The Value of Wetlands for Flood Mitigation
Transcript of The Value of Wetlands for Flood Mitigation
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The Value of Wetlands for Flood Mitigation
Eric J. Ziemba,
Allison M. Borchers (USDA ERS)
Martin D. Heintzelman (Clarkson University)
Abstract
Floods cause billions of dollars in property damages each year in the United States.
While programs like flood insurance and disaster relief help to lessen the burden on
those harmed, they do nothing to mitigate the severity of floods. Wetlands have a natural
ability to mitigate the impacts of flooding through the slowing of runoff and absorption of
excess rainwater. For this purpose they are inherently valuable. This study implements a
hedonic analysis to study the complicated interactions between property values,
wetlands, and flood risk using detailed property transaction data in the Hudson River
Valley of New York State. We augment this analysis with GIS data including FEMA flood
risk maps, the location of wetlands and other land uses, and various geographic layers.
We find, as expected, that higher levels of flood risk, as well as the realization of actual
flooding events, negatively impact property values. We also find that the presence of
wetlands mitigates the negative effect of floods to properties in flood zones, which is
likely due to a reduced severity of damages. The magnitudes of these effects suggest that
wetlands provide considerable benefits to property owners and the results provide a
partial benefit measure for policymakers, especially to state and federal programs, such
as the USDA’s wetlands and conservation reserve programs whose primary aim is to
preserve and restore these natural buffers.
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Floods are the most common natural disaster according to the National Flood Insurance
Program (NFIP). They cause extensive damages, 2.9 billion dollars annually on average,
to properties within flood plains in the United States. Indeed, evidence suggests that past
flood events, as well as the threat of future floods may harm property values (Bin and
Polasky, 2004; Bin et al., 2008; Harrison et al., 2001; Samarasinghe and Sharp, 2010;
Turnbull et al., 2013). One way that property owners realize flood threat is through areas
identified as high-risk. These high-risk areas, called flood plains, are published in Federal
Emergency Management Agency (FEMA) flood maps, and categorized by the percent
risk of a flood each year. Flood maps are used in real estate and mortgage markets
making them a common, well-understood measure of flood risk for property buyers.
Although flood insurance is available from the federal government at a subsidized rate to
households within FEMA designated high-risk areas this does not eliminate the threat of
floods. A recent discussion piece from Resources for the Future addresses the potential of
using floodplain conservation in general as a method for mitigating flooding (Kousky and
Walls, 2013). We hypothesize that the presence of wetlands will play a significant role in
mitigating the negative impact of flooding on property values by reducing the severity of
damages.
Wetlands are a vital piece of riparian, forest, and coastal ecosystems.1 They provide
valuable habitats for many species, including fish, frogs, turtles, and numerous varieties
1The U.S. Fish and Wildlife Service’s Classification of Wetlands and Deepwater Habitats of the United
States, defines wetlands as follows; “WETLANDS are lands transitional between terrestrial and aquatic
systems where the water table is usually at or near the surface or the land is covered by shallow water. For
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of migratory and non-migratory birds. Wetlands also provide a number of different
services to human populations. Being home to fish and waterfowl, they are popular
locations for recreational fishing and bird hunting, as well as other outdoor recreation
activities such as kayaking, bird watching, and hiking (Zedler and Leach, 1998).
Arguably one of the most important services they provide is their ability to mitigate
flooding (Bullock and Acreman, 1999). The soil composition acts like a sponge to soak
up excess runoff, reducing the amount of water that ends up in rivers. Soil also plays a
role in filtering toxins out of the surface and ground water. All of these “ecosystem
services” benefit communities, whether visibly or in the background. The value of these
services is not generally captured in existing markets (Costanza et al., 1997), which
means that they can be thought of as a positive externality or public good, which
generally implies that they will be underprovided. Therefore, non-market valuation
methods must be used for the valuation of these services.
We aim to partially quantify the benefit of wetlands for flood mitigation using hedonic
analysis. This approach assumes the market value of a good (often residential properties)
is related to the characteristics or the services the good provides. Hedonic analysis is well
documented in the literature (Bastian et al., 2002; Parmeter and Pope, 2009; Rosen, 1974;
Taylor, 2003) and has been used extensively to value many environmental amenities, air
purposes of this classification wetlands must have one or more of the following three attributes: (1) at least
periodically, the land supports predominantly hydrophytes;' (2) the substrate is predominantly undrained
hydric soil;2 and (3) the substrate is non soil and is saturated with water or covered by shallow water at
some time during the growing season of each year.”(Cowardin, 1992, p. 3)
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quality (Smith and Huang, 1995), the proximity to landscapes and open space (Cavailhès
et al., 2009; Kong et al., 2007), or the population of important or endangered species
(Loomis and White, 1996) as well as dis-amenities, such as hog farms (Palmquist et al,
1997). Many hedonic analyses of wetlands prior to this study were focused on
environmental amenities, mainly the recreational opportunities available to communities
(Brander et al., 2006). For other studies that examined ecosystem services, such as flood
protection and other hydrologic services, replacement costs and the production function
have been more common methods of valuation (Acharya and Barbier, 2000; Acharya,
2000; Gren, 1995).
Most existing studies of wetland valuation focus on small areas, often showing the value
of one wetland for conservation purposes (Fan and Yang, 2010; Frey et al., 2013).
Therefore, the value of wetlands in much of the previous research has been focused on
specific wetlands that are known to exist by homebuyers (Bin, 2005; Mahan, 1997).
