Water erosion, a notorious major threat to food security and ecosystem sustainability, is strongly conditioned by spatial and temporal scale effects. This paper systematically reviews the scale issues in runoff and sediment delivery (SIRSD) as a research field by integrating the traditional review approach and bibliometric analysis. This review summarises SIRSD's roots and the scale effect on runoff and sediment delivery. Then, we provide quantitative insights into the SIRSD domain's development history, thematic structure, geographic distribution, international cooperation, and methodologies. Findings show that: i) SIRSD arises from the gap between the non-linearity of runoff and sediment delivery across scales and our ability to measure it. Point-based and short-term measurements cannot capture the non-linearities from the spatio-temporal heterogeneities and cross-scale interactions of factors or processes. ii) Previous literature provides evidence that the spatial scaling of specific runoff (), soil erosion (), sediment yield (), or sediment delivery ratio () with drainage area () or slope length () exhibits contrasting patterns due to distinct mechanisms. Infiltration-excess and saturation-excess processes account for inverse and positive - relations, respectively. Interrill-erosion and rill-erosion cause inverse and positive relations. Hillslope-erosion and channel/bank-erosion explain inverse and positive relations. Downstream increasing deposition and additional sediment inputs drive inverse and positive relations. These scaling relationships can be nonlinear or complex due to spatial heterogeneities in land use, vegetation, topography, climate, lithology, and soil characteristics. Hence, applying an empirical scaling equation developed from the region with distinct environmental contexts is not recommended. Furthermore, the existing scaling patterns or equations may require updating given global climate and land use change. iii) SIRSD is a complex and multidisciplinary issue investigated by scientists from 93 countries since 1928. International research has substantially facilitated the understanding of SIRSD; still, more collaboration should focus on less-developed countries with high soil and water loss risks and urgent conservation needs, such as those in Africa and South America under cropland expansion. iv) Scale mismatch and scale break have discredited large-scale erosion and sediment assessments. Incorporating gully and bank erosion into modelling, extending the scale range of the factor, and expanding the sediment scaling scope from watershed to slope may make a difference. Therefore, more research with nested design incorporating multiple scales is necessary for cross-scale analysis and scalable modelling. Addressing global climate change requires improving real-time urban flood forecasting and integrating downscaled climate models with hydrology, erosion, and sediment transport models.

中文翻译：

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径流和沉积物输送中的规模问题（SIRSD）：系统评价和文献计量分析

水侵蚀是对粮食安全和生态系统可持续性的一个臭名昭著的主要威胁，它受到空间和时间尺度效应的强烈影响。本文结合传统综述方法和文献计量分析，对径流和沉积物输送中的尺度问题（SIRSD）这一研究领域进行了系统综述。这篇综述总结了 SIRSD 的根源以及对径流和沉积物输送的规模效应。然后，我们对 SIRSD 领域的发展历史、主题结构、地理分布、国际合作和方法进行定量分析。研究结果表明： i) SIRSD 是由于跨尺度径流和沉积物输送的非线性与我们测量它的能力之间的差距而产生的。基于点和短期的测量无法捕获时空异质性和因素或过程的跨尺度相互作用的非线性。ii) 以前的文献提供的证据表明，特定径流 ()、土壤侵蚀 ()、产沙量 () 或输沙比 () 与流域面积 () 或坡长 () 的空间尺度由于不同的机制而表现出对比模式。渗透过量和饱和过量过程分别说明逆关系和正关系。细沟间侵蚀和细沟侵蚀存在负相关和正相关关系。山坡侵蚀和河道/河岸侵蚀解释了逆关系和正关系。下游沉积物的增加和额外的沉积物输入驱动反向和正向关系。由于土地利用、植被、地形、气候、岩性和土壤特征的空间异质性，这些尺度关系可能是非线性的或复杂的。因此，不建议应用从具有不同环境背景的区域开发的经验缩放方程。此外，考虑到全球气候和土地利用的变化，现有的缩放模式或方程可能需要更新。iii) SIRSD 是一个复杂的多学科问题，自 1928 年以来已有来自 93 个国家的科学家进行了研究。国际研究极大地促进了对 SIRSD 的理解；尽管如此，更多的合作应集中在水土流失风险高、保护需求迫切的欠发达国家，例如非洲和南美洲正在扩大耕地的国家。iv) 尺度失配和尺度破坏使大规模侵蚀和沉积物评估失去可信度。将沟壑和河岸侵蚀纳入建模，扩大因子的尺度范围，将沉积物尺度范围从流域扩大到斜坡，可能会有所不同。因此，需要对包含多个尺度的嵌套设计进行更多研究，以进行跨尺度分析和可扩展建模。应对全球气候变化需要改进实时城市洪水预报，并将缩小规模的气候模型与水文、侵蚀和泥沙输送模型相结合。