Appendix 1
Indicators for exposure
Average precipitation
“It is widely supposed that global
warming will lead to more evaporation and a higher intensity of water cycling. A
warmer atmosphere is able to hold more water vapour and has a higher energy
potential, implying that the intensity and frequency of extreme rainfall events will
increase. In the south, the annual rainfall is generally decreasing, there is a higher
risk of longer dry spells and arid and semi-arid areas are expanding.” (JRC, 2008)
Lack of changes in average precipitation trend might mask changes in the extremes,
e.g., increase in both extreme rain and drought events and in changes of seasonality
(timing). Therefore the indicator Average precipitation always has to be examined
together with the indicators extreme high and low precipitation and seasonality
(timing) of precipitation.
Justification of indicator selection and policy relevance:
Precipitation is a key variable in the hydrological cycle. Long term
precipitation decrease will lead to water scarcity and will thus have negative impact
on all sectors. Long term precipitation increase may result in more frequent and
extreme flooding. Therefore all sectors will be affected.
Sectors affected:
Scenarios: B1,
B2, A1B, A2
Current situation: “While
the number of wet days is decreasing over much of Europe, the
average precipitation intensity on these days is generally increasing, with the
exception of some local areas in Spain. This implies that in many regions – the British
Islands, France, the Balkan – rainfall events become less frequent, but more intense.
In some of these areas this higher intensity compensates for the decrease in the
number of rain days, resulting in little change in the annual rainfall amount. Only in
Northern Europe both the precipitation frequency and intensity are rising, which
explains the strong increase of the annual precipitation amount in this region.” (JRC,
2008)
“The changes in precipitation are very different between
southern and northern Europe. In the south, the annual rainfall is generally
decreasing, there is a higher risk of longer dry spells, the differences between the
years are getting larger, and arid and semi-arid areas are expanding. In northern
Europe, on the other hand, the precipitation amounts are generally increasing,
particularly in winter. In between is a broad region where, on an annual basis, the
changes are fairly small, but where the differences between the seasons are more
pronounced: winter and spring are getting wetter, while summer and, to a lesser
extent, autumn are getting drier.” (JRC, 2008) (see Figure 1)
Effect of climate change:
1
Figure 1 . Change in average precipitation in the HIRHAM A2 scenario run compared to the control run for (a) nonfrost and (b) frost
seasons. Changes represent the average change over the entire upstream area rather than at the location itself, source Christensen and
Christensen, 2007
Threshold: Local
Uncertainty:
Low
Precipitation timing (seasonality)
Climate change can cause changes in
the amount and timing of seasonal precipitation. Such changes may have even more
negative impact on the crop productivity than decrease in annual average.
Justification of indicator selection and policy relevance:
Scenarios: B2,
A1B, A2
Effect of climate change: “These
changes are, however, not the same in every season: in
winter, the precipitation amount shows a strong increase (+21% on average) over
most of Europe, except for the very south; in summer, the rainfall is projected to
decrease almost everywhere except for the northeast (–11% over all of Europe).”
(JRC, 2008) (see also Figure 2)
2
Figure 2: Projected changes in seasonal precipitation (%) under the A1B scenario, multi-model ensemble mean of RCM
simulations for the time period 2071–2100 relative to 1961–1990 seasonal means. Top left panel is Dec Jan Feb, top right is
Mar Apr May, bottom left is Jun Jul Aug, bottom right is Sep Oct Nov , source ENSEMBLES project
Threshold: Local
Uncertainty:
Low
Changes in magnitude of high precipitation
Justification of indicator selection and policy relevance: Increase
in precipitation intensity might
lead to flooding and water logging. Changes in precipitation patterns modify also the
distribution of water at the land surface, and consequently influences river flow.
Scenarios: B2,
A1B, A2
“On rain days the intensity and variability of the precipitation
shows a general increase, even in areas that are getting much drier on average.
What is more, the rise in the precipitation extremes tends to be stronger than in the
average intensity. Considerably increases in extreme multiday precipitation amounts
may be very local, but occur almost everywhere across Europe and in every season,
except for summer in southern and western Europe.
