Spatial Scale Effects of Water Erosion Dynamics: Complexities, Variabilities, and Uncertainties

Severe water erosion is notorious for its harmful effects on land-water resources as well as local societies. The scale effects of
water erosion, however, greatly exacerbate the difficulties of accurate erosion evaluation and hazard control in the real world. Analyzing
the related scale issues is thus urgent for a better understanding of erosion variations as well as reducing such erosion. In this review
article, water erosion dynamics across three spatial scales including plot, watershed, and regional scales were selected and discussed.
For the study purposes and objectives, the advantages and disadvantages of these scales all demonstrate clear spatial-scale
dependence. Plot scale studies are primarily focused on abundant data collection and mechanism discrimination of erosion generation,
while watershed scale studies provide valuable information for watershed management and hazard control as well as the development of
quantitatively distributed models. Regional studies concentrate more on large-scale erosion assessment, and serve policymakers and
stakeholders in achieving the basis for regulatory policy for comprehensive land uses. The results of this study show that the driving
forces and mechanisms of water erosion variations among the scales are quite different. As a result, several major aspects contributing
to variations in water erosion across the scales are stressed: differences in the methodologies across various scales, different sink-
source roles on water erosion processes, and diverse climatic zones and morphological regions. This variability becomes more complex in
the context of accelerated global change. The changing climatic factors and earth surface features are considered the fourth key reason
responsible for the increased variability of water erosion across spatial scales.