An optimality-based model of the coupled soil moisture and root dynamics

S SCHYMANSKI, M SIVAPALAN, M RODERICK, Jason Beringer, Lindsay Hutley

    Research output: Contribution to journalArticleResearchpeer-review

    Abstract

    The main processes determining soil moisture dynamics are infiltration, percolation, evaporation and root water uptake. Modelling soil moisture dynamics therefore requires an interdisciplinary approach that links hydrological, atmospheric and biological processes. Previous approaches treat either root water uptake rates or root distributions and transpiration rates as given, and calculate the soil moisture dynamics based on the theory of flow in unsaturated media. The present study introduces a different approach to linking soil water and vegetation dynamics, based on vegetation optimality. Assuming that plants have evolved mechanisms that minimise costs related to the maintenance of the root system while meeting their demand for water, we develop a model that dynamically adjusts the vertical root distribution in the soil profile to meet this objective. The model was used to compute the soil moisture dynamics, root water uptake and fine root respiration in a tropical savanna over 12 months, and the results were compared with observations at the site and with a model based on a fixed root distribution. The optimality-based model reproduced the main features of the observations such as a shift of roots from the shallow soil in the wet season to the deeper soil in the dry season and substantial root water uptake during the dry season. At the same time, simulated fine root respiration rates never exceeded the upper envelope determined by the observed soil respiration. The model based on a fixed root distribution, in contrast, failed to explain the magnitude of water use during parts of the dry season and largely over-estimated root respiration rates. The observed surface soil moisture dynamics were also better reproduced by the optimality-based model than the model based on a prescribed root distribution. The optimality-based approach has the potential to reduce the number of unknowns in a model (e.g. the vertical root distribution), which makes it a valuable alternative to more empirically-based approaches, especially for simulating possible responses to environmental change.
    Original languageEnglish
    Pages (from-to)913-932
    Number of pages20
    JournalHydrology and Earth System Sciences
    Volume12
    Issue number3
    Publication statusPublished - 2008

    Fingerprint

    soil moisture
    water uptake
    dry season
    respiration
    fine root
    unsaturated medium
    interdisciplinary approach
    shallow soil
    vegetation dynamics
    soil respiration
    root system
    wet season
    biological processes
    savanna
    transpiration
    water use
    soil profile
    distribution
    environmental change
    infiltration

    Cite this

    SCHYMANSKI, S., SIVAPALAN, M., RODERICK, M., Beringer, J., & Hutley, L. (2008). An optimality-based model of the coupled soil moisture and root dynamics. Hydrology and Earth System Sciences, 12(3), 913-932.
    SCHYMANSKI, S ; SIVAPALAN, M ; RODERICK, M ; Beringer, Jason ; Hutley, Lindsay. / An optimality-based model of the coupled soil moisture and root dynamics. In: Hydrology and Earth System Sciences. 2008 ; Vol. 12, No. 3. pp. 913-932.
    @article{4a631a1fb4294e3c8b2b2258e2de9a67,
    title = "An optimality-based model of the coupled soil moisture and root dynamics",
    abstract = "The main processes determining soil moisture dynamics are infiltration, percolation, evaporation and root water uptake. Modelling soil moisture dynamics therefore requires an interdisciplinary approach that links hydrological, atmospheric and biological processes. Previous approaches treat either root water uptake rates or root distributions and transpiration rates as given, and calculate the soil moisture dynamics based on the theory of flow in unsaturated media. The present study introduces a different approach to linking soil water and vegetation dynamics, based on vegetation optimality. Assuming that plants have evolved mechanisms that minimise costs related to the maintenance of the root system while meeting their demand for water, we develop a model that dynamically adjusts the vertical root distribution in the soil profile to meet this objective. The model was used to compute the soil moisture dynamics, root water uptake and fine root respiration in a tropical savanna over 12 months, and the results were compared with observations at the site and with a model based on a fixed root distribution. The optimality-based model reproduced the main features of the observations such as a shift of roots from the shallow soil in the wet season to the deeper soil in the dry season and substantial root water uptake during the dry season. At the same time, simulated fine root respiration rates never exceeded the upper envelope determined by the observed soil respiration. The model based on a fixed root distribution, in contrast, failed to explain the magnitude of water use during parts of the dry season and largely over-estimated root respiration rates. The observed surface soil moisture dynamics were also better reproduced by the optimality-based model than the model based on a prescribed root distribution. The optimality-based approach has the potential to reduce the number of unknowns in a model (e.g. the vertical root distribution), which makes it a valuable alternative to more empirically-based approaches, especially for simulating possible responses to environmental change.",
    keywords = "hydrological modeling, infiltration, optimization, percolation, root, soil moisture, transpiration, water uptake",
    author = "S SCHYMANSKI and M SIVAPALAN and M RODERICK and Jason Beringer and Lindsay Hutley",
    year = "2008",
    language = "English",
    volume = "12",
    pages = "913--932",
    journal = "Hydrology and Earth System Sciences",
    issn = "1027-5606",
    publisher = "Copernicus GmbH",
    number = "3",

    }

    SCHYMANSKI, S, SIVAPALAN, M, RODERICK, M, Beringer, J & Hutley, L 2008, 'An optimality-based model of the coupled soil moisture and root dynamics', Hydrology and Earth System Sciences, vol. 12, no. 3, pp. 913-932.

