance records. With limited funds, better data aids wise investments in flood-proofing, drainage, and recovery efforts.

Other flood-prone cities could adopt a similar approach, using data like that available for Houston. Flood impacts transcend map lines and vary between houses on a street. Preparation by residents and authorities is essential.

Authors: Yilei Yu, Senior Researcher at Rice University; Dylan Connor, Associate Professor at Arizona State University; James R. Elliott, Professor at Rice University

This article is based on content from The Conversation and republished under a Creative Commons license.