However, wetlands may provide value in housing markets even if homeowners do not
have information about the existence and/or characteristics of nearby wetlands. This is
because homes with more nearby wetlands may be less likely to be damaged by floods,
and this reduced damage may be noticed and capitalized into property values.
This article is focused on seven counties within the Hudson River valley region in New
York State, generally a larger geographic area than past studies of this nature, allowing
for a more general depiction of the value of flood mitigation provided by wetlands to
landowners. We use detailed residential and agricultural property transaction data over
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the period 2004-2012, including information on the structures (for example, houses and
barns) as well as on the parcel itself. This data is augmented with a rich set of geospatial
data, including Digital Flood Insurance Rate Maps (DFIRMs) from FEMA, the location
of wetlands and other land uses, and various topographical and other geographic layers.
Given the impacts of flooding and the benefits provided by wetlands, it is likely that their
presence or absence interacts with real and perceived flood risk to impact property
values. That is, wetlands are likely to have more value to homes facing higher flood risks,
ceteris paribus. We capture these effects using FEMA flood risk to categorize properties
into their corresponding flood zones.
In addition, actual flooding events may also have short-term impacts on property values,
and affect the way wetlands and flood risk are capitalized. To capture this effect, we use
data on four flooding events that occurred in the Hudson River Valley during our study
period. It is expected that higher levels of flood risk, as well as the realization of actual
flooding events, will negatively impact property values, but that the presence of wetlands
will mitigate that effect.
Utilizing a triple interaction term (between a parcel’s stated flood risk, the occurrence of
major flooding, and the presence of wetlands), our results find significant capitalized
property values for wetland flood mitigation benefits following major flooding events.
This work, from a policy perspective, further supports public spending on wetland
restoration and mitigation efforts. Like many areas of the country, FEMA has recently
announced an expansion of the 100-year flood plains throughout New York State, to
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include 35,000 more properties than the current maps (Buckley, 2013). The results found
here may help policy makers understand the impacts of both flooding and wetlands on an
increasingly high number of property owners.
Existing research on flooding and wetland valuation using Hedonic Analysis
A fairly recent trend has been to utilize hedonic analysis in the study of environmental
amenities and dis-amenities. By including environmental variables like air quality (Smith
and Huang, 1995), the proximity to certain geographic features (Cavailhès et al., 2009;
Kong et al., 2007), or the population of important or endangered species (Loomis and
White, 1996) into econometric regressions, the value that those amenities add to the price
of a home can be understood. In order to make this type of research more effective,
Geographical Information System (GIS) software is frequently utilized to conduct spatial
analysis to be used with hedonic analysis.
The effect of flooding on property values has been studied rather extensively in the
hedonic literature. Most papers utilize currently available FEMA flood data to conduct
their analysis (Harrison et al., 2001; MacDonald et al., 1990; Speyrer and Ragas, 1991),
as we do. The studies have shown that living in a high risk, 100-year, flood zone
significantly reduces property values in comparison to similar homes with little to no
flood risk. In addition, flooding events have a similar effect which has been shown to be
diminishing over time after an event. Recent papers suggest that this discount for flood
zone properties after a significant flooding event decays quickly, disappearing completely
in as little as four to five years (Atreya et al., 2012; Bin and Landry, 2012).
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Although not all floods are caused by hurricanes and other news worthy storms, these
events capture the public imagination and are likely to increase the salience of flooding
and risk in real estate markets. Bin and Polasky (2004) study property values in and out
of flood zones following Hurricane Floyd in North Carolina. Their dataset includes
transaction from 1992-2002, which allows them to observe the effect of the storm for
three years after the fact. They find a significant decline in property values after the event
when their post-flood variable is interacted with the property being within a high-risk
flood zone. We utilize a similar approach of interacting floods with homes in flood zones,
focusing on the short-term effects, with additional focus put on the role that wetlands
play in flood mitigation and the utilization of year fixed effects.
Much of the previous research examining the value of wetlands through hedonic analysis
has been focused on small and localized areas, such as agricultural properties in a region
of Wyoming (Bastian et al., 2002), a multiuse urban wetland in Southern California (Frey
et al., 2013), or neighboring towns in Connecticut (Paterson and Boyle, 2002). While
flood mitigation is the primary focus of this article, wetlands may also provide the
community with recreational amenities, a rich and bio-diverse ecological community,
open-space, carbon sequestration (especially considering forested wetlands), and cleaner
water. Open-space is a general natural amenity, not only associated with wetlands, whose
value has been studied in great detail using hedonic analysis (Sander and Polasky, 2009;
Smith et al., 2002). Open-space can be valuable for specific amenities especially in urban
areas, or simply as a lack of development. In addition, open-space can be viewed as an
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amenity that might span across communities, much like the effects of wetlands, so it
seems reasonable to assume that hedonics might be a worthwhile tool in determining
their value. Okmyung Bin used hedonic analysis to study wetlands for a relatively small
community in Northern Portland (2005), and acknowledges the methods effectiveness,
though his study was limited to single family residential properties. Expanding a similar
study to include all residential properties and agricultural properties may lead to a greater
understanding of the effect of wetlands on property values.
A recent paper looks at the effect of restored, as well as natural, wetlands. While they
find that wetlands play a significant role in raising property values, it seems that the
restored type may harm properties nearby (Kaza and BenDor, 2013). This effect reverses
in properties that are greater than half a mile away, suggesting that the reduction in
property values may be linked to either the construction process, or a poor reputation of
the region’s ecosystem enhancement program. When the restoration process is less
observable, their results are similar to Ghermandi et al. (2010), which finds significantly
positive effects of property values, as part of a meta-analysis. This positive effect is
attributed highly to the improvements in water quality, biodiversity, and recreation,
provided by the new wetlands.
