Geomorphological evolution of small watershed on the Loess Plateau based on slope shape spectra

The Loess Plateau, the world's largest loess deposit, is characterized by distinctive landforms and severe soil erosion. Limited long-term observational data has hindered a comprehensive understanding of watershed evolution in this region. This study uses laboratory-based artificial rainfall simulations to investigate the long-term geomorphological evolution of watersheds on the Loess Plateau.Digital elevation models and terrain analysis techniques were employed to analyze geomorphological processes. Through correlation analysis and Sheffield entropy calculations, an optimal combination of terrain factors—including slope, aspect, plan curvature, profile curvature, and elevation—was identified to accurately describe slope characteristics. Multi-resolution image segmentation, Moran's I, and weighted variance were used to optimize segmentation parameters, achieving precise slope unit segmentation. Based on these parameters, we classified slope shapes, constructed slope shape spectra, and analyzed their changes over time. Results indicate that as the watershed evolves, the entropy of slope spectra increases while skewness and kurtosis decrease, indicating greater geomorphological complexity and diversity. The watershed's evolution progresses through three stages: slope shape development, slope shape growth, and slope shape maturity, each marked by distinct geomorphological features. By analyzing landscape indices at both class and landscape levels, we observed significant variation during the early development stage, followed by stabilization during the maturation phase. These findings demonstrate that slope shape spectra effectively capture the dynamic evolution of slopes in the Loess Plateau, offering new insights for understanding its geomorphological evolution and providing a novel method for quantitative geomorphology.