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question E. Finally a 10-member ensemble of ALADIN-
Climate forced in a Perfect Big Brother approach allows to
assess the impact of the internal variability of RCMs. The
numerical set-up of this suite of RCM experiments is
described in detailed in the following papers: Elguindi et al.
(in preparation, question A); Herrmann and Somot (2008,
question C), Radu et al. (2008, question C); Somot et al.
(2008, question D), SanchezGomez et al. (2008, question E)
and SanchezGomez et al. (in preparation, question F).
4. Observations estimates
In the literature, using surface observational datasets, the
MSWB estimates range from 520 to 950 mm/yr whereas the
Gibraltar Strait estimates of the water budget range from 630
to 1135 mm/yr. Other authors estimated the MSWB using
low resolution reanalysis and obtained a lower range going
from 391 to 524 mm/yr.
In our study, different surface datasets have been used to
estimate the MSWB. This surface datasets are derived from
in-situ and/or satellite measurements (see Table 1). This
observation estimates are used to evaluate and to sort out
between the different modeling techniques.
Variable Dataset Period
Evaporation OAFlux
HOAPS
1958-2006
1988-2006
Precipitation GPCP
HOAPS
1979-2003
1988-2006
River discharge Ludwig et al. (2009) 1960-2000
Black sea discharge Stanev et al. (2000) 1923-1997
Short wave ISCCP
NOC
1983-2008
1983-2006
Long wave ISCCP
NOC
1983-2008
1983-2006
Latent Heat OAFlux
NOC
1958-2006
1983-2006
Sensible Heat OAFlux
NOC
1958-2006
1983-2006
Table 1: Observation dataset allowing to evaluate the
Mediterranean Sea Water Budget and its components.
5. Results
Following the 6 main scientific issues defined in section 2
and the RCM experiments defined in section 3, we analyze
how the design of the RCMs impacts the mean behaviour,
the interannual variability and the trends of the MSWB.
The increase in spatial resolution from IPCC-like model to
state-of-the-art RCM improves the representation of the
MSWB in increasing the total water loss by the
Mediterranean Sea surface in agreement with the Gibraltar
Strait observed estimates. The choice of the RCM (same
resolution, same LBC, different set-up and physics) leads to
a large spread in terms of MSWB estimates. The highfrequency
air-sea coupling seems also to impact the MSWB
even if other coupled simulations are required to legitimate
this result. Impact of the RCM internal variability, of the
nudging technique and of the modeling technique is also
investigated.
6. Perspectives
A large part of the results relies on the ARPEGE-
ALADIN-Climate models and can therefore be modeldependent.
A broader analysis of the Mediterranean Sea
Water Budget using other AORCM or Regional Earth
System model should be carried out. Moreover the
uncertainty of the observed estimates of the MSWB can be
considered as a limitation of such a study and should be
reduced in the future through a intense in-situ and remote
observing effort. Both tasks are planned in an international
coordinated framework during the 2010-2020 HyMex
project (www.cnrm.meteo.fr/hymex/).
References
Elguindi N., Somot S., Déqué, M., Ludwig, Climate
chnage evolution of the hydrological balance of the
Mediterranean, Black and Caspians Seas: impact of
climate model resolution, Clim. Dyn, in preparation.
Ludwig, W., Dumont, E., Meybeck, M., and Heussner, S.,
River discharges of water and nutrients to the
Mediterranean Sea: Major drivers for ecosystem
changes during past and future decades, Progress In
Oceanography, accepted, 2009
Radu R., Déqué M. and Somot S., Spectral nudging in a
spectral regional climate model, Tellus, 60A(5):885-
897. doi: 10.1111/j.1600-0870.2008.00343.x, 2008
SanchezGomez E., S. Somot, M. Déqué, Ability of an
ensemble of regional climate models to reproduce the
weather regimes during the period 1961-2000. Clim.
Dyn., doi:10.1007/s00382-008-0502-7, 2008
SanchezGomez E, S. Somot, N. Elguindi, S. Josey,
Simulation of the Water and Heat budgets in the
Mediterranean Sea by an ensemble of high resolution
Regional Climate Models experiments, Clim. Dyn., in
preparation
Somot S. , Sevault F., Déqué M., Crépon M., 21st century
climate change scenario for the Mediterranean using a
coupled Atmosphere-Ocean Regional Climate Model.
Global and Planetary Change, 63(2-3), pp. 112-126,
doi:10.1016/j.gloplacha.2007.10.003, 2008
Herrmann, M. J., and S. Somot, Relevance of ERA40
dynamical downscaling for modeling deep convection
in the Mediterranean Sea, Geophys. Res. Lett., 35,
L04607, doi:10.1029/2007GL032442, 2008
Stanev E.V. Le Traon P.Y. and Peneve E.L., Sea level
variations and their dependency on meteorological and
hydrological forcing : analysis of altimeter and surface
data for the Black Sea, J. Geophys. Res., 105, 17203-
17216, 2000