Geography Reference
In-Depth Information
Figure 4.3
Differences in cyclone frequency in the
West Indies grid region for four periods during
1871-1995.
By focusing on individual land areas in the
Caribbean and using a combination of
documentary records and several existing
chronologies of hurricanes, it also proved possible
to examine cyclone frequency changes back to the
seventeenth century (Walsh and Reading 1991;
Reading and Walsh 1995; Walsh 1998). In the case
of the Lesser Antilles, it was demonstrated that
cyclone frequency was also high in parts of the
late eighteenth and early nineteenth centuries, but
much lower than in the twentieth century in
1650-1764, 1794-1805 and 1838-75 (Figure 4.5).
What the study also showed, however, was how
trends at the island sub-group scale differ both
from each other and from the regional pattern.
Peak frequency in the Windward Islands occurred
in 1876-1901, whereas in the Leeward Islands it
occurred in 1765-93 and in the French Islands/
Dominica in 1765-93 and 1806-37. The study
also demonstrated that changes in frequency
cannot be explained solely by changes in sea-
surface temperature but appear to be linked more
to shifts in key elements of the general circulation
and associated changes in the frequency and spatial
distribution of low vertical wind shear identified
by Gray (1968; 1988) as essential for cyclone
development.
Eyre and Gray (1990) examined trends since
1962 in cyclone frequency (as indexed by the
number of cyclone-hours) in 5°×5° degree
grids covering three areas: the Caribbean/
Atlantic, the eastern Pacific and the southwest
Pacific, finding no evidence of any increase in
each case (Table 4.2). They also found no
evidence of an increase in the intensity or
severity of cyclones, a finding since confirmed
for the North Atlantic/Caribbean by Landsea
(1993). However, other studies by geographers
have pointed to recent localised increases in
cyclone frequency. Thus Spencer (1994) has
reported that cyclones affecting Fiji in the
South Pacific have increased from 3.1 per
decade in 1941-80 to 11.4 per decade in the
1980s; and Nunn (1990a, b) has reported
increased cyclone activity in the Tuvalu,
Solomon Islands andVanuatu areas of the South
Pacific. Some of the local increases may reflect
Source:
Updated version of Reading and Walsh 1995.
Jamaica, peak frequency was actually recorded
around 1910, at a time when regional frequency
was very low, and cyclone frequency in the
southern Lesser Antilles has fallen little in recent
years compared with the dramatic declines in
Florida, the northern Lesser Antilles and Jamaica.
