Progress Towards Coupled Simulation of Surface/Subsurface Hydrologic Processes and Terrestrial Ecosystem Dynamics Using the Community Models PFLOTRAN and CLM

CONTROL ID: 1489802

TITLE: Progress Towards Coupled Simulation of Surface/Subsurface Hydrologic Processes and Terrestrial Ecosystem Dynamics Using the Community Models PFLOTRAN and CLM

AUTHORS (FIRST NAME, LAST NAME): Richard T Mills^{1, 2}, Gautam Bisht³, Satish Karra⁴, Forrest M Hoffman¹, Glenn E Hammond⁵, Jitendra Kumar¹, Scott Painter⁴, Peter E Thornton¹, Peter C Lichtner^{6, 4}

INSTITUTIONS (ALL): 1. Oak Ridge National Laboratory, Oak Ridge, TN, United States.
2. University of Tennessee, Knoxville, TN, United States.
3. Lawrence Berkeley National Laboratory, Berkeley, CA, United States.
4. Los Alamos National Laboratory, Los Alamos, NM, United States.
5. Pacific Northwest National Laboratory, Richland, WA, United States.
6. OFM Research, Redmond, WA, United States.

ABSTRACT BODY: Accurately simulating regional water cycle dynamics is challenging because of strong soil moisture-rainfall feedbacks and large uncertainties associated with vegetation and energy interactions. Earth system models of today cannot accurately capture such interactions, because current-generation land surface models (LSMs) 1) do not explicitly represent the fine-scale spatial variability of topography, soils, and vegetation that play a significant role in determining the response of hydrologic states (soil moisture) and fluxes (interception, infiltration, runoff, evapotranspiration) and 2) over-simplify or completely omit some key physical processes, such as lateral flow of water and heat, surface-subsurface interactions, realistic groundwater-vadose zone interactions, and freeze-thaw dynamics. Capturing such processes is critically important for predicting regional precipitation, vegetation productivity, and the disposition of carbon stored in potentially vulnerable permafrost under scenarios of climate change. Towards this end, we have added coupled surface water-groundwater interactions to the the open-source, massively parallel flow and reactive transport model PFLOTRAN, and have been developing a framework for coupling PFLOTRAN with the Community Land Model (CLM).

PFLOTRAN is an open-source (LGPL-licensed) code—with a growing community of users—developed for simulation of multiscale, multiphase, multicomponent subsurface flow and reactive transport problems on machines ranging from laptops to leadership-class supercomputers. It has been applied in studies of contaminant fate and transport, geologic CO₂ sequestration, and geothermal energy production, among others, and has been run using up to 262,144 processor cores on Jaguar, the Cray XK6 supercomputer at Oak Ridge National Laboratory. We have recently added a surface flow component in PFLOTRAN that is integrated with the subsurface. The underlying solver framework employed allows significant flexibility in how the governing equations are solved, and we will compare different surface flow formulations as well as coupling strategies between the surface and subsurface domains. Additionally, for studies of hydrology in Arctic regions, we have added a three-phase ice model. We will present some demonstrations of this capability and discuss solver strategies for handling the strong nonlinearities that arise.

To provide a unified treatment of the unsaturated and saturated zones and to enable lateral redistribution of soil moisture (and eventually surface water, heat, and nutrients) in regional climate models, we have developed an approach for coupling PFLOTRAN with CLM. CLM is the global land model component used within the Community Earth System Model (CESM) to simulate an extensive set of biogeophysical and biogeochemical processes occurring at or near the terrestrial surface. We will describe our approach for replacing the existing CLM hydrology using PFLOTRAN and present some preliminary simulations undertaken with the CLM-PFLOTRAN coupled model.

KEYWORDS: [1805] HYDROLOGY / Computational hydrology, [1813] HYDROLOGY / Eco-hydrology, [0475] BIOGEOSCIENCES / Permafrost, cryosphere, and high-latitude processes, [1830] HYDROLOGY / Groundwater/surface water interaction.
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CONTACT (NAME ONLY): Richard Mills
CONTACT (E-MAIL ONLY): rtm at utk dot edu
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