CHAPTER I.7. Soil Water Repellency: A Key Factor in Post-Fire Erosion?

Soil water repellency (hydrophobicity) prohibits water from wetting or infiltrating dry soil. This condition has been documented under a wide range of vegetation types and climates and particularly following forest fires. Water repellency is of considerable interest to land managers, hydrologists and soil scientists because (i) it can be induced, enhanced or destroyed during burning and (ii) its presence can cause a marked reduction in infiltration rate. This reduction in infiltration is commonly presumed to be the primary cause of the increases in runoff and erosion that are often observed at a range of scales following forest fires. The goal of this chapter is to provide a basic understanding of soil water repellency, its measurement, the effects of burning on soil water repellency, and its relative importance in runoff and erosion processes at different scales. It is widely accepted that water repellency is caused by the presence of organic compounds with hydrophobic properties on soil particle surfaces. During burning such substances in the litter and topsoil can be volatized and condensed in the soil, inducing or intensifying water repellency. During very hot fires, however, these compounds can b