FEMA Flood Maps and Limitations
FEMA flood maps are the gold standard for understanding flood risk in the U.S, but they have their limitations.
Flooding in the United States (U.S.) has cost over $1 trillion in inflation adjusted dollars since 1980 and represents more than 63% of the cost associated with all billion dollar or more natural disasters. It is therefore critical to understand both the economic and safety implications of flood risk by having a complete and accurate flood risk data set.
Federal Emergency Management Agency (FEMA) flood maps are the gold standard for understanding flood risk in the U.S. These maps are a fundamental element of the National Flood Insurance Program (NFIP), which was created to offer flood protection guidelines and provide a national program for floodplain management. The program requires participating communities to develop and adopt flood maps and enact minimum floodplain standards based on them. In addition, the NFIP encourages communities to adopt and enforce floodplain management regulations such as zoning codes, building codes, subdivision ordinances, and rebuilding restrictions.
Insurance offered through the NFIP includes different coverage levels and premium rates, which are determined by factors like property characteristics and location. To set premium rates, FEMA considers the following factors: location in flood zones, elevation of the property relative to the community’s base flood elevation, characteristics of the property, building type, number of floors, basement presence, and the year a structure was built relative to the year of it’s community’s original flood map.
The flood maps created by FEMA communicate flood vulnerability for properties by categorizing them as inside or outside of 100-year floodplains (1% annual chance of flooding) and 500-year floodplains (.2% annual chance of flooding), amongst other zones. These maps, while complicated, must remain accurate, because communities rely on them to assess flood risk.
There are 8 steps involved in the issuing of updated or new FEMA flood maps. These steps involve select local leaders and special interest groups, and are subject to budget constraints and directives from Congress or city officials. These groups often make revisions to the initial scientifically produced modeled outputs based on future plans or other factors. Therefore, FEMA flood maps may not accurately represent the actual total areas at risk, or may not accurately show the severity of the flood risk for a given area.
Though the National Flood Insurance Reform Act of 1994 requires that FEMA assess the need to revise and update all flood maps every 5 years, 75% of FEMA flood maps are older than 5 years and 11% date back to the 1970s and 1980s. A 2017 report from the Department of Homeland Security’s Inspector General’s Office found that despite the program’s goal of having 80% of its maps up-to-date, only 42% currently reflected accurate flood risk projections.
The delay in updating is mostly due to budget constraints applied to FEMA and the NFIP program. In addition to these delays, many areas in the U.S. are still unmapped by FEMA and none of the mapped areas have future environmental changes incorporated into the risk projections; the maps look at historical flooding events as predictors of current flood risk.
The issue with using historical risk alone to predict current risk is that these risks will change over time, increasing along with other environmental factors such as rising sea levels, surface temperatures, and sea surface temperatures. These factors will cause floods to increase in both frequency and severity, putting an increasing number of Americans at risk. Read more about why flooding is increasing here.
ENVIRONMENTAL FACTORS
High sea levels cause more water to be available for hurricanes to push onto land, resulting in greater (or more extreme) storm surge. That additional water also removes friction that would otherwise slow the surge. Research has shown that sea level rise has a non-linear positive impact on storm surge; one conservative model based on Hurricane Andrew showed that each unit of sea level rise resulted in an additional 23% increase in storm surge. This can drastically affect risk projections for coastal communities.
For example, sea level rise since 1970 was responsible for 43% of the 133,000 homes impacted by Hurricane Irma’s storm surge in 2017. The research that identified this used a geospatial analysis to model the impact of an Irma-like storm at the sea levels observed in 1970, and found that approximately 57,000 of the properties impacted would not have been affected with 1970 sea levels. Additionally, if a Hurricane Irma like storm were to hit at the sea level projected for 2050 by the Army Corps of Engineers, (approximately 15 inches above current levels), the storm surge would affect an additional 200,000 homes. In other words, a 1.26 foot increase in nearby sea levels would result in a 150% increase in the number of homes impacted.
Similar findings were discovered when this research was applied to Hurricane Florence, with sea level rise since 1970 responsible for 21.5% of the homes impacted by Hurricane Florence’s storm surge in 2018. A similar storm making impact at the sea levels of 1970 would have put 40,000 homes at risk from flooding, but in 2018 there were a total of 51,000 homes impacted. By 2050, this number would climb to over 100,000.
Adjusting current calculations to include pluvial (rain) and fluvial (riverine) flooding is also essential to having accurate projections. Rainfall-driven flooding contributes to a significant increase in risk for inland communities, a considerable amount of which are currently unmapped regions even though they experience flooding. When fully accounting for fluvial and pluvial risks, 41 million inland Americans are within a 100-year floodplain. However, FEMA currently only identifies 13 million of these people.
UNDERESTIMATED RISK
Coastal development, flood risk, and the population have all increased in the last decade. Because of several factors, including the aforementioned issues FEMA’s flood maps, many homeowners underestimate their level of risk, leaving them not only vulnerable and exposed, but likely to be underinsured. Looking at the costs of just two of the 2017 Atlantic hurricanes, an estimated 77% of the total loss came from uninsured homeowners, between $38 billion and $57 billion.
This unaddressed flood risk increases the amount of federal fiscal exposure, is almost invisible to Congress and taxpayers, and contributes to policyholders’ confusion concerning their flood risk. Underinsured properties can disrupt the NFIP’s functionality and result in monetary losses, as insurance premiums are unable to cover the cost of payouts. For example, the program has over 1.5 million flood insurance policies that provide over $1.3 trillion in coverage, but only collects roughly $3.6 billion in annual premium revenue. Over time, these losses have accumulated, and even with Congress forgiving $16 billion of debt in 2017, the program still owes more than $20.5 billion.
ACCURATE FLOOD MAPS
Beginning in 2020, FEMA will use private-sector data to shift the way that risk is calculated through the NFIP from merely inside or outside of a 100-year floodplain to a graduate range of property-specific risks, offering some improvements to the well-recognized limitations of current risk modeling. FEMA has already unveiled preliminary maps for certain areas in Florida, which will impact as many as 60,000 people between the city of Tampa and Hillsborough County. The new maps, which change the base flood elevation for many properties, will put some homeowners at less risk, some at more, and others that previously had no risk into a FEMA flood zone.
Though the updates and improvements that come with the newest set of FEMA flood maps are a step in the right direction, they will only partially solve the larger issue. The most accurate flood risk projections require the incorporation of future scenarios and environmental changes such as sea level rise, historic data, and pluvial and fluvial flooding. Only then will all homeowners in America understand their true flood risk and communities be adequately protected.
Originally published at FirstStreet.org on March 21, 2019.
First Street Foundation is a 501(c)(3) nonprofit that quantifies and communicates America’s flood risk.
