Vulnerability, Impacts and Adaptation of Coastal Zones to Global Change - Vulnerability of Coastal Ecosystems and Adaptation - page 150

4 . 3.4. Other impacts of climate factors on coastal zones
4.3.4.1. Tropical cyclones and extratropical storms
When tropical cyclones and strong extratropical cyclones strike the
seashore, the storm surges produce a temporary rise in sea level that,
coupled with the high waves, can cause devastating floods in coastal
zones. Tropical cyclones are convective mesoscale systems that form
in the oceanic intertropical regions and generate heavy rains, strong
winds that can reach more than 250 km/h and high waves. It is
difficult to reconstruct, reliably, the evolution of their frequency and
intensity during the 20th Century because the methods, regularity and
quality of the observations have changed a great deal. Nevertheless, it
is very probable that the intensity of the strongest cyclones (those
where the maximum sustained wind speed is higher) have been
increasing, especially in the North Atlantic [WEB 05]. It has also been
observed that tropical cyclones become more frequent during years
that are warmer globally and that the strongest are more sensitive to
the increase in temperature [GRI 12]. It is estimated that global
warming will double, by the end of the century, the number of
cyclones with the intensity of Katrina, one of the strongest cyclones in
the North Atlantic, which occurred in August 2005 and accounted for
1,800 victims in the United States, where it caused around 100 billion
dollars (in 2005) worth of damage [GRI 13].
The projections based on high-resolution dynamic models indicate
that anthropogenic climate change tends to decrease the mean global
number of tropical cyclones by 6 to 34% [KNU 10]. The same models
project an increase in the mean global intensity of tropical cyclones by
2 to 11%. This implies that in the future, the frequency of very intense
cyclones is likely to be higher, which will aggravate their impact on
coastal zones by increasing the flood risks associated with storm
surges, high waves and rising GMSL. When considering the impacts
of tropical cyclones in low elevation coastal zones it is necessary to
distinguish between the climate drivers and the non-climate drivers.
According to a recent United Nations report [GAR 11], the population
exposed to the risks of tropical cyclones has increased by 192% in the
period 1970-2010, while the global population has increased by 87%.
Nevertheless, since 2000 the mortality due to tropical cyclones has