This research adds two important aspects to the literature. First, it broadens the
geographic scope of wetland valuation by observing the effect of wetlands, in relation to
flood zones, over a five county region. Second, we utilize a triple interaction term to
quantify the ecosystem of flood mitigation. Through the use of our triple interaction term
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we are able to show that the presence of wetlands significantly reduces the impact that
flooding has on property values in high-risk areas. Higher property values in this
scenario, in relation to homes without wetlands nearby, is likely do to a reduction in the
damages caused by flooding thanks to the flood control services, which are known to be
provided by wetlands.
Methodology
The price of a home is determined by many factors; the size, features, condition, location,
and nearby amenities to name a few. The hedonic price model is utilized to calculate the
utility of the individual characteristics that make up that price. Although hedonic analysis
existed before Sherwin Rosen’s Hedonic Price and Implicit Markets: Product
Differentiation in Pure Competition (1974), this article is considered to be a seminal
piece in the field. Rosen’s publication developed an econometric framework that made
connections between the utility of individual characteristics for heterogeneous goods and
the equilibrium price. This provided evidence to say that specific characteristics raise or
lower the value of a good, ceterus paribus. Hedonic analysis has been used to study many
different things beyond the value of the individual characteristics of a home. Some
interesting examples include; open space in urban areas (Smith et al., 2002), the effects of
repeated wildfires (Mueller et al., 2009), riparian buffers (Bin et al., 2009), crime and
education (Dubin and Goodman 1982), railway and other public transportations (Mayor
et al., 2012), historic preservation (Heintzelman and Altieri, 2011), the premium paid by
customers for organic cotton (Nimon and Beghin, 1999) or baby food (Maguire et al.,
2004), and prescription drugs for arthritis (Cockburn and Anis, 2001).
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Our analysis utilizes the hedonic price model, which, like any empirical approach, is
subject to certain econometric challenges, many of which can be addressed using a fixed
effects approach (Greenstone and Gayer, 2009; Kuminoff et al., 2010). Fixed effects
estimation allows for multiple intercepts at the designated level of the fixed effects:
census block, block-group, tract, etc. This helps to control for otherwise omitted factors,
which are constant at the level of the fixed effects, but vary spatially between different
areas. The estimation of other effects then relies on variation within fixed effects zones.
In our case, we are hoping to identify how variation in flood risk and wetlands, within
small geographic areas (usually census blocks) following a flood, impacts relative
property values. While the magnitude of wetlands is likely to be very similar between
homes in the same census block, they may interact differently with homes depending on
their flood zone status.
We use log-log and log-linear functional forms, as is standard in many hedonic analyses.
Heteroskedasticity is dealt with by clustering the error terms in our regressions. In
standard OLS regressions concerning property values, the error terms of each house are
assumed to be independent of one another. In real life this is untrue since homes nearby
to each other are likely to be similarly affected by omitted variables. Some of this is
controlled for through the use of local area fixed effects, especially when using census
blocks; however there is still concern over the assumption that error terms are
independent. Clustering the error terms relaxes this assumption and allows for correlation
within the block, but continues to assume independence of error terms between blocks.
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In addition, we normalize sales prices to 2000 dollars using the quarterly House Price
Index (HPI) from the Federal Housing Finance Agency. Properties within a Metropolitan
Statistical Areas (MSA’s) utilized the corresponding HPI; all others were adjusted using
the general state level HPI.
Data
Our data is comprised of a nearly complete set of 50,135 property transactions throughout
five counties in the Hudson Valley region of New York State. These parcels consist
primarily of residential properties, though we also include agricultural parcels that are
categorized as including a permanent residence. The counties (Dutchess, Greene, Orange,
Putnam, and Ulster) were chosen for a number of reasons. This region has been subject to
a number of serious flooding events in the past decade with notable storms including
Tropical Storm Irene and Hurricane Sandy, although Sandy is not included in our study
since it happened so late in 2012. A table of summary statistics can be seen in the
appendix, and includes information on average sale price, property characteristics, and
the proximity to relevant environmental features.
All of the data on parcel level transactions were collected from the New York State
Department of Taxation and Finance (NYSDTF) SalesWeb application. Parcel level
characteristics were added to the data from the NYS Office of Real Property Tax Services
(ORPTS). The data collected here include information on the number of bedrooms,
bathrooms, fireplaces, etc., as well as square footage, building condition and other useful
variables, which are essential to understanding building and land valuation. This data was
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downloaded for every property known to the Department of Taxation and Finance, so we
merged it with the transactions data, dropping out any parcels that did not transact within
the years of our study.
To be able to take advantage of the spatial analysis capabilities of GIS, it was necessary
to collect polygon data for all parcels within the region of study. These were collected
from either the New York State GIS (NYSGIS) Clearinghouse or individual county
offices. The parcel polygons, once in a consistent format, were merged together to create
a single GIS layer for the entire set of counties. Data on the geographic location of
community and environmental features were also downloaded primarily from the
NYSGIS Clearinghouse. Flood zone data was accessed through the FEMA Map Service
Center, msc.fema.gov. These maps, generally in a GIS format, give an account of each of
the flood zone designations in a given area. These flood inundation maps, produced by
FEMA, are associated with a 100-year Base Flood Elevation (BFE) in an attempt to
measure the likelihood that a property will have a severe amount of flooding each year
(Sperl, 2013). Additional hydrologic analyses may be employed by outside agencies to
ensure the relevancy of the BFE in risk assessments. Although wetlands play a role in
controlling flow rate there is little to no mention of them in NFIP documentation
concerning the designation and regulation of flood zones. This is important because if
wetlands play a direct role in determining the flood zone classification of a property than
our measures of flood risk and wetlands will be positively correlated which will bias our
estimates of the effects of each towards zero. This data is frequently used in research
regarding flood hazards, and plays a critical role in this analysis.
