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.     

Soil erosion and its basic characteristics at karst rocky-desertified land consolidation area: A case study at Muzhe Village of Xichou County in Southeast Yunnan,China

Xichou County of Wenshan Zhuang and Miao Autonomous Prefecture in southeast Yunnan is one of the karst mountainous areas in southwest China showing typical rock desertification. During this study, we set up three soil erosion contrast test spots at Muzhe Village, Benggu Township, Xichou County, which was the birthplace of the Xichou rock-desertified land consolidation mode. The three spots included the terrace land spot (already consolidated land), sloping land spot (unconsolidated sloping land under rock desertification), and standard runoff spot (bare land spot). In 2007, a whole-year complete observation was conducted during the rainy season and "rainfall-erosion" data were obtained for 32 times. Our analysis showed that during the entire observation period, the number of the rainfalls that led to soil erosion accounted for 34.04% of the number of all rainfalls and the amount of the rainfalls that led to soil erosion accounted for 84.17% of the total amount of all rainfalls. The average erosive rainfall standard in the three test spots was 11.0 mm, slightly higher than the 10 mm standard that has been adopted all over China, but lower than the 12.7 mm standard of the US and the 13.0 mm standard of Japan. According to single-factor analysis, the soil loss in the sloping land spot (L2) and that in the bare land spot (L3) are correlated to certain extent to many other factors, including the single precipitation (P), rainfall intensity during the maximum ten minutes (I10), rainfall intensity during the maximum 20 minutes (I20), rainfall intensity during the maximum 30 minutes (I30), rainfall intensity during the maximum 40 minutes (I40), and rainfall intensity during the maximum 60 minutes (I60). Among these factors, they are of the highest relativity with I60. According to double-factor analysis, both L2 and L3 are of good relativity with P and I60. According to multi-factor analysis, L2 and L3 are also of good relativity with seven rainfall indexes, namely, P, Ia (average rainfall intensity), I10, I20, I30, I40, and I60, with their related coefficient R reaching 0.906 and 0.914, respectively. The annual soil losses in the three test spots are widely different: 1030.70 t/km2·a in the terrace land spot, which indicates a low-level erosion; 12913.22 t/km2·a in the sloping land spot (unconsolidated spot), some 12.5 times than that in the terrace land spot, which indicates an ultra-high-level erosion; and 19511.67 t/km2·a in the bare land spot, some 18.9 times than that in terrace land spot, indicating an acute erosion. These figures fully show that the Xichou rock-desertified land consolidation mode plays a significant role in soil conservation.