The article Emmanuel Goldstein posted addresses the many factors, including a lack of planning in building and constructiton without paying heed to the elevation and that the area was a flood plain contributed to the flood. 
Climate change has been around for as long as the world has exsisted. 
Deserts that were once gardens became deserts, it eventually will happen again. 
Remember the Dust Bowl ? 
Right now parts of the Southwest are into their seventh or eighth year of drought. I have letters from my great-grandfather written in the 1920's describing the sheep and cattle dying and "even the cactus " has turned brown . 
Wasn't the Ice Age a period of climate change ? 
If you build something without regard to common sense, as has happened in Houston and  New Orleans, sooner or later you pay the piper. 
The heavy rain received was not expected, but it's funny how things we don't plan for 
happen. 
In Ketchikan our average rain fall is 150 inches. As of 08/31/17 we have had 104 inches.