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The limited scope of the FEMA flood zones makes understanding the real risk of
flooding, on a parcel-by-parcel basis, somewhat difficult. These flood zones represent a
generalized, discrete, risk of flood damage, rather than a more precise, parcel-specific,
measure. However, we choose to rely on this approach because of the way NFIP data is
used in real estate and mortgage/insurance markets, making it a common, well-
understood measure of flood risk for homeowners.
Polygons for the transacted parcels were mapped using GIS (Environmental Systems
Research Institute, 2012) to allow the analysis of community level and geographic
features that were of interest. For a consistent distance measurement we created centroids
(central points) for each parcel. These were then spatially joined to a number of important
features such as, towns, major cities, streams, ponds, and highways. Doing this provided
distance measurements (in meters) to the nearest feature from each parcel.
Three categories of wetlands are included in the data we use from the U.S. Fish and
Wildlife Service (USFWS) National Wetlands Inventory: Freshwater Forest/Shrub
Wetland, Freshwater Emergent, and Estuarine and Marine Wetland (Cowardin, 1992). In
our analysis we choose to aggregate these wetland types into a single classification. It is
our understanding, after discussion with experts and a review of literature, that the ability
of wetlands to mitigate floods is determined primarily by their location and quality
(Bullock and Acreman, 1999; Zedler and Kercher, 2005; Zedler and Leach, 1998) as
opposed to their classification. Since the focus of our study is on flood mitigation rather
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than other attributes of wetlands, the aggregation of those types into one category seems a
reasonable course of action. While understanding that distinct types of wetlands exist and
play similar roles in this specific ecosystem service is important, the cumulative impact
of all nearby wetlands on flood mitigation is the important factor in this research.
Wetlands were initially integrated into the analysis using the same distance
measurements utilized for other features. However, due to the large number of small
wetlands in the area, we postulated that understanding the total acreage of wetlands
nearby would be more relevant. To determine the total acreage of wetlands in the vicinity
of each parcel, buffers were created around each centroid at distances of two and five
Kilometers. The sizes of the buffers were based on a desire to understand the effects of
nearby wetlands, and stops at five kilometers because of computational limitations. Those
buffers were then spatially joined to the wetland polygons, providing the number of
wetlands that fell at least partially within the buffer, and the total acreage of them. The
geographic features, produced in GIS, were integrated with the parcel level transactions
data using STATA (Stata Corp., 2011).
By interacting flood zone and wetland acreage variables with dummy variables flagging
properties sold within three or six months of a major flooding event, we examine the
average effect that wetlands have on property values in flood zones when perceived risk
is at an elevated state. The events were chosen by referencing a list of major flooding
events from the National Weather Service (NWS) (US Department of Commerce, n.d.)
and finding floods in the lower Hudson Valley region during the study. Four floods were
found to be important. They included flooding that occurred throughout April of 2005 in
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Ulster County, flooding through October of 2005 in Dutchess and Greene Counties, and
more specific events on April 15-16 in 2007 that hit the entire study area, and finally
Tropical Storm Irene in late August of 2011. The dummy variables for these “flood
windows” were constructed in such a way that they are only activated in counties that
were hit by flooding.
In our regressions, the total acreage of wetlands near to the parcel is interacted with a
dummy variable for being located within a 100-year flood zone. This interaction term
demonstrates the effect that wetlands have on properties purchased in a 100-year flood
zone. Since flood zones and flooding events likely reduce property values, and wetlands
can reduce the severity of floods, we would expect to find that having wetlands in the
vicinity would reduce the negative effects of living in a high-risk flood zone. Figure 2
illustrates the relationship between flood zones and the wetlands in the counties we study.
An elevation of perceived flood risk, for instance after a major storm, may have an
adverse effect on a consumers willingness to pay for a home (Kousky, 2010), so we take
this interaction term a step farther than is typical in this area of research. The triple
interaction term includes the total acreage of wetlands, the flood zone dummy variable,
and a dummy variable for transactions, which occurred within either the three or six
months post-flood window.
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Figure 1. Study region location within state of New York with Wetland and Flood Zone
Locations
Results
The results of our analyses are reported below for the Census Block fixed effects level.
We also ran regressions at the block-group level, a larger geographic area, as a robustness
check and we briefly discuss these results below. Table 1 presents the results of the
Census Block fixed effects for each of three specifications using different flood windows.
For brevity we report only the variables of primary interest to this analysis2. However, the
models have good fit and many of the standard structural and parcel characteristics have
the expected sign and significance. For example, the number of bathrooms and fireplaces,
2 Complete results are available upon request.
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along with the total acreage and square footage of the parcel show positive and
significant coefficients. The overall condition of the home, and whether it has central air
also produced positive and significant results, while the number of kitchens (indicating
that the unit may be, or was recently, a multi-family unit) and the age of the home were
negative and significant. Proximity to ponds, the Hudson River, and NYC increase sale
price, but distance from streets and town centers is preferred. Having a stream or pond
intersecting the property increases property values, as does the elevation of the parcel. All
of these results are consistent with literature utilizing the hedonic pricing model.
