Discover more from The Honest Broker
Unbelievable: U.S. Flood Damage
An incredible trend that you never hear about
[H]eavier rainstorms driven by global warming are sending more water into residential neighborhoods from the Gulf Coast to New England to Appalachia to the Pacific Northwest.
We know that as climate changes, the impacts are getting worse. We’re seeing more and more flooding going on as a result.
Everybody knows this — it is conventional wisdom.
Not only is the conventional wisdom on flooding wrong, data show that flood impacts as measured by direct economic losses have actually decreased by about 90% since 1940 as a proportion of U.S. GDP. The United States is in fact more resilient to flooding than it has ever been. The reduction in flood impacts is an incredible story of success sitting out in plain sight that is completely ignored, in favor of stories that instead tell us that down is up.
The figure below shows U.S. annual flood damage as a proportion of GDP. In 1940 flood losses amounted to a 2023 equivalent of about $50 billion per year, and in 2022 they totaled about $5 billion, a reduction of over 90%.1
The figure below shows annual losses adjusted only for inflation over the same period.2
Over course aggregate flood loss totals have increased — From 1940 to 2023 the U.S. population increased from about 130 million to over 330 million. Over that same period, U.S. GDP increased by more than 10x. The math is simple: Flood damage in constant dollars increased by about 3x (figure above) while GDP increased by more than 10x — that means that flood damage has dropped dramatically as a proportion of economic activity.
A word of caution — none of this tells us anything about the climate. If you want to explore climate trends, look at climate data not economic loss data. But it does tell us that those promoting trends in economic impacts of floods and other extremes as evidence of human-caused changes in climate are peddling misinformation.
What the most recent science assessments say about changes in extreme precipitation and flooding may be surprising. For instance the most recent National Climate Assessment (NCA) concludes (emphasis added):
The complex mix of processes complicates the formal attribution of observed flooding trends to anthropogenic climate change and suggests that additional scientific rigor is needed in flood attribution studies. As noted above, precipitation increases have been found to strongly influence changes in flood statistics. However, in U.S. regions, no formal attribution of precipitation changes to anthropogenic forcing has been made so far, so indirect attribution of flooding changes is not possible. Hence, no formal attribution of observed flooding changes to anthropogenic forcing has been claimed.3
Because there is no evidence of a nationwide decline in flooding (just as there is no evidence for an increase), the dramatic reduction in flood losses as a proportion of economic activity must be the result of overall better collective decisions about where to build and how to manage floodplains.
It is apparently easy to confuse readily available social media postings showing flooding — which of course continues to occur — with the hyperbole of “America Underwater,” as The Washington Post put it. Recent flood events in New York City and elsewhere show that there is still a lot of work to do to continue to improve the nation’s resiliency to floods. And of course, continuing changes in climate or different modes of variability could also result in a future increase in flood events. Improved resiliency makes uncertainty about the future less significant.
But make no mistake — In 2023 floods are far less of a threat to people and the economy than they were back in the 1940s when they were considered a major national problem. At the time, geographer Gilbert White explained: “Human encroachment upon the flood plains of rivers accounts for the high annual total of flood losses.”5
If White were still with us today, he’d no doubt be proud of the degree to which his conceptualization of the national flood problem has contributed to policy success as measured by the incredible decrease in flood impacts as a proportion of economic activity. I am sure he’d also be amazed how few actually realize how much progress we’ve made as others spin success into failure.
Thanks for reading! THB is reader-supported and reader-engaged. If you are not a subscriber, I invite you to join the community. If you are already a subscriber, please consider an upgrade. Your support makes THB possible. Comments, questions, suggestions all welcome.
Here is a bonus figure, showing historical losses in dollars scaled to 2023 GDP.
The NCA also concludes: “Formal detection-attribution studies indicate a human contribution to extreme precipitation increases over the continental United States, but confidence is low based on those studies alone due to the short observational period, high natural variability, and model uncertainty.”
For instance: “Large-flood occurrence was generally stable across the United States in the last five decades; this may or may not continue with projected warming.”
I’m lucky to have overlapped with White on the faculty of the University of Colorado Boulder, prior to his death in 2006, and had a chance to get to know him during my time at NCAR and then at the university.