The effect of rock fragment size and position on topsoil moisture on arid and semi-arid hillslopes

Rock fragments on arid hillslopes affect rainwater redistribution and overland flow, through various hydrological processes. The present study focuses on the evolution of topsoil moisture content under rock fragments following rain events. Measurement was taken under rock fragments in various sizes (large and small) and positions (‘on top’ of the soil surface and 'partially embedded' within the soil surface) at north- and south-facing hillslopes in arid and semi-arid areas. The main findings: (1) the topsoil moisture content under rock fragments was higher over time than that of bare soil areas; (2) rock fragments affect the topsoil moisture content for a longer time in semi-arid areas than in arid areas; and (3) large rock fragments and ‘partially embedded’ ones are favorable micro-environments for accepting and retaining rainwater and overland flowing water. This may have eco-geomorphic implications regarding the mosaic-like patterns of source and sink areas on arid hillslopes.