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This paper studies climatic drivers (air and water temperature, precipitation rates, river discharge, sea level and storm patterns) in four Mediterranean regions: the Catalan-Valencia Coast (Spain), the Oran (Algeria) and Gabès (Tunisia) Gulfs and the western Nile Delta (Egypt). The paper also considers the potential hazards that these drivers can induce. It first analyses climatic trends in the drivers, taking into account the available time series of recorded and simulated meteo-oceanographic data from different sources. Next, it presents the general framework to assess biogeophysical hazards (flooding, erosion, droughts and water quality), followed by a simple and yet robust evaluation of those hazards for the four studied coastal sites. Assuming climate change projections under different scenarios and considering the observed trends in drivers, the resulting erosion rates due to sea-level rise and wave storm effects have been estimated. The Nile and Ebro Deltas, together with the Oran Gulf, are more vulnerable than the Gulfs of Valencia and Gabès. Regarding water quality in terms of (a) precipitation and dissolved oxygen in the water column and (b) sea surface temperature, the results show that the most vulnerable zones for the projected conditions (a) are the Gulfs of Oran, Valencia and Gabès, while the Nile Delta is the region where the decrease in water quality will be less pronounced. For the projected conditions (b), the most vulnerable zone is the Ebro Delta, while the impact in the other three cases will be smaller and of comparable magnitude. Finally, the overall future impact of these hazards (associated to climatic change) in the four sites is discussed in comparative terms, deriving some conclusions. KeywordsMediterranean–Coastal hazards–Climatic drivers–Erosion–Flooding–Water quality
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ORIGINAL ARTICLE
Climatic drivers of potential hazards in Mediterranean coasts
Agustı
´nSa
´nchez-Arcilla Cesar Mo
¨sso
Joan Pau Sierra Marc Mestres Ali Harzallah
Mohamed Senouci Mohamed El Raey
Received: 10 March 2010 / Accepted: 27 November 2010 / Published online: 17 December 2010
ÓSpringer-Verlag 2010
Abstract This paper studies climatic drivers (air and
water temperature, precipitation rates, river discharge, sea
level and storm patterns) in four Mediterranean regions: the
Catalan-Valencia Coast (Spain), the Oran (Algeria) and
Gabe
`s (Tunisia) Gulfs and the western Nile Delta (Egypt).
The paper also considers the potential hazards that these
drivers can induce. It first analyses climatic trends in the
drivers, taking into account the available time series of
recorded and simulated meteo-oceanographic data from
different sources. Next, it presents the general framework
to assess biogeophysical hazards (flooding, erosion,
droughts and water quality), followed by a simple and yet
robust evaluation of those hazards for the four studied
coastal sites. Assuming climate change projections under
different scenarios and considering the observed trends in
drivers, the resulting erosion rates due to sea-level rise and
wave storm effects have been estimated. The Nile and Ebro
Deltas, together with the Oran Gulf, are more vulnerable
than the Gulfs of Valencia and Gabe
`s. Regarding water
quality in terms of (a) precipitation and dissolved oxygen
in the water column and (b) sea surface temperature, the
results show that the most vulnerable zones for the pro-
jected conditions (a) are the Gulfs of Oran, Valencia and
Gabe
`s, while the Nile Delta is the region where the
decrease in water quality will be less pronounced. For the
projected conditions (b), the most vulnerable zone is
the Ebro Delta, while the impact in the other three cases
will be smaller and of comparable magnitude. Finally, the
overall future impact of these hazards (associated to cli-
matic change) in the four sites is discussed in comparative
terms, deriving some conclusions.
Keywords Mediterranean Coastal hazards Climatic
drivers Erosion Flooding Water quality
Introduction
During this century, society will increasingly be confronted
with impacts of global change, such as pollution and land
uses (Metzeger and Schro
¨ter 2006). A ‘‘robust’’ illustration
for the driving climatic terms is provided by the global
average surface temperature, projected to increase by
1.1–6.4°C by 2100 (Bates et al. 2008).
There is a general agreement that impacts of climate
change are more likely to result from altered climate
A. Sa
´nchez-Arcilla (&)C. Mo
¨sso J. P. Sierra M. Mestres
Laboratori d’Enginyeria Marı
´tima, Universitat Polite
`cnica de
Catalunya, Jordi Girona 1–3, Edifici D1 Campus Nord, 08034
Barcelona, Spain
e-mail: agustin.arcilla@upc.edu
A. Sa
´nchez-Arcilla C. Mo
¨sso J. P. Sierra M. Mestres
Centre Internacional d’Investigacio
´dels Recursos Costaners,
Jordi Girona 1–3, Edifici D1 Campus Nord,
08034 Barcelona, Spain
A. Harzallah
Institut National des Sciences et Technologies de la Mer, 28,
rue du 2 mars 1934, 2025 Salammbo, Tunisia
e-mail: ali.harzallah@instm.rnrt.tn
M. Senouci
Membre du Groupe Intergouvernemental sur l’Evolution du
Climat (IPCC), Association de Recherche Climat
Environnement, ARCE, BP 4250, Ibn Rochd,
31037 Oran, Algeria
e-mail: msenouci@wissal.dz
M. El Raey
Alexandria University, Arab Academy of Science and
Technology and Maritime Transport, El-Guish Road, El-Shatby,
Alexandria 21526, Egypt
e-mail: melraey@gmail.com
123
Reg Environ Change (2011) 11:617–636
DOI 10.1007/s10113-010-0193-6
variability and extremes than from changes in mean trends
(Goubanova and Li 2007). Any intensification and/or
increase in the number of extreme events are likely to have
disastrous socioeconomic implications on developed and
developing countries (Changnon 2003). Indeed, global
climate modelling experiments suggest that climate
extremes may become more severe under increased
greenhouse concentrations in most regions of the globe
(Kharim and Zwiers 2000; Voss et al. 2002).
It is also expected that global warming will aggravate
disease and pest transmission. Stronger or more frequent
extremes (storms, floods, etc.) associated with climate
change would cause physical damage, population dis-
placement and adverse effects on food production, fresh-
water availability and quality. The combination of these
elements would also increase the risks of infectious and
vector-borne diseases, particularly in developing countries
such as those of the southern Mediterranean shores (Moreno
2006). Primary sectors, such as agriculture and forestry,
will be more sensitive to climate change than secondary
and tertiary sectors, such as manufacturing and retailing.
Nevertheless, some tertiary sectors can also be affected.
For example, climate is a crucial resource for tourism, so
climate variations would have a profound impact on tourism
producing shifts in the pattern of demand (Hamilton and Tol
2007), with direct implications on tourist areas such as
Mediterranean shores.
Climate change also has the potential to significantly
alter the conditions for crop production due to changes in
the precipitation regime that would affect the yield distri-
bution considerably (Torriani et al. 2007). Climate change
is expected to have positive impacts only in northern
countries, implying that areas of crop suitability may
expand northwards (Olesen et al. 2007). Southern areas
(such as Mediterranean coastal countries) will probably
have to face increasing water shortage and incidence of
extreme adverse events, reducing crop yields and the area
for cropping. Moreover, the higher temperatures are likely
to increase crop water requirements and more irrigation
water will be needed per hectare (Rodrı
´guez-Dı
´az et al.
2007). Different studies on the impacts of climate change
on crop yields have been performed at different levels
(Iglesias et al. 2000; Saarikko 2000; Chen et al. 2004; Parry
et al. 2004; Trnka et al. 2004; Reidsma et al. 2009), but the
overall conclusion does not vary with scale, although there
is a sharp spatial variability across the Mediterranean basin.
Low-lying coastal regions, such as deltas or bays, are
subject to a series of driving factors that dynamically
interact with the active (as a function of the considered
time-scale) geo and ecosystems. These areas are specially
sensitive to changes in climatic drivers. In particular, del-
taic systems show the consequences of many kinds of
human-induced changes such as variations in river liquid
discharge (flow regulation) or in river solid discharge
(erosion control in the catchment basin or barrier effect of
dams). Affected by changes in relative sea-level rise (SLR)
and in atmospheric and marine factors (precipitation, wind,
storminess), deltaic systems are, thus, highly sensitive
ecosystems subject to the interactions of river, sea, land
and atmospheric factors (Sa
´nchez-Arcilla and Jime
´nez
1997). Coastal bays are also influenced by meteo-oceano-
graphic factors as well as natural or man-made boundaries,
which can act as a barrier constraining water circulation
and, thus, affecting water quality (Sa
´nchez-Arcilla et al.
2007). The associated changes in land use have become a
major driver and indicator of environmental change. This
can be illustrated by conflicts between past and present
land uses or between economic and ecologic priorities (Hill
et al. 2008) and also by the large areas of the European
Mediterranean that are affected by land degradation or
desertification.
