Climate change impacts and vulnerability in Europe 2016

Climate change impacts on environmental systems
Map 4.10
Model-based estimate of past change in summer low flow
-30°
-20°
-10°
0°
10°
20°
30°
40°
50°
60°
70°
Model-based estimate of past
change in summer low flow
< 75 % of models agree
on sign of trend
Percentage
100
60°
80
60
50°
40
20
0
50°
– 20
– 40
– 60
40°
– 80
– 100
Outside model coverage
40°
Outside coverage
0 500 1000 1500 km
0°
10°
20°
30°
40°
Note:
This map shows the ensemble mean trend in summer low flow from 1963 to 2000. 'x' denotes grid cells where less than three-quarters
of the hydrological models agree on the direction of the trend.
Source: Adapted from Stahl et al., 2012.
Projections
An assessment of European meteorological droughts
based on different drought indices and an ensemble
of RCMs has projected drier conditions for southern
Europe for the mid-21st century, with increases in the
length, magnitude and area of drought events (van
der Linden and Mitchell, 2009). In contrast, drought
occurrence was projected to decrease in northern
Europe (Henrich and Gobiet, 2011). Similar results were
obtained in later studies based on different indices and
climate projections (e.g. Orlowsky and Seneviratne,
2013; Giorgi et al., 2014; Spinoni, Naumann, and Vogt,
2015; Touma et al., 2015).
A model ensemble from the EURO-CORDEX community
projects that the frequency and duration of extreme
meteorological droughts (defined as having a value
below – 2 of the SPI-6) will significantly increase in the
future (Stagge et al., 2015). These projections showed
the largest increases in frequency for extreme droughts
in parts of the Iberian Peninsula, southern Italy and
the eastern Mediterranean, especially at the end of the
century with respect to the baseline period 1971–2000
(Map 4.11). The changes are most pronounced for
the RCP8.5 high emissions scenario and slightly less
extreme for the moderate (RCP4.5) scenario.
Drought projections that also consider potential
evapotranspiration (e.g. based on the SPEI, the
Standardized Runoff Index (SRI) or the Supply–Demand
Drought Index (SDDI)) showed substantially greater
increases in the areas affected by drought than those
based on the precipitation-based SPI alone. For
example, the fraction of the Mediterranean region
under drought was projected to increase by 10 % by
the end of the 21st century based on RCP8.5 using the
SPI, whereas an increase of 60 % was projected using
the SPEI (Touma et al., 2015).
The projected increases in droughts in large parts of
southern Europe would increase competition between
different water users, such as agriculture, industry,
tourism and households (see also Section 5.3.5).
146 Climate change, impacts and vulnerability in Europe 2016 | An indicator-based report