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Potential Flood Map Inaccuracies within the Fed’s Second District


Nov 10, 2023


The Nationwide Flood Insurance coverage Program (NFIP) flood maps, which designate areas vulnerable to flooding, are up to date periodically by the Federal Emergency Administration Company (FEMA) and neighborhood efforts. Even so, many maps are a number of years outdated. Because the earlier two posts within the Excessive Climate collection present, climate-related dangers fluctuate geographically. It’s due to this fact necessary to provide correct maps of such dangers, like flooding. On this publish we use detailed information on the flood danger confronted by particular person dwellings in addition to digitized FEMA flood maps to tease out the diploma to which flood maps within the Second District are inaccurate. Since inaccurate maps could go away households or banks uncovered to the chance of uninsured flood injury, understanding map inaccuracies is vital. We present that, when aggregated to the census tract degree, numerous maps don’t absolutely seize flood danger. Nonetheless, we’re additionally capable of present that updates do in reality enhance map high quality.

Flood Map Updates

The NFIP was established within the late Nineteen Sixties following extreme riverine flooding within the U.S. heartland. As a part of the flood insurance coverage program, FEMA works with communities to create maps of areas in the USA that face heightened flood danger. One of the crucial necessary implications of those flood maps is the insurance coverage requirement for mortgage debtors. Mortgage candidates in areas which have no less than a 1 % likelihood of flooding every year should buy flood insurance coverage. This system in addition to the implications for the mortgage market are mentioned in earlier Liberty Avenue Economics posts (see right here and right here).

The possibility of a area flooding isn’t static, nevertheless. On the one hand, the local weather continues to alter, and the dangers posed by a rising sea degree, hurricanes, and even summer time rains are always evolving. However, many communities proactively handle flood dangers by the development of dams, floodways, or elevated dwellings to cut back the prospect of catastrophic injury. Consequently, FEMA periodically updates flood maps. These updates can see some beforehand “unmapped” areas obtain a flood danger designation whereas different areas could lose this categorization following native enhancements. Our information signifies that, though the variety of parcels designated as uncovered to “flood danger” grows on common, greater than a 3rd of all modifications contain some parcels of land receiving a decrease danger designation. Nonetheless, the difficult nature of modeling dangers—coupled with the need of neighborhood enter—implies that maps could also be up to date occasionally and thus develop into outdated shortly. Regardless of latest efforts to replace maps, many are nonetheless many years outdated.


A Federal Emergency Management Authority (FEMA) flood map taken from its mapping center as of June 2023.
Supply: Federal Emergency Administration Company.
Notes: This map depicts a FEMA South Centre, PA flood map as taken from FEMA’s mapping heart as of June 2023.. As may be seen from the pink spotlight, the map has been in place since 2008, with no amendments having occurred since then within the space depicted.

Outdated maps could lead to dangers that debtors or lenders are unaware of—see the above map that depicts a map that’s fifteen years outdated. 1 / 4 of all maps had been fifteen years outdated in 2022 and over half had been greater than 5 years outdated. It’s attainable that the flood zones depicted within the map have modified because the map was final up to date. As a consequence, some householders, who may need purchased insurance coverage had they been conscious of the dangers, shall be sick ready and under-insured within the occasion a catastrophe strikes. Though understanding the diploma to which properties face unknown dangers has been difficult by the paucity of knowledge, we try to deal with this challenge by capitalizing on new information that has just lately develop into obtainable.

Flood Map Accuracy

FEMA’s course of for updating maps includes neighborhood enter in addition to attainable amendments to the maps by particular person property homeowners prepared to contest maps utilizing their very own surveyors. Furthermore, its maps designate stark flooding boundaries—a location is both in or exterior of a flood zone. Third-party suppliers are ready to make use of flood fashions and elevation mapping, in addition to satellite tv for pc imaging to assign extra granular danger measures to an space with out the necessity for neighborhood enter. 

We use information for 2021 on the flood danger confronted by particular person properties in the USA, as offered by CoreLogic, to determine the diploma to which some properties could also be inaccurately flood-mapped. Lately, CoreLogic started estimating common annual flood injury for properties throughout the USA. We plot a property on the newest iteration of flood maps, which allows us to see whether or not the property has been assigned a 100-year, 500-year, or no flood danger standing. Subsequently, we examine the official danger designation with expectations from CoreLogic on the chance {that a} property would face greater than $1,000 in damages within the occasion of flooding (see an outline of CoreLogic’s methodology). We run this train for about fifteen million particular person properties within the Second District. We then combination the information to the census tract-level. A census tract with a better share of properties that might have acquired a flood zone designation utilizing the CoreLogic methodology, however would not have one beneath the FEMA map, is coloured a darker shade of blue within the map beneath.