In coastal zones, flooding occurs due to storm surges
generated by meteorological forcing, mainly due to the
tangential surface wind stress on the ocean surface and the
atmospheric pressure gradients associated with the weather
systems (Kurian et al. 2009). This, combined with
anthropogenic global warming, is expected to contribute to
an increase in flooding frequencies during this century and
beyond. Sea-level rise will increase the vulnerability of
coastal populations and ecosystems, via permanent inun-
dation of low-lying regions, inland extension of episodic
flooding, increased beach erosion and saline intrusion of
aquifers (Cooper et al. 2008). Finally, wind waves are
another component of Mediterranean coastal systems, and
changes in their characteristics can have important conse-
quences on off-shore activities such as ship traffic and,
even more critical, on coastal uses and resources (Lionello
et al. 2008a).
In this paper, the main climatic drivers affecting coastal
areas in the Mediterranean basin and their potential hazards
have been analysed. The study focuses on four areas of the
Mediterranean region, which represent a variety of features
and coastal environments that can be found in this region.
The diversity of environments is also reflected in the
available data sets, limited in time, restricted in spatial
coverage and showing important gaps that shall be high-
lighted in the paper.
Study area
The aim of this work is to characterize drivers and hazards
for typical Mediterranean conditions. Because of that, four
areas (representative of the Mediterranean coastal envi-
ronment and particularly sensitive to climate change) have
been selected. They all fulfil some minimum requirements
618 A. Sa
´nchez-Arcilla et al.
123
for observational evidence to allow performing an initial
analysis at climatic scales. The four areas in a west-east
direction are as follows: the Spanish NW Mediterranean
Coast (Spain), the Gulf of Oran (Algeria), the Gulf of
Gabe
`s (Tunisia) and the Alexandria and West Nile Delta
area (Egypt). Their locations are shown in Fig. 1.
The four cases present a typical Mediterranean climate,
but each area has some distinctive features. The studied
part of the Spanish Coast, in the north-western Mediterra-
nean, is located in front of the Balearic Islands, stretching
from the Creus Cape in the north to La Nao Cape in the
south, with a coastal length of about 750 km. Its location,
together with the local topography, exert a significant
control over the wind climate, which is characterized by
low to medium average winds, although some synoptic
events are responsible for strong winds in this region
(Sa
´nchez-Arcilla et al. 2008a). Moreover, this area also
presents some special features that determine the wave
climate, being the most important the short fetches (due to
the presence of the Balearic Islands), the high wind vari-
ability in time and space (Mo
¨sso et al. 2007) and the wave
calms during the summer and energetic storms from
October to May. This wave climate has a very defined
seasonal structure with yearly averaged significant wave
heights lower than 1 m (Garcia et al. 1993; Sierra et al.
2002). As a result of the oblique wave approach for the
more energetic E-NE storms, long shore sediment transport
shows a net S-SW component (Sa
´nchez-Arcilla et al.
2005).
As most of the Mediterranean coast, this is a microtidal
environment and, according to different tide gauges located
in the area, the maximum spring tide range observed is of
about 40 cm. Storm surges are also common, with inten-
sities up to 1.0 m for typical storm conditions (Sa
´nchez-
Arcilla et al. 2008b). In some areas, there is also subsi-
dence, as for instance in the Ebro Delta, where the average
rate is between 1.5 and 3.0 mm per year (Sa
´nchez-Arcilla
et al. 1996; Somoza et al. 1998).
The second analysed case, the Gulf of Oran, located in
western Algeria, is delimited by the Aiguille Cape in the
east and the Falcon Cape in the west, and it is about 50 km
wide. This gulf encompasses, in its western part, from the
port of Oran to the Mers El Kebir, and it is characterized by
high and escarped cliffs, going from 10 to almost 30 m in
height. In the eastern part, the coast presents smaller cliffs,
interrupted by small and narrow beaches.
This area has a semi-arid Mediterranean climate, with
mild and wet winters and hot and dry summers. The
average rainfall is of about 390 mm/year (varying from
2 mm in July to 120 mm in December). This sunny region,
with more than 3,300 h of sunshine per year, has monthly
average temperatures ranging from 12°C in January to
29°C in August (Chegaar and Chibani 2001). The wind
regime features 6% of calm periods and an average wind
velocity of 3.6 m/s (Merzouk 2000), with monthly average
wind speeds between 3 m/s (December) and 4.6 m/s
(April) (Mahmoudi et al. 2009).
Due to the prevailing currents in the area, the Gulf of
Oran receives waters of Atlantic origin (Millot 1987). The
circulation seems to be turbulent along the Algerian Coast,
and these turbulences favour the dispersion of eventual
pollution sources and allow a relative important primary
productivity (Millot et al. 1997).
The third studied zone, the Gulf of Gabe
`s, is a shallow
eastward-facing embayment area located in the Tunisia
Coast. It is 100 km long and 100 km wide, with depths
typically ranging from 20 to 50 m (Sammari et al. 2006). It
is bordered by a subdued topography formed mainly by
low plateaus (20–70 m) and plains (1–5 m), and it is
characterized by an arid Mediterranean climate, with an
average rainfall varying from 250 mm/year in the north to
100–150 mm/year in the south, although the rainfall rate is
highly irregular (Oueslati 1992).
The Gulf of Gabe
`s is one of the few Mediterranean
regions where astronomic tides are relatively important,
with a semi-diurnal pattern and spring tidal range of
Fig. 1 The Mediterranean
basin showing the four case
studies selected for this work
Climatic drivers of potential hazards in Mediterranean coasts 619
123
2.0–2.3 m (Morhange and Pirazzoli 2005). This is because
of resonance phenomena in the area which act to amplify
tidal levels (Sammari et al. 2006). On the other hand, wave
storms in the Gulf of Gabe
`s are generally low energy
events, because of the shallowness of the broad continental
shelf and the important meadows of phanerogams. The
wave energy is also bounded by the low wind velocities
and, in some positions, the limited fetch (Oueslati 1992),
which restricts the effect of the stronger easterly winds.
This area is also characterized by weak currents, with high
temperature (13.2–26.5°C) and high salinity in summer
(37.5–39.25%) (Pe
´rez-Domingo et al. 2008), although
lower salinities (37.3–37.5%) have been detected in the
region in other seasons and have been attributed to the
presence of Modified Atlantic Water (Be
´ranger et al. 2004;
Pelegrı
´et al. 2005; Poulain and Zambianchi 2007; Drira
et al. 2008; Bel Hassen et al. 2009).
In the last years, this area has suffered high anthropic
pressures due to urban and industrial activities (Drira et al.
2008), experiencing a substantial proliferation of microal-
gae and, particularly, toxic dinoflagellates (Turki et al.
2006). As a consequence, fish resources in the Gulf of
Gabe
`s (which represent 65% of the national fish production
in Tunisia) have declined, associated to the degradation of
seagrass meadows.
Finally, the fourth studied environment, the West Nile
Delta, is located in Egypt, in the eastern Mediterranean and
at the mouth of one of the world’s longest rivers
(6,690 km). The annual average water discharge averaged
84 billion m
3
during the twentieth century. More than 80%
of the Nile River total discharge occurs from August to
October, while about 20% is distributed during the
remaining 9 months (Stanley and Warne 1998).
This delta is located in a hyperarid region, with tempera-
tures over 30°C in July and mean annual precipitation
ranging from 100 to 200 mm. The deltaic plain encom-
passes about 22,000 km
2
, and its coast is about 225 km
long. It is characterized by a very low tidal range (spring
tides average 30–40 cm), N-NW offshore winds that are
active during most of the year, and a large-scale counter-
clockwise circulation pattern that drives water masses
eastward. The offshore surface (geostrophic) eddy veloci-
ties can exceed 0.25 m/s (Stanley and Warne 1998). Pre-
dominant waves feature an oblique approach, generating
longshore currents with velocities from 20 to 50 cm/s and
occasionally exceeding 100 cm/s. Storm waves with heights
of 1.5–3 m approach the coast from the northern quadrant
(commonly from the north-west), eroding and displacing
sediment eastwards (Stanley 1989; Stanley et al. 1998).
The Nile Delta is also experiencing relative sea-level
rise due to land subsidence. In the northern delta, this
happens at a rate between 1 and 5 mm per year (Emery
et al. 1988; Stanley 1988,1990; Stanley and Goodfriend
1997). Moreover, since the construction of the High Dam
at Aswan in 1964, less than 2% of sediment bypasses this
dam, and about 100 million tons of sediments per year
accumulate in the southern part of Lake Nasser reservoir.
As a consequence, less than 10% of the former Nile River
potential sediment load is now delivered to the Mediter-
ranean coast (Stanley and Warne 1998).
Drivers
General framework
One of the most robust indicators of climate change is air
temperature. Most of Europe has revealed increases in
surface air temperatures during the twentieth century. This
warming has been largest over north-western Russia and
the Iberian Peninsula (Nicholls et al. 1996), suggesting that
in Europe the balance (in terms of implications) of climate
change will be more negative in southern and eastern
countries (Maracchi et al. 2005).
