Changes in Design Numbers

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Changes in Design Numbers

Post by Karenz » Wed Feb 10, 2021 10:48 am

Good Morning.
Looking at the differences in reporting numbers between a v6 and a similar v7 report, specifically in the stormwater category...In the v6 report, overall benefits for 42 trees is $13,667, in the v7 30 trees is overall benefits are: $2,323. Thank you.
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Re: Changes in Design Numbers

Post by Jason.Henning » Wed Feb 17, 2021 9:39 am

Hi Karen,
Thanks for the question. It is tough to say exactly what is going on here. It could simply be that the differences in the sizes and species of the trees are enough to account those differences in results. It could also be due to changes in the underlying model. We generally try to incorporate the latest science in the model when it becomes available. To that end, we made changes to the stormwater modeling in all of the i-Tree tools that moved away from estimating how much precipitation a tree "intercepted" to estimating more precisely how much stormwater the tree keeps out of the storm drain, generally referred to as "avoided runoff". This new avoided runoff number is a better measure of the ecosystem services the tree is providing but it is generally smaller than the old stormwater intercepted number. Within the i-Tree Design report interface we currently report both interception and avoided runoff under the stormwater tab although, only the avoided runoff is used for the monetary estimates of ecosystem services. You may want to take a look at both of those numbers to see how they compare to your older report. Additionally, if you saved you old i-Tree Design project you may want to try reopening it Design v7 to get the benefit estimates reflecting the latest science. For more details on the underlying methods please check-out our Understanding i-Tree document here, ... nrs200.pdf.
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