High-Resolution Sensitivity Studies with the Regional Climate Model COSMO-CLM
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High-resolution regional ensemble climate simulations with the regional climate model COSMO-CLM are performed for Southwest Germany to study the sensitivity of meteorological and hydrological variables to simulation set-up, including the domain size, driving data, horizontal resolution and physical parameterisations and parameter settings. The model setup found adequate for such simulations is a domain including the Alps, ERA-40 reanalysis data as driving data, and a horizontal resolution of 7 km. The sensitivity of simulation results to a changed model setup is highest for the change in driving data and is higher in winter than in summer. This adequate model setup is used to investigate the influence of the land surface scheme on COSMO-CLM simulations. The standard land surface scheme TERRA_LM is replaced by the land surface scheme VEG3D, which contains an explicit vegetation layer. Standalone simulations with both land surface schemes show better agreement with observations for the VEG3D scheme, especially over high vegetation. Coupled online with the COSMO-CLM, both schemes yield similar results on the spatial patterns of the meteorological variables but the absolute values may differ considerably. No model system gives better results than the other for 2m-temperature and precipitation compared to observations, and the difference in TERRA_LM and VEG3D simulation is similar to the difference obtained by changing other physical parameterisations or the time-integration scheme. Freezing and melting processes in the soil are implemented in VEG3D to make the scheme applicable for climate simulations. Stand-alone simulations with the new scheme yield better results than those without the consideration of freezing and melting processes. Better results in stand-alone simulations are obtained when using different soil types within one soil column, instead of using one single soil type for the whole column. Therefore, a soil type inventory for Germany for the coupled model system COSMOCLM/ VEG3D is provided in this thesis, which contains several soil types within one soil column. A strategy for a statistical-dynamical downscaling method is developed and evaluated to replace time consuming day by day simulations. The method shows the ability to yield results similar to those of the continuous simulation.