Improving process representation and numerics for integrated hydrological modeling at the subsurface/land surface/atmosphere interface

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The proposed research will focus on the development and application of simulation models at the subsurface/land surface/atmosphere interface. The objective will be to advance the state of the art in integrated hydrological and ecohydrological modeling from both physical (process representation and parameterization) and numerical (robustness, accuracy, and efficiency) perspectives. The work will be based on one of only a handful of accepted, fully-distributed, physically-based, coupled hydrological models that use advanced computational algorithms to resolve the governing mass conservation equations for surface and subsurface water flow and solute transport. The main themes of the work, which will also be the bases for individual PhD and postdoctoral research projects, will include: mass transfer and transport phenomena of varying complexity; incorporation of additional ecohydrological processes into the existing model; proper resolution of exchange or coupling terms between different subsystems; extension of the model’s existing ensemble framework, implemented for data assimilation, to parameter estimation and sensitivity analysis; and applications of the model across multiple and nested scales, from field plot to river basin. Challenges in integrated, process-based hydrological modeling related to heterogeneity, grid resolution effects, competing submodel or parameterization schemes, strong nonlinearities, and boundary conditions will be addressed. Model performance will be assessed for different state variables, both integrated measures such as flow rate and solute concentration at the discharge outlet, total system water storage and solute mass, and total groundwater recharge, and distributed responses such as soil moisture, mass concentration, and exchange fluxes at different points along a sensor network. The project will rely on the availability of detailed, multivariate observation data from experimental hillslope and watershed scale study sites. The research will be highly collaborative at an international level and will include participation in multidisciplinary field experiments and model intercomparison and benchmarking studies. There is high demand in the research community for reliable, extendable, open source codes that can resolve integrated ecohydrological processes based on consistent and rigorous physical (and chemical/biological), mathematical, and numerical principles. The proposed research will result in improved simulation models to help us deepen our understanding of complex natural phenomena, of how different processes interact, and of how these systems can be impacted by anthropogenic stresses and other factors.