Considerable increases in the 20-year return level in the scenario period for 1-day
and 5-day precipitation extremes are occurring in many areas across Europe, even in
areas that are getting much drier on average. The rise in the 1-day precipitation
extremes tends to be stronger than in the 5-day extreme. Averaged over Europe the
increases amount to +27% and +17%, respectively, but note the large differences
from place to place.” (JRC, 2008)
Effect of climate change:
Threshold: Local
Uncertainty:
Low
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Changes in return period (frequency) of high precipitation events
Justification of indicator selection and policy relevance: Changes
in return period of precipitation
events (precipitation with given intensity or/and duration) mean that given
precipitation events might take place more frequently in the future, for example
precipitation which took part once in 10 years might start to take part once in two
years, or the intensity in precipitation event, taking place for instance once in 10
years in future, might become higher. This implies that among others better drainage,
more structures that can hold excessive water and better flood defence will be
needed, when the intensity of the precipitation event, used for design purposes, will
increase in future.
Scenarios: A2
“The wet day frequency (the mean annual number of wet days,
defined as days with a total precipitation of 1 mm or more) shows a clear tendency to
diminish, not just in the Mediterranean but also over France and the British Islands.
Only in northern Europe the number of wet days becomes larger, but the increases
here are smaller than the decreases in the south.
The rise in the 1-day precipitation extremes tends to be stronger than in the 5-day
extreme. Averaged over Europe the increases amount to +27% and +17%,
respectively, but note the large differences from place to place.” (JRC, 2008)
Flash and urban floods, triggered by local intense precipitation events, are likely to be
more frequent throughout Europe. Flood hazard will also probably increase during
wetter and warmer winters, with more frequent rain and less frequent snow.
Effect of climate change:
Threshold: Local,
Uncertainty:
included into model calculations
High
Changes in severity of low precipitation
Justification of indicator selection and policy relevance: Low
or no precipitation in combination
with higher temperature leads to dry spells and meteorological drought. The
propagation of a precipitation deficit through the hydrological cycle results in
decrease in soil moisture; it may eventually lead to low river flows and hence to
‘‘streamflow droughts’’ and to decrease or no groundwater recharge. It should be
noted, that by contrast with the flood events, for drought the cumulative water deficit
and its duration are the most important variables for defining its severity.
Scenarios:
B2, A1B, A2
“In summer the average rainfall amount is projected to decrease
considerably over most of the continent and, in combination with higher temperatures
and hence evaporation rates, this may increase the risk of serious drought
problems in this season. This was assessed by calculating the potential precipitation
deficit, that is, the cumulative difference between precipitation and potential
Effect of climate change:
4
evapotranspiration1 during the summer months (April – September. The resulting plot
of the potential precipitation deficit is given in Figure 3. A large part of
Europe, with the exception of the north and the mountainous areas, builds up a
potential precipitation deficit during summer. In the scenario run, this area is
expanding to the north and the severity of the deficit increases, especially in the
south. This suggests a higher risk of water deficits and soil moisture stress in the
future over most of Europe, except for the northern half of Scandinavia.” (JRC, 2008)
Figure 3: Potential cumulative precipitation deficit in summer in HIRHAM a) control run
(1961-1990) and b) relative change in the scenario run (2071-2100), source JRC, 2008
Threshold: Local
Uncertainty:
Low
Changes in return period (frequency) of low precipitation events
Justification of indicator selection and policy relevance: As
it was discussed earlier for high
precipitation events, changes in the return period of low precipitation events could
happen via increase in the frequency of these events or in increase of intensity of low
precipitation events with certain return period. Changes in the return period could
require deployment of extra water reserves.
Scenarios: A2
1 The potential evapotranspiration (or evaporative demand) is defined as the evaporation rate from a hypothetical reference vegetation with
specific characteristics and an unlimited availability of water, and is a measure of the amount of energy available for evaporation.
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Effect of climate change: “While
the average precipitation intensity is generally increasing,
the frequency of wet days is decreasing in many parts of Europe, especially in the
south. As a consequence, the risk of dry spells increases in these areas as well. This
is illustrated in Figure 4 by means of the annual longest period of consecutive dry
days, that is, with a precipitation amount of less than 1 mm. Clearly, the longest dry
spells occur mostly in the Mediterranean areas, especially in southern Spain and
Portugal. The scenario period shows a general tendency towards longer dry periods,
with the exception of central Europe and Northern Italy where a slight decrease is
simulated. The largest increases occur again in Southern Europe, meaning that those
regions that are already experiencing dry conditions face the risk of extended dry
spells.” (JRC, 2008)
Figure 4: Mean annual longest period of consecutive dry days in HIRHAM a) control run
(1961-1990) and b) relative change in the scenario run (2071-2100), source JRC, 2008
Threshold: Local
Uncertainty:
High
Average river flow
The justification of the indicator selection and policy relevance for river flow related indicators are the same
as the corresponding indicators for precipitation and therefore they will not be repeated.
