action of rainsplash detachment tends to smoothen the edges of soil surface roughness, leading to an overall decrease in RR. However, a recent study which examined the response of smooth soil surfaces on rainfall showed that RR can considerably increase for low initial microroughness length scales in the order of 0 – 5 mm. It was also shown that the increase or decrease is consistent among various SSR indices. Practical effects Surface structure plays a key role in governing contact mechanics, that is to say the mechanical behavior exhibited at an interface between two solid objects as they approach each other and transition from conditions of non-contact to full contact. In particular, normal contact stiffness is governed predominantly by asperity structures (roughness, surface slope and fractality) and material properties. In terms of engineering surfaces, roughness is considered to be detrimental to part performance. As a consequence, most manufacturing prints establish an upper limit on roughness, but not a lower limit. An exception is in cylinder bores where oil is retained in the surface profile and a minimum roughness is required. Surface structure is often closely related to the friction and wear properties of a surface. A surface with a higher fractal dimension, large value, or a positive , will usually have somewhat higher friction and wear quickly. The peaks in the roughness profile are not always the points of contact. The form and waviness (i.e. both amplitude and frequency) must also be considered. Surface roughness in Earth Sciences In Earth Sciences (e.g., Shepard et al., 2001; Smith, 2014) and Ecology (e.g., Riley et al., 1999; Sappington et al., 2007) surface roughness is interpreted differently from surface metrology (e.g., Leach 2013). In Earth Sciences it has a quite broad meaning (e.g. Smith, 2014), with multiple definitions, and generally it is considered a multi-scale property; it is often referred as surface texture (e.g., Trevisani et al., 2012), given the evident analogies to image texture (e.g., Haralick et al. 1973; Lucieer and Stein, 2005) when the analysis is performed on digital elevation models. From this perspective there are various interlinks with methodologies related to geostatistics (e.g., Herzfeld and Higginson, 1996), fractal analysis (e.g. Bez and Bertrand, 2011) and pattern recognition (e.g., Ojala et al. 2002), including many interrelations with remote sensing approaches. In the context of geomorphometry (or just morphometry, Pike, 2000) the applications cover many research topics in applied and environmental geology,