The overall objective of the research project CLIMOD (CLImate MODelling) was to contribute to the international research effort leading to an improved understanding of the climate system and to a better assessment of the impact of human activities on the global and regional climates. Two main tools were employed to reach this goal: modelling and data analysis. Four Belgian reaseach teams haved pooled their expertise in this project: ASTR-GCMG (global climate modelling), GI (ice-sheet modelling), ASTR-RCMG (regional climate modelling), and RMI-GCS (climate data).
At the beginning of the project, members of the research network CLIMOD had at their disposal a coupled atmosphereŠocean general circulation model (AOGCM), the first and the only one in Belgium, a regional atmospheric model (called MAR), and a Greenland ice-sheet model (GISM). Each of these complex three-dimensional models was run by a different team in a different location. At the end of the project, a community model, to which each team has contributed a component, is accessible to all in a common computer environment.
The physics of each component has been improved to stay in line with the latest advances of the climate science. Radiation, clouds, and oceanic vertical mixing have received a particular attention in the AOGCM, with the specific goal of reducing the drift observed with similar models. The GISM has been improved in the areas of mass balance, iceberg calving, and bedrock isostasy. After a thorough validation over Greenland, the MAR model has been used to refine the meltwater-budget parameterisation utilised by the GISM. The refinements proposed did not improve significantly the mass-balance results. So, we decided to use the original formulation in the climate-change experiments conducted with the GISM. In parallel, a 50-km-resolution version of MAR has been validated over Western Europe for the present climate. This validation was carried out by nesting the model in the European Centre for Medium Range Weather Forecast (ECMWF) re-analyses. We also evaluated the ability of a finer-resolution-version of MAR limited to Belgium to reproduce extreme events.
The AOGCM and GISM have been coupled together. The coupled model has then been forced by the Intergovernmental Panel on Climate Change (IPCC) scenario SRES B2 for both greenhouse-gas concentrations and sulphate-aerosol loading. By the end of the next century, the model simulates a global surface warming of 2.3C and a global increase in precipitation of 3%, which fall within the range of estimates obtained with other models. The projected rise in sea-level due to thermal expansion reaches 22 cm in 2100. The partial melting of the Greenland ice sheet induces an additional rise in sea level of 4 cm. Greenhouse-gas-induced changes in meltwater flux from the Greenland ice sheet do not seem to impact on the simulated climate, but this result must be taken with caution as the strength of the North Atlantic thermohaline circulation decreases with time in the control run performed with the model.
One of the initial objectives of CLIMOD was to perform with MAR a detailed assessment of the climate-change projections over Western Europe for the end of the 21st century. For several reasons explained in the main text, we were not able to reach this goal. We have however demonstrated that MAR is ready to carry out such as study.
We have also produced a high-quality (homogeneous) regional climatic database for Belgium from observational data covering the last few decades and characterised the regional patterns of the Belgium climate. Globally for Belgium, the extreme temperatures exhibit a warming trend of 2 to 2.5C per century over the last 50 years, mainly in summer. A particularly warm period started abruptly after 1988. The most significant regional warming trends are observed in the coastal regions for the maximum temperature, and in the central part of the country and in regions of highest altitude for the minimum temperature. Regarding the annual mean precipitation, no significant trend was detected.
Furthermore, we have reconstructed and analysed long-term series of temperature and precipitation in order to improve our knowledge of the secular evolution of the Belgian climate. The minimum temperature shows an overall warming trend over the country of 0.9C per century, with an abrupt increase around 1988. The results for the maximum temperature are less clear. For precipitation, a positive trend over the century is generally detected over the country, mainly related to an increase during the 1900 to 1935 period. It should be noted that all these data constitute an invaluable tool to evaluate the performance of regional climate models over Belgium.
Finally, the transition towards a more advanced AOGCM has been prepared.