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Geoscientific Model Development An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/gmd-2018-44
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Model description paper
02 Mar 2018
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Geoscientific Model Development (GMD).
Development and evaluation of a variably saturated flow model in the global E3SM Land Model (ELM) Version 1.0
Gautam Bisht1, William J. Riley1, Glenn E. Hammond2, and David M. Lorenzetti3 1Climate & Ecosystem Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720, USA
2Applied Systems Analysis and Research Department, Sandia National Laboratories, Albuquerque, NM 87185-0747, USA
3Sustainable Energy Systems Group, Lawrence Berkeley National,Laboratory, 1 Cyclotron Road, Berkeley, California 94720, USA
Abstract. Improving global-scale model representations of coupled surface and groundwater hydrology is important for accurately simulating terrestrial processes and predicting climate change effects on water resources. Most existing land surface models, including the default E3SM Land Model (ELMv0), which we modify here, routinely employ different formulations for water transport in the vadose and pheratic zones. In this work, we developed the Variably Saturated Flow Model (VSFM) in ELMv1 to unify the treatment of soil hydrologic processes in the unsaturated and saturated zones. VSFM was tested on three benchmark problems and results were evaluated against observations and an existing benchmark model (PFLOTRAN). The ELMv1-VSFM's subsurface drainage parameter, fd, was calibrated to match an observationally-constrained and spatially-explicit global water table depth (WTD) product. An optimal fd was obtained for 79 % of global 1.90 × 2.50 gridcells, while the remaining 21 % of global gridcells had predicted WTD deeper than the observationally-constrained estimate. Comparison with predictions using the default fd value demonstrated that calibration significantly improved prediction, primarily by allowing much deeper WTDs. Model evaluation using the International Land Model Benchmarking package (ILAMB) showed that improvements in WTD predictions did not degrade model skill for any other metrics. We evaluated the computational performance of the VSFM model and found that the model is about 30 % more expensive than the default ELMv0 with an optimal processor layout.
Citation: Bisht, G., Riley, W. J., Hammond, G. E., and Lorenzetti, D. M.: Development and evaluation of a variably saturated flow model in the global E3SM Land Model (ELM) Version 1.0, Geosci. Model Dev. Discuss., https://doi.org/10.5194/gmd-2018-44, in review, 2018.
Gautam Bisht et al.
Gautam Bisht et al.
Gautam Bisht et al.

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Short summary
Most existing global land surface models used to study impacts of climate change on water resources, routinely use different employ different models for near-surface unsaturated soil and the deeper groundwater table. We developed a model that uses unified treatment of soil hydrologic processes throughout the entire soil column. Using a calibrated drainage parameter, the new model is able to correctly predicted deep water table depth as reported in an observationally-constrained global dataset.
Most existing global land surface models used to study impacts of climate change on water...
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