Floods Not Increasing Across the U.S.

Global Science Report is a feature from the Center for the Study of Science, where we highlight one or two important new items in the scientific literature or the popular media. For broader and more technical perspectives, consult our “Current Wisdom.”

In our continuing examination of U.S. flood events, largely prompted by the big flood in Louisiana last month and the inevitable (and unjustified) global-warming-did-it stories that followed, we highlight a just-published paper by a research team led by Dr. Stacey Archfield of the U.S. Geological Survey examining trends in flood characteristics across the U.S. over the past 70 years.

Previous studies we’ve highlighted have shown that a) there is no general increase in the magnitude of heavy rainfall events across the U.S., and thus, b) unsurprisingly, “no evidence was found for changes in extreme precipitation attributable to climate change in the available observed record.”  But since heavy rainfall is not always synonymous with floods, the new Archfield paper provides further perspective.

The authors investigated changes in flood frequency, duration, magnitude and volume at 345 stream gauges spread across the country. They also looked to see if there were any regional consistencies in the changes and whether or not any of the observed changes could be linked to large-scale climate indices, like El Niño.

What they found could best be described largely as a “negative” result—basically, few departures from the a priori expectation (often called the null hypothesis) that there are no coherent changes in flood characteristics occurring across the U.S.  Here’s their summary of their research findings:

Trends in the peak magnitude, frequency, duration and volume of frequent floods (floods occurring at an average of two events per year relative to a base period) across the United States show large changes; however, few trends are found to be statistically significant. The multidimensional behavior of flood change across the United States can be described by four distinct groups, with streamgages either experiencing: 1) minimal change, 2) increasing frequency, 3) decreasing frequency, or 4) increases in all flood properties. Yet, group membership shows only weak geographic cohesion. Lack of geographic cohesion is further demonstrated by weak correlations between the temporal patterns of flood change and large-scale climate indices. These findings reveal a complex, fragmented pattern of flood change that, therefore, clouds the ability to make meaningful generalizations about flood change across the United States.

The authors added:

Observed changes in short term precipitation intensity from previous research and the anticipated changes in flood frequency and magnitude expected due to enhanced greenhouse forcing are not generally evident at this time over large portions of the United States for several different measures of flood flows.

“Negative” results of this kind are a refreshing change from the “positive” results—results which find something “interesting” to the researchers, the journal publishers, or the funding agencies—that have come to dominate the scientific literature, not just on climate change, but in general. The danger in “positive” results is that they can ingrain falsehoods both in the knowledgebase of science itself, and also in the minds of the general public.  We’ve discussed how the appetite for producing “interesting” results—which in the case of climate change means results that indicate the human impact on weather events/climate is large, unequivocal, and negative—leads to climate alarm becoming “a self promulgating collective belief.”

What is needed to break this positive feedback loop, aka availability cascade, are researchers like Archfield et al. who aren’t afraid to follow though and write up experiments that don’t find something “interesting” together with a media that’s not afraid to report them. In today’s world dominated by climate hype, it is the non-interesting results that are, in fact, the most interesting. But, bear in mind that the interesting aspect of them stems not so much from the results themselves being rare, but rather from the rarity of the reporting of and reporting on such results.


Archfield, S. A., et al., 2016. Fragmented patterns of flood change across the United States. Geophysical Research Letters, doi: 10.1002/2016GL070590.