Fourth Study Conference on BALTEX Scala Cinema Gudhjem

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- 164 - Using Multiple RCM Simulations to Investigate Climate Change Effects on River Flow to the Baltic Sea L. Phil Graham Swedish Meteorological and Hydrological Institute SE-601 76 Norrköping, Sweden e-mail: phil.graham@smhi.se 1. Introduction Changes to the climate in the Baltic Basin will not only affect the total amount of freshwater flowing into the sea, but also the distribution of the origin of these flows. These effects have been analyzed using a large-scale hydrological model driven by results from regional climate models (RCMs). Six different climate change simulations from a multiple RCMs and emissions scenarios were used. Additional simulations are under investigation. The resulting change to total mean annual river flow to the Baltic Sea ranges from -2 to +15 percent of present-day flow according to the different climate scenarios. The magnitude of changes within different sub-regions of the basin varies considerably. However, common to all of the scenarios evaluated is a general trend of reduced river flow from the south of the Baltic Basin together with increased river flow from the north. 2. Hydrological Modeling The hydrological modeling was performed with the HBV-Baltic model previously used in other studies (e.g., Graham and Jacob, 2000; van den Hurk et al., 2002). This model does a reasonable job of representing the large-scale hydrology of the present climate (Graham, 1999). Since its original development, improvements have been made to reduce the uncertainty of using it for future climate applications. This includes, among others, a revised calibration of the temperature-based evapotranspiration scheme to allow results from climate models to more specifically dictate climate changes to evapotranspiration. Changes were also made to better represent the effects of ice on river discharge from Lake Ladoga to the Gulf of Finland. Due to biases in results from climate models for the present climate—precipitation in particular—the climate change signal is typically added to an observational database that is then used as input to the hydrological model to represent the future climate. This is a common approach for impacts modeling, sometimes referred to as the delta change approach. Although some attempts have been made to use RCM results more directly in hydrological modeling (e.g., Graham, 2002), all of the hydrological simulations presented here result from a delta change type of approach. 3. Climate Modeling Six different climate change simulations from three different RCMs were used in this study. Four were produced with the Rossby Centre Atmosphere Ocean Model (RCAO), a coupled atmosphere – Baltic Sea regional climate model (Döscher et al., 2002). The other two were produced with the HIRHAM Model (Danish Meteorological Institute) and the CHRM Model (Swiss Federal Institute of Technology). Data from two global general circulation models (GCMs), HadAM3H (Hadley Centre) and ECHAM4/OPYC3 (Max- Planck-Institut für Meteorologie), were used as boundary conditions to drive the regional RCAO model (Räisänen et al., 2003, Kjellström, 2004). The horizontal resolution of the RCMs for all of these simulations is approximately 50 km. The time period for each of the simulations spans 30 years, corresponding to 2071-2100 and 1961-1990 for the scenario and control simulations, respectively. Simulations of the A2 and B2 emissions scenarios from the IPCC (Intergovernmental Panel on Climate Change) suite of SRES scenarios were used. The A2 scenario represents the more severe case of these two. Due to model specific parameterizations, the use of different GCMs and different RCMs provides different projections of the future climate, even when formulated to represent the same potential emissions scenario. Thus, the six RCM simulations provide a range of projected outcomes for the future climate as a response to anthropogenic influence on the atmosphere. However, it is impossible to specify which, if any, of the six scenarios is most likely to occur. For brevity, the simulations will hereafter be referred to as RCAO-H/A2, RCAO-H/B2, HIRHAM-H/A2 and CHRM-H/A2 for the HadAM3H projections, and RCAO-E/A2 and RCAO-E/B2 for the ECHAM4/OPYC3 projections. 4. Results Hydrological modeling results for a simulated changed climate for the six regional climate change scenarios are shown in Figure 1, which summarizes river discharge for the total Baltic Basin and its five main sub-regional drainage basins. The general trends in the north show increases in wintertime river flow coupled with somewhat lower and earlier springtime peak flows. This reflects the substantial changes that warmer temperatures will inflict on the snow regime in the north. Trends in the south show more pronounced effects on summertime river flow, while springtime peaks in some cases remain as high as presentday conditions. River flow to the Gulf of Finland exhibits a combination of these effects, even though these flows are highly dictated by the outflow from Lake Ladoga. Looking at river flow to the total Baltic Basin, it can be seen that the GCM model used for boundary conditions has as much impact on total river flow as the emissions scenarios used. The ECHAM4/OPYC3-based results show generally higher flows than the HadAM3H-based results, regardless of which SRES scenario is examined. Figure 2 shows how changes to river discharge translate into seasonal and annual flow volume changes for each climate change simulation. They range from a mean maximum decrease of -18 % for CHRM-H/A2 in the summer season (JJA) to a mean maximum increase of +54 % for RCAO-E/A2 in the winter season (DJF). RCAO- H/A2 and CHRM-H/A2 are the only scenarios that show a substantial decrease for the autumn season (SON).
