The Climate Local Model CLM

CLM, which stands for Climate version of the "Local Model", is a non hydrostatic European regional climate model, which can be used for simulations on time scales up to centuries and spatial resolutions between 1 and 50 km [3]. The boundary conditions of the CLM are provided by the simulation results of the coupled atmosphere-ocean global climate model ECHAM5/MPIOM [4] at six hourly intervals. This coupling results in a physical dynamical downscaling, where the Global Circulation Model (GCM) output data are used as boundary conditions (idem, "forcing") to dedicated Regional Climate Models (RCM) [5]. The CLM regional climate model covers the west European region including the Baltic Sea and the greater part of the Mediterranean Sea.

For the European region two simulation datasets were produced to investigate IPCC scenarios: one covers the past climate, i.e. from 1960 to 2000, and the other covers predictions until 2100. The climate of the twentieth century was simulated by three twentieth century realisation runs, which are all based on the same control run, but set off at different initialisation times. The climate of the twenty-first century was modelled based on the A1B and B1 IPCC climate scenarios, and five more transient experiments are planned, since the generation of results is still in progress.

For predictive studies, the main difficulties in using climate models at local level lie in the transfer of spatial scale, also known as "downscaling". Ad hoc downscaling statistical regression methods were developed for the transfer of CLM data to the hydrology model grid (Fig. 10.2).

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