In the last decades, extreme events registered in the
Mediterranean basin have shown an increase in heavy
precipitations and a raise of extreme temperatures (Sa
´nchez
et al. 2004; Giorgi et al. 2004). Present climate models
indicate a decrease in precipitation levels during the
twenty-first century (Gibelin and De
´que
´2003), mainly
during the summer months (Rowell 2005), with the central
and south Mediterranean being one of the regions most
affected by the precipitation decrease. This will exacerbate
drought episodes, land degradation and desertification,
particularly for the East-Mediterranean (Ko
¨rner et al. 2005;
Vicente-Serrano 2007). A pronounced warming is also
projected, being maximum in the summer season with a
greater occurrence of high temperature events (Giorgi and
Lionello 2008).
Global low-frequency sea-level trends are dominated by
the steric component, and the associated ocean volume
increase (Levitius et al. 2000; Calafat and Gomis 2009).
However, at a regional scale, atmospheric pressure and
wind effects can also play a key role (e.g. Gomis et al.
2008) such as it happens for the Mediterranean region.
Wind-generated waves are the more energetic driving
term among all meteo-oceanographic factors, given the
limited tidal range in the Mediterranean. The available
observational series span less than three decades, which
suggests the use of numerically generated series. However,
the hindcast fields should be used with care since the
accuracy of predicted waves is significantly smaller than
for open sea conditions (Be
´ranger et al. 2004; Cavaleri and
Bertotti 2006).
Some analyses suggest a milder future wave storm cli-
mate, being the significant wave height reduction linked to
620 A. Sa
´nchez-Arcilla et al.
123
the diminished ocean surface winds and storm activity. A
reduction in low-pressure centre intensity is consistent with
the overall decrease in precipitation and northward dis-
placement of storm tracks, which most models indicate for
the Mediterranean area (Lionello et al. 2008a). Neverthe-
less, within the last decades, the NW Mediterranean has
experienced some of the most severe storm events ever
recorded in the area (Sa
´nchez-Arcilla et al. 2008a).
Sea level
Sea level rise is an important indicator of climate change,
with great relevance in squeezed coastal regions, such as
those of the Mediterranean, for flooding, coastal erosion
and the loss of low-lying areas. Relative sea-level rise
increases the likelihood of storm surges, enforces landward
intrusion of salt water and endangers coastal ecosystems
and wetlands. Apart from natural ecosystems, coastal areas
often feature important managed ecosystems, economic
sectors and major urban centres. Thus, a higher flood risk
increases the threat of loss of life and property as well as of
damage to protection measures and infrastructures. This, in
turn, should result in a degradation of coastal functions
such as recreation, transport.
A change in relative mean sea level (MSL) at the coast
may have various origins. It can be caused by the vertical
movement of the land itself. This applies to the Mediter-
ranean basin, which is located on the boundary of an active
geological plate, so that any global sea-level rise induced
by climate change may be locally accentuated or mini-
mized by tectonic movements. Relative MSL can also arise
from local sea-level changes due to variations in prevailing
winds and ocean currents or from by a change in the vol-
ume of the world’s oceans, mainly controlled by
temperature.
It is generally accepted that the global sea level has
increased between 10 and 25 cm over the past 100 years
(e.g. Raper et al. 2001), and it is expected that the rise will
not only continue in the near future, but it will probably
also accelerate, although the range of predictions and
models is so large that precise forecasting is not possible.
Nicholls and Hoozemaans (1996) point out that the sea
level might rise between 0.2 and 0.9 m by the year 2100,
being the best estimates in the order of 0.5 m. In the past
100 years, European and global average sea level has risen
by 10–20 cm with a central value of 15 cm (IPCC 2001).
Currently, the sea level at Mediterranean coasts is rising at
a rate of 1.0 mm/year (Marseille), 1.3 mm/year (Genova or
Trieste), to 2.6 mm/year (Venice), which is close to the
global average (Liebsch et al. 2002). It is likely that the
observed trend in sea-level rise over the past 100 years is
mainly attributable to an increase in the volume of ocean
water as a consequence of global warming. The local
variations could be explained by some of the other pro-
cesses mentioned above. In what follows, we shall discuss
the trends in the Catalan (Spain) Coast and Gabe
`s Gulf.
There is no conclusive evidence for Oran and the case of
the Nile Delta will be discussed at the end of this section.
The relative sea level in the Spanish Mediterranean
Coast and Gulf of Gabe
`s do not present a common or well-
defined pattern. The available data in the Spanish Coast
case consist of hindcasted storm surge data (HIPOCAS)
from 1958 to 2001 (Ratsimandresy et al. 2008) and
observations of the residual tide within the ports of Bar-
celona and Valencia from 1992 to date. For the Gulf of
Gabe
`s case, there are only observed series since 1999.
For the Spanish coastal case, storm surge simulations
(Fig. 2a) suggest that the relative sea level is slightly
decreasing during the considered time span. The average
decrease in surge intensity is of about -0.54 m per decade.
The observations also suggest a fall in mean sea level of
-0.04 m per year, although the registered time series are
too short to allow any final conclusion. In both cases, it is
assumed that the land remains at a steady level since that is
the conclusion obtained from recent geological studies
(Somoza et al. 1998). The trend in mean sea level derived
from observations is, however, so small dependent on the
considered time-scale (due to the shortness of the series)
that the more robust conclusion is that it is almost steady.
In the case of the Gulf of Gabe
`s, the observed data,
provided by the Tunisia Hydrographic and Oceanographic
Center, suggest that the relative sea level is rising at a rate
of 2.6 cm per decade (Fig. 2b). These results are consistent
with altimetry data that show an increase in sea level of
2.1 cm per decade. Notably, for the Spanish case, if only
modelled data from 1992 to 2001 are considered (coin-
ciding temporarily with some of the observed data), they
suggest an increase in storm surge of 1.75 cm per decade.
This suggests an increase in mean sea level at both loca-
tions and illustrates the sensitivity of the relative sea-level
values to the selected time and space intervals.
Precipitation rates
Changes in average precipitation can have potentially far-
reaching impacts on ecosystems and biodiversity, agricul-
ture (food production), water resources and river flows.
Global climate model simulations indicate that there shall
be a decrease in yearly averaged values but that the return
period for heavy rainfall events may decrease (Lionello
et al. 2002). This change in precipitation patterns, associ-
ated to a decreasing mean and an increasing variance in the
corresponding probability function, should lead to an
intensification of flooding during the rainy period, parti-
cularly for low-lying coastal areas. This will be accompa-
nied by more frequent and severe drought periods, more
Climatic drivers of potential hazards in Mediterranean coasts 621
123
frequent land slides and increased soil erosion. Floods and
droughts can even occur in the same region in different
seasons of the same year (e.g. a region may be exposed to
drought in spring and summer and be flooded in autumn).
Brunet et al. (2007) have studied the changes in precipi-
tation extremes within Spain (from the beginning of the
twentieth century) indicating that there is a tendency
towards more intense rainy days and increases in heavy
precipitation during the twentieth century, a behaviour
consistent with a warmer planet.
Decreasing precipitation trends will mean reductions in
water quality and availability over the four regions.
Drought periods are likely to become more frequent as the
probability of dry days and the length of dry spells
increase. The more frequent extreme precipitation events
will intensify the hydrological cycle and the risk of extreme
flooding and erosion. Most scenarios suggest an increase in
the frequency of extreme events and, in particular, of
droughts and flooding in the western Mediterranean. The
potential coastal impact of modified precipitation rates is
largely associated to the supply of riverine sediment to
counter the enhanced land loss and erosion induced by the
sea-level rise and increased storminess. Therefore, and
taking into account that river sediment transport takes place
only when the river flow exceeds a given threshold, it is the
time distribution of extreme precipitation events that is of
interest, rather than a mean (e.g. yearly) precipitation trend.
Nevertheless, the real influence on the coast of larger
rainfall rates is limited due to the effective decoupling of
riverine systems from the coastal environment, because of
the intensive regulation of river flows by dams. In recent
works, it has been estimated that more than 90% of the
1958
1960
1962
1964
1966
1968
1970
1972
1974
1976
1978
1980
1982
1984
1986
1988
1990
1992
1994
1996
1998
2000
Year
-2
0
2
4
6
Annual Storm Surge (Hipocas Data) in cm
Mean Sea Level
Hipocas Data
Mean Sea Level Hipocas
Linear Trend from 1990-2001
Linear Trend from 1958-2001
1999 2000 2001 2002 2003 2004 2005 2006 2007 2008
Year
-10
-5
0
5
10
15
20
25
30
Monthly Storm Surge (Observed Data) in cm
Mean Sea Level
Observed Data
Sea Level Sfax
Linear Trend
(a)
(b)
Fig. 2 Storm surge at the Ebro
Coast in Spain (hindcasted data)
and at the Gabe
`s Gulf (observed
data). Considering the hindcast
time series (1954–2001), there
is a slight decreasing trend at
Ebro, while if we only look at
the last decade of data, there is
an increasing trend, consistent
with the observations of mean
sea level from Gabe
`s
622 A. Sa
´nchez-Arcilla et al.
