Adjusting Pollution Benefit Prices

[Vincent]

Hello! I am working on an Eco project for the nature center at my college. We are in a rural area of the US and the entirety of the project involves forests with relatively low management. I realize that this is not the sort of area that Eco was designed for, however I was drawn to its ease-of-use and from what I read on the forums before starting the project, it sounded like -- although it may have been designed with urban projects in mind -- it could still serve my purposes.

For the most part it absolutely has. My one problem is that I can not seem to find a way to adjust the benefit prices calculated in Eco for pollution prevention; I see where I can change the values for carbon and avoided runoff, but there does not seem to be an opption for pollution prevention. Is this possible within Eco?

Thanks in advance-

[Jason.Henning]

Hi Vincent,
Users don't currently have the ability to set their own pollution removal monetary valuations. This is planned for a future update. For the time being, the easiest workaround is to export something like the "Benefits and costs > Pollution Removal by trees and shrubs > Monthly Removal" report using the small save disk icon at the top left of the report window in Eco. You can save in a variety of formats including a spreadsheet. In a spreadsheet you can readily apply whatever monetary values you want to the amounts of pollutant removed.
On a side note, you can definitely use i-Tree Eco for trees wherever they are. Even within cities there are always patches of naturally regenerating unmanaged forests. The US Forest Service is currently in the process of exploring how to apply i-Tree Eco to estimate ecosystem services for their rural/natural forested plots.
Thanks,
Jason

[Vincent]

Thank you so much Jason, that process makes sense and is pretty much what I was planning on doing.

My next question (which I could make a seperate topic if that would be better, but I think it is related) is if there is any documentation on the calculations that eco makes to adjust for the rural nature of the study site. I noticed that whether or not the project is defined as "urban" makes a significant difference particularly for the values of runoff and pollution prevention. This makes sense to me in theory, but I was hoping there might be some more details available as to what the actual changes are in the model. I am still hoping to localize my benefit values as much as possible, so it would be really helpful to know where these values are coming from.

Thank you -
Vincent

[Jason.Henning]

Hi Vincent,

Here is some text from our modeler on the impact of the urban toggle on avoided runoff.

Average impervious cover is 25.5% for the urban areas across the 50 US States, while 1.5% for the rural areas in the lower 48 States2). Assuming the only urban area is assessed using i-Tree Eco, 25.5% was used to calculate avoided runoff. With a newer implementation of urban or rural designation in i-Tree Eco project settings, 1.5% impervious cover was recently employed for rural areas.

Due to the smaller impervious cover % in rural areas, a large amount of rainwater can infiltrate into the ground regardless of the effect of trees. Hence, avoided runoff in rural areas will be smaller than in urban areas.

1) Hirabayashi, S. i-Tree Eco Precipitation Interception Model Descriptions; US Department of Agriculture Forest Service: Washington, DC, USA, 2013; p. 21. Available online: http://www.itreetools.org/eco/resources ... ptions.pdf
2) Nowak, D.J.; Greenfield, E.J. Tree and impervious cover in the United States. Landsc. Urban Plan. 2012, 107, 21–30.

For the pollution removal the "mixing height" is calculated differently for urban versus rural areas. For me details on the pollution removal calculations and the associated documentation please see the "Air Pollution Removal" section beginning on page 34 of Understanding i-Tree

Thanks,
Jason

[Vincent]

Hi Jason,

Thanks for the quick reply! So if I understand this properly, the model changes how it calculates the amount of pollution prevention / runoff, but not the value of those benefits, is that correct?

I guess what I'm trying to ask is whether it is worth it to try to localize those values. I would think that each tree not only contributes less to runoff prevention in a rural area, but also that the value of the runoff that is prevented would be less, since there is likely less risk to property and the replacement costs of stormwater management would be significantly lower, no? And similarly I would imagine that the value of pollution prevention would also be less in a rural area, in addition to the mechanics being different. If it is the mechanics that are being adjusted in iTree, but not the values, then I will go ahead with trying to make adjustments, but I want to make sure it doesn't adjust the values themselves too so that I don't end up undervaluing anything.

I'm also a little confused because I have been estimating ground cover (duff, herbs, bare soil, etc.) for each of my plots -- are those average impervious cover percentages you mentioned only applied if ground cover is not recorded in a project, or is there a second level of calculations involved somehow?

Thank you for all your help-
Vincent

[Jason.Henning]

Hi Vincent,
You are correct as far as the impacts of the "urban" checkbox. It only impacts how those two benefit amounts are calculated. I'd suggest reviewing our Understanding i-Tree document for more details on the monetary value methods. For stormwater the monetary values are based on regional averages of the cost to treat an equivalent amount of waste water. For air pollution the values are based on the EPA's BenMap model which accounts for the size and demographics of the local human population. In urban areas there is a much higher population density. The more people that are exposed to the cleaner are the higher the monetary values are for those air pollution benefits.
The ground covers are only used to calculate the relative air pollution removal by grasses. They do not impact any of the other ecosystem service estimates in the models. You will get summaries of the amounts of different covers in your study area but they are not used in the ecosystem service calculations.
Thanks,
Jason

[Vincent]

Hi Jason,

Thanks so much again, your responses have been really helpful. I read through "Understanding i-Tree" in more detail and it was very informative, however it raised a few more questions too:

First, in that document (as in your last response), I read that the values for pollution prevention are based on the EPA BenMAP (apart for CO which is based on externality value of $1,599/tonne), however in the "i-Tree Eco Dry Deposition Model Descriptions" report from the documentations on your webpage, the section for valuation says that "Monetary value of pollution removal by trees is estimated using the median externality values for the United States for each pollutant." I assume that this is just an out-dated methodology, however this document is more recent than the previous, so I wanted to double check.

Second, what year are the dollar values for pollution in iTree from? I have read a few things; the externality for CO is in 2011 dollars, but updated from the producer price index with a citation for 2017 -- so is this in 2017 dollars, or is it updated "live" from the index? Are the other pollution values which (I assume) are coming from BenMAP in current dollars? And the value for carbon is in 2020 dollars, correct?

Thanks again, I think that these will probably be the last of my questions, my project is wrapping up and it seems like there is very little I could do in terms of localization that is not already being done within i-Tree.

Vincent