Scenarios: A2
Current situation: “In
northern Europe, mean annual river flow has in general increased,
in southern Europe it is slightly decreasing, while in western and central Europe no
changes are registered over the 20th century. In mountainous regions of central
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Europe, however, the main identified trends are an increase in annual river flow due
to increases in winter, spring and autumn river flow. Although there are some
measurable climate signals, the large part of the changes could be ascribed to
anthropogenic interventions. “(EEA, 2008)
Effect of climate change: “Annual
river flow is projected to decrease in southern and southeastern Europe and increase in northern and north-eastern Europe” (EEA, 2008).
(see Figure 5)
Figure 5 Projected change in mean seasonal and annual river flow between 2071–2100 and the reference period 1961–1990 Simulations
with LISFLOOD driven by HIRHAM — HadAM3H/HadCM3 based on IPCC SRES scenario A2, source: Dankers and Feyen, 2008
Threshold: Local
Uncertainty:
Low
Seasonal river flow
Effect of climate change: “Strong
changes are also projected in the seasonality of river
flows, with large differences across Europe. Winter and spring river flows are
projected to increase in most parts of Europe, except for the most southern and south
eastern regions. In summer and autumn, river flows are projected to decrease in
most of Europe, except for northern and north-eastern regions where autumn flows
are projected to increase. In snow-dominated regions, such as the Alps, Scandinavia
and the Baltic, the fall in winter retention as snow, earlier snowmelt and reduced
summer precipitation will reduce river flows in summer, when demand is typically
highest.” (EEA, 2008) (see Figure 5)
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Threshold: Local
Uncertainty:
Low
Changes in magnitude and return periods of high river flow
Scenarios: A2
Effect of climate change: “Although
there is as yet no proof that the extreme flood events
of recent years are a direct consequence of climate change, they may give an
indication of what can be expected: the frequency and intensity of floods in large
parts of Europe is projected to increase. Flood hazard will also probably increase
during wetter and warmer winters, with more frequent rain and less frequent
snow (Palmer and Räisänen, 2002). Even in regions where mean river flows will drop
significantly, as in the Iberian Peninsula, the projected increase in precipitation
intensity and variability may cause more floods. In snow‑ dominated regions such as
the Alps, the Carpathian Mountains and northern parts of Europe, spring snowmelt
floods are projected to decrease due to a shorter snow season and less snow
accumulation in warmer winters.” (EEA, 2008) (see Figure 6)
Figure 6 Projected change in 100-year return level of river discharge between 2071–2100 and the reference period 1961–1990, simulations
with LISFLOOD driven by HIRHAM — HadAM3H/HadCM3 based on IPCC SRES scenario A2, source: Dankers and Feyen, 2008
Threshold: Local
Uncertainty:
Low
Changes in magnitude and return period of low river flow
Scenarios: A2
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Effect of climate change Feyen
and Dankers (2009) stimulated the changes in 7-day
minimum flows with return periods of 2 and 20 years in both the nonfrost and frost
season. Thy find: “a decrease in minimum flows (indicated in red) means that low
flows are getting lower, while an increase (indicated in blue) implies that streamflow
droughts are becoming less severe. In the nonfrost season (Figures 7a and 7b)
minimum flows are projected to decrease in most parts of Europe, except in the most
northern and in northeastern regions. In many regions, for example the Iberian
Peninsula, southern France and the Alpine region, reductions of 20 up to 40% are
projected... In many regions of Europe the reductions in minimum flows are projected
to be relatively less severe at larger recurrence intervals than for those with shorter
return periods. This can be seen, for example, in the British Isles, the Benelux,
Germany, France, northern Italy and eastern parts of Europe. … The fact that in
these regions minimum flows with lower recurrence intervals are more affected by
climate change than those with higher recurrence intervals can be explained by the
projected changes in precipitation. In these regions, precipitation is projected to
reduce strongly in summer and to a lesser extent also in autumn, while increasing
strongly in winter and slightly in spring [see Dankers and Feyen, 2008]. Minimum
flows in these regions generally occur in summer or autumn and at lower recurrence
intervals they reflect the strong reduction in summer and autumn precipitation. More
severe streamflow droughts, i.e., with a higher recurrence interval, typically result
from precipitation deficits over longer periods (not only summer and autumn season).