123
sediment transported by, e.g., the Ebro River became
trapped in the numerous reservoirs built along its course.
The reduction is nearly complete for bed load (the only one
providing beach sized material) but is also affects sus-
pended and wash loads (Marin
˜o1992; Iba
´n
˜ez et al. 1996;
Jime
´nez 2005). The same applies to the Nile, as mentioned
in the previous section.
Precipitation data coverage in the Mediterranean is quite
heterogeneous, and the derived trends are uncertain,
because measurement techniques have changed during the
twentieth century. However, it is clear from the recorded
data that precipitation, in terms of standardized anomalies
(e.g. the case of the Catalan Coast), shows a large vari-
ability typical of the Mediterranean climate, preventing a
clear identification of sub-periods with differential beha-
viour (Fig. 3).
Precipitation patterns in the four studied sites (Fig. 3)
show the characteristic variability of the Mediterranean,
with negative or positive trends depending on location.
There are inverse trends between Barcelona and Ebro Delta
(200 km apart) in the Spanish case or between Gabe
`s and
Oran and important decadal shifts in the West Nile Delta.
Despite the great variability, any changes in precipitation
patterns will have a direct influence on the studied coasts.
Precipitation rates in the 4 cases show a large variance and
no significant commonalities. In the Spanish case, the
studied stations (Fabra in Barcelona from 1914 to 2008 and
Ebro Delta, from 1906 to 2008) show an opposite trend, the
yearly mean decreasing in Fabra and increasing in Ebro
Delta through the observed period, and without similarities
in the annual distribution of rainfall. Table 1summarizes
the different dry and wet periods recorded at the analysed
stations.
The registered series show some commonalities among
sites, such as the dry period around 1925 in the Catalan
Coast and Gulf of Gabe
`s or the rainy interval around
1970–1975 in the Catalan Coast, the Gulf of Oran and
Gabe
`s. There are no clear and statistically significant
trends, nor any common sustained patterns, for the 4
studied sites. Moreover, the Gabe
`s plot (where data pro-
vided by the Ministery of Agriculture and Water Resources
of Tunisia from other stations are included) illustrates the
high-level variability at a local scale (less that 200 km)
typical of Mediterranean shores.
Year
-2
-1
0
1
2
3
4
Precipitation Anomaly
Ebro Std Precip Anomal.
GaussianSmooth (3)
Ye a r
-2
-1
0
1
2
3
4
Precipitation Anomaly
Oran Std Precip Anomal.
GaussianSmooth (3)
Year
-2
-1
0
1
2
3
4
Precipitation Anomaly
Gabès Std Precip Anomal.
GaussianSmooth (3) Gabès
GaussianSmooth (3) Sfax
GaussianSmooth (3) Jerba
190519101915192019251930193519401945195019551960196519701975198019851990199520002005 1925 1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005
1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
Ye a r
-3
-2
-1
0
1
2
3
4
Precipitation Anomaly
West Nile Delta Std Precip Anomal.
GaussianSmooth (3)
(a)
(c)
(b)
(d)
Fig. 3 Precipitation rates, expressed as anomaly over standard
deviation, at the Spanish NW Mediterranean Coast (a), Gulf of Oran
(b), Gulf of Gabe
`s(c) and West Nile Delta (d). The Gulf of Gabe
`s
plot includes time series from www.tutiemp.net and from the Tuni-
sian Ministry of Agriculture and Water Resources, illustrating the
high level of local variability
Climatic drivers of potential hazards in Mediterranean coasts 623
123
This observational evidence agrees with predicted
regional changes (Lionello et al. 2008b), which suggest a
decrease in average precipitation together with an increase
in rainy events during fall/winter. These trends may be
different for the northern Mediterranean shore, particularly
in the region of Alpine influence, which may even expe-
rience an increase in precipitation.
Storms
Even assuming that the frequency and intensity of storms do
not vary due to climate change, the return period of extreme
water levels induced by storm surges at the coast will be
reduced because of relative sea-level rise (Sa
´nchez-Arcilla
et al. 2008b). This will eventually lead to a larger frequency
of flooding events in coastal low-lying areas. Particularly
vulnerable to this effect will be deltaic areas and coastal
lagoons (Sa
´nchez-Arcilla and Jime
´nez 1994), where the
combined effects of subsidence plus low topography will
induce flooding and enhanced erosion (Fig. 4).
Any variations in wave and storm characteristics will
play a critical role in determining the coastal impact of
climate change, since the present shoreline configuration is
in dynamic equilibrium with today’s meteo-oceanographic
patterns. Incident waves with larger average heights will
result in stronger longitudinal and return currents, which
will eventually lead to enhanced coastal sediment transport
and erosion rates. A further contribution to coastline ero-
sion can result from the increased frequency of moderate
storms, since the coast will not have enough recovering
time between storm events.
However, the exact response of the coast to these storms
depends not only on the energy of the event, but also on the
particular features of the storm, such as duration, wave
period or steepness (Sa
´nchez-Arcilla et al. 2008a). Related
flooding (due to storm surge and wave-breaking) is the
single most destructive type of natural disaster that strikes
humans and their livelihoods around the world (Ismail-
Zadeh and Takeuchi 2007), and this also holds true for
Mediterranean coasts.
The storms considered in this study have been defined
by two different criteria, in terms of meteorological con-
ditions for the Gulf of Oran and in terms of wave
conditions for the Spanish Mediterranean Coast (Bolan
˜os
et al. 2004). This provides the widest possible coverage of
meteo-oceanographic conditions for the available obser-
vations. The main result is the large variability, in time and
space, characteristic of Mediterranean conditions, which
are essentially torrential. The average number of observed
meteorological storms in the Gulf of Oran from 1950 to
2007 does not present significant changes throughout the
observation period, though there are more extremes since
1970. More specifically, autumn storms have increased
their frequency by about 10% since 1975. This increase is
related to recent floods in the north-western region of
Algeria.
Table 1 Summary of rainy and
drought periods in the four
study cases
Site Rainy period Drought period
Spanish Coast (Barcelona) (1970–1993) (1994–2008)
Spanish Coast (Ebro) (1936–1949) (1956–1976) (2001–2008) (1907–1932) (1976–2000)
Gabe
`s (1917–1922) (1948–1997) (1907–1916) (1923–1948)
(1998–2005)
Oran (1926–1926) (1948–1976) (1937–1947) (1997–2007)
West Nile Delta (1962–1969) (1988–2009) (1970–1987)
Fig. 4 Storm impact in the Ebro region and, in particular, in the
Trabucador Beach (top-left). Breaching after the impact of the
October 1990 storm (top-right). Breaching after the November 2001
storm (bottom)
624 A. Sa
´nchez-Arcilla et al.
123
In the Spanish case (Fig. 5), the annual number of
moderate and severe wave storms throughout the obser-
vation period (1990–2006) presents an opposite trend: a
decrease in the number of severe storms, while there is an
increase in the number of moderate storms.
Regarding the actual Hs magnitude, the observed data
series are too short (Fig. 6) to provide any definite con-
clusion. The hind-cast values, on the other hand, suggest an
increase at most stations, as illustrated in Fig. 6for the
Gabe
`s and Catalan Coasts. The Spanish data come from the
HIPOCAS project and have been supplied by Puertos del
Estado (Ministry of Public Works). The Tunisian data
come from the Direction Ge
´ne
´rale des services Aeriens et
Maritimes, Ministe
`re de l’Equipement et l’Habitat.
The average duration of the studied moderate storms is
fairly constant, while the corresponding value for severe
storms has shown an increasing trend during the last dec-
ade (Fig. 5). The directional distribution of incident waves
shows also large variations, as expected for the irregular
topo-bathymetric characteristics of Mediterranean coasts.
This is illustrated with data from the Spanish coast (Fig. 7).
In the sector around Barcelona, the more energetic waves
come from the East, corresponding to the longest fetch,
since this part of the coast is sheltered from Northern wave
components. The Ebro Delta Coast, in the middle of the
Spanish case, shows frequent wave events from the East
and North-West. The East corresponds to the same storms
as for the Barcelona sector, while the NW (Mistral) waves
are associated to winds from that direction blowing down
the valley of the Ebro River. The most southern Spanish
location (Cullera Bay) shows a predominance of NE waves
since this corresponds to the longest available fetch, with
other directional sectors being limited in occurrence and
energetic content, due to the coast orientation and the
presence of the Balearic Islands.
