Timothy Birdnow

Despite "extreme rainfall events" there has been no net increase in flooding nationwide.

From Roger Pielke Jr.'s site:

A new paper in Water Resources Research discusses an apparent paradox:

Extreme precipitation events, which fall into the 99th percentile of daily events, have increased across the contiguous United States since the 1950s in response to rising temperatures. But despite assertions by the climate community that increasing precipitation extremes inevitably lead to higher flood magnitudes, multiple studies have demonstrated that this has not been the case.

In this post I discuss this apparent paradox, which we wrote about 20 years ago, and its relationship to common misrepresentations of climate science. More after the jump.

The new paper is:

Sharma, A., Wasko, C., & Lettenmaier, D. P. (2018). If precipitation extremes are increasing, why aren’t floods?. Water Resources Research, 54:8545-8551.

Many people believe that flooding has been on the increase. It hasn’t. One reason for this confusion may be the fact that "extreme” precipitation has increased in many places. I put "extreme” in scare quotes because many scientific definitions of "extreme” are statistical and are not necessarily closely associated with flooding or flood damage (see Pielke and Downton 2000 linked below). However, another reason for confusion is that some enthusiastic advocates for climate action willfully misrepresent the science of flooding and precipitation. More on that at the conclusion to this post.

Back to Sharma et al. who conclude that the relationship between extreme precipitation and flooding is complicated.

Thus, any single measure of precipitation would be unlikely to explain much about flooding or flood damage. Hence, it is perfectly reasonable that some "extreme” precipitation metrics would show an increase, yet flooding or flood damage would not show a corresponding increase, and might even show no trends or a decrease. The figure at the top of this post comes from our paper and presents some of this complexity.

We concluded:

[W]hether 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. In addition, our analysis provides supporting evidence for the notion that increasing U.S. precipitation documented by Karl and colleagues has not led to a corresponding increase in the highest levels of streamflow documented by Lins and Slack. . . In conclusion, the relationship of climate, hydrology, and society in producing damaging floods is complex
and not fully understood.

The lack of trends in flooding — in the US or globally — is well documented and appears in the assessments of the IPCC and US National Climate Assessment. Yet despite this robust understanding, claims persist by many journalists and leading climate scientists that flooding has increased. Such false claims are made even worse when the (nonexistent) increases in flooding are attributed to an increase in greenhouse gases. A third misrepresentation occurs when the phantom trends flooding are then linked to increasing precipitation, which has an actual trend in some place that has been attributed to some degree to human influences (per IPCC).

As I have written about for years, the misrepresentation of the detection and attribution of trends in extreme weather events is common by advocates for climate action, many of whom certainly know better. My pointing this out has led to considerable career repercussions, but I’ll continue to do so because I’m on the right side of the evidence and have been for a long time. Good science wins out in the end, even if it takes 20 years.

Posted by: Timothy Birdnow at 10:42 AM | Comments (13) | Add Comment
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