As expected, we find that the dummy variable for a parcel being in a 100-year flood zone
was significant and negative—between -.073 and -.083. This translates to a reduction in
property values between 7.9-8.6% on average (following the method reported in
Halvorsen and Palmquist (1980)). This result is only slightly higher than Bin and
Polasky (2004), who report a 5.7% reduction.
We find that both the three-month and six-month flood windows were insignificant in
effecting property values for the entire region, which is not surprising since homes not
affected by the floods (outside of flood zones) are unlikely to experience any significant
depreciation as a result of the flooding events. When interacting these variables with
properties in 100-year flood zones, however, we observe coefficients that are negative
and significant showing that major floods harm property values in flood prone areas more
than the region as a whole. This interaction term suggests that property sales within the
100-year flood zone and within three months of a major flooding event experience a
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30.9% reduction in value relative to homes that are not located in flood zones and sold
prior to flood events. While the effect dissipates slightly for properties sold within six
months, those are still being reduced as much as 19.1%. Notice that we are using all four
storm events simultaneously in these specifications, so these estimates represent the
average flood effect across these events. These results support the findings by Bin and
Polasky (2004), providing further evidence that property values in 100-year flood zones
are harmed more severely by a major flooding event than are areas of lower risk.
No evidence that wetlands themselves have an effect on nearby property values is found,
nor do they have an effect within flood zones, as variables that interact acres of wetlands
within various buffers with the flood zone dummy variables are not significant.
However, we hypothesized that the value of wetlands might be most relevant in the wake
of flooding.
Using the interaction terms between flood zones and a transaction occurring three or six
months after a severe flood we then bring in the total acreage within each of the buffers
by creating a new interaction term. Through the use of this triple interaction term we are
able to see how the presence of wetlands within each buffer affects the price of homes in
flood zones that sold shortly after a major flood. The coefficients for these variables give
more significant results as the size of the buffer increases suggesting that the total acreage
of wetlands must be at a high magnitude, with less regard to the proximity, in order to be
significant. We find that when these interaction terms utilize either the two-kilometer or
five-kilometer buffers the results are positive and significant. This indicates that, while
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flood zones and major floods reduce the value of a home, ceterus paribus, the presence of
a large volume of wetlands helps to mitigate that negative effect. In essence, homebuyers
purchasing after a flood are willing to spend more on a home in a flood prone area when
a significant system of wetlands is in place. The presence of wetlands within the larger
buffers show no significant results on their own or when interacted directly with
properties in flood zones. However, since they do show significant results in this specific
situation, it is reasonable to attribute that effect to the flood mitigation service provided,
and not to other ecosystem services or recreational amenities that they may provide. It is
unlikely that the buyer observes all wetlands within five kilometers of a home, although
the reduced effect of floods due to their presence could likely be observed in the form of
decreased damages in comparison to areas that have fewer wetlands.
For properties which sold within the three month flood window which are within the
flood zone we find a positive coefficient of 0.000247 with increasing wetland acreage
within both the two and five kilometer buffer. Given that the average property has 198
acres of wetlands within 2k and 1115 acres within 5k, these results represent a potential
increase in property values of around 27.5% when an average amount of wetlands are
nearby homes that are in flood zones and sell after a flood occurs relative to properties
with no wetlands within these buffers. In the regressions that focused on transactions
within six months of a major flood, again, positive and significant results for wetlands in
both the two and five kilometer buffers are seen. The estimated effect is slightly less than
what we observed in the three-month window, with a slightly reduced level of
significance. If an average number of wetlands within five kilometers exist around a
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parcel, our results suggest that property values after a flood could be 14% higher, on
average, than parcels that do not have wetlands nearby.
Table 1. Wetland and Flood Zone Results for Specified Flood Windows and Buffer Sizes
To illustrate the value of a useful scenario, note the average total acreage within a 5km
buffer is 1,154. With a mean sale price of $306,435 a major flood is expected reduce the
value of properties within a flood zone, with no wetlands within 5km, by an estimated
$79,422. Within our sampled properties the average acreage of wetlands within a 5km
buffer is 1,154. Given a nearly average volume of wetlands within a five-kilometer radius
(1,000 acres) it is estimated that property values could only be discounted by $32,742—a
difference of over $46k. This mitigation in the loss of value following a major storm is
likely due to a reduction in observed damages. Given the role of wetlands as flood buffers
we attribute this significant mitigation to the presence of wetlands in the area.
Flood Window
2K Buffer 5K Buffer 2K Buffer 5K Buffer 5K Buffer
Variables
100yr Flood Zone -0.083*** -0.082*** -0.083** -0.083*** -0.073**
500yr Flood Zone -0.031 -0.031 -0.031 -0.031 -0.031
Wetland Acreage (within buffer) -0.000 0.000 -0.000 -0.000 0.000
Wetland Acreage * 100yr FZ 0.000 0.000 0.000 0.000 0.000
Property Sold in Flood Window -0.005 -0.005 -0.010 -0.010 -0.008
Sold in Window * 100yr FZ -0.226** -0.226*** -0.108** -0.108** -0.042
Sold * FZ * Acreage of Wetlands 0.000247*** 0.000247*** 0.000145*** 0.000145*** 0.000
note: *** p<0.01, ** p<0.05, * p<0.1
3-6 Months 0-6 Months 0-3 Months
Coefficient
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Interestingly, we can also observe how the effect of flood zone dissipates over time
following a flood event. We find that the additional negative effects of a flood zone in the
0-3 month window following a major storm dissipates in the following 3-6 month period.
