Scaling of soil water retention and hydraulic conductivity curves (Brooks–Corey model)

Abstract Scaling is a widely used technique in soil science to characterize the variability of water retention curves and hydraulic conductivity functions. This study aims to develop a method for scaling the water retention curve and hydraulic conductivity based on the Brooks–Corey equation using minimal field data. The proposed approach requires only a reference curve and either the water content or hydraulic conductivity at a specific suction level. To evaluate the method, 11 different soil texture classes were analyzed. The scaling methodology was tested and validated using optimization techniques, with sandy clay loam soil randomly selected as the reference soil. The optimal scaling factor for the water retention curve was determined to be 1.210. Additionally, scaling factors derived from water content at suction levels of 1000 and 2000 cm were calculated as 1.209 and 1.181, respectively. For the hydraulic conductivity curve, the optimal scaling factor was found to be 0.859, while the scaling factors based on hydraulic conductivity at suction levels of 1000 and 2000 were 0.863 and 0.848, respectively. To ensure the robustness of the method, additional soil types, including sand, loam, silty clay loam, and clay, were selected as reference curves and evaluated. Statistical analysis revealed that the choice of reference curve is arbitrary for both the water retention and hydraulic conductivity curves, meaning that any of the tested soils can be used effectively as a reference curve. This finding highlights the flexibility and applicability of the proposed scaling method across a wide range of soil types.