What is hierarchical roughness?

Hierarchical roughness refers to the complex texture of a surface that exhibits multiple scales of roughness, often seen in natural materials like rocks or soils. It encompasses variations in surface features at different levels, such as large protrusions combined with finer textures. This concept is crucial in fields like geology, materials science, and fluid dynamics, as it affects properties like friction, erosion, and fluid flow. Understanding hierarchical roughness can help in predicting how surfaces interact with their environment.