Geoscience Reference
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Figure 3.9 Annual numbers of major tropical cyclones for the 1981-2 to 2006-7
cyclone seasons, with linear trends
Source: Kuleshov et al., 2010
Notes
a Tropical cyclones (TC)
b Southern Hemisphere (SH) (squares, right axis),
c South Indian Ocean (SIO) (diamonds, left axis),
d South Pacific Ocean (SPO) (circles, right axis), and
e Australian Region (AR) (triangles, left axis), for the 1981-2 to 2006-7 cyclone
seasons, with linear trends.
Extreme sea level
Observations from tide gauges indicate that the global average sea level rose by
around 1.7mm per year over the 20th century. Since 1993, this rate has increased
to around 2.8-3.2mm per year based on tide gauges and satellite altimetry
(Church and White, 2011). Extreme sea level events can be due to high tides,
local storm surges due to low pressure systems such as cyclones, distant storms
that generate high waves, and a rise in average sea level. Worldwide, there has
also been an increase in extreme sea levels, for example those that occur when
high tides and storm surges coincide, since 1970 (Menendez and Woodworth,
2010). Increases in extreme sea level events around Australia have been
significant at most sites. The average sea level rise, rather than changes in storm
surges, is the major reason for the rise in extreme sea level. El NiƱo is one of the
most important factors responsible for the interannual variability of extreme sea
levels (Bureau of Meteorology and CSIRO, 2011), and this will have played a
role in the extreme sea level trends. Tidal contributions to extreme sea levels are
especially significant along the Australian coast (Menendez and Woodworth,
2010).
 
 
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