A new paper is out in
Water Resources Research that looks at flooding in the eastern United States. The paper looks at peak flood distributions for 572 stations over 75 years (pictured above). The paper concludes:
Only a small fraction of stations exhibited significant linear trends. For those stations with trends, there was a split between increasing and decreasing trends. No spatial structure was found for stations exhibiting trends. There is little indication that human‐induced climate change has resulted in increasing flood magnitudes for the eastern United States.
Villarini, G., and J. A. Smith (2010), Flood peak distributions for the eastern United States, Water Resour. Res., 46, W06504, doi:10.1029/2009WR008395. (PDF, subscription needed)
Logically, the inability to detect a signal of human-induced climate change in flood magnitudes means that it is impossible to detect such a signal in the damage record, which is comprised of
more moving parts than just high water.
4 comments:
Is this as significant as it sounds?
If this study looks at flood trends, not rainfall trends, and finds no pattern, then it seems to me that the likely rainfall pattern, if there is one, would be for less rainfall (subject to confirmation, of course, from rainfall gauges).
The reason I say this is that humans have created many more impervious surfaces over time, and drained many wetlands over time. For both reasons, there will be less absorbtion of rain on land and therefore (everything equal) more flooding. Rain will run off from the added roads and parking lots and buildings to add to flood waters. Instead of being absorbed in wetlands and flood plains, water will continue to add to floods downriver (as with the levees on the Mississippi around St. Louis, where after the big floods of several years ago they relocated towns out of the flood plains to create an overflow zone).
As noted, we'd need to see if the rain gauges show a downward trend over the same time period.
On the other hand, humans have also created flood control structures. In the part of the midwest in which I reside, almost every creek of any size is dammed, often more than once, to limit the extent of downstream flooding.
I doubt one can easily say, ignoring possible effects of AGW, how human activity has affected the propensity for floods, positively or negatively.
2. Tom G,
I'd go with no change or increased rainfall because, as you point out, flood defenses are adapted to the risk of flooding.
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