Floods are disasters that can cause great and can kill many people. They also destroy farmland and make millions of people homeless. Floods can drinking water and cause that spread throughout the population.

Ancient civilizations depended on river flooding to make land . When the Nile River flooded Egypt once a year it also deposited on fields, so that farmers could grow crops and bring in a good .

Large rivers, like the Mississippi, or the Huang He in China, experience floods once a year, when snow melts in mountain regions or after heavy rainfall. These rivers swell slowly and water often over the dikes and dams that were erected to protect the around them.

Coastal regions can be hit by tsunamis, large caused by earthquakes on the sea floor. In 2004 coastal regions in all of South and Southeast Asia were flooded and 250,000 people were killed.

In America, hurricanes move from the Gulf of Mexico and the Caribbean Sea to the and flood the coast. Hurricane Katrina flooded most of New Orleans in the summer of 2004. In the low-lying countries of northwestern Europe dams have been made to keep North Sea water out of areas that lie below level.

Sometimes flooding is also caused by . Destroying tropical rainforest leaves the ground without any . Water can not settle in to the ground slowly and flows away quickly, causing and other dangers.