Spatially explicit, process-based models have been developed to understand hydrological dynamics and solute transport at the watershed scale. Although these models reveal important insights of temporal and spatial dynamics with explicit distributions of land cover, soil type, topography, and bedrock depth, thesecomplex process-based models also suffer from the disadvantage of being computational-, labor-, parameter-, and data- intensive. In addition, earth system models beyond catchment scales cannot utilize these models directly. In this work, we upscale the hydrological processes in a complex, spatially-explicit model (Flux-PIHM) to a simple, spatially-implicit model with two grid blocks connected by a river channel. The simple model is characterized by average or effective parameters at the catchment scale. We utilize the hydrological data at the Shale Hills (one of the US Critical Zone Observatories) and aim to answer two questions: 1) what are the key upscaled parameters / processes that reproduce the discharge data at watershed scale? 2) How much details of water dynamics can be captured by the simple model? Preliminary results show that the upscaled simple model captures the daily dynamics of evapotranspiration, water storage, and discharge at the catchment scale. The effective parameters of land cover, soil type, and bedrock depth that best produce the discharge approximate the arithmetic mean of values from the complex model. An exception is the topography: the geographic slope in the simple model that best reproduces discharge is 90, much lower than the average of actual slopes from the topography data (~ 180) used in the complex model however close to the average slope of the shallow interflow water-table calculated from the complex model. Sensitivity analysis indicates that this is one of the most important parameters that reproduce discharge data. This underscores the important role of topography in reproducing water dynamics, suggesting existing earth system models that do not take into account of earth surface topography can potentially lead to erroneous predictions.
Hang Wen*, Li Li, Susan Brantley (2018): Upscaling Hydrological Dynamics at the Watershed Scale. Abstract H43C-2405 presented at 2018 AGU Fall Meeting, Washington, D.C., 10-14 Dec.
This Paper/Book acknowledges NSF CZO grant support.