Vol. 112, No. 3-4 * Pages 141–300 * July - December 2008

Observational records show that the global climate is changing and these changes are visible in the Central and Eastern European Countries (CEEC). Certainly negative impacts of climate change will involve significant economic losses in several regions of Europe, while others may bring health or welfare problems somewhere else. Within the EU funded project CLAVIER (Climate ChAnge and Variability: Impact on Central and Eastern EuRope) three representative CEEC are studied in detail: Hungary, Romania, and Bulgaria. Researchers from 6 countries and different disciplines identify linkages between climate change and its impact on weather patterns with consequences on air pollution, extreme events, and water resources. Furthermore, an evaluation of the economic impact on agriculture, tourism, energy supply, and public sector will be conducted. CLAVIER focuses on ongoing and future climate changes in CEEC using measurements and existing regional scenarios to determine possible developments of the climate and to address related uncertainties. Three regional climate models are used to simulate the climate evolution in CEEC for the period 1951 to 2050, the future regional climate projection being the first half of the 21st century. The issue of climate change uncertainties is addressed through the multi-model and multi-scenario ensemble approach. As a result, CLAVIER establishes a large data base, tools, and methodologies, which contribute to reasonable planning for a successful development of society and economy in CEEC under climate change conditions. Current regional climate projections show a strong warming and drying during the summer months, which seems partly due to a systematic error in model simulations. Detailed validation of the CLAVIER simulations, which goes much beyond this paper, is needed, and the results have to be related to possible climate changes projected for the region in future simulations.

Regional climate models are popular and efficient tools for the assessment of the regional aspects of the past and future climate. The application of such models is indispensable for the provision of climate simulations over a smaller region, such as Hungary. The ALADIN-Climate regional climate model was adapted by the Hungarian Meteorological Service in order to derive a regional climate model which can be used efficiently for climate change simulations over Hungary. In this paper three different recent past (1961–2000) regional climate simulations are examined and evaluated: the ERA-40-driven 10 km and 25 km resolution simulations and the ARPEGE-driven 10 km resolution simulation. Based on these investigations, the strengths and weaknesses of the simulations are analyzed in detail in order to understand the behavior and reliability of the ALADIN-Climate model for the past climate. Also, some examination regarding the sensitivity of the model with respect to the domain size and resolution was undertaken. It was demonstrated to what extent the model is capable of simulating the statistical characteristics of the climate for a 30-year period. The results obtained suggest: (1) the ALADIN-Climate model driven by ERA-40 “perfect” lateral boundaries is colder and wetter than reality for the period of 1961–1990, (2) the integration driven by the ARPEGE model slightly improved the results and, furthermore, (3) provided added value to the global model’s results. Additionally it was found that (4) the 25 km simulation on a larger domain provided better results than the 10 km one using a smaller domain, which can be attributed to the fact that 10 km domain is overly small. The results also (5) justify the application of the ALADIN-Climate model for climate change scenario experiments for Hungary.

A high resolution version of ALADIN over France is analyzed here in 30-year ERA-40-driven simulations. It is demonstrated that a resolution of 12 km improves some features of the mean precipitation field with respect to the same version at 50 km resolution. This version improves also the representation of precipitation upper quantiles in summer by producing less high precipitation rates.

A couple of years ago the REMO model originally developed by the Max Planck Institute for Meteorology (MPI-M) in Hamburg was adapted at the Hungarian Meteorological Service with the aim to become an essential tool for providing realistic regional climate estimations for the next few decades particularly for the area of the Carpathian Basin. This area of interest is especially important considering the fact that one of the largest uncertainties in climate projections can be found over the Carpathian Basin, as it had already been identified by former large international climate projects. Various versions of the REMO model have already been tested all over the world for different geographical domains, however, recently further validations and tests have been started also at the Hungarian Meteorological Service in the framework of the CLAVIER EU project. The article is dealing with the 100-year transient simulation of REMO5.0 model for the period 1951–2050. The lateral boundary conditions for the domain covering continental Europe with 25 km horizontal resolution were provided by the ECHAM5/MPI-OM global atmosphere-ocean general circulation model with the use of A1B SRES scenario for the future. On the one hand, present article is dedicated to summarize in detail the validation results of the experiment for the past climate, and on the other hand, to introduce the preliminary climate change estimations based on REMO results for the future. Special emphasis is put on evaluating the performance of the REMO model for the Carpathian Basin in general and for Hungary in particular.

