Fourth Study Conference on BALTEX Scala Cinema Gudhjem

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Present-Day and Future Precipitation in the Baltic Region as Simulated in
Regional Climate Models
Erik Kjellström
Rossby Centre, SMHI, SE 60176 Norrköping, Sweden
Erik.Kjellstrom@smhi.se
1. Introduction
Regional climate model (RCM) experiments for the
European region are studied focusing on future greenhouse
gas-induced changes in precipitation over the Baltic Sea.
Uncertainties in the results due to model formulation,
emission scenario, and choice of global model for the lateral
boundary conditions are illustrated.
2. Models and data
Results from the Rossby Centre Regional Climate Model
System (RCAO) are used in this work. The model consists
of an atmospheric part (RCA) coupled to an oceanic model
for the Baltic Sea including Kattegat (RCO). The RCAO and
the simulations used in this study are described in more
detail in Räisänen et al., (2003, 2004). The RCAO results
are compared to results from other European centers running
RCMs with different configurations. The results are
presently being used in the PRUDENCE (Prediction of
Regional scenarios and Uncertainties for Defining EuropeaN
Climate change risks and Effects) project, see Christensen,
et al. (2002). The RCMs have been run for the future time
period 2071-2100 using SRES emission scenarios A2 and
B2 (Nakićenović et al., 2000) and for a control time period
(1961-1990). All models have been run with forcing
boundaries from the Hadley Centre AGCM HadAM3H
(Gordon et al., 2000). In addition RCAO and the model
from the Danish Meteorological Institute (DMI) have been
run with forcing boundaries from ECHAM4/OPYC3 from
the Max-Planck Institute for Meteorology (Roeckner et al.,
1999). Apart from the lateral boundaries also sea surface
temperatures are provided from the driving GCMs. In
RCAO, Baltic Sea SSTs are calculated by the ocean model
component. The SSTs from the RCO has been used in two
of the other PRUDENCE simulations, at DMI and KNMI.
An additional simulation with RCA was also performed in
which the SSTs were taken directly from the HadAM3H.
The horizontal resolution of the RCMs has been in the order
of 50 km for most of the models. In addition two
experiments have been run at 20-25km. All the data
presented here have been interpolated to a regular latitudelongitude
grid with a resolution of 0.5 O .
3. Results
The annual mean calculated future precipitation increase
over the Baltic Sea ranges between 5 and 50% in an area
mean sense, depending on which RCM, which lateral
boundary conditions and which emission scenario is used. In
general, most of the experiments give increased precipitation
in the Baltic Sea region except for the summer when the
precipitation is expected to decrease in large parts of the
surrounding land areas.
In summer the changes in precipitation differ dramatically
between the different models (Figure 1). While many of the
RCMs simulate large increases in precipitation over the
Baltic Sea others simulate only small changes or even
decreased precipitation. In an area mean sense the changes
over the Baltic Sea range between a reduction of almost
20% up to more than a doubling of the amount of
precipitation (Figure 2). In general, the models simulate
larger changes in the high (A2) emission scenarios than in
the low (B2) emission scenarios.
SMHI(RCO)
SMHI
MF
HC
MPI
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KNMI(RCO)
DMI(RCO)
DMI
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GKSS
Figure 1. Change in summertime (JJA) precipitation over
the Baltic Sea and surrounding land areas. Shown are
simulated future conditions in SRES emission scenario A2
minus control run conditions. All RCMs at the different
centers in the plot have been run with the same lateral
boundary conditions (HadAM3H). SSTs are taken directly
from the GCM unless noted (RCO).
Precipitation (%)
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Temperature ( o C)
Figure 2. Change in summertime (JJA) precipitation and
2m-temperature over the Baltic Sea. Shown are simulated
future conditions in scenarios B2 (left) and A2 (to the right
of the dashed line) minus control run conditions. Each
RCM is given different symbols. Red (blue) indicates
RCMs run with HadAM3H (ECHAM4/OPYC3) boundary
data. Green denotes models using HadAM3H boundaries
and Baltic Sea SSTs from the RCAO.
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