Risk Assessment of North Carolina Tropical Cyclones (1925-2000)
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Date
2003-02-19
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Abstract
Previous tropical cyclone risk assessment studies have been national in scope. This study demonstrates the need for regional risk assessments, using the tropical cyclone history of North Carolina as an example. The standard normalization procedure for historical damage data was reevaluated. A housing factor was used instead of the more conventional population factor to go along with inflation and changes in wealth. For coastal counties in North Carolina, housing figures from 1940-2000 increased 780% while population figures increased only 370%. It is believed that use of housing data in lieu of population data in the normalization procedure provides a more realistic measure of impact. Using the new normalization method, 1954-55 tropical cyclone storm totals in North Carolina added together would have caused over $18 billion in damage (expressed in 2000 dollars). By comparison, the destructive period from 1996 to 1999 in North Carolina added up to $13 billion.
Storm damage totals were separated into damages caused by wind, flooding, and storm surge. For all 36 direct landfalling tropical cyclones in North Carolina from 1925-2000, flooding caused approximately 40% of all damages, while wind and storm surge caused an estimated 35% and 25%, respectively. From these results, it is clear that flooding produced relatively greater damage in North Carolina compared to the United States in general.
Rainfall was correlated to meteorological parameters of tropical cyclones making landfall in North Carolina. There was a weak relationship between intensity of the tropical cyclone and maximum rainfall totals. There was a stronger relationship between rainfall and translation speed. For those tropical cyclones that did not directly interact with synoptic-scale features such as upper-level troughs, lows, or surface fronts, the relationship between rainfall and translation speed can be expressed by the equation Y=29.529X-0.6134 where Y is the average of the five highest recorded rainfall totals and X is the translation speed (expressed in knots). Rain volume calculations quantified the magnitude of the September 1999 flood event in eastern North Carolina. Hurricane Floyd yielded an estimated 4.14 cubic miles of water on North Carolina only 10 days after Tropical Storm Dennis brought North Carolina out of drought conditions with 3.67 cubic miles of water. The next-highest value from previous tropical cyclones was Hurricane Fran (1996) with 3.14 cubic miles of water.
While major hurricanes accounted for 83% of the overall damage due to hurricanes nationally, this percentage changes regionally. Using the total normalized damage numbers for North Carolina, 70 % of all tropical cyclone damage was caused by major hurricanes, while category-2 hurricanes added a significant percentage (21.4%). The results of this study suggest a stronger consideration for weaker tropical cyclones, especially category-2 hurricanes, in risk management decisions.
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hurricanes, damage, flooding, wind, storm surge, rainfall, North Carolina, tropical cyclone
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Degree
MS
Discipline
Marine, Earth and Atmospheric Sciences
