Geography Reference
In-Depth Information
the occurrence of landslides that are known to be caused by
heavy rains (e.g. Schuster 1996). However, geological and
geomorphologic settings may also play an important role
here (Brunsden 1999). Yet another type of climate extreme
is that some weather conditions, which may seem more or
less normal from a purely anthropocentric perspective, nev-
ertheless could induce a strong impact on some other spe-
cies. Thus, such ecological climate extremes may not be easy
to identify as climate extremes. The dependence on factors
other than meteorological data makes it difficult to disentan-
gle the specific contribution of weather/climate in producing
the impacts and to describe the combination of extremes. A
possible solution to this problem is interactions with affected
and interested groups and individuals, such as the insurance
industry and design engineers.
Damage reports from (re)insurance companies may also
be useful. Nevertheless, since there is no long-term homo-
geneous data yet in this regard, the use of this approach in
climate change studies is not feasible at this point. Therefore,
this atlas will not discuss these kinds of extremes. Rather,
the focus will emphasize a set of indices well defined by
meteorological data that are available for relatively long time
periods, i.e. temperature and precipitation.
While an increasing number of climate model studies
indicate that rising contents of greenhouse gases in the at-
mosphere will probably lead to more severe weather condi-
tions in the future, it is of great importance to increase our
understanding regarding the occurrence of climate extremes
in the recent and more remote past. During recent years, a
large number of studies have been carried out focusing on
various aspects of climate extremes (mainly temperature and
precipitation) in different regions of the world (e.g. Tren-
berth 1999; Easterling et al. 2000; Beniston and Stephenson
2004). Depending on research tasks, different measures were
used to quantify extremes, but which do not always allow
direct comparison of results. A general conclusion of many
of these studies is, however, that changes in extreme tem-
perature and precipitation have occurred world-wide during
the past century along with the ongoing climate change in
terms of the mean temperature (Donat et al. 2013). Yet, it is
still hard to draw a firm conclusion from these studies con-
cerning the extent to which these changes are due to natural
variability or caused by anthropogenic activity (IPCC 2007;
Field et al. 2012), although more recent studies indicate that
increase in extreme events is indeed linked to man-made
global warming (Hansen et al. 2012).
In an attempt to summarize the changes around the globe,
Groisman et al. (1999) and Groisman et al. (2005) studied
the probability distribution of daily precipitation in eight
countries located on different continents and concluded
that increased mean precipitation is associated with an in-
crease in heavy rainfalls. In their near-global analysis, Frich
et al. (2002) found regions with both negative and positive
changes in extremes, with parts of Europe having more ro-
bust positive changes. Using extremes indices similar to
some of those produced by the EMULATE project, Moberg
and Jones (2005) investigated trends in daily temperature
and precipitation extremes across Europe over the past cen-
tury and found that both mean and extreme precipitation
have increased mainly during winter. Also Klein-Tank and
K￶nnen (2003) found an increase in the annual number of
moderate and very wet days between 1946 and 1999.
Several studies have also been carried out at the national
level. Fowler and Kilsby (2003) studied multi-day rainfall
events in the UK since 1961 and found significant but re-
gionally varying changes in the 5- and 10-day events, which
they consider as having important implications for the design
and planning of flood control measures. In Central Europe,
Schmidli and Frei (2005) found significant increasing trends
in winter and autumn rainfall in Switzerland and Hundecha
and B£rdossy (2005) found increasing precipitation extremes
across western Germany since 1958. The increase in Central
European daily precipitation beyond the 98th percentile has
occurred during all seasons except summer (Jacobeit et al.
2009). In northern Europe, Achberger and Chen (2006) stud-
ied the spatial patterns and long-term trends of precipitation
indices in Sweden and Norway on an annual and seasonal
basis for the years 1961 to 2004. These indices are based
on daily data from 471 stations. Analysis of the trends of
the various indices for the period 1961-2004 shows that the
magnitude and sign of the trends varies depending on index,
region and season. A clear majority of stations show increas-
ing trends, though the fraction having statistically significant
trends is small. In Norway, positive trends are most com-
mon during winter, while at Swedish stations, positive trends
are most frequent in spring and summer. Autumn has the
highest number of stations in both countries with negative
trends. The findings are generally in line with results from
other studies concluding that regions at middle and higher
latitudes are becoming wetter and extreme temperatures and
precipitation are becoming more frequent and more intense.
The importance of monitoring and analyzing climate ex-
tremes has been highlighted by the past assessment reports
of the IPCC, and during a special IPCC meeting on climate
extremes held in Beijing in June 2002 (Houghton et al.
2002). Since then, there has been increased research around
the world, particularly in the US and European countries,
that aims at a better understanding of the observed extremes
(e.g. Arndt et al. 2010), detection and attribution of extremes
(e.g. Christidis et al. 2005; Morak et al. 2011; Zwiers et al.
2011), factors that influence extremes (e.g. Haylock and
Goodess 2004; Vautard and Yiou 2009; Zhang et al. 2010),
and interpretation of observed extremes in a climate context
(e.g. Peterson et al. 2012). In 2012 IPCC published a Special
Report on Extremes (Field et al. 2012) which summarized
and assessed studies with regard to changes in climate
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