Forests play a major role in preventing and controlling floods. Tree stores water in its deep roots. So, Forests allow the water to go into the soil. They also prevent the extreme water run-off and hence prevents landslides & topsoil erosion. Most of the flooding disasters are caused by deforestation.
The volume of water retained by forests can depend on several characteristics such as forest cover area and tree density. A strong forest cover of 30-40% acts as a brake against flash floods and thus preventing enormous loss of lives & property, and reducing the damage from flooding.