The best answer is option (A) - hillside deforestation. By reducing vegetative cover upstream in the hills, run-off and discharge into rivers is significantly enhanced during heavy rainstorms increasing the threat of flooding downstream. The loss of natural vegetation in the delta (D)will not help the situation but it is not as significant as (A). Similarly, the increasing severity of monsoons (C) may be happening with global warming but the removal of trees is having the most dramatic impact. Irrigation diversion projects (B) actually reduce the risk of flooding as more water is consumed and it's path is managed by human built channels.