Climate Change Impact Assessment for Central and Eastern Europe in High Resolution – EC FP6 Project CECILIA

There is significant problem for decision making process arising from the weak link between climate change information based on global climate models and local impact studies necessarily based on regional climate change signal. Global Circulation Models (GCMs) can reproduce reasonably well climate features on large scales (global and continental), but their accuracy decreases when proceeding from continental to regional and local scales because of the lack of resolution. This is especially true for surface fields, such as precipitation, surface air temperature and their extremes, which are critically affected by topography and land use. However, in many applications, particularly related to the assessment of climate-change impacts, the information on surface climate change at regional to local scale is fundamental. To bridge the gap between the climate information provided by GCMs and that needed in impact studies, the most popular approaches are (i) statistical downscaling, i.e., identification of statistical relationships between large-scale fields and local surface climate elements, and (ii) dynamical downscaling, i.e., nesting of a fine scale limited area model (or Regional Climate Model, RCM) within the GCM. The latter approach is more correct from a physical point of view, but is much more demanding on computer resources.

In the region of Central and Eastern Europe the need for high resolution studies is particularly important. This region is characterized by the northern flanks of the Alps, the long arc of the Carpathians, and smaller mountain chains and highlands in the Czech Republic, Slovakia, Romania and Bulgaria that significantly affect the local climate conditions. A resolution sufficient to capture the effects of these topographical and associated land-use features is necessary. That is why 10 km resolution has been introduced in EC FP6 project CECILIA.

The main objectives of EC Project (STREP) CECILIA dealing with climate change impacts and vulnerability assessment in targeted areas of Central and Eastern Europe will be described. Emphasis is given to applications of regional climate modelling studies at a resolution of 10 km for local impact studies in key sectors of the region. The project contains studies on hydrology, water quality, and water management (focusing at medium-sized river catchments and the Black Sea coast), air quality issues in urban areas (Black Triangle – a polluted region around the common borders of the Czech Republic, Poland and Germany), agriculture (crop yield, pests and diseases, carbon cycle), and forestry (management, carbon cycle). The high spatial and temporal resolution of dense national observational networks at high temporal resolution and of the CECILIA regional model experiments uniquely feeds into investigations of climate change consequences for weather extremes in the regions under study. Comparison with the results based on statistical downscaling techniques is also provided. Statistical downscaling methods for verification of the regional model results is developed and applied, and assessments of their use in localization of model output for impact studies is performed.

The main goal of regional climate modelling activities in CECILIA project is to produce simulations on targeted domains for a past period (1961-1990) driven by ERA40 reanalysis used for validation of the models as well as for a reference period (1961-1990) and scenario time slices (2021-2050 and 2071-2100) based on ENSEMBLES 6FP EC IP A1B GCM simulations. Two models are used as source of driving fields over six target areas, ALADIN-Climate family using stretched climate change transient run by ARPEGE/Climat for ENSEMBLES project, RegCM family using RegCM transient ENSEMBLES run for whole Europe in 25km resolution driven by transient run of ECHAM5. Results of model validation and climate change signal based on this simulations will be presented with emphasis to the regional details of targeted areas as well as examples of impact studies using these high resolution scenarios runs.