Urban floods are mainly caused by the blockage of drains and waterways. In cities, rainwater is channelled through drainage systems, gutters, and waterways. When these become blocked by refuse, debris, silt, or unplanned construction, water cannot flow away efficiently. During heavy rainfall, the water accumulates on roads and in low-lying areas, resulting in flooding.
Urbanisation itself creates large areas of impermeable surfaces (concrete, tarmac, roofing) that prevent water from soaking into the ground, making cities already vulnerable to surface flooding. When blocked drains compound this problem, the result is severe urban flooding.
Clearance of vegetation on farmlands can contribute to flooding in rural areas through increased surface runoff, but it is not the primary cause of specifically urban flooding. Construction of dams and barrages is actually a flood-control measure, and establishment of shelter belts (rows of trees) is a method of reducing wind erosion, not a cause of flooding.
