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Vautard R.,CEA Saclay Nuclear Research Center | Gobiet A.,University of Graz | Jacob D.,Climate Service Center | Belda M.,Charles University | And 22 more authors.
Climate Dynamics | Year: 2013

The ability of a large ensemble of regional climate models to accurately simulate heat waves at the regional scale of Europe was evaluated. Within the EURO-CORDEX project, several state-of-the art models, including non-hydrostatic meso-scale models, were run for an extended time period (20 years) at high resolution (12 km), over a large domain allowing for the first time the simultaneous representation of atmospheric phenomena over a large range of spatial scales. Eight models were run in this configuration, and thirteen models were run at a classical resolution of 50 km. The models were driven with the same boundary conditions, the ERA-Interim re-analysis, and except for one simulation, no observations were assimilated in the inner domain. Results, which are compared with daily temperature and precipitation observations (ECA&D and E-OBS data sets) show that, even forced by the same re-analysis, the ensemble exhibits a large spread. A preliminary analysis of the sources of spread, using in particular simulations of the same model with different parameterizations, shows that the simulation of hot temperature is primarily sensitive to the convection and the microphysics schemes, which affect incoming energy and the Bowen ratio. Further, most models exhibit an overestimation of summertime temperature extremes in Mediterranean regions and an underestimation over Scandinavia. Even after bias removal, the simulated heat wave events were found to be too persistent, but a higher resolution reduced this deficiency. The amplitude of events as well as the variability beyond the 90th percentile threshold were found to be too strong in almost all simulations and increasing resolution did not generally improve this deficiency. Resolution increase was also shown to induce large-scale 90th percentile warming or cooling for some models, with beneficial or detrimental effects on the overall biases. Even though full causality cannot be established on the basis of this evaluation work, the drivers of such regional differences were shown to be linked to changes in precipitation due to resolution changes, affecting the energy partitioning. Finally, the inter-annual sequence of hot summers over central/southern Europe was found to be fairly well simulated in most experiments despite an overestimation of the number of hot days and of the variability. The accurate simulation of inter-annual variability for a few models is independent of the model bias. This indicates that internal variability of high summer temperatures should not play a major role in controlling inter-annual variability. Despite some improvements, especially along coastlines, the analyses conducted here did not allow us to generally conclude that a higher resolution is clearly beneficial for a correct representation of heat waves by regional climate models. Even though local-scale feedbacks should be better represented at high resolution, combinations of parameterizations have to be improved or adapted accordingly. © 2013 Springer-Verlag Berlin Heidelberg.

Guttler I.,Croatian Meteorological and Hydrological Service DHMZ | Brankovic C.,Croatian Meteorological and Hydrological Service DHMZ | O'Brien T.A.,Lawrence Berkeley National Laboratory | Coppola E.,Abdus Salam International Center For Theoretical Physics | And 2 more authors.
Climate Dynamics | Year: 2014

This study investigates the performance of two planetary boundary layer (PBL) parameterisations in the regional climate model RegCM4.2 with specific focus on the recently implemented prognostic turbulent kinetic energy parameterisation scheme: the University of Washington (UW) scheme. When compared with the default Holtslag scheme, the UW scheme, in the 10-year experiments over the European domain, shows a substantial cooling. It reduces winter warm bias over the north-eastern Europe by 2 °C and reduces summer warm bias over central Europe by 3 °C. A part of the detected cooling is ascribed to a general reduction in lower tropospheric eddy heat diffusivity with the UW scheme. While differences in temperature tendency due to PBL schemes are mostly localized to the lower troposphere, the schemes show a much higher diversity in how vertical turbulent mixing of the water vapour mixing ratio is governed. Differences in the water vapour mixing ratio tendency due to the PBL scheme are present almost throughout the troposphere. However, they alone cannot explain the overall water vapour mixing ratio profiles, suggesting strong interaction between the PBL and other model parameterisations. An additional 18-member ensemble with the UW scheme is made, where two formulations of the master turbulent length scale in unstable conditions are tested and unconstrained parameters associated with (a) the evaporative enhancement of the cloud-top entrainment and (b) the formulation of the master turbulent length scale in stable conditions are systematically perturbed. These experiments suggest that the master turbulent length scale in the UW scheme could be further refined in the current implementation in the RegCM model. It was also found that the UW scheme is less sensitive to the variations of the other two selected unconstrained parameters, supporting the choice of these parameters in the default formulation of the UW scheme. © 2013, Springer-Verlag Berlin Heidelberg.

