Investigating the spatial variations of sediment connectivity index in bare tilled soils with a new weighting factor for the plot scale

Abstract

Sediment connectivity reflects the linkage between sediment sources and downstream sinks within geomorphic systems. Among available approaches, the geomorphometric Index of Connectivity (IC) is widely used, yet its accuracy depends on selecting weighting factors (WFs) that properly represent soil and surface properties. This study aimed to develop and evaluate composite WFs for IC in bare tilled soils by integrating both physical and mechanical attributes. Rainfall simulation experiments were carried out on three soils from Iran’s dry farming areas—Kouhin, Sararud, and Gachsaran—at a 12 % slope under 110 mm h⁻¹ , intensity. Additional tests were conducted on Gachsaran soil at 6 % and 25 % slopes. Soil losses were measured after each event, and high-resolution digital elevation models (DEMs) were generated to compute IC. Results indicated that IC weighted solely by rainfall intensity (RI) produced inconsistent outcomes, particularly across different soil textures, and even showed a counterintuitive decline with increasing soil loss at a constant slope. In contrast, incorporating mean weight diameter of aggregates (MWD), penetration resistance (PR), and RI as a composite WF yielded a strong and statistically significant relationship with soil loss (r = 0.998, p < 0.05). Spatial analysis further revealed systematic IC variation along the flume, with higher connectivity downslope, reflecting enhanced sediment transfer pathways. Overall, the findings demonstrate that incorporating both soil structural and mechanical properties greatly improves IC applicability in tilled landscapes. The proposed composite WF provides a more reliable basis for predicting soil loss and sediment delivery in rainfed, bare slopes, and warrants validation under broader soil and slope conditions.