Since the effect of the flood zone dissipates during the second period, it is not surprising
that the triple interaction term becomes insignificant as well. This is likely because that
service from wetlands is no longer being observed. Additional research should be
conducted to investigate the duration of flood mitigation services to the housing market.
Specific major flooding dates were also regressed individually using dummy variables for
sale before or after those floods. Throughout the regressions for the individual flood
events, we do not find consistently significant results for the flood zone interaction terms
or for the three-way interaction term between flood zones, flood dates, and the total
acreage of wetlands in the area. Although insignificant, the coefficients from these are
positive, which is promising. It suggests that it is a lack of observations leading to
insignificance rather than that there is no effect.
Results of block-group fixed effect model
Many of the flood and wetland related variables were of the same sign in our block-group
level regressions when compared to the smaller census block, although they were in
general less significant or insignificant. Flood zones and the flood date variables, both
individually and together were still negative and significant. We also see a positive and
significant result from the two and five kilometer wetland buffer interacted with the flood
zone/flood date variable for sales within six months of a flood. On this larger census level
21
we also see more significant results for housing characteristics and geographic variables.
Notably, we can now see that within a block-group the distance to a lake becomes
significant showing that homebuyers do prefer to be near to a lake. This likely did not
show up in the block level regressions because of the distance to the nearest lake within
homes in the same block is so homogenous.3
Conclusions
The purpose of this research was to investigate the possible effects that wetlands have on
reducing the negative effects on properties within a flood prone area. Consistent with
previous literature our results find that flood zones negatively impact the value of those
properties within the flood zone. While we do not find a direct connection between
wetlands and property values we do find that in the wake of severe flooding, wetlands
play a significant role in mitigating the harm done to values of properties within the 100-
year flood zones. This indicates that the value of wetlands in flood prone areas may be
tied more closely to the flood mitigation service they provide than to other services or
amenities, or that the flood mitigation provided by wetlands reduces the visible damages
caused by flooding that would have otherwise lowered property values. Logically, we
find the value of that service increases as the total acreage of nearby wetlands increases.
3 At the block-group fixed effects level we are also able to capture a trend of increasing home prices as the
location moves from Albany to NYC, and buyers prefer to be near to the highway I-90. We do not find
significant results for I-87, also called “The Northway”, which is probably due to its proximity to the
Hudson River which shows very significant results suggesting that people prefer to be closer to it, just as
we saw in the block level regressions.
22
In addition, these results suggest that property owners are willing to pay more for
properties with nearby wetlands regardless of their visibility. This departs from past
literature, which suggests that visible wetlands increase property values (Boyer and
Polasky, 2004). Therefore our results suggest that not only are wetlands an important
feature for the ecology of the regions and the riparian systems, they provide an ecosystem
service that is valued in the real estate market beyond their visual or amenity
characteristics.
As flooding becomes a more frequent event, and flood maps are revised or redrawn
(Buckley, 2013), there is an opportunity for efficient investment into the conservation and
restoration of wetlands. Wetlands are a natural way to reduce the physical risk of
flooding, and have the potential to be far more visually pleasing and offer a greater
diversity of services than other options, such as a concrete dyke. Wetlands’ flood
mitigation could reduce the costs associated with flooding to property owners, as shown
in this article, but also to the NFIP. Through investments in wetlands and floodplain
conservation the NFIP might reduce its own financial risks. With less damaging flooding
events the rate and amount of claims needing to be paid to policyholders could be
reduced, and may also aid in generating a larger reserve fund for times of true disaster
when large claims may still need to be filed.
In addition, the evidence presented in this article directly provides Federal, State and non-
government conservation organizations, such as New York State’s Department of
Environmental Conservation or Federal programs such as the Conservation Reserve
23
Program’s wetland restoration initiative or the Agricultural Conservation Easement
Program’s Wetland Reserve Easements (formerly the Wetland Reserve Program), an
understanding of the value that wetlands add to communities. Specifically, estimating the
value added to properties by the flood mitigation service of wetlands provides a benefit
measure to these Federal, State or non-government conservation organizations when
wetlands are threatened by new development projects or expanding farmland acres.
Furthermore, when wetlands must be filled in to make room for new development, and
wetland mitigation banking is used, the location of new wetlands is a heated topic. The
significant value demonstrated in this article for wetlands within five kilometers of homes
in flood zones suggests significant value of constructing new wetlands very near to the
originals.
Estimating benefit measures of wetland services is an important step in supporting efforts
to protect and restore wetlands for the valuable services that they provide the community
by reducing both the severity of floods and bolstering property values in the wake of
major flooding events. Though this research suggests significant value for wetlands based
on their mitigation of damages caused by floods, it is not definitive. More research, in
other hurricane and flood prone regions, is necessary to develop a greater understanding
about the benefits that wetlands provide to housing markets and the community.
