Buildings and roads are usually designed around ordinary conditions. Rare extremes can test them in ways that ordinary days do not.

Wikipedia's current-events log for November 13, 2009, recorded that 38 people were killed in collapsed school buildings and road accidents caused by heavy snowfall in China, the heaviest in 60 years.

The limits of normal parameters

Above all, the entry records lives lost. It does not explain why the buildings collapsed or the accidents happened beyond the snowfall, and no cause is assumed here. In general terms, though, structures built for typical weather may have less margin for rare extremes, and planners may face hard choices about how much margin to build in.

Building every facility for the rarest conditions might be costly, while not doing so may carry serious risks. Decision-makers may have to weigh how likely a rare event is against how severe its outcome could be.

Cascading failures in complex environments

Severe weather may affect more than one kind of system at once. The entry mentions both buildings and roads, which suggests a broader question: what happens when several systems are under strain at the same time?

In general, a storm that strains buildings might also make the roads to them harder to use, so a problem in one place could make help harder to bring in another. Builders might find it useful to think about resilience across a whole network, not only in each part.

Perhaps resilience begins with planning for the days that are not ordinary.

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