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可细致展现不同景观下的水分运移过程，助力深化水文过程认知，并支持集成化水文分析。然而此类模型并未在常规建模实践中得到广泛应用，部分原因在于其庞大的数据输入需求、高昂的计算负荷以及汇流算法的复杂性。HYSATR是一款新型二维连续水文模型，它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）开发，旨在为模拟时空变化的流域尺度水文过程提供替代方案。该模型将时间面积汇流方案与动态产流子模型（dynamic rainfall excess sub-model）相结合，计算直接径流过程线，并显式考虑坡面汇流的下游再入渗过程。模型在每个时间步长内基于水量平衡方程（water balance equation）计算土壤含水率，并在时间面积地图上实现坡面与河道径流的汇流，以此表征暴雨事件中每个时间步长内水力特性的空间异质性。该模型的径流过程线模拟不依赖单位线理论（unit hydrograph theory），也无需求解圣维南方程（Saint Venant equation），但兼具单位线方法的简洁性与显式模拟二维汇流过程的能力。本模型借助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，可显式表征时空变化的水文过程机制。 随着流域汇流方案、遥感技术（remote sensing technology）与计算资源的发展，基于栅格的空间分布式水文模拟已具备可行性。然而，大规模计算资源下的长运行时长需求，阻碍了高空间分辨率的精细化建模程序得到广泛应用，在大尺度精细分辨率研究中尤为突出。成功并行化计算任务可有效缓解这一困境。本文提出了一种提升直接径流输运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，并将其应用于两个不同规模与景观类型的流域的径流汇流过程模拟。该方法在通用计算资源下，大幅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子流域层级关系限制，而这一限制曾在时间面积汇流方法的拉格朗日（Lagrangian）追踪中存在。