24
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30
APPENDIX:
Demographics
United States
New York State
Dutchess County
Greene County
Orange County
Putnam County
Ulster County
$59,511
$85,570
$108,241
$71,743
19,378,104.00
308,745,538.00$50,054
$50,636
$84,881
Median value of owner-occupied housing units,
2007-2011
Total Population 2010 (April,1) estimates base
2011 Mean Income (2011 Dollars)
$242,500
$406,000
$299,500
$181,300
$314,500
$301,000
$186,200
182,494.00
99,724.00
372,813.00
49,221.00
297,474.00
32
Block Level Results – 3-Month Flood Window
Variables coef se coef se
Property in 100-year Flood Zone -0.083*** 0.029 -0.082*** 0.026
Property in 500-year Flood Zone -0.031 0.023 -0.031 0.024
Acreage of Wetlands within 2 Kilometers -0.000 0.000
Acreage of Wetlands within 5 Kilometers 0.000 0.000
Acreage of Wetlands(2k) * 100yr Flood Zone 0.000 0.000
Acreage of Wetlands(5k) * 100yr Flood Zone 0.000 0.000
Flood Occurred 0-3 Months Prior to Sale -0.005 0.015 -0.005 0.015
Flood (0-3 Months) * 100yr Flood Zone -0.226** 0.089 -0.226*** 0.079
Flood (0-3 Months) * Flood Zone * Wetlands(2k) 0.000*** 0.000
Flood (0-3 Months) * Flood Zone * Wetlands(5k) 0.000*** 0.000
Acres 0.003* 0.001 0.003* 0.001
Number of Kitchens -0.078*** 0.016 -0.078*** 0.016
Number of Full Bathrooms 0.097*** 0.025 0.097*** 0.025
Number of Half Bathrooms 0.040** 0.020 0.040** 0.020
Number of Bedrooms 0.012 0.012 0.012 0.012
Number of Fireplaces 0.079*** 0.011 0.079*** 0.011
Central Air 0.048** 0.019 0.048** 0.019
Overall Condition 0.102*** 0.026 0.102*** 0.026
Square Footage 0.000*** 0.000 0.000*** 0.000
Age -0.001** 0.000 -0.001** 0.000
Age2 0.000 0.000 0.000 0.000
Agriculture -0.404 0.436 -0.404 0.436
Two Family -0.094*** 0.034 -0.094*** 0.034
Three Family -0.165** 0.066 -0.165** 0.066
Rural with Acreage 0.351*** 0.044 0.351*** 0.044
Estate 1.381*** 0.385 1.381*** 0.385
Seasonal -0.816*** 0.188 -0.816*** 0.188
Mobile Home -0.742*** 0.214 -0.741*** 0.214
Multi Residences 0.305*** 0.048 0.305*** 0.047
ln Dist. to Nearest Streams 0.003 0.006 0.003 0.006
ln Dist. to Nearest Lake 0.006 0.009 0.006 0.009
ln Dist. to Nearest Pond -0.008* 0.005 -0.008* 0.005
ln Dist. to Nearest DEC Land 0.002 0.012 0.002 0.012
ln Dist. to Nearest DEC Trail 0.001 0.005 0.001 0.005
ln Dist. to Nearest Towncenter 0.016** 0.007 0.016** 0.007
ln Dist. to NYC -0.155** 0.063 -0.155** 0.063
ln Dist. to Albany -0.053 0.107 -0.053 0.103
ln Dist. to Nearest Street (35-45 mph) 0.014*** 0.005 0.014*** 0.005
ln Dist. to Interstate - 90 -0.055 0.084 -0.055 0.080
ln Dist. to Interstate - 87 -0.006 0.008 -0.006 0.008
ln Dist. to Nearest Railroad 0.017 0.011 0.017 0.011
ln Dist. to Hudson River -0.027** 0.013 -0.028** 0.013
ln Dist. to Nearest Bridge over Hudson River 0.009 0.010 0.009 0.010
Acreage of nearest DEC Lands -0.000 0.000 -0.000 0.000
Acreage of nearest Lake 0.000* 0.000 0.000* 0.000
Acreage of nearest Pond -0.001 0.001 -0.001 0.001
Stream Intersects Property 0.073*** 0.009 0.073*** 0.009
Pond Intercepts Property 0.087*** 0.022 0.087*** 0.022
Lake Intercepts Property 0.147 0.100 0.147 0.100
Elevation in Meters 0.001*** 0.000 0.001*** 0.000
Year and Month Dummies Yes Yes Yes Yes
_cons 15.190*** 1.483 15.193*** 1.470
note: *** p<0.01, ** p<0.05, * p<0.1
2K Buffer 5K Buffer
33
Block Level Results – 6-Month Flood Window
Variables coef se coef se
Property in 100-year Flood Zone -0.083** 0.033 -0.083*** 0.030
Property in 500-year Flood Zone -0.031 0.023 -0.031 0.024
Acreage of Wetlands within 2 Kilometers -0.000 0.000
Acreage of Wetlands within 5 Kilometers -0.000 0.000
Acreage of Wetlands(2k) * 100yr Flood Zone 0.000 0.000
Acreage of Wetlands(5k) * 100yr Flood Zone 0.000 0.000
Flood Occurred 0-6 Months Prior to Sale -0.010 0.011 -0.010 0.011
Flood (0-6 Months) * 100yr Flood Zone -0.108** 0.052 -0.108** 0.052
Flood (0-6 Months) * Flood Zone * Wetlands(2k) 0.000*** 0.000
Flood (0-6 Months) * Flood Zone * Wetlands(5k) 0.000*** 0.000
Acres 0.003* 0.001 0.003* 0.001
Number of Kitchens -0.078*** 0.016 -0.078*** 0.016
Number of Full Bathrooms 0.097*** 0.025 0.097*** 0.025