- 165 - Figure 1. Modeled seasonal river discharge to the Baltic Sea from HBV-Baltic for present-day conditions (shaded) and six climate change simulations. Shown are daily means over the 23-year modeling period. Figure 2. Modeled percent volume change in river discharge to the Baltic Sea from HBV-Baltic, summarized as mean seasonal and annual values for the total Baltic Basin for the six climate change simulations. 5. Conclusions Analysis of the large-scale impacts of climate change on river flow to the Baltic Sea shows both pronounced spatial and seasonal effects. Although there are variations in magnitude and regional effects, trends from multiple climate change simulations show similar characteristics of the following: • increased winter flows • reduced summer flows • increased flow from northern basins • decreased flow from southern basins However, the GCM model used for boundary conditions appears to have a stronger effect on results than either the emissions scenarios used or the regional climate models used. References Döscher, R., Willén, U., Jones, C., Rutgersson, A., Meier, H.E.M., Hansson, U. and Graham, L.P., The development of the regional coupled oceanatmosphere model RCAO. Boreal Environ. Res. 7, 183-192, 2002. Graham, L.P., Modeling runoff to the Baltic Sea. Ambio 28, 328-334, 1999. Graham, L.P., A simple runoff routing routine for the Rossby Centre Regional Climate Model. In: A. Killingtveit (ed.) Proceedings from XXII Nordic Hydrological <strong>Conference</strong>. Røros, Norway, 4-7 August. Nordic Hydrological Programme Report no. 47, 573- 580, 2002. Graham, L.P. and Jacob, D., Using large-scale hydrologic modeling to review runoff generation processes in GCM climate models. Meteorol. Z. 9, 49-57, 2000. Kjellström, E., Recent and future signatures of climate change in Europe. Ambio, (in press), 2004. Räisänen, J., Hansson, U., Ullerstig, A., Döscher, R., Graham, L.P., Jones, C., Meier, M., Samuelsson, P. and Willén, U., European climate in the late 21st century: regional simulations with two driving global models and two forcing scenarios. Clim. Dynamics, published on-line 14 Nov 2003, DOI: 10.1007/s00382- 003-0365-x, 2003. van den Hurk, B.J.J.M., Graham, L.P. and Viterbo, P., Comparison of land surface hydrology in regional climate simulations of the Baltic Sea catchment. J. Hydrol. 255, 169-193 2002.
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Fourth Stu
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Preface The 4 th Study</str
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- I - Table of Abstracts Title Auth
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- III - Sensitivity in Calculation
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- V - Parameter Estimation of the S
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- VII - The Realism of the ECHAM5.2
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Adam, W. K. .......................
