Linking watershed geomorphic characteristics to sediment yield: Evidence from the Loess Plateau of China

- We studied the effects of watershed geomorphic characteristics on soil erosion.
- The PLSR performs well in solving co-linear problems.
- Watershed shape and relief parameters have great influence on sediment yield.

The geomorphic characteristics of a watershed affect the energy fluxes, mass movement, and water and sediment dispersion within the watershed. This paper examines how watershed complexity affects sediment yield in terms of rainfall and geomorphic characteristics. The geomorphic characteristics include primary, secondary and compound topographic attributes; watershed shape characteristics; relief parameters; and stream network characteristics. Because of the high co-dependence among these characteristics, partial least-squares regression (PLSR) was used to identify the relationships between the sediment yield and 29 selected watershed characteristics. The PLSR combines the features of a principal component analysis and multiple linear regression and is a robust multivariate regression method that is appropriate when the predictors exhibit multiple co-linearity. The first-order factors were determined by calculating the variable importance for the projection (VIP). Those variables with high VIP values are the most relevant for explaining the dependent variable. The results showed that the watershed shape and relief parameters have large influences on the sediment yield. The VIP values revealed that the sediment yield is primarily controlled by the plan curvature (VIP = 1.87) and the highest order channel length (VIP = 1.53), followed by the hypsometric integral (VIP = 1.49), rainfall (VIP = 1.44), basin relief (VIP = 1.19), slope (VIP = 1.15), sediment transport capacity index (VIP = 1.13), length ratio (VIP = 1.06), profile curvature (VIP = 1.01) and divide average relief (VIP = 1.00). This paper quantified the effects and relative importance of different geomorphic attributes on sediment yield. The insight provided by these results can be used in the selection of appropriate geomorphic variables for watershed erosion and hydrological models. Thus, this study is intended to elucidate the internal dynamics of sediment transport and storage in a watershed and provide a guide for watershed management.