Extremes and marine storms

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Extremes and marine storms in the Mediterranean
Sea
P.Lionello, Univ. of Lecce, Italy
1 Intro GEV and generalities examples from RON
and sea level in Venice 2 some insight I) Storm
surge trends for Venice 3 generalities on waves
and wave modeling 4 some insight II) futures
scenarios for storminess and implications for
waves and surges...
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EXTREME VALUE ANALYSIS is well established
common paradigm return values for relatively
long periods
But many of other aspects are in practice mostly
specific to the problem, and only general
guidelines are available
Event definition a set of independent event, the
set should contain many items, but few of them
are used
Data gathering long homogeneous series of data
from observations or models
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Cyclones (winds) , waves and surges
4 NOV. 1966 event
SLP and U10
Surge and waves
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alghero
crotone
monopoli
mazara
?0.300.14
?0.430.15
?0.070.28
?-0.100.22
?4.66?0.14
?7.42?0.21
?3.70?0.11
?4.76?0.16
la spezia
pescara
ponza
?0.020.17
?-0.100.19
?0.170.16
?4.74?0.15
?4.82?0.18
?4.29?0.14
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alghero
crotone
monopoli
pescara
mazara
ponza
la spezia
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Venice surge Extreme values distribution
1940 to 1969
1970 to 2000
GEV distribution
1940 to 1969
1970 to 2000
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EXTREMES WAVES, SURGES IN THE ADRIATIC SEA IN A
2xCO2 SCENARIO
P.Lionello, F.Dalan, E.Elvini, A.Nizzero
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The common element of wave and surges is WIND
More intense cyclones
Higher wind speeds
Higher waves and storm surges
Loss of lives, loss of properties, loss of
economic resources, cultural and environmental
heritages, increased costs of coastal defences
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CONSEQUENCES ON WAVE FIELDS AND STORM SURGE
A DOWNSCALING PROCEDURE APPLIED TO THE ADRIATIC
SEA
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The downscaling procedure consists of two steps.
2) The surge level and the wave field are
computed from the wind field using a barotropic
(single layer) circulation model and a spectral
wave model (WAM)
1) A regional wind field is derived from the sea
level pressure field (available every 6 hours) by
CCA of the PCA prefiltered fields
SIMULATED PREDICTOR
PREDICTOR SLP
SIMULATED WAVES AND SURGES
STATISTICAL MODEL
DYNAMICAL MODELS OF OCEAN WAVES AND STORM SURGES
PREDICTAND U10
SIMULATED PREDICTAND U10
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downscaling
downscaling
Observations
Observations
T106
T106
downscaling
T106
The downscaling procedure has been tested
applying it to the ERA-15 SLP data. The same
period has also been simulated using directly the
T106 winds. The downscaling produces a large
improvement in the simulated Significant Wave
Height and surge levels. However, levels during
peak events remain underpredicted.
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RESULTS SIGNIFICANT WAVE HEIGHT
scenario
max
100 years depth
OBS
6.75?0.6
5.1
CTR
5.6
6.1?0.4
CO2
4.5
5.6?0.3
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CTR
CTR
CTR
MAX
FREQUENCY
100-YEAR RETURN VALUES
CO2
CO2
CO2
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STORM SURGE
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Are the surges in Venice a result of recent
climate changes?
Is their frequency related to global processes?
East coast of England Frequency of surges
Figs from D.Camuffo, (1993)Theor.Appl.Climatol.47,
1-14
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Source Report by P.Canestrelli
Surges above 110cm level (reference fixed
reference level)
Trend in frequency/intensity of storm surges?
Sea level rise
2000
1865
Surges above 110cm level (reference annual mean
sea level)
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Trend in frequency/intensity of storm surges?
The observed trend is mostly produced by loss of
ground level. This has no relation with more
intense storms in a changed climate however, a
smaller trend could be present.
Is this small trend an indication of what could
be expected in a 2XCO2 CLIMATE?
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RESULTS SURGE
scenario
max
100 years depth
150?8
OBS
129
184
128 ?8
CTR
109
CO2
125?8
119
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CTR
CTR
CTR
MAX
FREQUENCY
100-YEAR RETURN VALUES
CO2
CO2
CO2
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The doubled CO2 simulation is characterized with
more extreme weather events, but the
(significant) difference between the two
scenarios is small, and not fully significant for
Mediterranean region
The CO2 scenario presents a marginally diminished
wave activity in the southern Adriatic.
The two scenarios present substantially
equivalent extreme surge levels. There is a minor
increase in the CO2 scenario.
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THE END
Clim. Res. (2002), 22, 147-159, Clim. Res. (2003)
23,217-231