Rethinking Flood Risk in Residential Areas

If your home is outside a federally designated flood zone, you might assume flooding isn’t your concern. Flood insurance might not be required, and the maps may seem reassuring. However, reality paints a different picture. Recent data suggests nearly 6 million more homes are at risk of flooding than indicated by FEMA’s 100-year flood maps, affecting 14.6 million properties in total based on some estimates.

The official FEMA flood maps are often outdated, with some maps being over two decades old. Even updated maps rely on historical flooding records rather than potential future risks. Additionally, these maps address only one specific question: Is my neighborhood likely to flood? They do not assess individual homes or potential impacts of rising water levels. Understanding these impacts requires comprehensive data, such as probable flood depth, the building’s age, quality of construction, and available insurance coverage.

Individual versus Neighborhood Risk

Taking these factors into account, the actual flood risk for your home could be more complex than the maps suggest. Two houses on the same street might experience vastly different flooding risks despite being in the same flood zone. Local authorities can play a role in understanding this variance.

For example, one home might be newer, in good repair, and insured against floods. Another nearby house might be older, situated in a low-lying area, in poor condition, and uninsured. A single storm could affect these homes in vastly different ways, resulting in varied recovery scenarios.

Neighborhood averages complicate identifying which homes are most at risk. Understanding individual property risks is vital for residents planning protection methods and for officials deciding on resource allocation for flood protection.

Detailed Flood Risk Assessment

To highlight the importance of house-specific differences, researchers—including Aaron Flores from Arizona State University and Sara Meerow from the University of Colorado Boulder—developed a detailed flood risk assessment for nearly 1 million homes in Houston, detailed in a study published in Applied Geography.

Prior research in Houston revealed that more than half of 100,000 flood-prone buildings lie outside official flood boundaries. These overlooked buildings tend to be in poorer condition and uninsured, thus more vulnerable to floodwaters.

Identifying Vulnerabilities

The study assessed each household’s vulnerability using four criteria:

• Water: Likely flood depth during a 100-year flood event at the residence level.
• Building: Age and condition of the home. Older or poorly maintained homes suffer more damage.
• Mobility: Traffic levels around the home. Busier roads increase disruption during floods.
• Finances: Repair costs and the prevalence of flood insurance among nearby homes.

These factors influence how severely a flood can impact a community, affecting water arrival, building resilience, accessibility, and recovery costs. Cities can adapt these measures based on available data.

The study’s findings show significant variance in flood vulnerability within neighborhoods. This indicates that neighborhood-level flood risk assessments might not accurately reflect individual home risk.

Steps for Residents and Communities

Homeowners can evaluate their own risk by querying city flood plain offices and reviewing local property records. Additionally, checking potential flood routes and current insurance coverage is critical.

Communities can apply these assessment methods using their own data to identify vulnerable homes that neighborhood averages might obscure. Starting with address-level flood scores like First Street’s, adding building, road, and insurance data, communities can better allocate limited resources for flood protection and recovery efforts.

Similar data is available across the US, allowing other flood-prone cities to adopt these strategies. Floods often disregard designated lines and do not affect each home equally. Residents and flood authorities must prepare for this reality.

Yilei Yu, Senior Researcher and Postdoctoral Fellow in Geography, Rice University; Dylan Connor, Associate Professor of Geographical Sciences and Urban Planning, Arizona State University, and James R. Elliott, Professor of Sociology, Rice University. This article is republished from The Conversation under a Creative Commons license.