There are more physical than human factors, but this has come up before.
Physical factors
- Rock type- if the underlying bedrock is impermeable then the transfer of water via percolation will be very small hence once the magnitude of the soil moisture store has reached its maximum capacity will lead to an oversaturation of the soils and cause any excess water to flow as surface run off.
- Gradient – if water is flowing down a steep hill that this will lead to surface run off happening quickly because the magnitude of the soil moisture store is much smaller on a hill than on flat land. Therefore, during infiltration, the soil moisture store on a steep hill would have been reached much quicker than on flat land, hence on a hill surface runoff would have been reached much quicker.
- Magnitude of vegetation- a surface that has large amounts of vegetation will lead to an increase in the rate of interception and stemflow. Hence there is a time lag where it can take longer for any excess water to begin infiltration which means the risk of flooding is reduced.
Human factors
- Urbanisation- if there is percpitation in an urban area, then there is likely to be a high number of concrete surfaces which is impermeable, so there will be no infiltration but only surface runoff. This will increase the risk of flooding in the area.