Development and evaluation of a variably saturated flow model in the global E3SM Land Model (ELM) Version 1.0

Abstract

16Improving global-scale model representations of coupled surface and groundwater 17 hydrology is important for accurately simulating terrestrial processes and predicting 18 climate change effects on water resources. Most existing land surface models, 19 including the default E3SM Land Model (ELMv0), which we modify here, routinely 20 employ different formulations for water transport in the vadose and pheratic zones. 21In this work, we developed the Variably Saturated Flow Model (VSFM) in ELMv1 to 22 unify the treatment of soil hydrologic processes in the unsaturated and saturated 23 zones. VSFM was tested on three benchmark problems and results were evaluated 24 against observations and an existing benchmark model (PFLOTRAN). The ELMv1-25 VSFM's subsurface drainage parameter, " , was calibrated to match an 26 observationally-constrained and spatially-explicit global water table depth (WTD) 27product. An optimal " was obtained for 79% of global 1.9 0 × 2.5 0 gridcells, while the 28 remaining 21% of global gridcells had predicted WTD deeper than the 29 observationally-constrained estimate. Comparison with predictions using the default 30 " value demonstrated that calibration significantly improved prediction, primarily 31 by allowing much deeper WTDs. Model evaluation using the International Land Model 32Benchmarking package (ILAMB) showed that improvements in WTD predictions did 33 not degrade model skill for any other metrics. We evaluated the computational 34 performance of the VSFM model and found that the model is about 30% more 35 expensive than the default ELMv0 with an optimal processor layout. 36Geosci. Model Dev. Discuss., https://doi

The DOE E3SM v1.1 Biogeochemistry Configuration: Description and Simulated Ecosystem‐Climate Responses to Historical Changes in Forcing

“…The land model in future versions of E3SM will also be updated with a refactored model grid to enable better representation of subgrid heterogeneity in the land surface, particularly surface topography (Tesfa & Leung, 2017). A new soil hydrology scheme will be available, the Variable Saturation Flow Model (Bisht et al, 2018). The addition of regionally resolved grids in the atmosphere model, with higher resolution over North America will support representation of managed systems (e.g., built energy and water infrastructure) with greater fidelity.…”

Representing Intercell Lateral Groundwater Flow and Aquifer Pumping in the Community Land Model

“…In general, model overestimation in many of basins/catchments could be attributed to the lack of water withdrawals for other sectors than agriculture (e.g., industrial, domestic, thermoelectric power), absence of reservoir operation, and systematic biases in ET, irrigation return flow, and forcing data. Furthermore, the small difference in river discharge among different simulations highlights the fact that: (1) inclusion of lateral flow and groundwater pumping does not substantially alter river discharge simulations over large basins (e.g., Mississippi River, Ohio River), especially at the current model grid of ∼13 km, (2) the impact of pumping was minimal because pumping occurs mostly in semiarid and dry regions where the water table is relatively deep and has low impact on river flow (again, at the current model grid and spatial extent) (Winter et al., 1998), and (3) the subsurface runoff parameters (i.e., q drai,max and f drai ) are not specifically calibrated for the selected basins and hence are not highly sensitive to groundwater table depth that characterized the primary difference between the four simulations (Bisht et al., 2018). It is expected that by increasing the MOSART resolution and calibrating the subsurface runoff parameters, the direct impact of lateral flow and pumping on the river discharge could be better represented.…”

Global Irrigation Characteristics and Effects Simulated by Fully Coupled Land Surface, River, and Water Management Models in E3SM

“…The model (2SGM) simulated mean monthly irrigation withdrawal is compared with Huang et al (2018) at the global administrative unit level (Figure 3) from 1986 to 1990. With calibration, our model captures the general pattern and magnitude of Huang et al (2018) very well with the total global irrigation withdrawal about 2,000 km 3 /year.…”

“…It consists of six major components: an atmosphere model, an ocean model, a sea ice model, a land model, a land ice model, and a river model, as well as a coupler that synchronizes the time steps and exchanges information among the components. The E3SM Land Model (ELM) was built from the Community Land Model Version 4.5 (CLM4.5), with a few changes including a new soil hydrology solver called Variably Saturation Flow Model (VSFM) (Bisht et al, 2018) and two new biogeochemistry (BGC) frameworks to represent plant and soil carbon‐nutrient mechanisms. One of the two BGC approaches, Converging Trophic Cascade (CTC) (X. Yang et al, 2014) is the default BGC configuration in ELM and therefore is activated in this study.…”