Using an Isotope Enabled Mass Balance to Evaluate Existing Land Surface Models

Haagsma, Marja [Department of Biological and Ecological Engineering Oregon State University Corvallis OR USA] (ORCID:0000000217777284); Finkenbiner, Catherine E. [Department of Biological and Ecological Engineering Oregon State University Corvallis OR USA] (ORCID:0000000232137787); Noone, David C. [Department of Physics University of Auckland Auckland New Zealand] (ORCID:0000000286427843); Bowen, Gabriel J. [Department of Geology and Geophysics University of Utah Salt Lake City UT USA, Global Change and Sustainability Center University of Utah Salt Lake City UT USA] (ORCID:0000000269283104); Still, Christopher [Department of Forest Ecosystems &amp, Society Oregon State University Corvallis OR USA] (ORCID:0000000282954494); Fiorella, Richard P. [Earth and Environmental Sciences Division Los Alamos National Laboratory Los Alamos NM USA, New Mexico Consortium Los Alamos NM USA] (ORCID:0000000208244777); Good, Stephen P. [Department of Biological and Ecological Engineering Oregon State University Corvallis OR USA, Water Resources Graduate Program Oregon State University Corvallis OR USA] (ORCID:0000000343631577)

doi:10.1029/2024wr037530

DOE OSTI · 2480373

Using an Isotope Enabled Mass Balance to Evaluate Existing Land Surface Models

Haagsma, Marja [Department of Biological and Ecological Engineering Oregon State University Corvallis OR USA] (ORCID:0000000217777284)·Finkenbiner, Catherine E. [Department of Biological and Ecological Engineering Oregon State University Corvallis OR USA] (ORCID:0000000232137787)·Noone, David C. [Department of Physics University of Auckland Auckland New Zealand] (ORCID:0000000286427843)·Bowen, Gabriel J. [Department of Geology and Geophysics University of Utah Salt Lake City UT USA, Global Change and Sustainability Center University of Utah Salt Lake City UT USA] (ORCID:0000000269283104)·Still, Christopher [Department of Forest Ecosystems &amp, Society Oregon State University Corvallis OR USA] (ORCID:0000000282954494)·Fiorella, Richard P. [Earth and Environmental Sciences Division Los Alamos National Laboratory Los Alamos NM USA, New Mexico Consortium Los Alamos NM USA] (ORCID:0000000208244777)·Good, Stephen P. [Department of Biological and Ecological Engineering Oregon State University Corvallis OR USA, Water Resources Graduate Program Oregon State University Corvallis OR USA] (ORCID:0000000343631577)

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Abstract

Abstract Land surface models (LSMs) play a crucial role in elucidating water and carbon cycles by simulating processes such as plant transpiration and evaporation from bare soil, yet calibration often relies on comparing LSM outputs of landscape total evapotranspiration ( ET ) and discharge with measured bulk fluxes. Discrepancies in partitioning into component fluxes predicted by various LSMs have been noted, prompting the need for improved evaluation methods. Stable water isotopes serve as effective tracers of component hydrologic fluxes, but data and model integration challenges have hindered their widespread application. Leveraging National Ecological Observation Network measurements of water isotope ratios at 16 US sites over 3 years combined with LSM‐modeled fluxes, we employed an isotope‐enabled mass balance framework to simulate ET isotope values ( δET ) within three operational LSMs (Mosaic, Noah, and VIC) to evaluate their partitioning. Models simulating δET values consistent with observations were deemed more reflective of water cycling in these ecosystems. Mosaic exhibited the best overall performance (Kling‐Gupta Efficiency of 0.28). For both Mosaic and Noah there were robust correlations between bare soil evaporation fraction and error (negative) as well as transpiration fraction and error (positive). We found the point at which errors are smallest ( x ‐intercept of the multi‐site regression) is at a higher transpiration fraction than is currently specified in the models. Which means that transpiration fraction is underestimated on average. Stable isotope tracers offer an additional tool for model evaluation and identifying areas for improvement, potentially enhancing LSM simulations and our understanding of land‐surface hydrologic processes.

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58 GEOSCIENCES Earth Sciences NEON evapotranspiration evapotranspiration partitioning fluxes hydrological cycle land surface models stable isotopes

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Haagsma, Marja [Department of Biological and Ecological Engineering Oregon State University Corvallis OR USA] (ORCID:0000000217777284), Finkenbiner, Catherine E. [Department of Biological and Ecological Engineering Oregon State University Corvallis OR USA] (ORCID:0000000232137787), Noone, David C. [Department of Physics University of Auckland Auckland New Zealand] (ORCID:0000000286427843), Bowen, Gabriel J. [Department of Geology and Geophysics University of Utah Salt Lake City UT USA, Global Change and Sustainability Center University of Utah Salt Lake City UT USA] (ORCID:0000000269283104), Still, Christopher [Department of Forest Ecosystems &amp, Society Oregon State University Corvallis OR USA] (ORCID:0000000282954494), Fiorella, Richard P. [Earth and Environmental Sciences Division Los Alamos National Laboratory Los Alamos NM USA, New Mexico Consortium Los Alamos NM USA] (ORCID:0000000208244777), Good, Stephen P. [Department of Biological and Ecological Engineering Oregon State University Corvallis OR USA, Water Resources Graduate Program Oregon State University Corvallis OR USA] (ORCID:0000000343631577). 2024-12-07. Using an Isotope Enabled Mass Balance to Evaluate Existing Land Surface Models. https://doi.org/10.1029/2024wr037530

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