(still problems leaving a comment…I am signed into TypeKey, but Prometheus
apparently doesn’t think so…)

Comment on California Flooding (Dec 6th Precipitation and Flood Damage
article):

A paper that just recently appeared in Geophysical Research Letters by
Florsheim and Dettinger (Florsheim, J.L, and M.D. Dettinger, 2007. Climate
and floods still govern California levee breaks. Geophysical Research
Letters, 34, L22403, doi:10.1029/2007GL031702) examined flooding in the
Sacramento-San Juan River systems of California over the past 150 years or
so and concluded that despite “extensive flood control infrastructure
developed during the 20th Century” the frequency of flooding (identified as
levee breaks) was unchanged-and not because the flood control
efforts/expenditures were offsetting climate change-related river flow
trends (they checked that).

-Chip Knappenberger

If you want to consider expense, though, nothing matches the expense of removing all of San Francisco Bay’s levees and abandoning all development built behind the levees.

If for some reason you wish to discuss non-structural expenses used for flood protection, I expect those expenses will have gone up much faster in the last 50 years.

Here is a graph for Louisiana 1955-1999 (and just FYI, note that Katrina in 2005 would not be classified a flood under the NWS methods, but instead under hurricane damage):
http://www.sip.ucar.edu/sourcebook/flood/lafld.jsp

The notion that flood protection reduces flood damages is Fallacy #3 in the following paper:

Pielke Jr., R.A., 1999: Nine fallacies of floods. Climatic Change, 42, 413-438.
http://sciencepolicy.colorado.edu/admin/publication_files/resource-78-1999.15.pdf

New Orleans, Louisiana would seem to be exhibit A in that argument. And I discussed this issue at length in this post:

http://sciencepolicy.colorado.edu/prometheus/archives/disasters/000670does_disaster_mitiga.html

Thanks!

All these expenditures are missing from your argument. I expect a chart showing expenditures on flood protection would show a significant rise over the last 50 years. Your charts only show half of the equation.

Incidentally, it would be interesting to see a similar chart for Louisiana.