Urban floods are mainly caused by

Urban floods are mainly caused by the blockage of drains and waterways. Urbanization often leads to the construction of roads, buildings, and other impervious surfaces, which prevent rainwater from soaking into the ground. This runoff must be carried away through drains, gutters, and other waterways. If these channels are blocked or overwhelmed by the amount of water, flooding can occur. In urban areas, drains and waterways can become blocked by a variety of debris, including trash, leaves, and branches. In some cases, the infrastructure may not be sufficient to handle the amount of water produced during heavy rainfall. In addition, cities often have limited green spaces, which can help to absorb excess water. While the other options listed can contribute to flooding, they are not the primary cause of urban floods. The construction of dams and barrages, for example, can impact downstream flooding but is not a significant factor in urban flooding. The clearance of vegetation on farmlands and the establishment of shelter belts may contribute to flooding in rural areas, but are not major factors in urban flooding.