Many watershed models employ the Soil Conservation Service Curve Number (SCS-CN) approach for runoff simulation based on soil and land use information. These models implicitly assume that runoff is generated by the Hortonian process and; therefore, cannot correctly account for the effects of topography, variable source area (VSA) and/or soil moisture distribution in a watershed. This paper presents a new distributed CN-VSA method that is based on the SCS-CN approach to estimate runoff amount and uses the topographic wetness index (TWI) to distribute the runoff-generating areas within the watershed spatially. The size of the saturated-watershed areas and their spatial locations are simulated by assuming an average annual value of potential maximum retention. However, the literature indicates significant seasonal variation in potential maximum retention which can considerably effect water balance and amount of nonpoint source pollution. This paper focuses on developing a modified distributed CN-VSA method that accounts for the seasonal changes in the potential maximum retention. The results indicate that the modified distributed CN-VSA approach is better than distributed CN-VSA to simulate runoff amount and spatial distribution of runoff-generating areas. Overall, the study results are significant for improved understanding of hydrological response of watershed where seasonal factors describe the potential maximum retention, and, thus, saturation excess runoff generation in the watershed.

中文翻译：

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一种改进的分布式CN-VSA映射季节性变化源区域

许多分水岭模型都采用土壤保护服务曲线编号（SCS-CN）方法，基于土壤和土地利用信息进行径流模拟。这些模型隐含地假设径流是由霍顿过程产生的；并且；因此，不能正确考虑地形，流域可变源面积（VSA）和/或土壤水分分布的影响。本文提出了一种新的分布式CN-VSA方法，该方法基于SCS-CN方法估算径流量，并使用地形湿度指数（TWI）在流域内空间分布径流生成区域。通过假设潜在最大保留量的年平均值来模拟饱和流域区域的大小及其空间位置。然而，文献表明，潜在最大保留量存在明显的季节性变化，这可能会严重影响水平衡和非点源污染量。本文着重于开发一种改进的分布式CN-VSA方法，该方法考虑了潜在最大保留量的季节性变化。结果表明，改进后的分布式CN-VSA方法在模拟径流产生区径流量和空间分布方面优于分布式CN-VSA方法。总体而言，该研究结果对于增进对流域水文响应的了解具有重要意义，其中季节因素描述了潜在的最大保留量，因此，该流域中的饱和超额径流产生。本文着重于开发一种改进的分布式CN-VSA方法，该方法考虑了潜在最大保留量的季节性变化。结果表明，改进后的分布式CN-VSA方法在模拟径流产生区径流量和空间分布方面优于分布式CN-VSA方法。总体而言，该研究结果对于增进对流域水文响应的了解具有重要意义，其中季节因素描述了潜在的最大保留量，因此，该流域中的饱和超额径流产生。本文着重于开发一种改进的分布式CN-VSA方法，该方法考虑了潜在最大保留量的季节性变化。结果表明，改进后的分布式CN-VSA方法在模拟径流产生区径流量和空间分布方面优于分布式CN-VSA方法。总体而言，该研究结果对于增进对流域水文响应的了解具有重要意义，其中季节性因素描述了潜在的最大保留量，因此，该流域中的饱和超额径流产生。