Why do urbanisation and deforestation make flooding more likely?
Urbanisation and deforestation are responsible for the loss of vegetation and soils. The vegetation holds down the soil, and contributes to its protection from heavy rains. The soils are very important because they act as a sponge, and absorb most of the water when it rains.
When we cut trees and build roads, we make it easier for the rains to erode the soils. And when the soils disappear, rainwater simply rushes to the lowest point in the topography, where it accumulates and causes flooding.