In the particular case of the Ebro region, eastern wave
storms tend to occur simultaneously with surged water
levels, related to the passage of low-pressure systems off
the delta (Sa
´nchez-Arcilla and Jime
´nez 1994; Jime
´nez
et al. 1997). In this case, the most important effects are
related to the inundation of agricultural zones plus the
affectation of natural values due to wave exposure and
flooding. All these effects result in a large ‘‘impulsive’
coastal erosion (see Fig. 4for a sample illustration).
Sea surface temperature
The oceans have a large capacity for storing and redis-
tributing heat. By storing heat, they delay global tempera-
ture increases, but this goes together with an increase in
evaporation and, thus, precipitation. Overall ocean tem-
peratures show a rising trend consistent with the observed
increase in air temperatures (Levitius et al. 2000). The
western Mediterranean and North Atlantic react in a
manner similar to that of global oceans. In the 1990s, these
seas warmed by about 0.5°C (Rixen et al. 2005; Vargas-
Ya
´n
˜ez et al. 2009).
More specifically, the annual mean, maximum and
minimum values of sea surface temperature (SST) show a
clear increasing trend (Fig. 8a). However, the intra-annual
viability is so pronounced that it tends to mask this longer
term trend, which is about 0.77°C/decade in the Ebro sta-
tion (Fig. 8b). The increasing trend of SST is linked to a
similar behaviour in air temperature evolution (Fig. 9a
for the Catalan Coast). This pattern is also observed
(Fig. 9b–d) for the rest of coastal sites. In particular, the
Year
10
15
20
25
30
35
duration of storms (hrs.)
Mean Duration of Storms
Hs=1.5
Sens Slope Hs=1.5
Hs=2.0
Sens Slope Hs=2.0
1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 200 6
Year
0
5
10
15
20
25
30
35
40
45
50
55
number of storms
Number of Storms
Hs=1.5
Linear Trend Hs=1.5
Hs=2.0
Linear Trend Hs=2.0
Fig. 5 Mean duration of moderate (above an Hs threshold of 1.5 m)
and severe (above an Hs threshold of 2.0 m) storms (left) and number
of occurrences (right) for the same two storm types. Both panels
correspond to the observed wave data series off the Ebro Delta, in the
Spanish NW Mediterranean coast
Climatic drivers of potential hazards in Mediterranean coasts 625
123
Gabe
`s mean-maximum temperature data from 1950 to
2005 (provided by the Tunisia National Meteorological
Centre) show a 0.29°C/decade increase with a clear
acceleration during the last 30 years. This means that,
although no instrumental records are available, there
should be a general SST increase in all coastal stations.
Among the extreme natural events that struck the Earth
and our coastal societies in recent times, some of the most
violent (e.g. hurricane Charley (category 4 on the Saffir-
Simpson scale, in August 2004), Ivan (category 3, in
September 2004), Katrina (category 4, August 2005), etc.)
have been related to this increase in sea surface temperatures
(SST). Several studies suggest that global warming will
likely result in SST increase, which will enhance the inten-
sity of extreme storms (Sun et al. 2007) and mean sea levels.
This also applies regionally, where the largest, ever recor-
ded, significant wave height in the Catalan coast occurred in
the Costa Brava region—near the border between Spain and
France—in December 2008. Therefore, it is a matter of when
rather than if such extreme natural events will occur.
Year
1
2
3
4
5
Wave Height (m)
Swell Gabès
Swell Site2 34º00.5'N 10º20.0E
Swell Site2 Linear Trend
1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 19 84 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994
1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005
Year
2
3
4
5
6
7
8
9
Wave Height (m)
Ebro Delta
Swell Ebro Hs Max Hipocas
Swell Ebro Hs Max Linear Trend
Fig. 6 Yearly mean hind-cast
Hs values for the Gabe
`s(top)
and Catalan (bottom) coasts.
The data have been provided by
the Ministe
`re de l’Equipement
et l’Habitat for Tunisia and by
Puertos del Estado, Ministry of
Public Works for Spain (see
text)
626 A. Sa
´nchez-Arcilla et al.
123
Hazards
General framework
In this section, we present the implications of climatic
variability on erosion and water quality [both bio-geo-
physical hazards (Adger 2006)], driven by changes in
physical parameters. The assessment should be in terms of
the average trend and the estimated changes in variance.
However, in order to be consistent with the paucity of
available data, we shall only perform the exercise for the
medium trend.
Even with this simplified approach, there remain a large
number of uncertainties. They can be classified in seven
large blocks, of which the first four are the normally
accepted sources of uncertainty in climatic scenarios
(Somot et al. 2006,2008; Terray and Braconnot 2007).
They can be summarized as follows:
Green house gas emissions, related to the socioeco-
nomic behaviour and technological developments.
Modelling performance, related to the employed equa-
tions and parameterizations.
Type of downscaling (physical or statistical) and selected
boundary conditions, plus the considered feedbacks.
The inherent limits of predictability, which vary
depending on the nonlinearity of the sub-system prop-
erty considered (for instance, about 1 year for features
such as the North Atlantic oscillation or the ENSO).
It is also important to include three additional sources of
uncertainty, which may become even dominant in terms of
the resulting hazards. They are related to:
The response function that links climatic drivers to the
desired ‘‘property’’ of the coastal system and that is
normally poorly known. For instance, computations of
sediment transport rates may present errors of up to
100% (see e.g. Ca
´ceres et al. 2009).
The threshold needed to calculate hazards, which is
also an open question mark for many practical appli-
cations related to erosion, flooding or water quality.
ENE
E
ESE
SE
SSE
S
SSW
SW
WSW
W
WNW
NW
NNW N
(c)
NNE
NE
30%
25%
20%
15%
10%
5%
Fig. 7 Directional wave distribution along the Spanish Coast. The
radial axis indicates frequencies of occurrence. aLlobregat wave
buoy that corresponds to the Barcelona coast, bCap Tortosa buoy that
corresponds to the Ebro Delta cost and cCullera Bay that corresponds
to the central/south Valencia Gulf (sources:Sa
´nchez-Arcilla et al.
2008a a,band Mo
¨sso et al. 2007 c)
1970 1975 1980 1985 1990 1995 2000 2005 2010
Year
14
15
16
17
18
19
20
Temperature ºC
Estartit Yearly Averaged Mean, Min and Max Temp.
Yearly Averaged Mean Temperature
Yearly Averaged Max Temperature
Yearly Averaged Min Temperature
(a)
(b)
Fig. 8 a Annual mean (middle curve), maximum (upper curve) and
minimum (lower curve) sea surface temperature (SST) at the Northern
Catalan Coast (Estartit station), for the period 1969–2008 (left) and
bmonthly SST in front of the Ebro Delta, for the period 1990–2008
(right). Data sources: SMC (Servei Meteorologic de Catalunya) and
Josep Pascual
Climatic drivers of potential hazards in Mediterranean coasts 627
123
The probability distribution functions of drivers and
responses which is seldom known and is introduced in
terms of a mean, or, at most a mean plus a standard
deviation. This presents particular problems, especially
for extremes since the tail of the distributions are
sensitive to all previous hypotheses.
Such a wide fan of uncertainties also applies to the four
studied field sites, which are characteristic examples of
Northern and Southern Mediterranean coasts (Fig. 1). They
have been analysed covering a wide range of physical
drivers with some Esocioeconomic implications. Uncer-
tainties begin with the fact that the Mediterranean is a
particularly vulnerable region to climate changes (Gouba-
nova and Li 2007) and has shown large climatic shifts in
the past, being identified as one of the most prominent
‘hot-spots’’ in future climatic change projections (Giorgi
2006). Given that the Mediterranean is a transition area
between the temperate climate of central Europe and the
arid climate of northern Africa, changes have the potential
to deeply modify the climatic characteristics of the
Mediterranean. The population density plus these effects
could result in devastating impacts on water resources,
natural ecosystems (both terrestrial and marine), human
activities (e.g. agriculture, recreation, tourism) and health
(Giorgi and Lionello 2008).
Flooding is the most common of these environmental
hazards, and the number of people vulnerable to it is
increasing as populations rise and the alternative settlement
sites decrease. In particular, floods are the most common
kind of natural hazard in the Western Mediterranean region
(Milelli et al. 2006), either in river basins by intense
rainfalls over small catchments (flash floods) or by ener-
getic sea storm events, acting on low-lying coastal areas.
