HYSTAR_HP6

Distributed, continuous hydrologic models promote better understanding of hydrology and enable integrated hydrologic analyses by providing a more detailed picture of water transport processes across the varying landscape. However, such models are not widely used in routine modeling practices, due in part to the extensive data input requirements, computational demands, and complexity of routing algorithms. HYSATR is a new two-dimensional continuous hydrologic model developed using a time-area method within a grid-based spatial data model with the goal of providing an alternative way to simulate spatiotemporally varied watershed-scale hydrologic processes. The model calculates the direct runoff hydrograph by coupling a time-area routing scheme with a dynamic rainfall excess sub-model, explicitly considering downstream ‘reinfiltration’ of routed surface runoff. Soil moisture content is determined at each time interval based on a water balance equation, and overland and channel runoff is routed on time-area maps, representing spatial variation in hydraulic characteristics for each time interval in a storm event. Simulating runoff hydrographs does not depend on unit hydrograph theory or on solution of the Saint Venant equation, yet retains the simplicity of a unit hydrograph approach and the capability of explicitly simulating two-dimensional flow routing. The model offers a way to simulate watershed processes and runoff hydrographs using the time-area method, providing a simple, efficient, and sound framework that explicitly represents mechanisms of spatially and temporally varied hydrologic processes.
Grid-based spatially distributed hydrological modeling has become feasible with advances in watershed routing schemes, remote sensing technology, and computing resources. However, the need for long-running times on a substantial set of computational resources prevent a spatially detailed modeling program from being widely used, particularly in fine-resolution large-scale studies. Parallelizing computational tasks successfully mitigates this difficulty. A novel way to improve the simulation efficiency of direct runoff transport processes is proposed; watershed areas are grouped based on a time-area routing scheme; this was applied to simulating the runoff routing processes of two watersheds in different sizes and landscapes. The method substantially improved the computational efficiency of the time-area routing method with common computing resources. In addition, the efficiency of the parallelization scheme was not limited by the hierarchical relationship between upstream and downstream catchments along the flow paths, which could be possible with the Lagrangian tracking of the time-area routing method.

分布式连续水文模型（distributed continuous hydrologic model）可通过精细刻画异质景观下的水分运移过程，深化人们对水文过程的认知，并支撑集成化水文分析。然而这类模型在常规建模实践中尚未得到广泛应用，部分原因在于其海量数据输入需求、较高的计算开销以及汇流算法的复杂性。HYSATR是一款基于栅格空间数据模型（grid-based spatial data model）、采用时间面积法（time-area method）构建的新型二维连续水文模型，旨在为模拟时空异质性的流域尺度水文过程提供一种替代方案。该模型通过将时间面积汇流方案与动态降雨产流子模型（dynamic rainfall excess sub-model）耦合，计算直接径流过程线（direct runoff hydrograph），并显式考虑了汇流过程中地表径流的下游再入渗（reinfiltration）过程。模型基于水量平衡方程（water balance equation）逐时段计算土壤含水量，并在时间面积图上开展坡面与河道径流（overland and channel runoff）汇流，以此表征暴雨事件中各时段水力特性的空间异质性。该模型的径流过程线模拟无需依赖单位线理论（unit hydrograph theory）或圣维南方程（Saint Venant equation）的求解，却兼具单位线方法的简洁性与显式模拟二维流汇流的能力。该模型采用时间面积法实现流域过程与径流过程线的模拟，构建了简洁高效且严谨的框架，可显式表征时空异质性水文过程的作用机制。
随着流域汇流方案、遥感技术（remote sensing technology）与计算资源（computing resources）的发展，基于栅格的空间分布式水文建模已具备可行性。然而，高空间分辨率的流域建模程序往往需要大量计算资源与较长的运行时长，限制了其广泛应用，在精细分辨率的大尺度研究中这一问题尤为突出。并行化计算任务（parallelizing computational tasks）可有效缓解这一难题。本文提出了一种提升直接径流输移过程模拟效率的新方法：基于时间面积汇流方案对流域单元进行分组，并将该方法应用于两个不同规模、不同景观特征的流域的径流汇流过程模拟。在通用计算资源环境下，该方法显著提升了时间面积汇流方法的计算效率。此外，该并行化方案的效率不受沿水流路径的上下游流域层级关系限制，而这一限制在采用拉格朗日追踪（Lagrangian tracking）的时间面积汇流方法中曾可能存在。