Extended Abstract (56K)11A.6
Enhancing the efficacy of hurricane advisories
Bernhard Lee Lindner, College of Charleston, Charleston, SC; and C. Cockcroft and S. Brueske
With financial support from the NOAA COMET program, a research team from the College of Charleston and the Charleston National Weather Service administered surveys of the public in the Charleston, South Carolina region to better understand their knowledge of the physics behind hurricanes, and how best to convey the risks associated with hurricanes in National Weather Service advisories. Ideas initially considered included the use of graphics, the use of inverted strike probability maps, less use of undefined terms in NWS advisories, and the use of graphic and textual landmark references. The project also attempted to measure the public’s understanding of probability. The survey had 45 questions which allowed us to determine the understanding and comprehension of 202 subjects in a variety of scenarios, and also allowed us to examine the varied comprehension of various ethnic, gender and income level groups.
Over 57% of our sample did not know the definition of hurricane warning. The NWS could overcome this problem by stating there was a hurricane warning and then proceeding to state that a hurricane warning means the NWS expects hurricane conditions in the forecast area within 24 hours. This idea extends to other terms such as hurricane conditions, storm surge, storm tide, etc.
55% of our sample did not realize the main threat from a hurricane in coastal areas was from storm surge and 53% did not understand that a decrease in the forward speed of a hurricane would increase the time spent by a hurricane over their location causing an increase in the amount of rainfall experienced. Additionally, over 32% did not understand that errors by NWS in forecasting the forward speed and direction of hurricanes would affect the time available for evacuation (i.e. increase or decrease). These results support our hypothesis that the public often does not understand basic scientific principles and this lack of understanding could cause them to ignore, misinterpret or underestimate the threat.
We found that a large majority of the sample preferred a graphical approach to information dissemination in contrast to the text-based approached used in local NWS advisories. This was especially true in probability issues. Over 62% of the sample answered correctly, from a map of the probabilities, that there was a 20% chance of the center of Hurricane Georges striking within 75 miles of Mobile, Alabama within 72 hours. This result was in striking contrast to a correct answer of 24.75% on a similar question using a copy of a text-based warning issued by the NWS for the probability of Georges striking Panama City, Florida. Also, in a comparison of a test-based wind advisory and a graphical wind advisory, 74.75% of the sample preferred the graphical advisory as opposed to 11.88% preferring the text-based product. Besides the expressed preference for the graphical approach the strike probability results strongly support the hypothesis that the public is better able to interpret the graphs versus the text products.
We also found the use of references, whether text or pictorial, aided in the dissemination of warnings. 63.89% expressed a preference for an advisory containing specific text informing the public of storm surge heights in relation to landmarks such Charleston’s city hall. Pictorial references accompanied the text. These references can help increase the perceived risk by the people who reside in close proximity to the reference points. In contrast 12.83% preferred a copy of an NWS advisory that contained no reference points, either textual or pictorial. Although local weather service offices are currently limited to text-based warnings such as the Hurricane Local Statement, a combination of text and pictorial references seems most effective. Perhaps as an interim measure NWS personnel could make pictorial references available on the local NWS web site so that media could cut and paste these references into their weather forecasts. This would personalize the information, increase the perceived risk, and confirm the urgency for taking self-protective action.
A small percentage of our sample expressed interest in Internet based information dissemination. 6.93% felt the use of an Internet based system of information was very important. 8.42% found it moderately important, 33.17% unimportant, and 45.55% did not know. It seems logical that the preferred graphical approach would work well with an Internet approach especially since the use of the Internet is growing rapidly.
The results of the survey did not support the use of an inverted strike probability map (i.e. the probability of a hurricane missing a location versus the probability of a hurricane striking a location). 42.08% did not support this alternative while 37.13% felt it could prove useful. The chief concern expressed by many centered on possible misinterpretations of the graph since the information has historically been presented as the probability of a hurricane striking a location. Any attempt to use this method would require a large investiture in education to decrease any chance of the public misinterpreting the inverted probabilities.
This abstract is funded in part from a subaward under the cooperative agreement between NOAA and the University Corporation for Atmospheric Research, and is pursuant to the National Oceanic and Atmospheric Administration Award No. NA97W0082 (Sub-award number UCAR-S00-22461). The views expressed herein are those of the authors and do not necessarily reflect the views of NOAA, its subagencies, or UCAR.
Session 11A, Tropical cyclone impacts and vulnerability
Wednesday, 5 May 2004, 3:45 PM-5:30 PM, Le Jardin Room
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