In the last 7 years, the USA has been getting a very large number of floods of the kind that are supposed to happen roughly every 500 years.
A 500-year flood is an event that has a 1 in 500 chance of occurring in any given year.
"For a 500-year flood, there is a 0.2 percent chance of having a flood of that magnitude occurring" in any given year, according to the National Weather Service.
The Washington Post has more details.
Donald and melania Trump set off to Texas to see the floods. 
Texans greet Donald Trump.