Building on the floodplain
The most dangerous things are those that don’t come often enough.
As this is being written, Hurricane Lee is out in the Atlantic southeast of us, headed north-northwest. It is still too far away to make any definite forecast for Alexandria, but there is certainly a strong possibility we’ll feel some effects. To be prudent, we’ve started going trough our hurricane-emergency kits. Already we’ve found that the fuel can for the camp stove has gotten rather rusty, and we’ve transferred the contents to a more secure flask. We need to do more examining and testing yet. We really should do this at least every year as the hurricane season starts, but we’ve put it off, mostly because no tropical storm has really threatened us for some time. A few remnants have tracked to one side of us or the other, but the actual effects hereabouts have been small.
We suspect our neglect of proper preparations is rather general. It’s very human to discount dangers that don’t happen often. We prepare for winter and summer, but the storm that appears only once in decades catches us by surprise. There’s lots of nice, flat land covered with grass over next to the river, excellent sites (one would think) for a new development of houses. Well, the land is a floodplain. It doesn’t flood every year; maybe once in 20 or 30 years spring brings enough sudden downpours that the river bursts its banks. When it does, anything built on the floodplain is quickly gone.
Of course, the disaster that strikes at very long intervals does little damage on the average. The 200-year flood may look horrible at the time, but a lot of building and living can be done in two centuries. And we’re prepared for normal seasonal storms. Likewise, regions that almost never experience earthquakes are by definition not affected by them much over time; those that constantly shake have strict building codes. Somewhere in between is the maximum danger. Somewhere in between, human memory has faded enough so that we make no preparations, and are caught.
What is that interval of maximum destruction? We think it depends on the threat, and the needed preparations. For letting one’s hurricane kit rust, it only takes a few years without a tropical storm. For building on the floodplain, it’s measured in decades.
[Can we extend this to man-made disasters? If the financial world’s response to the 2008 crisis had been the same as its response to the 1929 crisis, there would almost certainly have been another Great Depression. That argues for a long memory. But we could point to other mistakes being made over and over again, as the wrong lessons are learned. So can you.]
The real danger, however, is when the interval of return changes. The Earth’s climate is changing. Storms and droughts are going to happen in different places and at different times from in the past. In a metaphorical sense, we may all be living on the floodplain.
