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--- Sehmi N.S. Climatic h azards an d water man agemen t in th e Mediterran ean region . In : D upuy B. (ed.). Aspects économiques de la gestion de l'eau dans le bassin méditerranéen . Bari : CIHEAM, 1997. p. 69-77 (Options Méditerranéennes : Série A. Séminaires Méditerranéens; n. 31)
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http://www.ciheam.org/
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S. Sehmi
Hydrology and water resources department
Geneva, Switzerland
SUMMARY
-
The Mediterranean Sea Basin lies in the transitional zone which falls under the influence of the subtropical high-pressure system during the summer and under the temperate low-pressure system during winter, drawing in cyclonic depressions from the Atlantic Ocean.These depressions penetrate almost unobstructed the entire length of the Mediterranean Sea to the Middle East and beyond. The Mediterranean climate produces many beneficial effects which, throughout the ages, have led to economic progress, stemming from the flowering of a succession of centres of civilization. The extremes of this climate, however, have often turned into destructive forces, manifesting themselves in the form of rainstorms, severe thunderstorms, snow storms, floods, droughts and dust storms. This destructive impact has increased over the years on account of the growing population and expanding economy. The climatic hazards in this region sometimes coincide with other natural disaster-producing forces such as volcanic eruptions, earthquakes, and landslides, as well as with man-made events such as accidental air and water pollution. This paper looks into the origin and nature of the climatic hazards, mitigation of their impacts, and proposes cooperative regional studies and projects.
Key words: Flood, flash flood, forecast, climate change, probable maximum precipitation.
LES RISQUES LIES AU CLIMAT ET LA GESTION DE L'EAU DANS LA REGION MEDITERRANEENE
RESUME
-
Le bassin méditerranéen est situé dans la zone de transition, sous l'influence du système subtropical de haute pression pendant l'été et du système tempéré de basse pression pendant l'hiver, attirant des dépressions cycloniques de l'Océan Atlantique. Les dépressions pénètrent, presque sans rencontrer d'obstacle, sur toute la distance de la Méditerranée au Moyen-Orient et au-delà. Le climat méditerranéen produit beaucoup d'effets bénéfiques qui,durant toute l'histoire, ont contribué au progrès économique, favorisé par l'éclosion d'une série de centres de civilisation. Les manifestations extrêmes de ce climat se sont cependant souvent transformées en forces destructrices sous forme de tempêtes de pluie, d'orages violents, de tempêtes de neige, d'inondations, de sécheresses et de tempêtes de poussière. Ces incidences destructrices se sont accrues au cours des ans, du fait de la poussée
démographique et de l'expansion économique. Les risques liés au climat dans cette région coïncident parfois avec d'autres forces naturelles dévastatrices, telles que éruptions
volcaniques, tremblements de terre et glissements de terrain, ainsi qu'avec des événements causés par l'homme, tels que la pollution accidentelle de l'air et de l'eau. Cet exposé examine les origines et la nature des risques climatiques et l'atténuation de leurs incidences, et propose des études et des projets régionaux coopératifs.
Mots-clés: Crue, crue éclair, prévision, changement climatique, hauteur maximale probable des précipitations.
Along the of
and south of the the lati-
tudes of 30" and 40", lies the fal-
ling of the
the
wing in cyclonic the west. the
the length (3700 km) of
the Sea the of
to the
climate, known as the
times. The co-
mes mainly with the the
Atlantic that often
in (the mis-
in and the in the in
spite of of
(it can snow in the
As a the
west to east: progressive continentali-
ty. The in the
oceanic influences (Lisbon: 10.6"C in 22.2"C in
mes continental in
the abundance of and flo-
it of the
liday have been established in
The tides in the sea sea
is
To the south lies the
the
it, the of the
the Atlas and the tation, which is the of
of the
vast lodged in the
the piedmont and the plains since ancient times and
many beneficial and ha- the whole socio-economic spec- and development; but the of econo-
is be a moving of the
multiple and civilizations that have in the the distant past. These cul-
but only
to a of
by The Egyptian and the
succeeded by those of the the
and the the of
the in
wheat of what became known as the of The seem to have amal- gamated all and technological ad- vancements which witness geniuses such
climatic conditions in
the of man need
the
until the beginning of the twentieth when the situation
of the population
and the consequent development policies, which had a
of be
the situation, of
into munities of food and
of of
in of
population is
level of al-
so a causative element is
of in the
is Fig. 1.
SIGNIFICANT DAMAGE PERSONS AFFECTED
Volcano 49%
Drought í
SIGNIFICANT DAMAGE PERSONS AFFECTED
Storrns,Other 5
Floods
l
-
disasters-
. Source: (1994)
functional phases
1 3
2 4
The two "pro-active" phases and the two "reactive".
a simple dissemination
system can not loss of life
and but also enhance the effectiveness of focuses on the
to
the of in
the context of
constitute studies and evaluations, such as defining a vulnerability analysis. The
sist of activities to the
management of the all
those using affected by the system. The best example of such an activity is forecasting and warning systems and response planning
a commonly held belief that
is changing as a of the effect, al- though it is as yet difficult to the conse- quences of such a availability and quality, mainly because of the in modelling the
significant changes in the of soil intensity can be ex-
pected to situated
at
sensitive to climate change. The
in an et al.,
1993) and the of soon
limit economic Even a change in cli-
mate can the ecosystem,
with on the people and economy. The situation calls
planning than waiting of
often linked with in- intensity
nessing; of flood
of flow of which highly vul-
to and in
the flow of the Fijch the main
of ftom 1.5
to 28 m3sm1).
floods in many of the
last two
amounts fi-om a of low
systems. While the
of flows is about 40% of all
days, the a 60%
also had an
(55%). situations have
in the past and a of cli-
mate in the They cannot be
as an indication of
climate change. the issue of climate change should not be dismissed. With to climatic
about how any human-induced climate change will manifest itself, in the
floods and
depends, among on the
and intensity of the events. Will, example, the
will spells will
both of these to
two types of study as a activity of the in the
Analysis of changes in
that affect the and associated events in
to climate change and im-
pact on and flooding;
0 on the
of
of of
ena (ECSN, 1995).
