The transferability of the regional climate model REMO with a standard setup over different regions of the world has been evaluated. The study is based on the idea that the modeling parameters and parameterizations in a regional climate model should be robust to adequately simulate the major climatic characteristic of different regions around the globe. If a model is not able to do that, there might be a chance of an “overtuning” to the “home-region”, which means that the model physics are tuned in a way that it might cover some more fundamental errors, e.g., in the dynamics. All simulations carried out in this study contribute to the joint effort by the international regional downscaling community called COordinated Regional climate Downscaling EXperiment (CORDEX). REMO has been integrated over six CORDEX domains forced with the so-called perfect boundary conditions obtained from the global reanalysis dataset ERA-Interim for the period 1989 to 2008. These six domains include Africa, Europe, North America, South America, West Asia and the Mediterranean region. Each of the six simulations was conducted with the identical model setup which allows investigating the transferability of a single model to regions with substantially different climate characteristics. For the consistent evaluation over the different domains, a new evaluation framework is presented by combining the Köppen-Trewartha climate classification with temperature-precipitation relationship plots and a probability density function (PDF) skill score method. The evaluation of the spatial and temporal characteristics of simulated precipitation and temperature, in comparison to observational datasets, shows that REMO is able to simulate the mean annual climatic features over all the domains quite reasonably, but still some biases remain. The regions over the Amazon and near the coast of major upwelling regions have a significant warm bias. Wet and dry biases appear over the mountainous regions and East Africa, respectively. The temperature over South America and precipitation over the tundra and highland climate of West Asia are misrepresented. The probable causes leading to these biases are discussed and ideas for improvements are suggested. The annual cycle of precipitation and temperature of major catchments in each domain are also well represented by REMO. The model has performed well in simulating the inter- and intra-seasonal characteristics of different climate types in different regions. Moreover, the model has a high ability in representing the general characteristics of different climate types as measured by the probability density function (PDF) skill score method. Although REMO seems to perform best over its home domain in Europe (domain of development and testing), the model has simulated quite well the climate characteristics of other regions with the same set of parameterization options. Therefore, these results lead us to the conclusion that REMO is well suited for long-term climate change simulations to examine projected future changes in all these regions.

A regional-scale sensitivity study has been carried out to investigate the climatic effects of forest cover change in Europe. Applying REMO (regional climate model of the Max Planck Institute for Meteorology), the projected temperature and precipitation tendencies have been analysed for summer, based on the results of the A2 IPCC-SRES emission scenario simulation. For the end of the 21st century it has been studied, whether the assumed forest cover increase could reduce the effects of the greenhouse gas concentration change.

Atmospheric observations demonstrate that, during the last decades, the climate has changed. As reported by the Intergovernmental Panel on Climate Change (IPCC, 2001, 2007), a mean increase of temperature by 0.09 K per decade was observed globally from 1951 to 1989. Up to now, 2008, this trend has continued. Europe experienced an extraordinary heat wave in summer 2003, with daily mean temperatures being about 10° warmer than the long-term mean. The increase of temperature varies depending on the region and season. It seems to be accompanied by changes in several hydro-meteorological quantities, like number and duration of heat waves, frost periods, storminess, or precipitation. In some regions of Germany, for example, winter precipitation has increased by more than 30% within the last four decades. In addition, very intense precipitation was observed in summer 2002 in parts of the Elbe drainage basin, which faced a severe flooding. The quantification of these changes and their possible impacts on health is a very important topic, for which regional climate change scenarios provide useful information. The analyses of possible climate change focusing on hydro-meteorological quantities, which have a major influence on vectors and rodent reservoirs will be an ongoing challenge for future research.

Global climate change initiates changes in regions as well. These changes can be calculated using regional climate change scenarios. For Germany first results show an increase of the annual mean temperatures between 2.5 and 3.5°C depending on the assumed emission scenario. Winter temperatures can rise by about 4°C in the South or Southeast of Germany. It seems that the annual precipitation sums do not change, but the annual cycle of precipitation might get more extreme. The results indicate a decrease of summer precipitation up to 30% in some regions of Germany and an increase in the winter months of more than 30%.