Incorporating land-atmospheric-vegetation feedbacks into subsurface models used for agriculture water management.
Colorado School of Mines
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The need for new technologies and improved management strategies for the efficient agricultural water use and sustainability has become imperative due to increasing demand for food due to global population growth as well as climate change driven stresses. Groundwater is a critical resource in the water-energy-food nexus. The problems and challenges associated with groundwater are not only limited to the semi-arid west but also many parts of the word facing with water shortages. Numerical models of both subsurface flow and transport play a central role in assessing the impacts of over water withdrawal and water quality degradation, developing strategies for efficient use and conservation, and management during droughts. In traditional models used in these applications, only the flow processes in the surface water systems, and the unsaturated and saturated zones are simulated. The conditions that determine the mass and energy fluxes at the land surface are incorporated as external boundary conditions. These types of models where the land-atmospheric interactions are decoupled do not allow for the accurate representation of the feedback processes occuring between the soils, plants and the atmosphere. In agriculture applications, such models should capture the boundary layer interactions with the surface topography that is modified by land preparation, vegetation density and distribution on bare soil surfaces and soil structure affected by macroporosity. This paper discusses the knowledge gaps that need to be filled to develop better conceptual and numerical models. Many challenges exist in developing and validation of such models. First the models need to couple drastically different flow dynamics in the boundary layer and the shallow soil in the unsaturated zone. The models also need to capture simultaneously occurring heat and mass fluxes across interfaces. How to parameterize these coupling processes at different scales associated with the soil heterogeneity, micro-topography of land surface and vegetation distribution is not well understood. Validation of these types of models in the field is not practical due to lack of control of the climate conditions. A validation methodology at the intermediate scale using a unique coupled porous media/climate wind tunnel facility is presented.