Abstract
Abstract. Hydrologic modeling is an essential strategy for understanding and predicting natural flows, particularly where observations are lacking in either space or time or where complex terrain leads to a disconnect in the characteristic time and space scales of overland and groundwater flow. However, significant difficulties remain for the development of efficient and extensible modeling systems that operate robustly across complex regions. This paper introduces the Simulator for Hydrologic Unstructured Domains (SHUD), an integrated, multiprocess, multiscale, flexible-time-step model, in which hydrologic processes are fully coupled using the finite volume method. SHUD integrates overland flow, snow accumulation/melt, evapotranspiration, subsurface flow, groundwater flow, and river routing, thus allowing physical processes in general watersheds to be realistically captured. SHUD incorporates one-dimensional unsaturated flow, two-dimensional groundwater flow, and a fully connected river channel network with hillslopes supporting overland flow and baseflow. The paper introduces the design of SHUD, from the conceptual and mathematical description of hydrologic processes in a watershed to the model's computational structures. To demonstrate and validate the model performance, we employ three hydrologic experiments: the V-catchment experiment, Vauclin's experiment, and a model study of the Cache Creek Watershed in northern California. Ongoing applications of the SHUD model include hydrologic analyses of hillslope to regional scales (1 m2 to 106 km2), water resource and stormwater management, and interdisciplinary research for questions in limnology, agriculture, geochemistry, geomorphology, water quality, ecology, climate and land-use change. The strength of SHUD is its flexibility as a scientific and resource evaluation tool where modeling and simulation are required.
Highlights
The complexity of today’s environmental issues, the multidisciplinary nature of scientific and resource management questions, and the diversity and incompleteness of available observational data have all led to the need for models as a means of synthesis
The objective of this paper is to introduce the design of Simulator for Hydrologic Unstructured Domains (SHUD), from the fundamental conceptual model of hydrology to governing hydrologic equations in a watershed to computational structures describing hydrologic processes
When application rate is less than the maximum infiltration capacity, the infiltration is controlled by soil matrix flow; when application rate is larger than Kmax, effective conductivity is a function of the soil matrix and macropores (Chen and Wagenet, 1992)
Summary
The complexity of today’s environmental issues, the multidisciplinary nature of scientific and resource management questions, and the diversity and incompleteness of available observational data have all led to the need for models as a means of synthesis. One challenge for multiprocess distributed models is addressing uncertainties in spatial parameters (soils, hydrogeology, landsurface processes, etc.) and limited predictive skill for large, high-resolution catchments, even if the estimated model parameters (e.g., soil properties, surface characteristics, and aquifer properties) and atmospheric inputs have incommensurate resolutions. The latter is important to watershed calibration and has led to a major source of uncertainty (Beven, 2012; Blöschl et al, 2019).
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