Tropical cyclones - Extreme Events: A Physical Reconstruction and Risk Assessment - page 80

Table 4.1 Tropical cyclone intensity and damage costs

Cyclone intensity
Saffir--Simpson scale

Median damage
(US$)

Potential damage (relative
to category 1 event)

Tropical storm <1 000 000 0

Category 1 33 000 000 1

Category 2 336 000 000 10

Category 3 1412 000 000 50

Category 4 8224 000 000 250

Category 5 5973 000 000 500

Table information from Pielke and Landsea ( 1998 ).

geometrically with increasing cyclone intensity. Pielke and Landsea (1998)sug-
gest that a category 4 cyclone (on the Saffir--Simpson scale) may produce, on
average, up to 250 times the damage of a category 1 cyclone. Table 4.1 from
Pielke and Landsea (1998)shows the median damage caused by US hurricanes
between 1925 and 1995. It is interesting to note that the median damage in US
dollars increases from $33 million for a category 1 event to nearly $6 billion for
a category 5 event.
Topography plays a major role in the ability of cyclonic winds to damage
buildings. Buildings on ridge crests are more exposed than those on flat ground.
The lee sides of hills can be prone to damage due to turbulence where wind
velocities can increase by up to 20%. The design of buildings is also important
in minimising damage. Generally, brick and concrete block buildings are more
resistant to damage because they are less likely to be punctured by flying debris.
The shape of roofs is also important; hip roofs, as opposed to flat or low-pitched
roofs and those with gable ends, tend to experience less damage.
Storm surge is an elevation of the sea surface both ahead of and during the
passage of a tropical cyclone towards the coast. The surge is really a long grav-
ity wave with a wavelength similar to the diameter of the generating tropical
cyclone. The surge wavelength is on average approximately 4 times the radius
of maximum winds, which can be anywhere from 10 to 50 km; hence the surge
wavelength can vary, depending upon the size of the radius of maximum winds,
from 40 to 200 km. Storm surges, therefore, are not like the shorter wavelength
or shorter period (periods of seconds) waves generated directly by the wind that
sit on top of the surge. A surge can be likened to a raised, low angle, dome
of water that inundates the coast. The water level associated with the surge at
the coast can take several hours to reach its peak height, which usually coin-
cides approximately with the time of cyclone landfall. The height of the surge is
dependent upon a number of factors including the intensity or central pressure