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The 100-year flood level along the coasts will be changed by sea-level rise. Current sea level changes, as I inexpertly understand them, are hard to document or attribute to anthropogenic GW, but future rise is a robust prediction. Given where global populations are located, changing flood levels along coastlines is hardly trivial.

I think this post could benefit from clarification that only current flooding damage is not easily attributed to AGW, but today, it is clearly a good use of science to allege a connection between greenhouse gases and flood damages in the upcoming decades.

Brian- Thanks for your comment. My post was actually only referring to river flooding. On the relationship of precipitation and river flooding see this paper:

Pielke, Jr., R.A., and M.W. Downton, 2000: Precipitation and Damaging Floods: Trends in the United States, 1932-97. Journal of Climate, 13(20), 3625-3637.
http://sciencepolicy.colorado.edu/admin/publication_files/resourse-60-2000.11.pdf

I'd welcome reference to others studies on this subject.

I'm not sure what you mean by river flooding, unless it's "river flooding that occurs nowhere near sea level." There are many areas (including my neighborhood in south San Francisco Bay) that are at or near sea level and are adversely affected by flooding rivers and streams. The river flooding we experience will worsen as sea level rises and the area flooded will extend higher upstream than it would otherwise.

Even areas substantially upstream could suffer worse floods. Flood control structures might choose to not release enough water to prevent upstream floods, because of the impact it would have on severe flooding downstream near sea level. This assertion is somewhat speculative, but I think the assertion of worsened river flooding near sea level is pretty straightforward.

Brian-

Thanks. FEMA uses the following definition:

"A flood, as defined by the National Flood Insurance Program is: "A general and temporary condition of partial or complete inundation of two or more acres of normally dry land area or of two or more properties (at least one of which is your property) from:

# Overflow of inland or tidal waters,
# Unusual and rapid accumulation or runoff of surface waters from any source, or
# A mudflow."

http://www.fema.gov/hazards/floods/

By "river flood" I simply mean the second category as driven by precipitation (e.g., not a dam break). This is in contrast to coastal flooding from storm surges. If you'd like to get into some details, see this paper:

Pielke, Jr., R. A., 2000: Flood Impacts on Society: Damaging Floods as a Framework for Assessment. Chapter 21 in D. Parker (ed.), Floods. Routledge Press: London, 133-155.
http://sciencepolicy.colorado.edu/admin/publication_files/2000.11.pdf

Thanks. I'm curious if you'd agree with my suggestion in my first comment, which I'll alter somewhat here as saying that today, it is clearly a good use of science to allege a connection in future decades between greenhouse gases and damaging, precipitation-induced, river flooding in and near coastal areas.

I've thought that FEMA should be petitioned to determine what it anticipates the 100-year flood at low elevations will be like following sea-level rise. This might be similar to your suggestions elsewhere that greater effort should be spent preparing for the effects of climate change.

Brian- Thanks. Here is what we concluded on this question in this paper:

Pielke, Jr., R.A., and M.W. Downton, 2000: Precipitation and Damaging Floods: Trends in the United States, 1932-97. Journal of Climate, 13(20), 3625-3637.
http://sciencepolicy.colorado.edu/admin/publication_files/resourse-60-2000.11.pdf

Short answer: "The study shows clearly that increased precipitation is associated with increased flood damage."

The following text: "Similarly, increasing population growth and wealth are also associated with increased total flood damage. Much of the
variance in damage is not explained by the statistical models and is likely to depend on local differences of climate and policy. For example, whether a given increase in precipitation leads to increased hydrologic flooding will depend on its geographical distribution and timing, and whether population growth leads to increased flood damage depends on whether and how the growth occurs within the flood plain."

Read more details here:

http://sciencepolicy.colorado.edu/admin/publication_files/resourse-60-2000.11.pdf

Also, the 100-year flood doesn't make much sense in a non-stationary climate. See the discussion here:

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

I'm starting to wonder if it is also clearly a good use of science to allege an existing, present-day connection between greenhouse gases and damaging, precipitation-induced, river flooding in and near coastal areas. From the site:

http://www.grida.no/climate/ipcc_tar/wg1/409.htm

"The estimated rate of sea level rise from anthropogenic climate change from 1910 to 1990 (from modelling studies of thermal expansion, glaciers and ice sheets) ranges from 0.3 to 0.8 mm/yr. It is very likely that 20th century warming has contributed significantly to the observed sea level rise, through thermal expansion of sea water and widespread loss of land ice."

Projecting from 1990 to today gives an anthropogenic sea level rise of just under 3 cm to just under 8 cm, and near sea-level, precipitation induced, river floods should rise a similar amount. It might not sound like a lot, but every inch counts. It also might be more than that in some areas, especially depending on how high tides move that extra water volume into bays. I understand that near sea level river flooding is at its worst in high tides.