WeatherZine #18


Floyd, the Fire Drill

Roger A. Pielke, Jr.
Environmental and Societal Impacts Group

Hurricane Floyd was in many places the equivalent of a fire drill – it was a trial run for future storms. (Unfortunately, for many in North Carolina in particular, it was a fire, not a drill.) It revealed ample opportunities to improve hurricane preparedness, response, and particularly evacuation based on forecasts and warnings. It also revealed that we as a nation are lacking critical information necessary to improve our priorities and preparedness, not only for hurricanes, but extreme weather in general.

Floyd holds the dubious distinction of being the first billion-dollar storm in which the costs of the evacuation rival the costs of the storm's impacts. How can this be? Assuming that the costs of evacuation are in the neighborhood of the oft-cited $1 million per coastal mile, then an evacuation of about 2,000 miles of coast totals $2 billion. According to the insurance industry, insured losses associated with Floyd totaled more than $1 billion, and flood costs add at least several billion to that.

This distinction is significant because it dramatically reveals one of the hidden costs ( Hidden Costs of Coastal Hazards) of hurricanes – that of overwarning. Because forecasts are uncertain, a larger area of coast must be warned than actually experiences a hurricane's impact. Consider that a hurricane typically directly affects about 100 miles of coast, and the average length of coastline warned per storm is 400 miles. This means that, on average, 300 miles of coast are warned but do not experience the direct effects of the hurricane. Floyd was obviously an extreme example of overwarning but perhaps also an indication of the sorts of problems faced in the future as more and more people move to coastal locations.

Improved forecasts offer the promise of reducing the costs of overwarning by providing greater accuracy and reliability to emergency management officials who must make difficult evacuation decisions (in concert with the National Hurricane Center, the Federal Emergency Management Agency, and in some cases, elected officials). How might this occur and what might be saved? Based on work done by Mark Demaria (formerly with the Tropical Prediction Center []), in 1997, the average error in hurricane track forecasts at 24 hours was about 90 miles (where error is the difference between where a storm is predicted to go and where it actually does go). And 95% of such forecast errors were less than 200 miles. By inference, this means that the average 400 miles of coastline warned per storm equates to a 95% confidence level (i.e., +/- 200 miles = 400 miles). Thus, only 1 in 20 storms will cross the coast over an area that was not warned at 24 hours.

If improved forecasts can reduce the magnitude of the 95% error in miles of coastline warned by, say, 20% from 200 miles to 160 miles, then all else being equal, this would lead to a reduction in miles-of-the-coastline-warned from 400 miles to 320 miles (+/- 160 miles) or a cost savings of $80 million per storm (80 miles times $1 million per mile), without changing the level of risk faced by coastal communities.

Some have suggested that instead of reducing the level of overwarning, it would be more important to increase the lead time available to the emergency management community. This argument makes good sense, given how long it takes to evacuate many communities and how those times are increasing. But it is impossible to effectively compare the relative benefits of reducing miles-of-coastline-warned versus increased lead time, because we simply do not know the value of improved lead time. And the back-of-the-envelope calculation in the paragraphs above of the benefits of reducing overwarning is no substitute for a rigorous empirical analysis. In our April 1999 issue Jerry Jarrell, National Hurricane Center Director, provided a list of such needed analyses (What Does the National Hurricane Center Need from Social Scientists?).

The hurricane case is representative of a broader problem. Simply put, in the area of weather we as a nation lack the information necessary to make informed public policy decisions about scientific research priorities, forecast tradeoffs, and community risks. The need clearly exists and there are experts with skills appropriate to the task, so why hasn't the community seen fit to prioritize this important area? Until we do public policy will suffer. Floyd is the most recent example of some important lessons. When will we finally learn them?

— Roger A. Pielke, Jr.


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