update hydraulic conductivity scaling model

[xuchongang]

Taper improvement.pdf

This pull request update the petiole length parameter to match the scaling of conduit size from Olson 2020 (https://nph.onlinelibrary.wiley.com/doi/10.1111/nph.16961)

Description:

The original scaling model has a much larger scaling of conduit size compared to the data from Olson 2020. To resolve this issue, I have added a new taper function based on Olson 2020. Please see attached the derivation of the taper components. Our hydraulic model optimization showed that this version of the taper function should be much closer to observations. This could also resolve the issue of size distribution of water potential. By lowering the hydraulic conductivity for taller trees, it will give a higher water stress for larger size of tree and thus higher mortality.

Collaborators:

@bchristo

Expectation of Answer Changes:

By change this values, we will see more reasonable scaling and make the model easier to fit to observed sapflow.

Description of generative AI usage (as necessary)

No AI used.

Checklist

If this is your first time contributing, please read the CONTRIBUTING document.

All checklist items must be checked to enable merging this pull request:

Contributor

• [ x] The in-code documentation has been updated with descriptive comments
• The documentation has been assessed to determine if updates are necessary
• Describe use of generative AI (if necessary)

Integrator

• FATES PASS/FAIL regression tests were run
• Evaluation of test results for answer changes was performed and results provided
• FATES-CLM6 Code Freeze: satellite phenology regression tests are b4b

If satellite phenology regressions are not b4b, please hold merge and notify the FATES development team.

Documentation

No need to change to the documentation.

Test Results:

See attached figures of scaling with the impact of change.

CTSM (or) E3SM (specify which) test hash-tag:

CTSM (or) E3SM (specify which) baseline hash-tag:

FATES baseline hash-tag:

Test Output:

[ckoven]

Thanks Chonggang and really interesting. Should this be in the parameter file, rather than hard-coded though?

[xuchongang]

Charlie, Given that we have the p-taper in the parameter file, I do not feel that we need to create a new parameter. Meanwhile, this is a really confusing parameter as its definition is not clearly defined in the scaling model and thus put it into the fates parameter file could create a lot of confusion. Yours Chonggang

…

________________________________ From: Charlie Koven ***@***.***> Sent: Thursday, May 7, 2026 3:38 PM To: NGEET/fates ***@***.***> Cc: Xu, Chonggang ***@***.***>; Author ***@***.***> Subject: [EXTERNAL] Re: [NGEET/fates] update the petiole length parameter to match the scaling from Olson 2020 (PR #1565) [https://avatars.githubusercontent.com/u/10852790?s=20&v=4]ckoven left a comment (NGEET/fates#1565)<https://urldefense.com/v3/__https://github.com/NGEET/fates/pull/1565*issuecomment-4401362162__;Iw!!Bt8fGhp8LhKGRg!GzgsOuwj0KESgGPBPcU1VaKT3KLaCseFmgUeTS--4mNouHzUgLdCyCBhF1TSHtTred4sA9DrAzadlsGDosnLsw$> Thanks Chonggang and really interesting. Should this be in the parameter file, rather than hard-coded though? — Reply to this email directly, view it on GitHub<https://urldefense.com/v3/__https://github.com/NGEET/fates/pull/1565*issuecomment-4401362162__;Iw!!Bt8fGhp8LhKGRg!GzgsOuwj0KESgGPBPcU1VaKT3KLaCseFmgUeTS--4mNouHzUgLdCyCBhF1TSHtTred4sA9DrAzadlsGDosnLsw$>, or unsubscribe<https://urldefense.com/v3/__https://github.com/notifications/unsubscribe-auth/AB6ZRR2LO4G6MYXTXKUSZR34ZT64LAVCNFSM6AAAAACYVF7D4SVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHM2DIMBRGM3DEMJWGI__;!!Bt8fGhp8LhKGRg!GzgsOuwj0KESgGPBPcU1VaKT3KLaCseFmgUeTS--4mNouHzUgLdCyCBhF1TSHtTred4sA9DrAzadlsEC-bAh-g$>. Triage notifications on the go with GitHub Mobile for iOS<https://urldefense.com/v3/__https://apps.apple.com/app/apple-store/id1477376905?ct=notification-email&mt=8&pt=524675__;!!Bt8fGhp8LhKGRg!GzgsOuwj0KESgGPBPcU1VaKT3KLaCseFmgUeTS--4mNouHzUgLdCyCBhF1TSHtTred4sA9DrAzadlsEltAwAOQ$> or Android<https://urldefense.com/v3/__https://play.google.com/store/apps/details?id=com.github.android&referrer=utm_campaign*3Dnotification-email*26utm_medium*3Demail*26utm_source*3Dgithub__;JSUlJSU!!Bt8fGhp8LhKGRg!GzgsOuwj0KESgGPBPcU1VaKT3KLaCseFmgUeTS--4mNouHzUgLdCyCBhF1TSHtTred4sA9DrAzadlsE9CRz6dw$>. You are receiving this because you authored the thread.Message ID: ***@***.***>

[xuchongang]

@JunyanDing, @jennykowalcz , @yfang-pnnl , it would be great if you could review.

@rgknox, it would be great if you could do some test on the most recent version of FATES!