Evaluating the Community Land Model (CLM4.5) at a coniferous forest site in northwestern United States using flux and carbon-isotope measurements
Droughts in the western United States are expected to intensify with climate change. Thus, an adequate representation of ecosystem response to water stress in land models is critical for predicting carbon dynamics. The goal of this study was to evaluate the performance of the Community Land Model...
| Main Authors: | , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-09-01
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| Series: | Biogeosciences |
| Online Access: | https://www.biogeosciences.net/14/4315/2017/bg-14-4315-2017.pdf |
| _version_ | 1819154560286982144 |
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| author | H. F. Duarte B. M. Raczka D. M. Ricciuto J. C. Lin C. D. Koven P. E. Thornton D. R. Bowling C.-T. Lai K. J. Bible J. R. Ehleringer |
| author_facet | H. F. Duarte B. M. Raczka D. M. Ricciuto J. C. Lin C. D. Koven P. E. Thornton D. R. Bowling C.-T. Lai K. J. Bible J. R. Ehleringer |
| author_sort | H. F. Duarte |
| collection | DOAJ |
| description | Droughts in the western United States are expected to intensify with climate
change. Thus, an adequate representation of ecosystem response to water
stress in land models is critical for predicting carbon dynamics. The goal of
this study was to evaluate the performance of the Community Land Model (CLM)
version 4.5 against observations at an old-growth coniferous forest site in
the Pacific Northwest region of the United States (Wind River AmeriFlux
site), characterized by a Mediterranean climate that subjects trees to water
stress each summer. CLM was driven by site-observed meteorology and
calibrated primarily using parameter values observed at the site or at
similar stands in the region. Key model adjustments included parameters
controlling specific leaf area and stomatal conductance. Default values of
these parameters led to significant underestimation of gross primary
production, overestimation of evapotranspiration, and consequently
overestimation of photosynthetic <sup>13</sup>C discrimination, reflected in
reduced <sup>13</sup>C : <sup>12</sup>C ratios of carbon fluxes and pools. Adjustments
in soil hydraulic parameters within CLM were also critical, preventing
significant underestimation of soil water content and unrealistic soil
moisture stress during summer. After calibration, CLM was able to simulate
energy and carbon fluxes, leaf area index, biomass stocks, and carbon isotope
ratios of carbon fluxes and pools in reasonable agreement with site
observations. Overall, the calibrated CLM was able to simulate the observed
response of canopy conductance to atmospheric vapor pressure deficit (VPD)
and soil water content, reasonably capturing the impact of water stress on
ecosystem functioning. Both simulations and observations indicate that
stomatal response from water stress at Wind River was primarily driven by VPD
and not soil moisture. The calibration of the Ball–Berry stomatal
conductance slope (<i>m</i><sub>bb</sub>) at Wind River aligned with findings from recent CLM experiments at sites characterized by the same plant functional
type (needleleaf evergreen temperate forest), despite significant differences
in stand composition and age and climatology, suggesting that CLM could
benefit from a revised <i>m</i><sub>bb</sub> value of 6, rather than the default
value of 9, for this plant functional type. Conversely, Wind River required a
unique calibration of the hydrology submodel to simulate soil moisture,
suggesting that the default hydrology has a more limited applicability. This
study demonstrates that carbon isotope data can be used to constrain stomatal
conductance and intrinsic water use efficiency in CLM, as an alternative to
eddy covariance flux measurements. It also demonstrates that carbon isotopes
can expose structural weaknesses in the model and provide a key constraint
that may guide future model development. |
| first_indexed | 2024-12-22T15:23:01Z |
| format | Article |
| id | doaj.art-fd36131d86f54082a59245b6f4dfe230 |
| institution | Directory Open Access Journal |
| issn | 1726-4170 1726-4189 |
| language | English |
| last_indexed | 2024-12-22T15:23:01Z |
| publishDate | 2017-09-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Biogeosciences |
