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Improvement of modeling plant responses to low soil moisture in JULESvn4.9 and evaluation against flux tower measurements

Harper, Anna B. ; Williams, Karina E. ; Mcguire, Patrick C. ; Duran Rojas, Maria Carolina ; Hemming, Debbie ; Verhoef, Anne ; Huntingford, Chris ; Rowland, Lucy ; Marthews, Toby and Breder Eller, Cleiton , et al. (2021) In Geoscientific Model Development 14(6). p.3269-3294
Abstract

Drought is predicted to increase in the future due to climate change, bringing with it myriad impacts on ecosystems. Plants respond to drier soils by reducing stomatal conductance in order to conserve water and avoid hydraulic damage. Despite the importance of plant drought responses for the global carbon cycle and local and regional climate feedbacks, land surface models are unable to capture observed plant responses to soil moisture stress. We assessed the impact of soil moisture stress on simulated gross primary productivity (GPP) and latent energy flux (LE) in the Joint UK Land Environment Simulator (JULES) vn4.9 on seasonal and annual timescales and evaluated 10 different representations of soil moisture stress in the model. For... (More)

Drought is predicted to increase in the future due to climate change, bringing with it myriad impacts on ecosystems. Plants respond to drier soils by reducing stomatal conductance in order to conserve water and avoid hydraulic damage. Despite the importance of plant drought responses for the global carbon cycle and local and regional climate feedbacks, land surface models are unable to capture observed plant responses to soil moisture stress. We assessed the impact of soil moisture stress on simulated gross primary productivity (GPP) and latent energy flux (LE) in the Joint UK Land Environment Simulator (JULES) vn4.9 on seasonal and annual timescales and evaluated 10 different representations of soil moisture stress in the model. For the default configuration, GPP was more realistic in temperate biome sites than in the tropics or high-latitude (cold-region) sites, while LE was best simulated in temperate and high-latitude (cold) sites. Errors that were not due to soil moisture stress, possibly linked to phenology, contributed to model biases for GPP in tropical savanna and deciduous forest sites. We found that three alternative approaches to calculating soil moisture stress produced more realistic results than the default parameterization for most biomes and climates. All of these involved increasing the number of soil layers from 4 to 14 and the soil depth from 3.0 to 10.8 m. In addition, we found improvements when soil matric potential replaced volumetric water content in the stress equation (the "soil14_psi" experiments), when the critical threshold value for inducing soil moisture stress was reduced ("soil14_p0"), and when plants were able to access soil moisture in deeper soil layers ("soil14_dr&z.ast;2"). For LE, the biases were highest in the default configuration in temperate mixed forests, with overestimation occurring during most of the year. At these sites, reducing soil moisture stress (with the new parameterizations mentioned above) increased LE and increased model biases but improved the simulated seasonal cycle and brought the monthly variance closer to the measured variance of LE. Further evaluation of the reason for the high bias in LE at many of the sites would enable improvements in both carbon and energy fluxes with new parameterizations for soil moisture stress. Increasing the soil depth and plant access to deep soil moisture improved many aspects of the simulations, and we recommend these settings in future work using JULES or as a general way to improve land surface carbon and water fluxes in other models. In addition, using soil matric potential presents the opportunity to include plant functional type-specific parameters to further improve modeled fluxes.

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publishing date
type
Contribution to journal
publication status
published
subject
in
Geoscientific Model Development
volume
14
issue
6
pages
26 pages
publisher
Copernicus GmbH
external identifiers
  • scopus:85107553488
ISSN
1991-959X
DOI
10.5194/gmd-14-3269-2021
language
English
LU publication?
yes
id
dbc4630d-65fb-4cc7-bb42-34000ade7fb9
date added to LUP
2021-06-28 13:24:23
date last changed
2022-04-27 02:36:34
@article{dbc4630d-65fb-4cc7-bb42-34000ade7fb9,
  abstract     = {{<p>Drought is predicted to increase in the future due to climate change, bringing with it myriad impacts on ecosystems. Plants respond to drier soils by reducing stomatal conductance in order to conserve water and avoid hydraulic damage. Despite the importance of plant drought responses for the global carbon cycle and local and regional climate feedbacks, land surface models are unable to capture observed plant responses to soil moisture stress. We assessed the impact of soil moisture stress on simulated gross primary productivity (GPP) and latent energy flux (LE) in the Joint UK Land Environment Simulator (JULES) vn4.9 on seasonal and annual timescales and evaluated 10 different representations of soil moisture stress in the model. For the default configuration, GPP was more realistic in temperate biome sites than in the tropics or high-latitude (cold-region) sites, while LE was best simulated in temperate and high-latitude (cold) sites. Errors that were not due to soil moisture stress, possibly linked to phenology, contributed to model biases for GPP in tropical savanna and deciduous forest sites. We found that three alternative approaches to calculating soil moisture stress produced more realistic results than the default parameterization for most biomes and climates. All of these involved increasing the number of soil layers from 4 to 14 and the soil depth from 3.0 to 10.8 m. In addition, we found improvements when soil matric potential replaced volumetric water content in the stress equation (the &amp;quot;soil14_psi&amp;quot; experiments), when the critical threshold value for inducing soil moisture stress was reduced (&amp;quot;soil14_p0&amp;quot;), and when plants were able to access soil moisture in deeper soil layers (&amp;quot;soil14_dr&amp;z.ast;2&amp;quot;). For LE, the biases were highest in the default configuration in temperate mixed forests, with overestimation occurring during most of the year. At these sites, reducing soil moisture stress (with the new parameterizations mentioned above) increased LE and increased model biases but improved the simulated seasonal cycle and brought the monthly variance closer to the measured variance of LE. Further evaluation of the reason for the high bias in LE at many of the sites would enable improvements in both carbon and energy fluxes with new parameterizations for soil moisture stress. Increasing the soil depth and plant access to deep soil moisture improved many aspects of the simulations, and we recommend these settings in future work using JULES or as a general way to improve land surface carbon and water fluxes in other models. In addition, using soil matric potential presents the opportunity to include plant functional type-specific parameters to further improve modeled fluxes.</p>}},
  author       = {{Harper, Anna B. and Williams, Karina E. and Mcguire, Patrick C. and Duran Rojas, Maria Carolina and Hemming, Debbie and Verhoef, Anne and Huntingford, Chris and Rowland, Lucy and Marthews, Toby and Breder Eller, Cleiton and Mathison, Camilla and Nobrega, Rodolfo L.B. and Gedney, Nicola and Vidale, Pier Luigi and Otu-Larbi, Fred and Pandey, Divya and Garrigues, Sebastien and Wright, Azin and Slevin, Darren and De Kauwe, Martin G. and Blyth, Eleanor and Ardo&die;, Jonas and Black, Andrew and Bonal, Damien and Buchmann, Nina and Burban, Benoit and Fuchs, Kathrin and De Grandcourt, Agnès and Mammarella, Ivan and Merbold, Lutz and Montagnani, Leonardo and Nouvellon, Yann and Restrepo-Coupe, Natalia and Wohlfahrt, Georg}},
  issn         = {{1991-959X}},
  language     = {{eng}},
  month        = {{06}},
  number       = {{6}},
  pages        = {{3269--3294}},
  publisher    = {{Copernicus GmbH}},
  series       = {{Geoscientific Model Development}},
  title        = {{Improvement of modeling plant responses to low soil moisture in JULESvn4.9 and evaluation against flux tower measurements}},
  url          = {{http://dx.doi.org/10.5194/gmd-14-3269-2021}},
  doi          = {{10.5194/gmd-14-3269-2021}},
  volume       = {{14}},
  year         = {{2021}},
}