Over such a long period of time, the strong reduction in summer and autumn
precipitation may be partly offset by higher subsurface storages at the beginning of
the summer season due to increased winter and spring precipitation. As such, the
change in minimum flows for higher recurrence intervals more closely follows the
average change in precipitation over the nonfrost season which, especially in areas
without or with a short frost season, reflects the change in average annual
precipitation.”
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Figure 7 Change in the estimated minimum flow in the scenario run relative to the control run for recurrence intervals of (a and c) 2 and (b
and d) 20 years for nonfrost and frost seasons, source Feyen and Dankers, 2009
Threshold: Local
Uncertainty:
High
Integrated index for heat wave, high precipitation and dry spells
Justification of indicator selection and policy relevance: There
are areas in EU, which suffer
simultaneously from droughts and flooding. Global warming may change the
vulnerability of European areas to this combined water-related hazard. Policy makers
in such areas has to plan for adaptation measures for both droughts and flooding.
How is this indicator constructed: JRC(2008) developed
this indicator, using the following
approach: In order to integrate hazards from indicators of extreme events, changes in
the Heat Wave Duration Index (HWDI) (increase of more than 5 events in areas of
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mean daily temperatures of more than 20ºC), the mean annual maximum amount of
precipitation in 5 consecutive days (increase of 10%) and the mean annual longest
period of consecutive dry days (increase of 5 days) were combined. The resulting
hazard map of these climate extremes is given in Figure 8.
Figure 8: Combined hazard map from heat wave, high precipitation and dry spells, source
JRC 2008
Scenario: A2
Effect of climate change: “Up
to a latitude of about 45ºN an extension of periods of dry
spell is prevalent. At latitudes between 45º and 52ºN a marked increase of heat
waves is projected fro the European mainland. Above this band, extremes of
abundant precipitation pose the main hazard. An increase in the variability of
precipitation is indicated mainly for eastern Greece and Bulgaria, where the
precipitation intensity increases but also the duration of dry periods.” (JRC, 2008)
Soil Moisture
Soil moisture forms a major buffer
against flooding, and water capacity in subsoil is a major steering factor for plant
growth. The effects of changes in soil water retention depend on the proportions of
the textural components and the amount of organic carbon present in the soil. (Jones
et al, 2009)
Soil is a key part of the hydrological cycle. Maintaining and enhancing the water
retention capacity of soils is of great importance for mitigating the impacts of more
extreme rainfall intensity and more frequent and severe droughts. Soil water that is
Justification of indicator selection and policy relevance:
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not retained or used by plants may contribute to the groundwater recharge or to
surface flow. Improving soil organic matter and soil texture through measures such
as organic agriculture, no tillage practices and mulching is therefore one of the most
important win-win adaptation measures.
Current situation: The
soils in whole Southern Europe, parts of Western and Central
Europe and even part of Scandinavia have very dry soils (see Figure 9 )
Figure 9 Left: example of a forecast of topsoil moisture (15 July, 2008), right: subsoil available water capacity
derived from modelling data, sources: European Soil Data Centre (ESDAC),
http://eusoils.jrc.ec.europa.eu/library/esdac/index.html (left); and European Flood Alert System (EFAS)
http://efas.jrc.ec.europa.eu/ (right)
Available scenarios: A2
Effect of climate change: “Projections
(for 2070–2100) show a general reduction in
summer soil moisture over most of Europe, significant reductions in the
Mediterranean region, and increases in the north-eastern part of Europe. “(Jones et
al., 2009)
Threshold: Local,
Uncertainty:
depend on land cover and use.
High
Figure 10 Simulated soil moisture by ECHAM5/T106L31 for the baseline period (1961–1990) (left) and relative changes in
% under the IPCC A2 scenario (2070–2100) (right), source: Calanca et al., 2006
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