I just learned a new term while reading a news article about the preps for the coming rain--post-fire hydrophobic soil. I haven't seen a more scientific explanation of exactly how this occurs, but apparently the soil becomes resistant to absorbing moisture, so it runs off at greater volume than it would if it rained on normal, bare soil. That would certainly explain why authorities are always particularly worried about burned areas when it rains.

I'm wondering if the very top layer of soil turns into a water-resistant crust due to the heat? Until erosion or plants breaking through come along, the crust remains intact. I don't know, just conjecture on my part. Anyone know how the soil becomes less absorbent after a fire?