RACMO simulation of the North Sea flood of 1953. Color yellow indicates 12 Bft windspeed.
RACMO is the Regional Atmospheric Climate MOdel of the KNMI. It is developed and maintained by the Regional Climate division. RACMO played a crucial role in the formulation of the climate scenarios for the Netherlands. Long climate scenario integrations (up to 2100) with RACMO have been performed in previous EU projects PRUDENCE and ENSEMBLES, and will be performed in new EU projects and WCRP CORDEX activity. Besides long climate integrations, RACMO is also an important tool to understand local and regional processes in the present-day climate. As such, we mention the influence of the North Sea on the Dutch climate and the ice mass balance of the Greenland ice sheet.
Recently RACMO has been identified as the best European regional climate model participating in the ENSEMBLES project. In ENSEMBLES 15 European regional climate models are compared for the present-day climate, and long climate scenario integrations from 1950 to 2100 are performed.
Figure 1. Weights assigned to different models (numbers 1 to 15) based on the quality of the simulation for the present-day climate. The three bars denote different methods to assign weights. In all of the three methods RACMO (model 7) yields the highest score (see Christensen et al. 2010; Climate Research, 44, 179-194,
doi:10.3354/cr00916).
The present version of RACMO, version 2, consists of the physics package of the global circulation model of the ECMWF (European Centre for Medium-Range Weather Forecasts) embedded in the dynamical kernel of the numerical weather prediction model HIRLAM (HIgh Resolution Limited Area Model). More detailed information about RACMO can be found in the technical documentation of the present version RACMO2.1:
Meijgaard, E. van, L.H. van Ulft, W.J. van de Berg, F.C. Bosveld, B.J.J.M. van den Hurk, G. Lenderink and A.P. Siebesma, The KNMI regional atmospheric climate model RACMO, version 2.1 KNMI publication: TR-302, 24/12/2008, pp43 (pdf).
Meijgaard, E. van, L.H. van Ulft, G. Lenderink, S.R. de Roode, L. Wipfler, R. Boers, R.M.A. Timmermans, 2012. Refinement and application of a regional atmospheric model for climate scenario calculations of Western Europe. Climate changes Spatial Planning publication: KvR 054/12, ISBN/EAN 978-90-8815-046-3, pp 44 (pdf).
Previous versions of RACMO
A previous version of RACMO, version 2.0, is described in:
Lenderink, G., B. van den Hurk, E. van Meijgaard, A. van Ulden, and H. Cuijpers. Simulation of present-day climate in RACMO2: first results and model development. 2003, KNMI publication TR-252 (pdf)
Before that, RACMO version 1 was based on a different physics package using an adaptation of the ECHAM4 physics.
What is a regional climate model ?
Regional climate models are in many respects similar to global climate models, based on very similar prescriptions of the climate system. The main difference between the two is the model resolution and the model domain. A global climate model computes with averages over an area of typically 200 x 200 km2 ; they have a resolution of typically 200 km. A regional climate model has a resolution of typically 10-50 km. At the same time, whereas the computational grid of global climate models cover the whole earth, regional climate models usually have a domain as large as Europe (or another continent) or even smaller. At the (lateral) boundaries of the domain the atmospheric flow conditions (winds, temperature, moisture) have to be prescribed. This is either done based on observation-based analysis (like, ERA40 or ERA-interim) forcing the model as close as possible to reality, or global climate model simulations in the case of climate change scenarios. It is also common to prescribe sea surface temperature and sea ice extent from either observations or the forcing GCM. Regional climate model are used as a tool to:
- understand processes on a regional level. Examples are the work on coastal precipitation and the mass balance of large ice sheets.
- downscale coarse resolution information from global climate model to high resolution information needed for many climate change impact assessments. An example is the work on precipitation extremes, and the work on the Dutch climate scenarios (link to the paper on the downscaling of the KNMI’06 scenarios). These long integrations are often done in large international projects, like the EU funded projects PRUDENCE and ENSEMBLES and the WCRP project CORDEX.
Figure 2. Results of a simulation of the present-day climate with RACMO2. Shown are mean summer temperature (oC) and mean summer precipitation (mm/day). This model simulation is driven by ERA40 boundary conditions, which prescribe realistic flow conditions at the lateral boundaries of the domain. The quality of these fields has been rated as the best amongst 15 European regional climate models (see Figure 1).
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