Because of this torrential character of the climate,
droughts are one of the main climatic hazards affecting
Mediterranean regions. In Spain, they have become a fre-
quent phenomenon due to the high spatial and temporal
variability of precipitation. They are controlled by atmo-
spheric circulation patterns in the North Atlantic (Barri-
endos and Llasat 2003; Vicente-Serrano and Cuadrat 2007)
Year
15
16
17
18
19
Temperature ºC
Ebro Delta
Air Temperature
Running average
Year
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
Deviation ºC
Gulf of Oran
Deviation ºC
Polynomial Fit
Year
-4
-3
-2
-1
0
1
2
3
4
5
Deviation ºC
Sfax
Summer Daily MaximumTemperature
Linear Trend
SUM 0.36 0.55 0.75 ºC/decade
1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 1925 1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
1970 1975 1980 1985 1990 1995 2000 2005 2010 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
Year
-1.5
-1
-0.5
0
0.5
1
1.5
2
2.5
3
Deviation ºC
West Nile Delta
Deviation Annual Mean Temperature
Polynomial Fit
(a) (b)
(c) (d)
Fig. 9 Air temperature evolution at aCatalan Coast, bGulf of Oran,
cGulf of Gabe
`s and dWest Nile Delta. In all four cases, disregarding
the type of statistical analyses or whether they refer to absolute
temperature data or temperature deviation, there is an increasing trend
over the observation period
628 A. Sa
´nchez-Arcilla et al.
123
and also by local cyclo-genesis. Drought periods can result
in significant loses for crop yields (Quiring and Papa-
kryiakou 2003), increasing the risk of forest fires (Pausas
2004), gradual reduction in tree growth (Ko
¨rner et al. 2005)
and triggering processes of land degradation and deserti-
fication (Schlesinger et al. 1990).
Sea temperatures control atmosphere–ocean exchanges
and are, thus, linked to evaporation and precipitation rates.
The associated hazards come, mainly, from coastal flood-
ing due to continental run-off. Water temperature also
controls the solubility of certain substances—among them
dissolved oxygen—and primary production (Manasrah
et al. 2006; Markfort and Hondzo 2009). This results in a
factor affecting water quality, as described below.
Water temperature regulates ecosystem functioning both
directly, through physiological effects on organisms, and
indirectly, as a consequence of habitat loss. Photosynthesis
and aerobic respiration and the growth, reproduction,
metabolism and mobility of organisms are all affected by
changes in water temperature. Indeed, the rates of bio-
chemical reactions usually double when temperature is
increased by 10°C within the given tolerance interval of an
organism, and this also applies to microbial processes such
as nitrogen fixation, nitrification and denitrification.
Aquatic organisms can only survive within a particular
temperature range. If temperature goes too far above or
below (positive or negative temperature anomalies of only
a few degrees can induce mortality), the tolerance for a
given species (e.g. fish, insects, benthic invertebrates,
zooplankton, phytoplankton & microbes) and its ability to
survive may be compromised. Unnatural changes in water
temperature impact indirectly upon biota through loss of
supporting habitat, by changing the solubility of oxygen
and calcium carbonate (calcite or aragonite) in water or by
influencing the extent to which metal contaminants and
other toxicants are assimilated by physiological processes.
Water temperature is also, probably, the most important
factor influencing viral persistence in estuarine environ-
ments, since it affects the density, conductivity and pH of
the water column.
In addition, the solubility of gases (e.g. dissolved oxy-
gen and carbon dioxide) decreases with increasing tem-
perature (solubility being the maximum amount of gas that
can be dissolved in a given volume of water). Water is
more likely to become anoxic or hypoxic under warmer
conditions, because of increased bacterial respiration and a
decreased ability of water to hold dissolved oxygen.
If SST warming continues, the solubility of CO
2
and
thus the net uptake of it by the oceans will decrease. On the
other hand, ocean warming can activate zoo- and phyto-
plankton, the so-called ‘‘biological pump’’, which is
responsible for the oceans’ biological uptake of CO
2
.
However, the decreasing physical solubility of CO
2
in
warmer seas could override the positive effect of the bio-
logical pump, in terms of global average and also for
regional scales, such as in the case of the Mediterranean
(Westby et al. 2002).
Physical hazards based on sediment balance:
forcing terms
Within the framework just presented, there is a variety of
physical hazards that can be considered. We shall focus on
erosion and water quality at climatic scales. Coastal ero-
sion will be addressed in terms of the corresponding sedi-
ment balance, whose main drivers are analysed in what
follows.
The first obvious climatic driver is sea-level rise which,
as mentioned in previous sections, has experienced during
the twentieth century in the Mediterranean an average rise
of about 10 cm. By 2100, all SRES scenarios (Nakicenovic
et al. 2000) predict an average rise of 18–59 cm. No better
estimation is presently available for the Mediterranean, far
less distinguishing between the Eastern and Western sides
or Northern vs. Southern shores. Based on the available
time series, the short-term rates of SLR for the four studied
sites, excluding subsidence, are found to be smaller than
5 mm per year for Spain (Catalan Coast), Oran and Gabe
`s
and between 5 and 10 mm per year for the Nile Delta.
More specifically, there appears to be a relatively steady
sea level in the Spanish case (less than 1 mm per year of
change), while mean sea level appears to be increasing in
the southern shore (e.g. Gabe
`s) since 1992, at a rate of
about 2 mm per year.
The subsidence rates have been taken as close to 0 for
Gabe
`s and Oran, as 2.5 mm per year for sinking areas in
the Catalan coast such as the Ebro Delta and of about 4 mm
per year for the Nile Delta. These values correspond to the
last decades, being representative of some ‘‘contemporary’
interval in the last century. They are in agreement with the
present state-of-art (Emery et al. 1988;Sa
´nchez-Arcilla
et al. 1998; Somoza et al. 1998; Ericson et al. 2006) but
should be considered as the best possible educated guess at
this time, due to the lack of more solid geophysical evi-
dence. However, they are considered to be suitable for the
vulnerability analysis to be performed in next section.
A more accurate estimation is, however, urgently
required in the near future, since even small increases or
variations in these parameters can produce a large impact.
As an example, 1 cm of sea-level rise increases the flooded
area by various metres in the low-lying areas along the
Mediterranean coast, and a sea-level rise of 1 m has been
estimated to produce a loss of 10% of the available
emerged plain in the Nile Delta (Dasgupta et al. 2007).
This justifies the need for an enhanced monitoring effort in
the coming future.
Climatic drivers of potential hazards in Mediterranean coasts 629
123
These same limitations apply to other climatic vari-
ables such as river discharge or wave storminess. In the
case of river discharge, there should be a distinction
between liquid and solid transport, and this latter variable
should be split into bed, suspended and wash loads.
Bed-load transport, which is mostly sand, has been
significantly reduced in all regulated rivers (see e.g.
Sa
´nchez-Arcilla et al. 1996). However, wash-load and
suspended fluxes are not so sharply reduced, although
they only provide fine material such as silt or clay, which
is not suitable for building a stable shoreline. The same
fate applies to nutrient discharges, important for the bio-
logical productivity of the coastal sea, which is also
dependent on the liquid discharge. In the case of regulated
rivers, the experience from Northern Mediterranean
shores of the European Union (e.g. the Deltas of the Ebro,
Rhone or Po) is that river regulation exerts a stronger
control than climatic variability (Sa
´nchez-Arcilla et al.
1996; Sierra et al. 2004).
Physical hazards: erosion
We shall now estimate coastal erosion due to relative sea-
level rise, without considering any further reductions in
river sedimentary supplies with respect to the present sit-
uation, because of the stronger effects of river regulation
when compared to climate variability. The corresponding
erosion rates appear in Table 2. In this table, the ‘‘recent
past’’ corresponds to the last century, while the ‘‘present’
estimates have been obtained assuming a 1 mm sea-level
rise per year as an average figure for the whole domain.
The ‘‘near future’’ rates correspond to the interval
2050–2100 and have been obtained assuming an increase
in sea level by 2100 of about 50 cm. The displayed figures
correspond to an average estimate, assuming a ‘‘solid’
response of the shoreline to sea-level rise based on a
simplified version on Bruun’s rule. However, it should be
explicitly stated that the actual response will vary from
beach to beach, depending on sediment and profile features
and the availability of space for the required beach erosion.
Because of that these numbers, expressed in horizontal
metres of erosion, should be considered as rough estimates
to illustrate the variability across Mediterranean coasts.
The numbers can nevertheless be used to perform a
regional scale analysis.
Regarding storm events, there appears to be a slight
increase in the number of moderate storms during the fall
period, based, as it was described in previous sections, on
the thunderstorms for the Oran Gulf and on the wave
storms for the Catalan region. However, the number of
more energetic events appears to be decreasing, while there
is an increase in storm duration (based on a limited set of
data from the Catalan case).
The beach profile erosion associated to wave storms
depends on both intensity and duration (see e.g. Sa
´nchez-
Arcilla et al. 2008b). If, as justified in previous sections, we
assume an increase in duration of 2 h per decade, then we
can estimate the corresponding increase in eroded volume
as approximately 2 m
3
/m (for the extra 2 storm hours)
based on the previous reference. This results in an erosion
increase of 2 m per decade, using a berm height of between
1.0 and 2.0 m, since we are including also part of the
submerged beach profile to calculate the balance. This
would result in 20 m of extra erosion by 2100 for the
Catalan, Nile and Oran cases, while the Gabe
`s case, more
sheltered, has not been considered to be subject to this
effect. The increase in number of storms reported from the
Oran case has been considered to be included in the 2 h per
decade increase in duration (in terms of resulting erosion)
since these 2 h per decade may come from either a longer
duration or an increase in the number of storms.
