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 samuel.somot@meteo.fr

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

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.

Simulations Two twin 140-year simulations Scenario following the SRES-A2 hypothesis Control run with the 1960-1980 forcings described in Somot et al. 2006, Clim. Dyn., 27

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

Surface forcings 2070-2099 Average 2070-2099 Average CTRL : -0.72 m/yr E-P-R (mm/d) Heat Flux (W.m-2) 2070-2099 Average CTRL : -6.2 W/m2 SCEN : -1.8 W/m2 2070-2099 Average CTRL : -0.72 m/yr SCEN : -0.94 m/yr

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)

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 [2070-2099] : Scenario – Control

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)

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.)

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

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: +0.25 Levantine Basin: +0.10 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

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) samuel.somot@meteo.fr

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 samuel.somot@meteo.fr