    An optimality-based model of the coupled soil moisture and root dynamics. / SCHYMANSKI, S; SIVAPALAN, M; RODERICK, M; Beringer, Jason; Hutley, Lindsay.

    In: Hydrology and Earth System Sciences, Vol. 12, No. 3, 2008, p. 913-932.

    Research output: Contribution to journalArticleResearchpeer-review

    TY - JOUR

    T1 - An optimality-based model of the coupled soil moisture and root dynamics

    AU - SCHYMANSKI, S

    AU - SIVAPALAN, M

    AU - RODERICK, M

    AU - Beringer, Jason

    AU - Hutley, Lindsay

    PY - 2008

    Y1 - 2008

    N2 - The main processes determining soil moisture dynamics are infiltration, percolation, evaporation and root water uptake. Modelling soil moisture dynamics therefore requires an interdisciplinary approach that links hydrological, atmospheric and biological processes. Previous approaches treat either root water uptake rates or root distributions and transpiration rates as given, and calculate the soil moisture dynamics based on the theory of flow in unsaturated media. The present study introduces a different approach to linking soil water and vegetation dynamics, based on vegetation optimality. Assuming that plants have evolved mechanisms that minimise costs related to the maintenance of the root system while meeting their demand for water, we develop a model that dynamically adjusts the vertical root distribution in the soil profile to meet this objective. The model was used to compute the soil moisture dynamics, root water uptake and fine root respiration in a tropical savanna over 12 months, and the results were compared with observations at the site and with a model based on a fixed root distribution. The optimality-based model reproduced the main features of the observations such as a shift of roots from the shallow soil in the wet season to the deeper soil in the dry season and substantial root water uptake during the dry season. At the same time, simulated fine root respiration rates never exceeded the upper envelope determined by the observed soil respiration. The model based on a fixed root distribution, in contrast, failed to explain the magnitude of water use during parts of the dry season and largely over-estimated root respiration rates. The observed surface soil moisture dynamics were also better reproduced by the optimality-based model than the model based on a prescribed root distribution. The optimality-based approach has the potential to reduce the number of unknowns in a model (e.g. the vertical root distribution), which makes it a valuable alternative to more empirically-based approaches, especially for simulating possible responses to environmental change.

    AB - The main processes determining soil moisture dynamics are infiltration, percolation, evaporation and root water uptake. Modelling soil moisture dynamics therefore requires an interdisciplinary approach that links hydrological, atmospheric and biological processes. Previous approaches treat either root water uptake rates or root distributions and transpiration rates as given, and calculate the soil moisture dynamics based on the theory of flow in unsaturated media. The present study introduces a different approach to linking soil water and vegetation dynamics, based on vegetation optimality. Assuming that plants have evolved mechanisms that minimise costs related to the maintenance of the root system while meeting their demand for water, we develop a model that dynamically adjusts the vertical root distribution in the soil profile to meet this objective. The model was used to compute the soil moisture dynamics, root water uptake and fine root respiration in a tropical savanna over 12 months, and the results were compared with observations at the site and with a model based on a fixed root distribution. The optimality-based model reproduced the main features of the observations such as a shift of roots from the shallow soil in the wet season to the deeper soil in the dry season and substantial root water uptake during the dry season. At the same time, simulated fine root respiration rates never exceeded the upper envelope determined by the observed soil respiration. The model based on a fixed root distribution, in contrast, failed to explain the magnitude of water use during parts of the dry season and largely over-estimated root respiration rates. The observed surface soil moisture dynamics were also better reproduced by the optimality-based model than the model based on a prescribed root distribution. The optimality-based approach has the potential to reduce the number of unknowns in a model (e.g. the vertical root distribution), which makes it a valuable alternative to more empirically-based approaches, especially for simulating possible responses to environmental change.

    KW - hydrological modeling

    KW - infiltration

    KW - optimization

    KW - percolation

    KW - root

    KW - soil moisture

    KW - transpiration

    KW - water uptake

    M3 - Article

    VL - 12

    SP - 913

    EP - 932

    JO - Hydrology and Earth System Sciences

    JF - Hydrology and Earth System Sciences

    SN - 1027-5606

    IS - 3

    ER -