Improved regional scale processes reflected in projected hydrological changes over large European catchments |
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| Authors: | Stefan Hagemann Holger Göttel Daniela Jacob Philip Lorenz Erich Roeckner |
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| Institution: | (1) Max Planck Institute for Meteorology, Bundesstr. 53, 20146 Hamburg, Germany |
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| Abstract: | For the fourth assessment report of the Intergovernmental Panel on Climate Change (IPCC), the recent version of the coupled
atmosphere/ocean general circulation model (GCM) of the Max Planck Institute for Meteorology has been used to conduct an ensemble
of transient climate simulations These simulations comprise three control simulations for the past century covering the period
1860–2000, and nine simulations for the future climate (2001–2100) using greenhouse gas (GHG) and aerosol concentrations according
to the three IPCC scenarios B1, A1B and A2. For each scenario three simulations were performed. The global simulations were
dynamically downscaled over Europe using the regional climate model (RCM) REMO at 0.44° horizontal resolution (about 50 km),
whereas the physics packages of the GCM and RCM largely agree. The regional simulations comprise the three control simulations
(1950–2000), the three A1B simulations and one simulation for B1 as well as for A2 (2001–2100). In our study we concentrate
on the climate change signals in the hydrological cycle and the 2 m temperature by comparing the mean projected climate at
the end of the twenty-first century (2071–2100) to a control period representing current climate (1961–1990). The robustness
of the climate change signal projected by the GCM and RCM is analysed focussing on the large European catchments of Baltic
Sea (land only), Danube and Rhine. In this respect, a robust climate change signal designates a projected change that sticks
out of the noise of natural climate variability. Catchments and seasons are identified where the climate change signal in
the components of the hydrological cycle is robust, and where this signal has a larger uncertainty. Notable differences in
the robustness of the climate change signals between the GCM and RCM simulations are related to a stronger warming projected
by the GCM in the winter over the Baltic Sea catchment and in the summer over the Danube and Rhine catchments. Our results
indicate that the main explanation for these differences is that the finer resolution of the RCM leads to a better representation
of local scale processes at the surface that feed back to the atmosphere, i.e. an improved representation of the land sea
contrast and related moisture transport processes over the Baltic Sea catchment, and an improved representation of soil moisture
feedbacks to the atmosphere over the Danube and Rhine catchments. |
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| Keywords: | Regional climate change Hydrological cycle European catchments GCM and RCM ensembles Robustness |
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