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- 1 - Activities of the GEWEX Hydro
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eference site archive (Cabauw, Neth
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- 5 - Remote Sensing of Atmospheric
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minute averages around the satellit
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- 9 - Precipitation Type Statistics
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- 11 - Assimilation of New Land Sur
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Multichannel Microwave Radiometer f
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output has been processed in an equ
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height dependence of the Z-R-relati
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- 19 - CERES and Surface Radiation
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- 21 - Coastal Wind Mapping from Sa
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- 23 - Clouds and Water Vapor over
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- 25 - Broadband Cloud Albedo from
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- 27 - Observation of Clouds and Wa
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shows a ground-track of the vessel
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- 31 - Determination and Comparison
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- 33 - Spatial Variability of Snow
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- 35 - EVA-GRIPS: Regional Evaporat
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- 37 - LITFASS-2003 - A Land Surfac
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-39- Calibrated Surface Temperature
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- 41 - The Marine Boundary Layer -
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- 43 - Characteristics of the Atmos
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Figure 2. Surface stress from two d
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During the experiment the water was
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While the number of smallest drops
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SCANDIA will not be supported any l
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- 53 - Relationships Between Precip
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- 55 - Analysis of the Role of Atmo
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- 57 - Meteorological Peculiarities
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Baltic Sea Inflow Events Jan Piechu
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- 61 - The Different Baltic Inflows
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- 63 - Observations of Turbulent Ki
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- 65 - The Influence of Synoptic Si
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-67- Improved Method for the Determ
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-69- The Helicopter-Borne Turbulenc
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- 71 - CEOP Reference Site Data fro
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- 73 - The BALTEX Hydrological Data
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- 75 - Hydrological and Hydrochemic
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-77- Sea-level Monitoring at MARNET
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1 0.8 0.6 0.4 0.2 GO(CLD-M) ERA40 S
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Figure 2. Monhly mean values of lat
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In the case of an ideal fit, the co
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- 85 - Influence of Atmospheric For
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The largest inter-annual variabilit
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References Andrejev, O, Sokolov, A.
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On the other hand, if the stratific
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Cyberska 1989, Cyberska and Krzymin
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- 95 - Continental-Scale Water-Bala
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- 97 - ICTS (Inter-CSE Transferabil
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The subsurface flow calculation is
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functions only data with higher qua
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- 103 - Modelling the Impact of Ine
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- 105 - Objective Calibration of th
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- 107 - Validation of Boundary Laye
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- 109 - Simulated Dynamical Process
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spreads along isobaths (fig.2). As
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Page 131 and 132: Figure 2. Long-term variability in
Page 133 and 134: obvious from temperature charts. Ho
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Page 137 and 138: Maximum 5 day precipitation (mm) Nu
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Page 143 and 144: - 127 - Storminess on the Western C
Page 145 and 146: - 129 - Trends in Wind Speed over t
Page 147 and 148: - 131 - Wind Energy Prognoses for t
Page 149 and 150: - 133 - Detection of Climate Change
Page 151 and 152: Figure 3. Cross section of salinity
Page 153 and 154: of 35 m/s up to 3 hours. Data on wi
Page 155 and 156: Figure 2. Time series of Mean Sea L
Page 157 and 158: - 141 - Calculation and Forecast of
Page 159 and 160: - 143 - An Overview of Long-Term Ti
Page 161 and 162: - 145 - Baltic Sea Saltwater Inflow
Page 163 and 164: - 147 - Significance of Feedback in
Page 165 and 166: Lindström, G., Johansson, B., Pers
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Page 169 and 170: - 153 - The Realism of the ECHAM5.2
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Page 175 and 176: Figure1. Modeled percent volume cha
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Page 179: surface heat fluxes close to zero.
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Page 185 and 186: - 169 - Extreme Precipitation on a
Page 187 and 188: at the stations Pärnu (Estonia) an
Page 189 and 190: 6. Results There are many possible
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Page 193 and 194: The structure of water bodies cadas
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Page 199 and 200: - 183 - Generating Synthetic Daily
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Fourth Study Conference on BALTEX Scala Cinema Gudhjem

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