Representing the role of soil moisture on erosion resistance in sediment models: Challenges and opportunities.

Soil's resistance to erosion or its susceptibility to resist detachment is a key parameter in the majority of soil erosion and sediment models. Although soil resistance is a function of both the intrinsic properties of soil and dynamic environmental variables (e.g., soil moisture), the influence of the latter is seldom explicitly incorporated in the definition of soil resistance. The significant and complex role of soil moisture content on erosion resistance is recognized by many studies, however, much of the emphasis regarding the role of soil moisture on sediment yield modeling has been on its impacts on runoff generation rather than on soil resistance. In this paper, we synthesize the existing state of knowledge on the processes and mechanisms by which moisture affects erosion resistance of soil, and highlight the challenges and opportunities associated with incorporating this relation in sediment yield assessment models. Through a detailed analysis of literature, we find that dry soil has the lowest resistance to erosion and thus has a high erodibility, and erosion resistance increases (erodibility decreases) with increasing antecedent moisture content until a certain threshold. After this threshold is reached, soil resistance decreases with further increase in moisture content, and soils become more susceptible to erosion. Next, the study identifies the candidate variables that may be used to quantitatively represent the soil's resistance to erosion vis-à-vis moisture, and discuss the challenges in incorporating this relation in modeling frameworks. As a way forward, through a meta-analysis of published data, we develop an exemplar relation that could be used to represent the variation in erosion resistance with soil moisture content. We find that the parameters of such a relation vary significantly across soil types, thus raising the possibility for developing a soil-type based moisture-resistance relations. Overall, this review underscores the considerable impact of antecedent soil moisture on the erosion resistance of soils, and makes a case for integrating the influence of dynamic soil moisture content on erosion resistance into predictive modeling frameworks. • Erosion resistance of soil is significantly influenced by soil moisture content. • Erosion resistance increases with increasing moisture content until a threshold. • Erosion resistance vs. soil moisture relation depends on soil type. • An exemplar relation to represent erodibility variation with soil moisture is presented. • Including moisture-erodibility relation in models will improve soil loss predictions. [ABSTRACT FROM AUTHOR]