I've had students who wanted to estimate benefits of greenways for years. We never could find much in the literature. Here is something new. Carolyn Kousky and Margaret Walls:
In the twentieth century, flooding caused more deaths and property damage in the United States than any other natural disaster. Most climate models predict that flooding will worsen in the future, a prospect that is leading a growing number of communities to explore the use of natural areas as protection against extreme events. These areas are currently providing flood mitigation benefits. ... But how much more valuable will the lands become if floods are more frequent or severe in the future [?]
With our coauthor, Ziyan Chu, we recently came up with a dollar value of these climate resilience benefits for the case of a specific investment in natural areas in the state of Missouri—the Meramec Greenway. ... In this study, we calculated the additional benefits that the greenway might provide in four climate change scenarios, two in which peak discharges increase and two in which the frequency of flooding increases.
... According to our estimates, the current protected lands yield an average annual benefit in the form of avoided flood damages of $13.1 million a year, or about $6,000 per acre. If climate change causes peak discharges to rise by 30 percent, an increase consistent with some of the (limited) literature on how climate change will affect flood risks in the region, the benefits of the greenway are $4.5 million higher. If peak discharges rise by 50 percent, which we look at as an upper bound, the benefits of the greenway are $7.9 million higher. If the frequency of flood events doubles, the benefits double. And finally, if the frequency of only the worst events doubles (the 100-, 250-, and 500-year events), we find that the benefits increase by just $1.2 million, or 9 percent.
And, you can thank me for the link to the paper.