Adding this enhanced erosion due to wave storminess to
the previously calculated figures, resulting from relative
sea-level rise, we end up with the estimates presented in
Table 3, which again correspond to the horizontal average
erosion expected for 2100.
The combined erosion for the year 2100 is, therefore,
around 70 m for the most favourable cases of the Spanish
NW Mediterranean Coast (excluding deltas) and Gabe
`s
Gulf, while it goes up to 95 m or even 110 m for subsiding
areas (Nile and Ebro Deltas) or the Oran case. This illus-
trates the high vulnerability of many of the beaches located
in our four sites which, for the urban beaches, seldom have
widths in excess of 100 m.
It is also possible to estimate the ‘‘coping capability’’ of
a given beach, based on the minimum beach width needed
to perform the protection function associated to a given
sandy stretch (Valdemoro et al. 2007). Defining that the
minimum reserve width for protection should be similar to
the erosion produced by two consecutive storms (Bolan
˜os
et al. 2007), we can estimate the storm induced erosion as
Table 2 Shoreline erosion rates in horizontal metres, due to SLR for
the last century (recent past), present conditions (present) and by the
year 2100 (near future)
Site Recent past Present Near future
No sub Sub No Sub Sub No sub Sub
Valencia 0 10 50
Ebro Delta 25 35 75
Oran 25 35 75
Gabe
`s25 35 75
Nile 40 50 90
A distinction is made between the sites without subsidence (no sub)
and those with subsidence (sub). The uncertainty in the estimates
should be always considered
630 A. Sa
´nchez-Arcilla et al.
123
30 m
3
/m (Sa
´nchez-Arcilla et al. 2008b). This results in
erosion, approximately, 30 m of horizontal retreat, using
again a berm height between 1 and 2 metres and consi-
dering also part of the active submerged beach profile.
The effect of these 2 consecutive storms would, there-
fore, require a width of about 60 m, which would be the
minimum sub-aerial beach required to cope with present
meteo-oceanographic conditions. For the corresponding
climatic-scale assessment, it is necessary to add the margin
due to the worsening of climatic conditions, which are
shown in Tables 2and 3. The end result of all that is that
an average width of 150 metres should be prescribed
throughout Mediterranean coasts to ensure the survival for
many of our beaches.
Physicochemical hazards: water quality
Looking now at coastal water quality, we can relate it to
climate dynamics in terms of precipitation and dissolved
oxygen in the water column. Precipitation affects water
quality, in the sense that it determines the concentration of
pollutants coming from river discharges or from the dis-
tributed continental run-off. If we assume that concentra-
tion is inversely proportional to the discharged volume and,
therefore, for a constant drainage area, inversely propor-
tional to the precipitation rate, this results in water quality
being directly proportional to precipitation rate (assuming
that the amount of pollutants remains constant). Intuitively,
this simply means that higher precipitation rates produce a
higher dilution and therefore should improve water quality.
Of course this is a crude simplifying hypothesis, since
impulsive rain events (at least the first of a series) would
have to ‘‘cleanse’’ the drainage system and, thus, contribute
a higher concentration of pollutants. However, the extra
momentum of torrential discharges favour river plumes
that are able to cross the continental shelf (Sa
´nchez-Arcilla
and Simpson 2002) and, thus, reduce the local pollutant
load. All things considered, we have opted for a robust,
simple analysis to achieve some regional order of magni-
tude estimates as presented below.
Yearly average precipitation has experienced a reduc-
tion from about 400 mm in the interval 1927–1997 to
around 300 mm in the interval 1978–2007 (for the Oran
case). This supposes a decrease in precipitation, and thus
water quality, of about 20%. Future scenarios, although
less robust for precipitation than for variables such as
temperature, predict a reduction in precipitation of about
5% for the Northern Mediterranean Coast and of about
20–25% for the Southern Mediterranean Coast (rounded
estimates after Christensen et al. 2007). This corresponds
to A1B scenarios, where the rapid economic growth goes
accompanied by more efficient technologies.
Based on these numbers and the work performed within
the CIRCE project, we are assuming that, under present
conditions, the precipitation in the Spanish case has
remained reasonable steady, while there has been an
increase in the Gabe
`s case in winter and a decrease in the
Oran case starting in 1970 (this includes the 30-year severe
drought experienced by Oran from 1977 to 2007). The Nile
case has shown a decrease in precipitation in the 1970 and
1980 s and a further decrease in the 1990 and 2000s. The
associated changes in water quality (expressed as per-
centages) for the four studied cases appear in Table 4.
These numbers should be considered as representative
of the trend, since they constitute a rough estimate of the
variation in water quality due to precipitation changes.
They also fail to consider the local scale differences in
climatic variability. Moreover, the distinction between
summer and winter periods should be also handled with
care since it represents the forecast variation in precipita-
tion, depending on the season within the year. Regarding
water quality, we should also consider that the expected
change towards more pulsed river discharges, linked to
more torrential precipitations concentrated in time, should
also increase the amount of pollutants discharged to the
coastal sea. This effect is nearly impossible to assess with
the present level of information and has not, therefore, been
included in the analysis.
Table 3 Shoreline erosion rates in horizontal metres due to
SLR ?storm effects for the last century (recent past), present con-
ditions (present) and by the year 2100 (near future)
Site Recent past Present Near future
No sub Sub No sub Sub No sub Sub
Valencia 0 10 70
Ebro Delta 25 35 95
Oran 25 35 95
Gabe
`s253575
Nile 40 50 110
A distinction is made between the sites without subsidence (no sub)
and those with subsidence (sub)
The uncertainty in the estimates should be always considered
Table 4 Water quality percentual variations driven by precipitation
Present (%) Near future
Average (%) Summer (%) Winter (%)
Oran -20 -40 -50 -40
Spanish coast 0 -5-30 0
Gabe
`s0-20 -25 -20
Nile 0 -20 -5-20
Present conditions are indicated by ‘‘present’’, while the estimates for
the year 2100 appear as ‘‘near future’
The uncertainty in the estimates should be always considered
Climatic drivers of potential hazards in Mediterranean coasts 631
123
Water quality can also be assessed from the amount of
dissolved oxygen (DO) in a water ‘‘parcel’’. The DO will
change within the water column and as a function of the
spatial hydrodynamic pattern. It will also depend on the
water temperature and several other physicochemical
parameters. In this work, we have considered only the
relation to water temperature to infer the impact of future
climatic scenarios.
Based on previous campaigns and analyses, we have
found out that the DO range in the Mediterranean is
roughly between 5 and 12 mg/l. Below 5 mg/l, the aquatic
system becomes stressed and the WQ degrades sharply
(Benson and Krause 1984; Boyd 2000). Assuming a linear
relation of DO with temperature, it is obtained that DO
decreases by about 2% (0.15 mg/l) for each Celsius degree
of temperature increase. In terms of water quality, con-
sidering that we would need about 15°C of temperature
increase to reach the 5 mg/l threshold, this means a WQ
decrease of about 7% for each Celsius degree of temper-
ature increase. This means that we would need an increase
in temperature of 5°for the dissolved oxygen to get below
the 5 mg per litre for deep water and an increase of 17°for
dissolved oxygen to go below this threshold for surface
water.
Water quality is, therefore, inversely related to the
temperature via the level of dissolved oxygen. This means
that the sea surface temperature (SST) range included in
climatic projections can be translated into percentual
decreases in water quality via the dissolved oxygen rate
proposed above. This relationship amounts to about a 7%
decrease per Celsius degree. If we apply that to the pro-
jected scenarios, we end up with the numbers presented in
Table 5.
The obtained variations in water quality correspond to
the forecast changes in air and water temperatures in the
Mediterranean, which are higher than the world average
(Somot et al. 2008). These numbers have been obtained
based on the A2 scenario. The expected increase in the
warm period or summer season, estimated in about 10 days
per decade for the Gabe
`s case, should also lead to a dete-
rioration of the corresponding water quality since the water
volume and the contained aquatic ecosystem would be
exposed to the forecast increases for a longer period of
time.
The performed analyses illustrate the possible range of
effects of climatic variability in a given coastal region.
These effects will be linked to socioeconomic impacts
originated by an increase in mean sea level, storminess
and/or water/air temperatures. We have seen how these
increases vary for the four studied sites and the uncer-
tainties in the quantifications. The resulting erosion,
flooding, water quality degradation and salinization will
require, as schematized in Fig. 10, further energy
consumption and they are, thus, likely to enhance human-
induced climatic change.
