TCS Daily


Could the Tragedy Have Been Averted?

By Roy Spencer - September 2, 2005 12:00 AM

The tragedy currently unfolding in New Orleans is in many ways unprecedented in U.S. history, and it is tempting to think that the misery we are witnessing could have been avoided. I would like to suggest that some level of misery and loss of life was unavoidable. With all of the rhetoric in recent days regarding the possible role of global warming in hurricane activity, it is useful to examine weather disasters in general, and Katrina in particular, from both historical and practical points of view.

Forecast Accuracy and Warnings

Everyone knows that weather forecasts are not totally accurate. For potentially destructive and life-threatening events such as tornadoes, hurricanes, and floods, forecasters necessarily err on the side of caution. This leads to over-warning, which in turn results in some level of complacency on the part of the public. While over-warning leads to a high "probability of detection" (very few events go without warnings), it is at the expense of increased false alarms. But there really is no other acceptable choice. The only alternative would be to issue fewer warnings. But given the imprecision of hurricane forecasts, this would be at the cost of numerous events for which there were no warnings. Many, possibly most, hurricanes that hit land would either have no warnings, or would have insufficient lead time for evacuations and property protection to take place. This would be totally unacceptable to the public. Thus, we are left with the unavoidable situation where some portion of the people will not heed warnings - for example, I personally ignore most tornado warnings -- and so people will die.

Hurricane intensity and track forecasts for Hurricane Katrina were, from a historical perspective, pretty darn accurate. Early forecasts had the hurricane tracking farther east in the Florida panhandle. But as of 11 p.m. Saturday night (48 hours before high winds started reaching the coast of Louisiana) the National Hurricane Center (NHC) was forecasting an "intense hurricane". The forecast track issued at that time was almost dead-center on the eventual landfall location. Katrina ended up intensifying and moving more rapidly than normal, leading to less lead time than would have been desired for the warned areas.

Nevertheless, warnings of a "catastrophic event" were made in time for virtually all of the people who were willing and able to leave New Orleans and coastal areas to do so. Most people did indeed leave the warned areas -- but not all of them. NHC makes it a special point in the case of especially broad hurricanes such as Katrina to tell people to not focus on the exact forecast track of the eye since such a broad area will be impacted anyway.

How Did Katrina Rank?

From a meteorological perspective, Katrina was unusually intense and large, but not unprecedented. At one point it had the fourth lowest recorded air pressure for an Atlantic hurricane (902 mb, or 26.64 inches), but this statistic should be taken with a grain of salt since we have only a few decades of good measurements, and many systems that do not threaten land are never measured directly. At initial landfall southeast of New Orleans, Katrina was a category 4 storm with maximum sustained winds estimated at 145 mph.

The Galveston Hurricane of 1900, also estimated to be a category 4 storm, caused over 6,000 deaths. This is commonly considered to be the greatest natural disaster in U.S. history. The much lower casualty figures for modern hurricanes, even in the face of explosive population growth in hurricane prone areas, is a testament to current satellite, weather forecasting, communications, and transportation technologies. Were it not for modern technology, we could well experience what Bangladesh has endured in the not too distant past -- an estimated 300,000 to one million dead from a 1970 tropical cyclone. Tropical cyclone disasters with 10,000+ dead are not uncommon there.

Adjusted to 2004 dollars, Hurricane Andrew of 1992 was the costliest hurricane on record, at about $44 billion. It remains to be seen whether the Katrina event will exceed this record. If it does, it will be more attributable to the desire of so many people to live and build in coastal areas than to the inherent strength of the hurricane itself. Indeed, if we ask the question, "which land falling hurricane in U.S. history would be the most expensive if it happened today?" the clear front-runner would be the Great Miami Hurricane of 1926. It is estimated that, if that hurricane occurred today, the costs would reach about $110 billion.

Global Warming and Hurricanes

There is some recent research that suggests that of all Atlantic and West Pacific tropical cyclones measured since the 1970's, a warming trend in sea surface temperatures has been accompanied by stronger and longer-lived storms. In fact, the increase in the total power generated by the storms that the study computed was actually much larger than could be accounted for by theory, suggesting changes in wind shear or other processes are operating in addition to just increased temperatures. (Unpublished results by the same researcher suggests, however, that this trend was not apparent in land falling hurricanes since the 1970's).

Given the recent work, how should we view the role of global warming? First, we know that category 4, and even category 5, storms have always occurred, and will continue to occur, with or without the help of humans, as the above examples demonstrate. Therefore, if we are prepared for what nature can throw at us, we will be prepared for the possible small increase in hurricane activity that some studies have suggested could occur with man-made global warming. To suggest that Katrina was caused by mankind is not only grossly misleading, it also obscures the real issues that need to be addressed, even in the absence of global warming. From a practical point of view, there is little that we can do in the near term to avert much if any future warming anyway, no matter what you believe that warming will be, including participating in the Kyoto Protocol. So why even bring it up (other than through political, philosophical, or financial motivation)?

Living with the Risk

It has long been known that New Orleans was at greater risk of catastrophe than most coastal areas, especially from flooding and the hurricane storm surge. While the storm surge itself is not what inundated the city, it was responsible for the levee failures that then caused flooding over the couple of days following the hurricane.

Another geographical area of concern is the U.S. 1 evacuation route out of the Florida keys. A rapidly approaching and intensifying hurricane in this area could also lead to a great loss of life.

The only way to completely avoid the loss of life and property in these areas is for people to not live there, and for businesses to not operate there. The stark reality, however, is that this will not happen. People in these areas live at greater risk than most of the rest of the country, and they will continue to in the future. No human endeavor is risk-free, and coastal residents simply take greater risks than most of the rest of us. As long as weather forecasts are not perfect, and as long as severe weather events are (necessarily) over-warned, weather disasters will continue to happen.

For more coverage of Hurricane Katrina and its aftermath, and to learn how you can help the victims of this disaster, please visit our special section Tragedy on the Gulf Coast.

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