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Task 5.3.3. Synoptic-hydrologic evaluation of Mediterranean
to dryland floods under climate change
Jonathan Laronne, Isabela Shentsis
(BGU, Israel)
This research segment aims at the synoptic meteorologyhydrologic analysis of Mediterranean dryland floods, as a
regional derivative of climate and hydrology.
Such a descriptor is deemed fundamental for surface water
resources and flood risk issues in the Mediterranean region
under ephemeral or intermittent flow regimes and
especially under various scenarios of climatic changes.
To serve the purpose, two databases will be employed:
• The digitized flood database of the Israel Hydrological Survey
for the Negev (Shentsis & Laronne, 2006) - 24 hydrometrical
stations, basin areas 60 - 3400 km2, data-series to 50 years and
150-200 flood events,
• The digitized database of daily synoptic systems over the
Eastern Mediterranean (Alpert et al., 2004) covering a period of
more than 50 years.
Floods will be statistically categorized to the synoptic oriented
classes with due regard for seasons, physiographic
regionalization, flood magnitude (peak and volume) and duration.
Rivers and stations network in the Negev
BGU
Importance of floods also in the Negev :
Paran River, Bridge downstream the Bottleneck Station
Arugot River – Bridge Station
during the flood…
after the flood…
It is planned to develop
a statistical season-regional model for flood events, including
research into flood peak, volume, shape and duration, as well
as relationships between flood peak and other flood
characteristics.
Here flood peak is a predictor which is commonly determined
at gauging stations and can also be estimated at ungauged
sites immediately after occurrence of a flood event based on
identification and surveying of maximum flood levels. Under
certain conditions historical flood marks may also be used.
The developed model will increase the potential of this
methodology, thereby permitting not only determination of
flood peaks, but also estimation of other flood characteristics,
particularly flood volumes at ungauged sites.
The project results will include estimates of flood volumes based
on flood peaks for any gauged or ungauged site in the study
region.
e.g., an example of such approach for the Negev as a seasonregion relationships between parameter a and basin area, when
flood peak Q and volume V are related by the linear function
V=aQ.
Sinai
Functional
relationships
for coefficient a
We shall concomittantly utilize he vast database on daily synoptic
conditions (Alpert et al., 2004) to which flood volumes and peaks
will be interrelated.
700
1st
For example, a analysis has
been undertaken to determine the
frequency of occurrence of floods
of given volume and peak with
respect to daily synoptic systems
over the Mediterranean.
600
500
400
300
200
100
0
RST
Pers
Cyprus Sharav
High
Trough
Low Low
Total
308
25
387
612
28
Spring
19
12
82
68
18
Winter
184
0
237
499
10
Autumn 105
13
68
45
0
The following is an example analyzing
major floods chosen by criteria of volume:
Events with V/V10 equal or greater than 0.5
(where 10 is recurrence interval, in years)
40
30
20
10
0
RST
Pers
T roug
High
Cypru Shara
s Low v Low
T ot al
22
2
10
39
1
Spring
0
0
4
2
1
Wint er
19
0
5
34
0
Aut umn
3
2
1
3
0
Primary Goals
The correlation between flood characteristics such as
flood peak or volume and synoptic weather system
will enable prediction of flood characteristics under
given synoptic conditions.
One of the primary project results will be estimates of
flood volumes based on peaks from weather conditions
for any gauged site in the study region, also suitable as
a method for the wide-spread ungauged river basins.
Thus a regional climate model for the Mediterranean is
expected to yield not only a determination of flood
magnitude, but a projected climate change leading to
changes in synoptic conditions and their prevalence
will drive predetermined changes in flood
magnitude.