The accumulation of storm water depends on many factors like the rate of rain or snow melt, the pitch of the slope in the immediate area, and the type of surface that it falls on. It is pretty logical. The steeper the ground, the faster gravity can move the water. It also makes sense that the surface properties are a large determining factor. If I dump 500 gallons of water all at once on a concrete slope, it has zero chance of being absorbed and decreased in volume by any absorption by the surface under it.
If I dump the same amount on a soil with a high degree of permeability and a large amount of vegetation, it is obvious that by the time the water reaches the bottom of the slope, it will have decreased somewhat whereas the concrete slope will experience no decrease at all. The stormwater on the hillside with vegetation also will have moved with much less speed and force.
It is then not a surprise that stormwater is a more prevalent concern in largely populated areas where the earth’s surface is covered predominantly by concrete or building roofs. More rural areas with lots of exposed ground offer much more opportunity for the water to find it’s way quickly into the ground and back into the water table. Stormwater can still be an element of concern in rural areas where there are low lying areas or areas along riverbeds and lakes prone to flooding.