Water scarcity and droughts
of has been an age-long night-
of the in the One ma-
way of meeting the demands has been the conti-
of the to estimate the
the data in the
of 1995).
Country Year of estimate Amount (billion m3 year")
Morocco 1955
25.0 1968
13.2 30.0 1980
Algeria 1972 14.0
1987 19.0
Tunisia 1970s
1980 4.1
1985 4.35
The of the climatologi-
cal
off mates is bound to level off
ominous.
the the
of that
is liable to flooding. is a well-known so-
ciological fact that The evi-
dence is the land is intensively developed and 20
a minute insignificant to a level which
it 100 out of its
its ancient flood plain, causing millions of of damage
of people.
The main aim of is to balance
the
in the
example, if a dam is
it can
fail The total damage can
be it does not exist.
the
flood level in the the same time
impede inflow,
has, like the
god Janus, the two-faced aspect which must be in the design of new schemes. When flood the population moves to the
"safe" zones. Cities and of
levee the damage to life and
is in such zones since eva- cuation becomes almost impossible even if a good
is issued.
The is
the phenomena of in flood of
Changes in the
intensive human activities;
Climate change.
While the impact of climate change might not be in the the impact of change in catchment is the past, evaluation of this
of the design of
A of
the action that should be taken by the scientists,
best illus- a well-documented flood that
the city of in 1966.
under flood
The city of floods since
ancient times. The flood in the
on 4 the
and to help in the invaluable
the to mitigate flood impacts on life
in the
(a) The scientific study on the
the of floods was completed in 1977.
of
the
2900m3/s to 3200m3/s, which is still less than the 1966 flood flow estimate of 4300m3/s.
(c) Within the of the pealc
the
is still difficult of a 1966-type
flood. The 120
to 150 but the
in
of an a
a of non-
of a
of a sys-
in 1966 followed by a new flood- system in 1990 based on 45
gauges and eight feeding
data in a
Some specific scientific of new technologies:
and it can be now used fective planning of
(ii) A quantitative
was installed in the Amo catchment.
vided valuable the Octo-
1992 flash floods.
(iii) Satellite
mine of in advance. The
so is input to a
simulation model to levels and flows.
Flood useful only if they axe dissemi- nated to
the Some
to evaluate A lot
to
floods in deserts
The size and type of catchment of the
typical of the They
suitable ponse flooding, as well as special
flash the
flash-flood situation the time between the causative event
and the flood is usually less than 1988). The
flood, a flood
it
falls because it sys-
it away.
the in a
a little time the
collection of data and issue of the lead time is
non-existent indeed. Such situations high
ín in cent decades.
been focused on finding solutions which would
enable the in
nings. The new solutions usually based on the combined use of
one application, a event was ana-
estimates
l fall
flash floods is
analysis, and a knowledge of the
the into
of the flash
2).
efficient of amounts of sediment (EOS, 1994). This
cast flash floods. im-
of
Egypt, in the days of the the would be floods in the coming season. They did this
into Ethiopia to the of the of an in
liable to the same penalties if
the of
no
5 10 15 20 25 30 35 40 45 50 55 60 65 70 75
Time, Min
l 2
-
Stage hydrograph ofjlash flood 11,1993Source: et al. (1994)
only in but also in the con-
of and land. Less
is in the of basins and
it flows to the plains. Floods have be- come
less The is also the most
is, flash flooding in
the land cannot into
the soil and so almost all of it off immediately the smooth
the
the landscape now becomes in a
of all be-
it.
speed the flood"
which an embankment a dam 40
ago "ten-
flood", which means that the dams and levees
will be and, if thus de-
lead flood damage than
in The second
is in the floods themselves: man
his physical suit
poses and, in so conditions which
Just assisted the hy-
of his assessment
of the of design
data of exist-
ing
is the estimation of the
and its into the
mum flood. is the of
tion
of a given size at
of The is
in the for of
("0, 1986). view of
ing of of
vated by human activities and possibly by climate
change, of the
mates, especially the design safety of the existing
can save
cannot be
ized the amount and quality of data available, basin size and location, basin and
types and
this the
found in
1992, failed to launch this study
in among some
institutions because it was difficult to find adequate in one
With the of the
System the
it should be feasible to pool human and financial
estimates the as
Elimination of by in
of is
lem and is
of 60 indus-
of is
ing
Talal 1994).
Although it not disas-
it is lessen im-
pact on people The
that by the each ing
into account in community development plans;
the national local level, involving
to global, national, and local
of
ECSN Climate
(1993). and economic development. Water in Crisis, 1993,
the Flash Flood
( W A ) on Conference,
of the
Desertification. W O , Geneva (in preparation).
(1995). the on
Geneva. >
Powell, J.B. (1994). Flash Floods in Studying the
Vol. 75,
in The A m o
No. 591, Geneva.
(1994). Disasters Around the World - A No. 4,
Wernly, (1994). The of in
598, Geneva.
(1986). for of
No. 1, 332, Geneva.
(1988). Volume
m,
(1994). Guide to