Second District Census Tract with Doubtlessly Inaccurate Flood Maps

A map of the Federal Reserve’s Second District excluding overseas territories, shows census tracts and the extent of potential mapping inaccuracies.
Supply: Authors’ calculations based mostly on FEMA maps, SHELDUS, FirstStreet, and CoreLogic information.
Word: This map depicts the Second District excluding Puerto Rico and the U.S. Virgin Islands. We present census tracts and colour these by the diploma to which they could be inaccurately flood-mapped. An inaccurately mapped property is one which faces important flood danger, however isn’t designated as being in a flood zone. We then combination to the census tract degree, with darker shaded areas dwelling to a better share of inaccurate properties. The utmost mirrored on the map is 60 % inaccurate, with lighter shaded areas displaying barely any inaccuracies.

Flood Map Updates

It’s reassuring to see that probably the most precisely mapped areas are the place maps have been up to date most just lately. Within the subsequent map, we once more plot the Second District, and spotlight these census tracts with important (constructive) map modifications. These are areas the place the flood zone designation has been expanded, based mostly on map modifications between 2013 and 2022 in our historic map information.

Second District, excluding Connecticut, Puerto Rico, and U.S. Virgin Islands

A map of the Federal’s Reserve’s Second District excluding Connecticut and overseas territories, highlights census tracts with positive map changes, that is, regions where the flood zone designation has been expanded, based on map changes between 2013 and 2022.
Supply: Authors’ calculations based mostly on FEMA maps.
Notes: This map exhibits constructive map updates. Blue shaded areas are people who noticed substantial progress of mapped areas between 2013 and 2022. The darkest shading signifies areas that weren’t flood-map lined in 2013 however are fully lined in 2022. Lacking information means we exclude CT on this illustration.

Probably the most shaded areas within the above map are these areas which have undergone important map modifications—with areas in darkish blue changing into absolutely mapped, the place no map existed earlier than. The extra darkly shaded areas within the above map are these which can be much less shaded within the second map above, implying a detrimental correlation between map updates and map inaccuracies. The correlation coefficient is bigger than -0.5 and important, implying map updates cut back inaccuracies. This means that FEMA’s updating efforts are precious in bettering map high quality, regardless of the related prices to FEMA and communities. The outcome holds true within the nation as a complete and never simply within the Second District. Thus, latest map updates have diminished map inaccuracies.

Concluding Remarks

FEMA maps are sometimes inaccurate as a result of delay in updating maps to replicate modifications within the flood dangers. This follows naturally from the truth that updating takes a very long time and requires expensive surveys, neighborhood enter, and injury assessments. Outdated maps are probably imperfect reflections of danger. A number of areas within the Second District could also be inaccurately mapped with penalties for the under-insurance of households. Nonetheless, map updates–once they happen–cut back the inaccuracies, that means FEMA’s updating efforts are each crucial and precious. The following publish within the Excessive Climate collection examines how these inaccuracies could influence financial institution lending within the Second District.

Photo: portrait of Kristian Blickle

Kristian Blickle is a monetary analysis economist in Local weather Threat Research within the Federal Reserve Financial institution of New York’s Analysis and Statistics Group.

Katherine Engelman is a former information scientist within the Knowledge and Analytics Workplace within the Financial institution’s Know-how Group.

Theo Linnemann is an information scientist within the Knowledge and Analytics Workplace within the Financial institution’s Know-how Group.

Photo: portrait of João A.C. Santos

João A.C. Santos is the director of Monetary Intermediation Coverage Analysis within the Federal Reserve Financial institution of New York’s Analysis and Statistics Group.

Learn how to cite this publish:
Kristian Blickle, Katherine Engelman, Theo Linnemann, and João A.C. Santos, “Potential Flood Map Inaccuracies within the Fed’s Second District,” Federal Reserve Financial institution of New York Liberty Avenue Economics, November 10, 2023, https://libertystreeteconomics.newyorkfed.org/2023/11/potential-flood-map-inaccuracies-in-the-feds-second-district/.

The views expressed on this publish are these of the creator(s) and don’t essentially replicate the place of the Federal Reserve Financial institution of New York or the Federal Reserve System. Any errors or omissions are the duty of the creator(s).


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