The debate concerning future changes in tropical cyclone activity is far from settled (Idso et al. 1990, Hobgood and Cerveny 1988, Emanuel 1987). Speculations on changes in the frequency and intensity of hurricanes under global warming focus on limiting processes and climate feedback mechanisms leading to a hypothesis of little overall change (Lighthill et al. 1994). This does not rule out the possibility of trends in landfall probabilities as shifts in preferred location of activity occur. Here we examine temporal changes in hurricane landfall probabilities using historical and proxy records along the U.S. coastline.
A hurricane landfall at any one location is an extreme, rare event usefully described using the Poisson distribution. As such, the return intervals (times between successive landfalls) follow an exponential distribution. Using a parametric method outlined in Keim and Cruise (1998), we test for trends in the rate of hurricane occurrences for states along the Gulf and Atlantic coasts from historical records. Along most of the U.S. coastline the tendency is for reduced hurricane landfall probabilities. A statistically significant trend toward lower annual probabilities is found along the northwestern Florida coast. A slight increase in probabilities is noted from North Carolina to Maine. The trends are consistent with a tendency for more baroclinically-enhanced hurricanes over the past three decades (Elsner and Kara 1999). Proxy records from coastal lake sediments along the Gulf of Mexico coast suggest ultra low frequency changes at millennial timescales in the probabilities of major hurricanes.
REFERENCES
Elsner, J. B., and A. B. Kara, 1999: Hurricanes of the North Atlantic: Climate and Society, Oxford.
Emanuel, K. A., 1987: Nature, 326, 483--485.
Hobgood, J. A., and R. S. Cerveny, 1988: Nature, 333, 243--245.
Idso, S. B., R. C. Balling, Jr., and R. S. Cerveny, 1990: Meteorol. Atmos. Phys., 42, 259--263.
Keim, B. D., and J. F. Cruise, 1998: J. Climate, 11, 848--855.
Lighthill, J., G. Holland, W. Gray, C. Landsea, G. Craig, J. Evans, Y. Kurihara, and C. Guard, 1994: Bull. Amer. Meteor. Soc., 75, 2147--2157.