Thinking that people might be interested, reader David Delmonte sent a link to a site which features different types of maps. Due to the recent catastrophic rains which you may have heard about, I (Tom) decided to highlight some areas and mark their approximate drainage area. There are many factors which determine what happens to rainwater once it hits the ground but four important ones are: the area of surface receiving rain, the rate of rain, the height/steepness of the slopes, and the characteristics of the land.
A really clear example is the Neo Klima map (below) which shows that the town sits at the base of a bowl of steep mountains as high as 600 meters. A recipe for disaster according to the map. However, a thick pine forest mitigates the rainfall and saves the town from complete destruction.
[Maps enlarge with a click]