Wildfires burn dead and living vegetation that accumulates on the surface of the soil.
This burning produces volatile hydrophobic substances which can penetrate the soil up to a depth of six inches. Soils that water repellent exhibit a decreased water infiltration rate and an increased water runoff rate, creating extreme soil erosion potentials. Initially, rain and irrigation water will run off hydrophobic soils instead of infiltrating and promoting germination of seed and growth of roots. This makes it difficult to establish a stand of vegetation on a hydrophobic soil for erosion control purposes. Water repellency will be the worst where the fuel and burn temperatures were extreme, especially around buildings which burned to the ground.