The Expanding Bullsh*t Effect
Tropical storm Barry has provided another opportunity to roll out the latest fancy for the climate confused, a new meme called the “expanding bull’s eye effect” that downplays the role of climate change in extreme weather disasters.
The meme is built around a nifty (if misleading) graphical concept that illustrates the idea quite well. Unfortunately, while the graphical framing is new, the concept is quite old. It’s a long de-bunked argument dressed up with a new metaphor. But score one for recycling.
The bull’s-eye concept focuses on the impact of increasing wealth in long-term damage trends. And the trick employed here is to consider only one side of the coin.
What is the “expanding bull’s-eye” effect? According to one proponent, the “targets” of weather disasters — i.e., humans and their possessions — “are enlarging as populations grow and spread. It is not solely the population magnitude that is important in creating disaster potential, it is how the population and built environment are distributed across the landscape that defines how the fundamental components of risk and vulnerability are realized in a disaster.”
“Why is it important? While climate change may amplify the risk of certain hazards, the root cause of escalating disasters is not necessarily event frequency, or risk, related. Rather…the upward trend in disasters is predicated on increasing exposure and vulnerability of populations.”
At first blush this argument is enticing. After all there is certainly is a lot of new wealth in harm’s way. But what this framing carefully elides is the fact that all that extra wealth has also bought a LOT of protection from extreme weather.
If one is going to “normalize” damage trends for increasing wealth, you can’t cherry pick the impact of that wealth. Hundreds of billions of dollars have been spent on flood control in the U.S. So one has to either assume all that money was wasted or one has to acknowledge it has been suppressing massive damages. Can one imagine the damage that Barry might bring to New Orleans but for all those levees? The advantages of increased wealth extend to better building codes and materials, weather forecasting models, health care systems, evacuation capacity, emergency response crews, etc.
At the global level, where one would expect to see the clearest signal, there is a beautiful expression of this dynamic. According to Munich RE, damages from climate disasters have been rising dramatically, but not damages from geophysical disasters such as earthquakes. If increasing wealth is really the “fundamental risk,” why does more wealth increase the damages incurred by climate disasters but not the damages delivered by earthquakes?
An example of the wealth protection effect can be seen in the contrasting impact of Hurricane Sandy vs. the infamous 1938 Long Island Express Hurricane, one of the deadliest and most destructive tropical cyclones to strike Long Island, New York, and New England.
Back in 1938 New York had only a handful of hours to prepare for the Long Island Express. In contrast, New York had as much as a week’s notice to prepare for Sandy — evacuating residents, shutting down systems, sandbagging, protecting the subway etc. That weeks’ notice came thanks to billions of dollars spent on satellites, models, and weather forecasting. Can one imagine the untold damage and lives that would have been lost has there only been a handful of hours notice to prepare for Sandy?
There is one more “gap” in the expanding bull’s-eye concept worth calling out.
Per above, proponents claim that “it is how the population and built environment are distributed across the landscape that defines how the fundamental components of risk and vulnerability are realized in a disaster.” [emphasis added]. This is a fancy way of saying — “look at all that asphalt, no wonder there is so much flooding!”
However, as it turns out there’s not much difference between asphalt and saturated soils when it comes to run-off, and it doesn’t take much to saturate the top level of soil. Changes in the built environment make little, if any, difference in the level of flooding for events of the magnitude of Harvey, Florence, and (potentially) Barry.
According to the USGS: “Under these conditions, essentially all of the rain that falls, whether on paved surfaces or on saturated soil, runs off and becomes streamflow.”
So, the next time you hear someone talk about the “expanding bull’s-eye effect,” you might call out expanding bullsh*t.
P.S. A friendly hydrometeorologist has commented off-line, pointing out that while total runoff can be almost identical for saturated soils vs. pavement, runoff still tends to flow a bit more quickly over pavement than it does over saturated soil — and so the resulting flood can be “flashier” and higher-impact. Also, there’s usually more objects that can impede and slow the flow such as trees on undeveloped land than on pavement. This effect isn’t particularly applicable to major inundation events such as Harvey (and potentially Barry) which aren’t short-term flash floods. But still, it’s a helpful bit of nuance, so sharing here.[would that the proponents of the “expanding bullsh*t” meme engaged in such nuance!]