| spelling | doaj.art-fd36131d86f54082a59245b6f4dfe2302022-12-21T18:21:34ZengCopernicus PublicationsBiogeosciences1726-41701726-41892017-09-01144315434010.5194/bg-14-4315-2017Evaluating the Community Land Model (CLM4.5) at a coniferous forest site in northwestern United States using flux and carbon-isotope measurementsH. F. Duarte0B. M. Raczka1D. M. Ricciuto2J. C. Lin3C. D. Koven4P. E. Thornton5D. R. Bowling6C.-T. Lai7K. J. Bible8J. R. Ehleringer9Department of Atmospheric Sciences, University of Utah, Salt Lake City, 84112, USADepartment of Biology, University of Utah, Salt Lake City, 84112, USAOak Ridge National Laboratory, Oak Ridge, 37831, USADepartment of Atmospheric Sciences, University of Utah, Salt Lake City, 84112, USALawrence Berkeley National Laboratory, Berkeley, 94720, USAOak Ridge National Laboratory, Oak Ridge, 37831, USADepartment of Biology, University of Utah, Salt Lake City, 84112, USADepartment of Biology, San Diego State University, San Diego, 92182, USAUnited States Forest Service, Pacific Northwest Research Station, Corvallis, 97331, USADepartment of Biology, University of Utah, Salt Lake City, 84112, USADroughts in the western United States are expected to intensify with climate change. Thus, an adequate representation of ecosystem response to water stress in land models is critical for predicting carbon dynamics. The goal of this study was to evaluate the performance of the Community Land Model (CLM) version 4.5 against observations at an old-growth coniferous forest site in the Pacific Northwest region of the United States (Wind River AmeriFlux site), characterized by a Mediterranean climate that subjects trees to water stress each summer. CLM was driven by site-observed meteorology and calibrated primarily using parameter values observed at the site or at similar stands in the region. Key model adjustments included parameters controlling specific leaf area and stomatal conductance. Default values of these parameters led to significant underestimation of gross primary production, overestimation of evapotranspiration, and consequently overestimation of photosynthetic <sup>13</sup>C discrimination, reflected in reduced <sup>13</sup>C : <sup>12</sup>C ratios of carbon fluxes and pools. Adjustments in soil hydraulic parameters within CLM were also critical, preventing significant underestimation of soil water content and unrealistic soil moisture stress during summer. After calibration, CLM was able to simulate energy and carbon fluxes, leaf area index, biomass stocks, and carbon isotope ratios of carbon fluxes and pools in reasonable agreement with site observations. Overall, the calibrated CLM was able to simulate the observed response of canopy conductance to atmospheric vapor pressure deficit (VPD) and soil water content, reasonably capturing the impact of water stress on ecosystem functioning. Both simulations and observations indicate that stomatal response from water stress at Wind River was primarily driven by VPD and not soil moisture. The calibration of the Ball–Berry stomatal conductance slope (<i>m</i><sub>bb</sub>) at Wind River aligned with findings from recent CLM experiments at sites characterized by the same plant functional type (needleleaf evergreen temperate forest), despite significant differences in stand composition and age and climatology, suggesting that CLM could benefit from a revised <i>m</i><sub>bb</sub> value of 6, rather than the default value of 9, for this plant functional type. Conversely, Wind River required a unique calibration of the hydrology submodel to simulate soil moisture, suggesting that the default hydrology has a more limited applicability. This study demonstrates that carbon isotope data can be used to constrain stomatal conductance and intrinsic water use efficiency in CLM, as an alternative to eddy covariance flux measurements. It also demonstrates that carbon isotopes can expose structural weaknesses in the model and provide a key constraint that may guide future model development.https://www.biogeosciences.net/14/4315/2017/bg-14-4315-2017.pdf |
| spellingShingle | H. F. Duarte B. M. Raczka D. M. Ricciuto J. C. Lin C. D. Koven P. E. Thornton D. R. Bowling C.-T. Lai K. J. Bible J. R. Ehleringer Evaluating the Community Land Model (CLM4.5) at a coniferous forest site in northwestern United States using flux and carbon-isotope measurements Biogeosciences |
| title | Evaluating the Community Land Model (CLM4.5) at a coniferous forest site in northwestern United States using flux and carbon-isotope measurements |
| title_full | Evaluating the Community Land Model (CLM4.5) at a coniferous forest site in northwestern United States using flux and carbon-isotope measurements |
| title_fullStr | Evaluating the Community Land Model (CLM4.5) at a coniferous forest site in northwestern United States using flux and carbon-isotope measurements |
| title_full_unstemmed | Evaluating the Community Land Model (CLM4.5) at a coniferous forest site in northwestern United States using flux and carbon-isotope measurements |
| title_short | Evaluating the Community Land Model (CLM4.5) at a coniferous forest site in northwestern United States using flux and carbon-isotope measurements |
| title_sort | evaluating the community land model clm4 5 at a coniferous forest site in northwestern united states using flux and carbon isotope measurements |
| url | https://www.biogeosciences.net/14/4315/2017/bg-14-4315-2017.pdf |
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