Conclusions
From the presented analysis, it is concluded that the more
direct and robust climatic indicators for the state of coastal
zones are mean sea level and wave storminess for erosion
and flooding and water temperature and precipitation for
water quality. Erosion due to increases in relative mean-
sea-level appears due to the incident waves being able to
reach higher parts of the Coastal Winter-land, normally not
expressed directly to wave action without that rise in sea
level. Erosion also appears due to enhanced wave storms
due to offshorewards directed transport and, in general, a
reshaping of the shore to get in equilibrium with the new
wave conditions. Erosion is, thus, related to (1) relative
level between land and sea, (2) energy of storms and (3)
other storm features such as duration, wave steepness (ratio
of wave height to wave length), wave orientation with a
respect to the coast and repetition of energetic events (i.e.
frequency of occurrence).
Water quality on the other hand is related to (1) water
temperature and (2) precipitation features such as volume,
duration and repetition or frequency of occurrence.
Increased precipitation favours dilution, and this leads to
improved water quality, although the amount of discharged
pollutants may also become larger. The raise in water
temperature decrease the amount of dissolved oxygen in
the water and should, therefore, lead to a worsening of
ecosystem conditions, which may reach anoxia for certain
semi-enclosed bodies of water such as the Mediterranean
lagoons found in our study sites.
Table 5 Percentual variation in water quality driven by temperature
changes for present conditions and by the year 2100 (denoted as near
future)
Present rates Near future
Spanish Coast ?3.3°C?5.0°C
-20% -40%
Oran Gulf ?4°C?2°C?6°C
-30% -10% -50%
Gabe
`s Gulf ?4°C?2°C?6°C
-30% -10% -50%
Nile Coast ?4°C?2°C?6°C
-30% -10% -50%
Winter Summer
Present Near future
Values of average variation in SST (sea surface temperature) and WQ
(water quality) are shown simultaneously (SST/WQ) for the present
conditions and the accelerated rate due to climate change. The
uncertainty in the estimates should be always considered
632 A. Sa
´nchez-Arcilla et al.
123
Sea surface temperature appears to be increasing in all
studied sites, with a clear upward trend for the annual
mean. This should lead to lower values of dissolved oxygen
which, together with the decrease in average precipitation
plus a concentration into more torrential events, will result
in water quality degradation.
Although the available level of instrumental information
and the errors in simulated fields preclude any final con-
clusion, there are a number of commonalities and differ-
ences to be observed. Precipitation interannual variability
is so large that it hampers deriving any common pattern for
all studied sites. There appears, however, to be a slight
increasing trend in the number of moderate storms. This
could support the incipient evidence towards a higher
number of impulsive events (wave storms, precipitation,
etc.) in the area. The resulting impact, for a squeezed coast
such as the Mediterranean, subject to storms from more
than one direction, would be enhanced erosion and flood-
ing. The human response should, accordingly, be an
‘ordered’’ retreat from the immediate coastline, in what is
nowadays called managed realignment. Alternatively, for
selected stretches of the coast where this realignment is not
possible (e.g. coastal cities), there should be a reenforce-
ment of defence structures, including if at all possible a
wide enough beach (natural or, more likely, artificial) in
front. The human response should, thus, be a careful design
of sea-outfalls, avoiding semi-enclosed bodies of water and
periods of abnormally high temperature and/or low water
renovation. This implies managing coastal waters using the
available knowledge on oceanographic variables and the
corresponding wave and current operational predictions.
This information could also be used to achieve safer
bathing water conditions, regulating access and preferential
areas as a function of the prevailing meteo-oceanographic
conditions.
The associated impacts will be cross-sectorial and with
feedbacks at multiple scales, some of which may, in turn,
require higher energy consumption and an enhancement of
climatic change. This illustrates the importance to act in an
anticipatory manner, invoking in case of doubt the
Fig. 10 Schematization of the
conceptual relation between
climate hazards and cross-
sectorial socioeconomic
impacts, for the coastal cases
studied in this paper
Climatic drivers of potential hazards in Mediterranean coasts 633
123
precautionary principle, so that we can preserve an envi-
ronment as valuable and unique as the Mediterranean
coastal fringe.
Acknowledgments This work has been funded by the EU project
CIRCE (ref. TST5-CT-2007-036961) and the research project ARCO
(ref. 200800050084350) from the Spanish Ministry of Environment.
The authors also went to acknowledge the use of data from various
public organizations in the four studied sites, as described in the text,
with a special mention to Mr. Josep Pascual.
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... Coastal areas are very exposed to hazards like erosion and flooding (Arnoux et al., 2021;Gallien, 2016;Kron, 2013;Xie et al., 2019). Risks associated to these hazards are expected to increase in the next years due to sea level rise (SLR) and extreme events related to waves and storm surge (Casas-Prat et al., 2016;Grases et al., 2020;Izaguirre et al., 2011;Kirshen et al., 2008;Lin et al., 2016;Neumann et al., 201 ;Nicholls et al., 2011;Sánchez-Arcilla et al., 2011;oodruff et al., 2013). ...
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... Coastal areas in some countries particularly in the global south are highly susceptible to the various impacts of climate change due to anthropogenic and natural climatic factors (Bouwer 2011;DasGupta and Shaw 2013;Nath and Behera 2011;Sivakumar and Stefanski 2010). Severe changes in climatic and weather conditions, rapid sea-level rise (SLR), storm surge, temperature fluctuations and irregular rainfall trends have increased coastal vulnerability problems in the majority of coastal regions across the globe, resulting in huge losses of coastlines, properties and damage to coastal communities (Burkett 2012; Gupta et al. 2019;Lal 2003;Mimura 2013;Sánchez-Arcilla et al. 2011). Likewise, many coastal states of India suffer severe cyclonic storms leading to flooding. ...
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One of the most used measures to counteract coastal erosion is beach nourishment. It has advantages with respect to the use of rigid structures that sometimes entail non desired impacts on the surrounding areas. However, beach nourishments are often unsuccessful, requiring frequent refills due to the use of sediments that are not suitable. In this paper, a methodological framework for increasing the probability of success of beach nourishment projects is presented. First, this framework consists of detecting potential borrowing areas, by analysing shoreline evolution and selecting the stretch that shows a more accretive character. Once the borrowing area has been identified, several sand extraction options are defined. The beach response (in terms of erosion and flooding) to each sand extraction alternative is analysed by using two numerical models, which simulate the hydro-morphodynamic patterns in the studied area. The numerical model results allow to find the best extraction alternative, which is that producing the least impact in the borrow area. As an example, the methodology is applied to a stretch of the Catalan coast (NW Mediterranean) to illustrate its potential. The proposed methodology shows to be a useful tool for helping coastal managers to optimize their available resources.
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Book
The revised second edition updates and expands the discussion, and incorporates additional figures and illustrative problems. Improvements include a new chapter on basic chemistry, a more comprehensive chapter on hydrology, and an updated chapter on regulations and standards. This book presents the basic aspects of water quality, emphasizing physical, chemical, and biological factors. The study of water quality draws information from a variety of disciplines including chemistry, biology, mathematics, physics, engineering, and resource management. University training in water quality is often limited to specialized courses in engineering, ecology, and fisheries curricula. This book also offers a basic understanding of water quality to professionals who are not formally trained in the subject. Because it employs only first-year college-level chemistry and very basic physics, the book is well-suited as the foundation for a general introductory course in water quality. It is equally useful as a guide for self-study and an in-depth resource for general readers.
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Data points summarized in the present study are largely from samples collected prior to 1964 and thus provide a pre-Aswan High Dam baseline. Recommended systematic resampling of the margins and analyses of heavy minerals one quarter-Century after closure of the High Aswan Dam would help measure recent sedimentation changes and predict future modifications likely to affect these margins. -from Author
Chapter
This paper reviews observationally based estimates of past global-mean temperature change and sea-level rise and compares them with model-based estimates. The climate model used is a simple upwelling-diffusion, energy-balance model, which is coupled to a set of simple ice-melt models to give total sea-level change. For best-guess model parameter values there is reasonable agreement between observed and modelled results. The same models are used to estimate future temperature changes and sea-level rise for the standard IPCC95 set of emissions scenarios, updating earlier work. Projected warming over 1990–2100 ranges between 1.4 and 2.9°C for the central emissions scenario (1595a), while sea-level rise ranges between 20 and 86 cm. Mid-value estimates for a climate sensitivity of 2.5°C for a CO2 doubling are 2.0°C and 49 cm. Temperature and sea-level rise estimates are also given (out to 2500) for five standard (IPCC) CO2 concentration scenarios in which CO2 levels stabilize at 350, 450, 550, 650 and 750 ppmv. The sea-level-rise commitment after stabilization is very large: for stabilization levels of 550 ppmv or above, sea-level rise continues for many centuries at rates similar to those occurring at the stabilization point in spite of the constancy of radiative forcing. Finally, the sensitivity of these results to changes in the ocean’s thermohaline circulation is examined. The effects of a thermohaline slowdown are reduced warming rate and increased rate of sea-level rise.