Two present-time climate simulations performed with a regional climate model ALADIN-Climate/CZ in the framework of the EU FP6 project CECILIA were investigated to assess the model’s ability to reproduce the main patterns of 2-meter temperature and precipitation in the orographically complicated region of Central Europe. To allow a direct comparison of high-resolution model outputs with the station data over the territory of the Czech Republic, a new gridded dataset with the same 10 km resolution was created. The obtained results of the first evaluation dealing with the model’s performance during the control period 1961–1990 are presented here. In term of mean values, the model driven by the ERA-40 re-analyses is in better accordance with the observed data than when it is forced by the global circulation model ARPEGE-Climat. The selected characteristics based on daily maximum and minimum temperatures and sum of precipitation are very similar in both simulations. Although the evaluation has revealed weaknesses originating either from the model itself or driving data, the overall performance of the model is reasonably good in both simulations.

Sensitivity experiments of present-day climate (1961-1970) using the well-known regional climate model RegCM3 are analyzed over a complex topography domain covering the Carpathian Basin and its surroundings. The horizontal resolution of the model experiments is 10 km, the highest so far used with the RegCM modeling framework. When RegCM3 is run with the original settings used for coarser resolutions, highly unrealistic precipitation values are found in the selected domain, namely a large overprediction of precipitation. In order to reduce this large precipitation bias we adjusted some of the parameters in the precipitation parameterization and compared results with the original model set up. Annual and seasonal average temperature and precipitation over different sub-regions of the domain are intercompared across the model versions and compared to observational datasets. The results show that the performance of the modified model is considerably better for the Carpathian Basin, especially for annual and seasonal precipitation, which show small biases with the new parameter setting. Our study indicates that some model parameters may have to be suitably modified to use the RegCM at very high resolutions.

Expected temperature and precipitation changes are analyzed for the Carpathian Basin and, especially, in Hungary, for the 2071-2100 period using outputs of the PRUDENCE project for the A2 and B2 emission scenarios. Different regional climate models (RCMs) of PRUDENCE use 50 km as horizontal spatial resolution, which enables us to estimate the climate change on regional scale. Composite maps of the expected seasonal temperature change and trend analysis of extreme temperature indices suggest that a regional warming trend is evident in the Carpathian Basin. According to the results the largest warming is expected in summer. Negative temperature extremes are projected to decrease while positive extremes tend to increase significantly. The climate simulation results suggest that the expected change of annual total precipitation is not significant in the Carpathian Basin. However, significantly large and opposite trends are expected in different seasons. Seasonal precipitation amount is very likely to increase in winter, and it is expected to decrease in summer, which implies that the annual distribution of precipitation is expected to be restructured. The wettest summer season may become the driest (especially in case of A2 scenario), and the driest winter is expected to be the wettest by the end of the 21st century. The extreme precipitation events are expected to become more intense and more frequent in winter, while a general decrease of extreme precipitation indices is expected in summer.

On the basis of different regional climate model (RCM) outputs of the PRUDENCE project, several precipitation-, temperature-, and wind-related extreme parameters were investigated at the Hungarian Meteorological Service: the occurrence of extreme precipitation events, the rate of frost, summer, hot, and extremely hot days, the number of heat waves, hot and freezing periods, and the frequency of the maximum wind speed exceeding given thresholds. The changes of these extreme events were computed for the period of 2071–2100 with respect to the reference period of 1961–1990 focusing on the Hungarian territory. The chosen regional models, which were driven with the same or similar general circulation models, are using 50 km horizontal resolution and two (A2 and B2) climate change scenarios. The investigations based on several models serve as an excellent opportunity to explore those uncertainties in the projections, which are due to the different regional climate models and different emission scenarios. Besides the abovementioned analysis of the future trends, the results of the reference period were validated with Hungarian (gridded) observational time series. In the paper the evaluation of the regional extreme parameters for the past over the Carpathian Basin is briefly introduced, and the changes of these extreme characteristics are summarized based on the RCM outputs of the PRUDENCE project. The results indicate, that by the end of the 21st century the number of days with precipitation would slightly decrease over Hungary, whereas the frequency of the days with heavy precipitation would expectedly be enhanced. The warm extremes, heat waves, and hot periods will occur more often, which were accompanied by the reducing number of cold extreme events. The occurrence of intensive and stormy winds will likely increase, however, the projected change has very small magnitude.

Regional photochemical model calculations were performed for three decadal time periods: 1991–2000, 2041–2050, and 2091–2100 under changing climate conditions for Europe. While the climatic conditions changed between the decades, all other input fields of the chemical model were held constant in order to separate climate effects from others. In particular, model results for summer ozone concentrations were investigated. These show increasing ozone values in response to higher temperatures and net radiation associated with increases in anthropogenic greenhouse gases. The increase of ozone is stronger in the second half of the 21st century than in the first half. In the course of the whole century, the average summer ozone maxima will rise by several ppbv over most parts of Europe with the highest change in the northwest of the continent. This increase suggests more frequent concentrations above legal thresholds in the future and is partly caused by higher emissions of biogenic hydrocarbons in the model calculation.