Floods and the tragedy of the commons

As I write, Nashville's Mayor Karl Dean and his emergency-management team are briefing the media. It's on TV. The chief of water services said that the flood has decreased Nashville's capability to produce fresh water by 50 percent. So, he said, everyone needs to use half as much water as before. The mayor said that water should be used only for personal hygiene and cooking.

This is a classic example of the "problem of the commons," also known as the "tragedy" of the commons.

The tragedy of the commons refers to a dilemma described in an influential article by that name written by Garrett Hardin and first published in the journal Science in 1968. The article describes a situation in which multiple individuals, acting independently, and solely and rationally consulting their own self-interest, will ultimately deplete a shared limited resource even when it is clear that it is not in anyone's long-term interest for this to happen.

Central to Hardin's article is an example (first sketched in an 1833 pamphlet by William Forster Lloyd), of a hypothetical and simplified situation based on medieval land tenure in Europe, of herders sharing a common parcel of land, on which they are each entitled to let their cows graze. In Hardin's example, it is in each herder's interest to put the next (and succeeding) cows he acquires onto the land, even if the carrying capacity of the common is exceeded and it is temporarily or permanently damaged for all as a result. The herder receives all of the benefits from an additional cow, while the damage to the common is shared by the entire group. If all herders make this individually rational economic decision, the common will be depleted or even destroyed to the detriment of all.

Usually, announcement of a shortage jump starts hoarding. People rush to get what they can while they can.

The issue in Nashville is maintaining pressure within the water system. The system's pressure has to remain at or above 20 pounds per square inch. If it falls below that in a flooded system, contamination from the flood waters can seep into the pipes through cracks or dislocations. That's the main reason for telling people to use half as much water - water use decreases pressure. The city has only two water plants. One is operating normally but the other is completely submerged.

Will this fact alleviate the problem of the commons? Only if people understand that the more water they draw from the faucet, the greater the chance that the water they are drawing for their own use will be contaminated. That wrinkles the problem in the way that theorists Hardin didn't enfold in his 1968 article. The farmer who overgrazed the commons was hurting his neighbors but not himself. In Nashville, water over-users are (at least potentially) harming both their neighbors and themselves.

The city's government needs to explain it that way to the people.

Update: It may all be moot: the flood may take out the one remaining operating water plant.