Number of Half Bathrooms 0.040** 0.020 0.040** 0.020
Number of Bedrooms 0.012 0.012 0.012 0.012
Number of Fireplaces 0.079*** 0.011 0.079*** 0.011
Central Air 0.048** 0.019 0.048** 0.019
Overall Condition 0.102*** 0.026 0.102*** 0.026
Square Footage 0.000*** 0.000 0.000*** 0.000
Age -0.001** 0.000 -0.001** 0.000
Age2 0.000 0.000 0.000 0.000
Agriculture -0.405 0.436 -0.405 0.436
Two Family -0.094*** 0.034 -0.094*** 0.034
Three Family -0.165** 0.066 -0.165** 0.066
Rural with Acreage 0.351*** 0.044 0.351*** 0.044
Estate 1.380*** 0.385 1.380*** 0.385
Seasonal -0.815*** 0.188 -0.815*** 0.188
Mobile Home -0.741*** 0.215 -0.741*** 0.215
Multi Residences 0.304*** 0.048 0.304*** 0.048
ln Dist. to Nearest Streams 0.003 0.006 0.003 0.006
ln Dist. to Nearest Lake 0.006 0.009 0.006 0.009
ln Dist. to Nearest Pond -0.008* 0.005 -0.008* 0.005
ln Dist. to Nearest DEC Land 0.002 0.012 0.002 0.012
ln Dist. to Nearest DEC Trail 0.001 0.005 0.001 0.005
ln Dist. to Nearest Towncenter 0.016** 0.007 0.016** 0.007
ln Dist. to NYC -0.155** 0.063 -0.155** 0.063
ln Dist. to Albany -0.052 0.107 -0.052 0.103
ln Dist. to Nearest Street (35-45 mph) 0.014*** 0.005 0.014*** 0.005
ln Dist. to Interstate - 90 -0.055 0.084 -0.055 0.080
ln Dist. to Interstate - 87 -0.006 0.008 -0.006 0.008
ln Dist. to Nearest Railroad 0.017 0.011 0.017 0.011
ln Dist. to Hudson River -0.027** 0.013 -0.027** 0.013
ln Dist. to Nearest Bridge over Hudson River 0.009 0.010 0.009 0.010
Acreage of nearest DEC Lands -0.000 0.000 -0.000 0.000
Acreage of nearest Lake 0.000* 0.000 0.000* 0.000
Acreage of nearest Pond -0.001 0.001 -0.001 0.001
Stream Intersects Property 0.073*** 0.009 0.073*** 0.009
Pond Intercepts Property 0.087*** 0.022 0.087*** 0.022
Lake Intercepts Property 0.147 0.100 0.147 0.100
Elevation in Meters 0.001*** 0.000 0.001*** 0.000
Year and Month Dummies Yes Yes Yes Yes
_cons 15.195*** 1.480 15.195*** 1.465
note: *** p<0.01, ** p<0.05, * p<0.1
2K Buffer 5K Buffer
34
Block Level Results – 3-6 Month Flood Window
Variables coef se
Property in 100-year Flood Zone -0.073** 0.029
Property in 500-year Flood Zone -0.031 0.024
Acreage of Wetlands within 2 Kilometers
Acreage of Wetlands within 5 Kilometers 0.000 0.000
Acreage of Wetlands(2k) * 100yr Flood Zone
Acreage of Wetlands(5k) * 100yr Flood Zone
Flood Occurred 0-3 Months Prior to Sale -0.006 0.015
Flood (0-3 Months) * 100yr Flood Zone -0.235*** 0.084
Flood (0-3 Months) * Flood Zone * Wetlands(5k) 0.000*** 0.000
Flood Occurred 3-6 Months Prior to Sale -0.008 0.012
Flood (3-6 Months) * 100yr Flood Zone -0.042 0.072
Flood (3-6 Months) * Flood Zone * Wetlands(5k) 0.000 0.000
Acres 0.003* 0.001
Number of Kitchens -0.078*** 0.016
Number of Full Bathrooms 0.097*** 0.025
Number of Half Bathrooms 0.040** 0.020
Number of Bedrooms 0.012 0.012
Number of Fireplaces 0.079*** 0.011
Central Air 0.048** 0.019
Overall Condition 0.102*** 0.026
Square Footage 0.000*** 0.000
Age -0.001** 0.000
Age2 0.000 0.000
Agriculture -0.404 0.436
Two Family -0.094*** 0.034
Three Family -0.165** 0.066
Rural with Acreage 0.351*** 0.044
Estate 1.381*** 0.385
Seasonal -0.815*** 0.187
Mobile Home -0.741*** 0.214
Multi Residences 0.305*** 0.047
ln Dist. to Nearest Streams 0.003 0.006
ln Dist. to Nearest Lake 0.006 0.009
ln Dist. to Nearest Pond -0.008* 0.005
ln Dist. to Nearest DEC Land 0.002 0.012
ln Dist. to Nearest DEC Trail 0.001 0.005
ln Dist. to Nearest Towncenter 0.016** 0.007
ln Dist. to NYC -0.155** 0.063
ln Dist. to Albany -0.052 0.103
ln Dist. to Nearest Street (35-45 mph) 0.014*** 0.005
ln Dist. to Interstate - 90 -0.055 0.080
ln Dist. to Interstate - 87 -0.006 0.008
ln Dist. to Nearest Railroad 0.017 0.011
ln Dist. to Hudson River -0.028** 0.013
ln Dist. to Nearest Bridge over Hudson River 0.009 0.010
Acreage of nearest DEC Lands -0.000 0.000
Acreage of nearest Lake 0.000* 0.000
Acreage of nearest Pond -0.001 0.001
Stream Intersects Property 0.073*** 0.009
Pond Intercepts Property 0.087*** 0.022
Lake Intercepts Property 0.147 0.100
Elevation in Meters 0.001*** 0.000
Year and Month Dummies Yes Yes
_cons 15.192*** 1.468
note: *** p<0.01, ** p<0.05, * p<0.1
5K Buffer