Development and Evaluation of a Variably Saturated Flow Model in the Global E3SMLand Model (ELM) Version 1.0

TitleDevelopment and Evaluation of a Variably Saturated Flow Model in the Global E3SMLand Model (ELM) Version 1.0
Publication TypeJournal Article
Year of Publication2018
JournalGeoscientific Model Development Discussions
Pages1-40
Date Published06/2018
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.

URLhttp://dx.doi.org/10.5194/gmd-2018-44
DOI10.5194/gmd-2018-44
Funding Program: 
Journal: Geoscientific Model Development Discussions

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.

DOI: 10.5194/gmd-2018-44
Year of Publication: 2018
Citation:
Bisht, G, W Riley, G Hammond, and D Lorenzetti.  2018.  "Development and Evaluation of a Variably Saturated Flow Model in the Global E3SMLand Model (ELM) Version 1.0."  Geoscientific Model Development Discussions 1-40, doi:10.5194/gmd-2018-44.