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Title: Sensitivity of transpiration to subsurface properties: Exploration with a 1-D model

Abstract

The amount of moisture transpired by vegetation is critically tied to the moisture supply accessible to the root zone. In a Mediterranean climate, integrated evapotranspiration (ET) is typically greater in the dry summer when there is an uninterrupted period of high insolation. We present a 1-D model to explore the subsurface factors that may sustain ET through the dry season. The model includes a stochastic parameterization of hydraulic conductivity, root water uptake efficiency, and hydraulic redistribution by plant roots. Model experiments vary the precipitation, the magnitude and seasonality of ET demand, as well as rooting profiles and rooting depths of the vegetation. The results show that the amount of subsurface moisture remaining at the end of the wet winter is determined by the competition among abundant precipitation input, fast infiltration, and winter ET demand. The weathered bedrock retains math formula of the winter rain and provides a substantial moisture reservoir that may sustain ET of deep-rooted (>8 m) trees through the dry season. A small negative feedback exists in the root zone, where the depletion of moisture by ET decreases hydraulic conductivity and enhances the retention of moisture. Hence, hydraulic redistribution by plant roots is impactful in a dry season,more » or with a less conductive subsurface. Suggestions for implementing the model in the CESM are discussed.« less

Authors:
ORCiD logo [1]; ORCiD logo [2]
  1. Univ. of California, Berkeley, CA (United States). Dept. of Earth and Planetary Science; Science and Technology Facilities Council (STFC), Rutherford Appleton Lab. (United Kingdom). Central Laser Facility
  2. Univ. of California, Berkeley, CA (United States). Dept. of Earth and Planetary Science
Publication Date:
Research Org.:
Univ. of California, Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1393555
Grant/Contract Number:
SC0010857; SC0014080
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of Advances in Modeling Earth Systems
Additional Journal Information:
Journal Volume: 9; Journal Issue: 2; Journal ID: ISSN 1942-2466
Publisher:
American Geophysical Union (AGU)
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES

Citation Formats

Vrettas, Michail D., and Fung, Inez Y. Sensitivity of transpiration to subsurface properties: Exploration with a 1-D model. United States: N. p., 2017. Web. doi:10.1002/2016MS000901.
Vrettas, Michail D., & Fung, Inez Y. Sensitivity of transpiration to subsurface properties: Exploration with a 1-D model. United States. doi:10.1002/2016MS000901.
Vrettas, Michail D., and Fung, Inez Y. Thu . "Sensitivity of transpiration to subsurface properties: Exploration with a 1-D model". United States. doi:10.1002/2016MS000901. https://www.osti.gov/servlets/purl/1393555.
@article{osti_1393555,
title = {Sensitivity of transpiration to subsurface properties: Exploration with a 1-D model},
author = {Vrettas, Michail D. and Fung, Inez Y.},
abstractNote = {The amount of moisture transpired by vegetation is critically tied to the moisture supply accessible to the root zone. In a Mediterranean climate, integrated evapotranspiration (ET) is typically greater in the dry summer when there is an uninterrupted period of high insolation. We present a 1-D model to explore the subsurface factors that may sustain ET through the dry season. The model includes a stochastic parameterization of hydraulic conductivity, root water uptake efficiency, and hydraulic redistribution by plant roots. Model experiments vary the precipitation, the magnitude and seasonality of ET demand, as well as rooting profiles and rooting depths of the vegetation. The results show that the amount of subsurface moisture remaining at the end of the wet winter is determined by the competition among abundant precipitation input, fast infiltration, and winter ET demand. The weathered bedrock retains math formula of the winter rain and provides a substantial moisture reservoir that may sustain ET of deep-rooted (>8 m) trees through the dry season. A small negative feedback exists in the root zone, where the depletion of moisture by ET decreases hydraulic conductivity and enhances the retention of moisture. Hence, hydraulic redistribution by plant roots is impactful in a dry season, or with a less conductive subsurface. Suggestions for implementing the model in the CESM are discussed.},
doi = {10.1002/2016MS000901},
journal = {Journal of Advances in Modeling Earth Systems},
number = 2,
volume = 9,
place = {United States},
year = {Thu May 04 00:00:00 EDT 2017},
month = {Thu May 04 00:00:00 EDT 2017}
}

Journal Article:
Free Publicly Available Full Text
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  • Several authors have determined the sensitivity of transpiration to different environmental parameters using the Penman-Monteith equation. In their studies, the interaction between transpiration and, for example, the humidity of the air is ignored: the feedback with the planetary boundary layer (PBL) is not accounted for. Furthermore, surface-layer (SL) feedback (e.g., stability effects in the surface layer) is often neglected. In our study, both PBL feedback and SL feedback are accounted for by coupling the big-leaf model to a detailed model for the PBL. This study provides an analysis of the sensitivity of transpiration to net radiation calculated after an albedomore » change, aerodynamic resistance calculated after a change in the aerodynamic roughness, and surface resistance. It is shown that PBL feedback affects the sensitivity of transpiration to the tested variables significantly. The sensitivity of transpiration to surface resistance and to aerodynamic resistance, or aerodynamic roughness, is decreased by the PBL feedback. In contrast, PBL feedback enlarges the sensitivity of transpiration to the net radiation, or albeds, and appears to be highly dependent on the specific conditions, especially on the aerodynamic roughness of the vegetation. It is recommended that future sensitivity studies for prognostic use account for PBL feedback.« less
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