How Floods form
Floods form when water overflows or overloads land thats normally dry can take days to develop. Things that can cause this is rain, overflow in rivers or streams, melting ice or tsunamis. most common with heavy rainfall when a water source do not have the room for more water.
some historical floods is the 2013 north India flood and the 1931 central china floods. First is the north india floods and kills a total of 5,700 people destroying houses, causing flash floods and landslides.
1931 central china floods killing a total of 2,500,000–3,700,000 people covered 110,000 square miles of land destroying food sources and cities also diseases.
They are both similar because they both killed thousands of people and both destroyed lots of land it was worse with the 1931 china flood because they didn't have as much ways to stop the flood.
Ways to Prepare
There are many ways and I will list a couple sea walls to slow down the floods also vegetation to prevent run off so it won't overflow and now we have technology to tell us to leave before the flood.
1931 china flood