1. Samuel SOMOT1 and Michel CREPON2
Special session, Umit Unluata, CIESM congress
21st century climate change scenario of the Mediterranean Sea: a high resolution modelling approach
Samuel SOMOT1 and Michel CREPON2
(1) CNRM/GAME, Météo-France, Toulouse, France
(2) LOCEAN, IPSL, CNRS, Paris, France

2. Motivations Regional climate change:
The Mediterranean climate might become warmer and drier during the 21st century (IPCC, 2001; IPCC, 2007)
Robust results among GCMs and RCMs (FP5-PRUDENCE project)
Already observed T-S trends (Rixen et al. 2005)
Possible regional impact on the Mediterranean sea:
Temperature, Salinity, Surface circulation, MTHC, Biochemistry
Atlantic intermediate water through the Gibraltar Strait and the MOW

3. Models High resolution ocean model: OPAMED8
OPA8.1, limited to the Mediterranean Sea
Collaboration : CNRM, LOCEAN, MERCATOR
x = 1/8°x1/8°cos   10 km
43 vertical levels
C.I. : MedAtlas-II + 20-yr spin-up
see my poster tomorrow afternoon (C2)
BATHYMETRY
OROGRAPHY
Forcings (present climate):
High resolution daily air-sea fluxes coming from ARPEGE-Climate at 50 km: Heat flux, Evap., Precip., Wind stress
Explicit river runoff: UNESCO database (33 rivers) + Black Sea
No SSS relaxation
SST relaxation: 8 days
Atlantic buffer zone 3D relax.

4. Simulations Two twin 140-year simulations
Scenario following the SRES-A2 hypothesis
Control run with the forcings
described in Somot et al. 2006, Clim. Dyn., 27

5. Scenario configuration
ARCM
ARPEGE-Climate
Global stretched
High resolution
Anomaly filter
trends
seasonal changes
x interannual
Surface
fluxes
River runoff
fluxes
anomalies
SST
anomalies
SST ano.
AOGCM
OPA, global
Low resolution
ARPEGE-Climate
global
OPAMED8
High resolution
Atlantic Ocean
T3D et S3D
anomalies

6. Surface forcings 2070-2099 Average 2070-2099 Average CTRL : -0.72 m/yr
E-P-R (mm/d)
Heat Flux (W.m-2)
Average
CTRL : -6.2 W/m2
SCEN : -1.8 W/m2
Average
CTRL : m/yr
SCEN : m/yr

7. Surface changes: SST and SSS
Mediterranean Sea average
SST and SSS time series
T and S scaling for comparing density effect
SST increase more than SSS in terms of density effect
Lead to a decrease in surface density
SSTmed = 3.1°C
SSSmed = 0.48
SST - Control
SST - Scenario
SSS - Control
SSS - Scenario
SST (°C)
SSS (psu)

8. Surface changes: spatial pattern
Spatial pattern in Summer and Winter
SST: strong seasonal cycle
SST: spatially homogeneous changes (due to SST relaxation ?)
SSS: weak seasonal cycle
SSS: strong spatial pattern due to changes in river runoff fluxes
SST anomaly (°C)
SSS anomaly
summer
summer
winter
winter
[ ] : Scenario – Control

9. Subbasin maximum mixed* layer depth (m)
* Diffusivity criterion (5 cm2/s)
Subbasin maximum mixed* layer depth (m)
1200
800
400
1960
2000
2050
2100
Adriatic: - 10%
2000
1000
3000
1960
2050
2100
500
1500
2500
Gulf of Lions: - 71%
1960
2000
2050
2100
1200
800
1600
400
Aegean: - 12%
1960
2000
2050
2100
1500
2500
500
1000
Levantine: - 43%
Change in the monthly-mean maximum of the MLD
Significant decrease for the deep convection
Spatial inhomogeneity (due to SSS changes)

10. Mediterranean THC 1.5 Sv 1.2 Sv Mediterranean ZOF 0.5 Sv, 1400 m MAW
Zonal Overturning stream Function (Myers & Haines 2002)
Good index for MTHC changes and for model intercomparisons
Stable during the control run
Control
Scenario
MAW
LIW
EMDW
Large decrease during the scenario
Possible impact on the biochemistry
0.2 Sv,
500 m
Gibraltar Strait
Sicily Strait
Greece
(from Somot et al. 2006, Clim. Dyn.)

11. Deep changes: heat and salt content
< Tmed > = 1.5°C
< Smed > = 0.23 psu
HC: heat content (°C)
SC: salt content (psu)
HC: Control, HC: Scenario
SC: Control, SC: Scenario

12. Deep changes: heat and salt content
< Tmed > = 1.5°C
< Smed > = 0.23
HC anomaly
(exponentiel fit in 2099)
Med Sea: 1.5°C
Gulf of Lions: +1.6°C
Levantine Basin: +1.3°C Adriatic Sea: +3.7°C Aegean Sea: +2.7°C
HC: heat content (°C)
SC: salt content (psu)
HC: Control, HC: Scenario
SC: Control, SC: Scenario
SC anomaly
(exponentiel fit in 2099)
Med Sea: 0.23
Gulf of Lions:
Levantine Basin: Adriatic Sea: +0.80
Aegean Sea: +0.41
Changes in the Mediterranean heat (HC) and salt content (SC):
HC increase > SC increase
Lightening of the water masses
Sub-basin inhomogeneity due to inhomogeneity in the MLD and THC changes

13. Conclusions Somot et al. 2006, Climate Dynamics, 27
Stable and realistic control run with OPAMED8 over 140 years
High resolution transient climate change scenario for the Med Sea
Quantification of the salinity and temperature increase
Deep convection and MTHC weakening
Warming and salting in the deep layers
Warming and salting of the Mediterranean Outflow Waters
Spatial inhomogeneity mainly due to SSS changes and river changes
Uncertainty assessment is required : intercomparison project
SRES scenario
Atmosphere model
Ocean model
Design of the simulation (towards a regional coupled model)

14. SSS anomaly (G. of Lions)
On-Going Work
Towards a Mediterranean AORCM
FM: Control, FM: Scenario
CM: Control, CM: Scenario
SSS anomaly (G. of Lions)
SSS increase quicker in the regional coupled model
MTHC: more stable
Forced model
OPAMED8
OPA
GCM
RCM
River
Surface
fluxes
SST
Atlantic
T3D, S3D
OPAMED8
OPA
GCM
RCM
SST
Atlantic
T3D, S3D
Coupled model
Somot et al. 2007, Global and Planetary change