Intensity has a lot to do with it. We need that old slow, misty, drizzle for weeks on end to fill the streams and the aquifers. Short storms just tend to run off. Then, we pave over and make it run off faster.

One other bump to flows is actually Falll. As the deciduous trees and shrubs drop leaves they stop transpiring water. So, in the Fall, flows will diminish slower, or even may increase slightly, as the trees shut down.

May have had more of an impact back when we had deciduous trees out there instead of fir/hemlock monoculture...