The erosional impact of soil hydrophobicity: current problems and future research directions

Soil hydrophobicity affects the susceptibility of soils to erosion in a variety of ways (e.g. increased aggregate stability, reduced infiltration capacity, enhanced overland flow), but there are problems concerning the overall assessment of its erosional impact. Three current problems are discussed: (1) poor isolation of hydrophobicity from other effects; and poor understanding of its overall impact; (2) areally, at slope and catchment scales; and (3) temporally, over periods of months or years rather than on a storm basis. These problems are highlighted with reference to the literature and to research in Portugal on highly hydrophobic forest soils. A conceptual model relating erosion risk to three key aspects of soil hydrophobicity (temporal contiguity, spatial contiguity and the thickness of any overlying hydrophilic soil) is presented in order to provide a framework for future research into hydrophobicity–soil erosion links.