1) vegetation cover on land trees, plants, grass etc, obstruct the run of rainwater and slows down the speed of its flow . This slowing down helps rainwater to percolate into the soil.
2) floods are often caused by sudden increase in the volume of water reaching a river. vegetation allows the water to flow slowly into the river, thus preventing sudden flooding.
3) it also helps to increase the amount of water which goes into the soil.
4) it reduces the erosion of soil by rain water.
5) if the surface of the land is covered with vegetation then soil erosion is greatly reduced