Climate change impacts and vulnerability in Europe 2016

Climate change impacts on environmental systems
Projections
Future changes in the risk of river floods in Europe
have been simulated using a hydrological model
driven by an ensemble of climate simulations (Rojas
et al., 2012; Alfieri, Burek et al., 2015). Of particular
interest is the frequency analysis of flood peaks
above the 100-year flood level, which is the average
protection level of the European river network
(albeit with significant differences) (Rojas et al., 2013;
Jongman et al., 2014).
Map 4.8 shows the change in the level of one‐in‐a‐century
(Q100) floods between the reference period and three
future time periods based on the hydrological model
LISFLOOD and an ensemble of seven climate models
(Alfieri, Burek et al., 2015). Blue rivers indicate an increase
in flood level and red rivers indicate a decrease. For the
end of the 21st century, the greatest increase in Q100
floods is projected for the British Isles, north-west and
south-east France, northern Italy and some regions
in south-east Spain, the Balkans and the Carpathians.
Mild increases are projected for central Europe, the
upper section of the Danube and its main tributaries. In
contrast, decreases in Q100 floods are projected in large
parts of north-eastern Europe owing to a reduction in
snow accumulation, and hence melt-associated floods,
under milder winter temperatures. These results are
consistent with earlier studies (e.g. Dankers and Feyen,
2009; Ciscar et al., 2011; Rojas et al., 2012). While the
ensemble mean presented in Map 4.8 provides the best
assessment of all model simulations together, individual
simulations can show important differences from the
ensemble mean for individual catchments. This is partly
the result of significant decadal-scale internal variability
in the simulated climate (Feyen et al., 2012). Furthermore,
the LISFLOOD analysis is restricted to the larger rivers
in Europe, which may not be representative of a whole
country or region. For example, in northern Europe,
rainfall-dominated floods in smaller rivers may increase
because of projected increases in precipitation amounts,
even where snowmelt-dominated floods in large rivers
are projected to decrease (Vormoor et al., 2016).
Changes in flood frequencies below the protection level
are expected to have less significant economic effects
and affect fewer people than even small changes in the
largest events (e.g. with a return period of 500 years).
For a number of European river basins, including the
Po, Duero, Garonne, Ebro, Loire, Rhine and Rhone, an
increase in extreme floods with a return period above
500 years is projected; this includes river basins such
as Guadiana and Narva, where the overall frequency of
flood events is projected to decline (Alfieri, Burek et al.,
2015). A follow-up study combined the results of this
flood hazard assessment with detailed exposure maps
to estimate the economic and health risks from river
floods in Europe. The results suggest that a high climate
change scenario could increase the socio-economic
impact of floods in Europe more than three-fold by
the end of the 21st century. The strongest increase in
flood risk is projected for Austria, Hungary, Slovakia
and Slovenia (Alfieri, Feyen et al., 2015). A combination
of different adaptation measures has been estimated
to reduce economic damage from (fluvial and coastal)
floods substantially by 67 to 99 % and reduce the
number of people flooded by 37 to 99 % for the
100‐year event (Mokrech et al., 2014).
142 Climate change, impacts and vulnerability in Europe 2016 | An indicator-based report