24 October 2011

Are US Floods Increasing? The Answer is Still No.

A new paper out today in the Hydrological Sciences Journal shows that flooding has not increased in the United States over records of 85 to 127 years.  This adds to a pile of research that shows similar results around the world.  This result is of course consistent with our work that shows that increasing damage related to weather extremes can be entirely explained by societal changes, such as more property in harm's way.  In fact, in the US flood damage has decreased dramatically as a fraction of GDP, which is exactly whet you get if GDP goes up and flooding does not.

I do not expect research to change anyone's views on the topic or alter the debate over climate change and extreme events.  The debate has moved well beyond that which can be resolved empirically.


  1. I cannot believe how blatantly dishonest the climate denier movement is.

    You lie to people OUTRIGHT and then assume they will not read your sources for themselves. (Or maybe you know or suspect your readers are morons who would not understand the studies you cite if they read them for themselves.)

    Well, I clicked on your link. I read the article for myself. Not only does it NOT say what you say, it says the opposite. The whole article is premised on the INCREASE in flooding in the US in recent years. The study looks at what is causing the increase--that is the whole point of the article! It very clearly states as much both in the abstract and the text of the article.

    Shame on you and all of your intellectually dishonest con men who seek to deliberately mislead people about such an important issue. I have no idea what motivates you people, but I am so sick of it.

  2. -1-Lauren

    Thanks fro dropping by, though you may wish to re-read the paper, especially this part:

    "What these results do indicate is that except for the decreased flood magnitudes observed in the SW there is no strong empirical evidence in any of the other 3 regions for increases or decreases in flood magnitudes in the face of the 32% increase in GMCO2 that has taken place over the study period. "

  3. Lauren, I just read the abstract only, and sentences four and five read:

    'In none of the four regions defined in this study is there strong statistical evidence for flood magnitudes increasing with increasing GMCO2. One region, the southwest, showed a statistically significant negative relationship between GMCO2 and flood magnitudes.'

  4. Lauren

    The scientists said "There is “virtually no evidence of increases or decreases in flood magnitudes” during the last 100 years in the northwestern and southeastern United States, USGS said. The study found that the northeastern United States “shows a tendency towards increases in flooding over this period.”

    But the study was able to identify a clear relationship between flooding and climate change in the southwestern portion of the United States. In that region, floods have become less severe as greenhouse gas emissions have increased, the study says.

    More to the point,there is absolutely no evidence that any of these changes are anything other than natural or that they can predict future changes.

  5. Roger,
    I attended a lecture last night by a Nobel Prize winner in Chemistry.
    He made the same false claim in a very disappointing lecture on alternate energy that literally only offered a slide with the word "SOLAR" on it as the solution to the great CO2/energy crisis.

    Your faith is far too brittle if you have to rely on spittle flecked reactionary temper tantrums and denigrate those with whom you disagree by using bigotry to hide your ignorance.
    You should look in a mirror and ask yourself- if you can- if maybe the person you are looking at is the one getting conned.

  6. Even the NE results, which show a non-statistically significant positive trend, are heavily dependent on the Red River basin (parenthetically, it's really odd to see Fargo, ND being assigned to the North East). Those are rather unusual floods, because they're usually caused by abrupt Spring melting of a heavy snowpack dispersed over a large watershed area. They're as much a result of rapid temperature change as of precipitation trends.

  7. Flooding may not have increased in the USA in line with the increase in carbon dioxide, but it does seem to have passed a tipping point globally.

    Last year we saw extreme floods in Pakistan (repeated to a lesser extent this year), in Queensland, Australia, and in China. There were severe floods in mid-western USA this summer. Now we are seeing floods in Bangkok, Dublin, and northern Italy. Taken individually, each of these events is not outside of what might be expected every 100 years or so, but for all to happen over so short a period could be significant.

    The fact that rainfall has not increased in line with the rise in CO2 is no guarantee that it will not do so in the future.

  8. The nature of extreme events means that there are many different metrics which can be used to measure them. The study Roger links to here uses streamflow guages. I'm not saying that it is necessarily a bad measure, just that it is only one. As another example, you can go to the US Climate Extremes Index and choose from among a variety of metrics and get a plot of statistics.

    I chose the NE US, all year, and extreme 1 day precipitation events. There was a very clear trend of an increase in such events since the 1960's. These events don't necessarily correlate with floods. Because while we have been building in flood-prone areas, we have also been building flood control structures.

    So what are we to make of an increase in extreme precipitation events but not an increase in floods? Time will tell, but the point is that there is evidence of climate change increasing extreme weather events, but how you measure them makes a big difference. Roger's statement is not untrue, but it is incomplete.

  9. -8-Dean

    Thanks ... on your question:

    "So what are we to make of an increase in extreme precipitation events but not an increase in floods? "

    We wrote about this apparent "paradox" back in 1999:

    Pielke, Jr., R. A. and M. W. Downton (1999), U.S. trends in streamflow and precipitation: Using societal impact data to address an apparent paradox. Bulletin of American Meteorological Society 80 (7) 1435-1436

    Here is what we concluded:

    "How can it be that on a national scale extreme rainfall is increasing while peak
    streamflow is not?"

    "On the one hand, increasing "extreme" precipitation has not been the most important factor in documented increase in flood damage. On the other hand, evidence of a lack of trends in peak flows does not mean that policy makers need not worry about increasing precipitation or future floods. Advocates pushing either line of argument in the policy arena risk misusing what the scientific record actually shows. What has thus far been largely missed in the debate is that the solutions to the nation's flood problems lie not only in a better understanding of the hydrological and climatological aspects of flooding, but also in a better understanding of the societal aspects of flood damage."

    I don't think I'd change a word in 2011.

  10. You can stand by your paragraph and I have no problem with it. I said before that I think your statement is incomplete, not wrong. Rather than just saying that there is no evidence of an increase in floods, it would be more complete to say that there is no evidence that the measured increase in extreme rainfall events is causing floods.

  11. -10-Dean

    Well, here we will have to differ. I do not see evidence of an increase in floods across the US or the world (individual basins will of course have various ups and downs).

    Do you?

  12. Did I say that I did?

    "it would be more complete to say that there is no evidence that the measured increase in extreme rainfall events is causing floods."

    The point being that there is evidence that AGW is affecting and causing extreme events, just not floods. Nor is the distinction trivial.

  13. -12-Dean

    "The point being that there is evidence that AGW is affecting and causing extreme events"

    Maybe so ... but this is a post about floods specifically, which have often been linked to climate change (including that caused by humans). Clearly such attributions are flawed.

    You are correct that the data on floods does not speak to phenomena other than floods, but I don't think that point has been argued here in the slightest.


  14. There were severe floods in mid-western USA this summer.

    Yes, but unless you're going to blame global warming for the incompetence of the Army Corps of Engineers, I doubt we can pin that on CO2.