Pasicko R.,United Environment & Energy, Llc | Brankovic C.,Croatian Meteorological and Hydrological Service DHMZ | Simic Z.,University of Zagreb
Renewable Energy | Year: 2012

Although the subject of climate change attracts enormous attention, there is limited number of analyses dealing with climate change impacts on the power system planning. It is important to understand these influences since the power system planning must consider very long time spans, and therefore it might be affected by potential climate change in multiple ways.This study focuses on the initial evaluation of climate change impacts on renewable energy sources in Croatia - specifically, photovoltaic, wind and hydro energy. The climate data used for this assessment were taken from the global climate model ECHAM5-MPIOM and dynamically downscaled by the regional climate model RegCM at Croatian Meteorological and Hydrological Service (DHMZ). The results based on the IPCC A2 scenario for the two future climate time periods, 2011-2040 and 2041-2070, are analyzed.The climate change that would potentially have the most significant impact on renewables is expected in the coastal and adjoining areas of Croatia during summer where an increase by 20% in the mean wind speed is projected already for the first time period, and more than 50% until 2070. This would, theoretically, imply almost a doubling in electricity production even in the first period. The impact of climate change on electricity production from photovoltaics might be neutral since it is balanced by opposing dominant factors, while a reduction of more than 10% in the production of electricity from hydro power plants could be expected after 2050.Estimates of uncertainties related to climate change are necessary in order to be able to determine the importance of climate change impacts on the future power generation from renewable energy sources. © 2012 Elsevier Ltd.

Brankovic C.,Croatian Meteorological and Hydrological Service DHMZ | Guttler I.,Croatian Meteorological and Hydrological Service DHMZ | Gajic-Capka M.,Croatian Meteorological and Hydrological Service DHMZ
Climate Dynamics | Year: 2013

The 2m temperature (T2m) and precipitation from five regional climate models (RCMs), which participated in the ENSEMBLES project and were integrated at a 25-km horizontal resolution, are compared with observed climatological data from 13 stations located in the Croatian coastal zone. The twentieth century climate was simulated by forcing RCMs with identical boundary conditions from the ERA-40 reanalysis and the ECHAM5/MPI-OM global climate model (GCM); climate change in the twenty-first century is based on the A1B scenario and assessed from the GCM-forced RCMs' integrations. When forced by ERA-40, most RCMs exhibit cold bias in winter which contributes to an overestimation of the T2m annual cycle amplitude and the errors in interannual variability are in all RCMs smaller than those in the climatological mean. All models underestimate observed warming trends in the period 1951-2010. The largest precipitation biases coincide with locations/seasons with small observed amounts but large precipitation amounts near high orography are relatively well reproduced. When forced by the same GCM all RCMs exhibit a warming in the cold half-year and a cooling (or weak warming) in the warm period, implying a strong impact of GCM boundary forcing. The future eastern Adriatic climate is characterised by a warming, up to +5 °C towards the end of the twenty-first century; for precipitation, no clear signal is evident in the first half of the twenty-first century, but a reduction in precipitation during summer prevails in the second half. It is argued that land-sea contrast and complex coastal configuration of the Croatian coast, i.e. multitude of island and well indented coastline, have a major impact on small-scale variability. Orography plays important role only at small number of coastal locations. We hypothesise that the parameterisations related to land surface processes and soil hydrology have relatively stronger impact on variability than orography at those locations that include a relatively large fraction of land (most coastal stations), but affecting less strongly locations at the Adriatic islands. © 2013 Springer-Verlag Berlin Heidelberg.

Brankovic C.,Croatian Meteorological and Hydrological Service DHMZ | Patarcic M.,Croatian Meteorological and Hydrological Service DHMZ | Guttler I.,Croatian Meteorological and Hydrological Service DHMZ | Srnec L.,Croatian Meteorological and Hydrological Service DHMZ
Climate Research | Year: 2012

The RegCM climate model was used at a 35 km resolution to downscale the 3-member global ECHAM5/MPI-OM ensemble based on the IPCC A2 scenario covering the European-Mediterranean domain. Within the reference climate (1961-1990), the model high 2 m temperatures (T2m) were reduced and low temperatures were increased relative to verification in a large portion of the domain. Precipitation was underestimated in summer over the Mediterranean region but was overestimated over western Europe in winter, probably due to excessive westerlies in the global model. When RegCM was forced by ERA-40, the dominant errors in the summer T2m appear to be genuine RegCM errors, but a large fraction of errors in winter precipitation was imported from the lateral boundaries. In the near future (2011-2040), the summer T2m is projected to increase by +1.8°C over southwest Europe. The simulated change in precipitation is small and is significant only in regions around the Mediterranean. The wetter north and drier south, a major feature in projections of the European winter climate in the late 21st century, is not predicted for the near future. Similarly, summer drying is confined to western Europe in contrast to nearly continental scale drying observed in projections of the late 21st century. This finding may influence the approaches for adaptation to climate change in the first half and at the end of this century. The effects of downscaling at small scales are analysed for the case of Croatia. The spatial distribution of the number of days with extreme T2m and precipitation in RegCM is consistent with observations. However, this metric is generally underestimated, indicating that over complex orography, even higher horizontal resolution is needed to better resolve climate extremes. © 2012 Inter-Research.

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