[Gogar]

I did a little more googlin' and looks like the evacuation totals are more like 36,000. I think the 4,000 I found earlier must have been just a Des Moines total or something.

http://www.chicagotribune.com/news/nationworld/chi-61508-iowa-floods-governor,0,3662360.story

Nearly 36,000 Iowans have been forced to evacuate their homes this past week, with Cedar Rapids residents accounting for about 25,000 of them.

And, Katrina stats according to some are over 1 million people evacuated or displaced from the storm. almost 30 times as many people.

http://en.wikipedia.org/wiki/Hurricane_Katrina

Katrina redistributed over one million people from the central Gulf coast elsewhere across the United States, which became the largest diaspora in the history of the United States.[63] Houston, Texas, had an increase of 35,000 people; Mobile, Alabama, gained over 24,000; Baton Rouge, Louisiana, over 15,000; and Hammond, Louisiana received over 10,000, nearly doubling its size. Chicago received over 6,000 people, the most of any non-southern city.[64] By late January, 2006, about 200,000 people were once again living in New Orleans, less than half of the pre-storm population.[65] By July 1, 2006, when new population estimates were calculated by the U.S. Census Bureau, the state of Louisiana showed a population decline of 219,563, or 4.87%


So, I still contend that while both disasters are sad and unfortunate, you can't really compare the two at this point.