DisastersFinding the right balance for natural hazard mitigation

Uncertainty issues are paramount in the assessment of risks posed by natural hazards and in developing strategies to alleviate their consequences.

In a paper published last month in the SIAM/ASA Journal on Uncertainty Quantification, the father-son team of Jerome and Seth Stein describe a model that estimates the balance between costs and benefits of mitigation — efforts to reduce losses by taking action now to reduce consequences later — following natural disasters, as well as rebuilding defenses in their aftermath. A Society for Industrial and Applied Mathematics (SIAM) release reports that the authors used the 2011 Tohoku earthquake in Japan as an example, helping answer questions regarding the kinds of strategies to employ against such rare events.

“Science tells us a lot about the natural processes that cause hazards, but not everything,” says Seth Stein. “Meteorologists are steadily improving forecasts of the tracks of hurricanes, but forecasting their strength is harder.  We know a reasonable amount about why and where earthquakes will happen, some about how big they will be, but much less about when they will happen. This situation is like playing the card game ‘21’, in which players see only some of the dealer’s cards. It is actually even harder, because we do not fully understand the rules of the game, and are trying to figure them out while playing it.”

Earthquake cycles — triggered by movement of the Earth’s tectonic plates and the resulting stress and strain at plate boundaries — are irregular in time and space, making it hard to predict the timing and magnitude of earthquakes and tsunamis. Hence, forecasting the probabilities of future rare events presents “deep uncertainty,” Stein says. “Deep uncertainties arise when the probabilities of outcomes are poorly known, unknown, or unknowable. In such situations, past events may give little insight into future ones.”

Another conundrum for authorities in such crisis situations is the appropriate amount of resources to direct toward a disaster zone. “Much of the problem comes from the fact that formulating effective natural hazard policy involves using a complicated combination of geoscience, mathematics, and economics to analyze the problem and explore the costs and benefits of different options. In general, mitigation policies are chosen without this kind of analysis,” says Stein. “The challenge is deciding how much mitigation is enough. Although our first instinct might be to protect ourselves as well as possible, resources used for hazard mitigation are not available for