Measuring Resilience to Climate Change: The Benefits of Floodplain Land Conservation

Communities are increasingly interested in land conservation as a means of reducing damages from flooding. Forests can intercept rainwater and their soils can store water, reducing the amount that reaches rivers and streams. Coastal wetlands and dunes can buffer storm surge, and strategically placed wetlands can store flood waters. Moreover, simply limiting the amount of development in risky areas can reduce exposure to hazards and lower damages. With climate change expected to worsen extreme weather events in many regions, this natural infrastructure approach holds great appeal.

But preserving land from development comes at a cost, and the benefits are highly uncertain; very few studies have attempted to measure the benefits—particularly under future climate conditions—and compare them to costs. We undertake such a study, evaluating a floodplain conservation investment, a greenway along the Meramec River in St. Louis County, Missouri.

This evaluation involves three steps. First, we estimate the opportunity costs of the investment – i.e., the value of the land in its next best use, which is residential development. We then calculate the flood damages avoided by keeping the land out of development—i.e, we compare losses under current conditions to those in a hypothetical counter-factual scenario in which the greenway lands are developed. We do this by undertaking a detailed parcel-level analysis using the User Defined Facility tool in the Hazus-MH flood model. Hazus-MH is a GIS-based model developed for the Federal Emergency Management Agency that includes a hydrology and hydraulics model coupled with a damage model relating flood depths to property damage. Finally, because creation of the greenway was motivated by the range of benefits it would provide, including aesthetic and recreational benefits, we undertake a hedonic price model to estimate the capitalization of proximity to the greenway in property values.

We find that the benefits of increased property values are roughly equal to the avoided flood damages, and that taken together, the benefits of the greenway outweigh the opportunity costs of keeping the land out of development. We then reassess our estimate of avoided flood damages under a range of assumptions about future flooding in a world with climate change. Specifically, we look at increases in peak discharges and increases in the frequency of flood events. In all of our scenarios, there are added benefits from the greenway, reinforcing the positive net benefits from this investment. However, the main story is the value of the lands today, under current conditions; the additional benefits in the climate change scenarios are not large in magnitude.

This work is funded under a grant from NOAA's Climate Program Office's Climate and Societal Interactions, Sectoral Applications Research Program.