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The main goal of this analysis is to provide an assessment of the fine grid regional climate model (RCM) ensemble over the broader Adriatic region, which is the domain with orographically complex terrain and a developed coastline. The results of this study are a beneficial complement to earlier work on using modified bivariate bias correction methods. This analysis was based on an ensemble of 12 combinations of three RCMs and four global climate models (GCMs) from 1971 to 2004, divided into calibration and validation parts. A comparison of one univariate and three versions of bivariate bias correction methods of summer and winter monthly temperature and precipitation was performed. To examine the effect of various methods, we used different marginal distributions and distributions of dependence (copula). Bivariate bias correction was conducted with parametric and empirical marginal distributions. In the quantile mapping (univariate) and the parametric bivariate method, gamma (precipitation) and normal (temperature) probability distributions were used. We documented the bias and the influence of bias correction methods on precipitation and temperature, including their climate change signals in historical data. The considered methods maintained the spatial distribution of trends from the native ensemble. If the relationship between variables was not distinct and the correlation coefficient was low, bivariate bias correction methods tended to weaken the correlation coefficient from the model. Two experiments on how the bias correction methods influence statistical measures of the considered variables and their relationships showed that the bivariate method with empirical distributions (eeG) performed slightly better than other methods. Although the eeG method performed better than the other methods, none of the considered methods was able to fully preserve the correlation coefficient between variables detected from observations. Considering two copulas (Gaussian and Student's t), we conclude that the effect of different copula types on method performance is small.

We present the first evaluation of the wind field from the CORDEX-FPS ensemble of kilometer-scale simulations, with focus on the Adriatic region. Kilometer-scale climate models, also known as convection-permitting models (CPMs), produce a good representation of small-scale topographic features and consequently a more detailed depiction of dynamical and thermal circulation. These enable a reliable view of climate characteristics of the wind field, especially in coastal regions and over complex terrain, such as the Adriatic. We investigate the (potential) added value introduced by CPMs compared to classical “cumulus-parametrized” regional climate models (RCMs), reanalysis and station observations. For this purpose, wind components at 10 meter level are used at 3-hourly frequency. All simulations cover a 10-year period, extending from 2000 to 2009. In terms of the standard statistical parameters such as correlation coefficient and temporal standard deviation, CPMs are very dependent on their parent RCM performance. However, the orographic forcing emphasizes the potential added value and CPMs contain some fine spatial scale variability (i.e. stronger extremes by 25% and accurate wind direction) that is absent in coarser RCMs and reanalysis. The potential added value is higher in the cold season compared to the warm season due to the proportion of severe wind events. CPMs reproduce well the typical wind regimes along the Adriatic coast, namely Bora and Sirocco. The benefit of using CPMs is especially pronounced in simulating Bora maximum wind speeds in northern Adriatic and Sirocco frequencies in southern Adriatic. Based on our overall analysis, we conclude that CPMs provide added value compared to coarser models, especially in the complex coastal terrain.

One of the Mediterranean hotspots for extreme precipitation is the coastal mountainous eastern Adriatic and Dinaric Alps regions, which are often affected by heavy precipitation events (HPEs) that can cause severe damage. Representing these events at different time scales and projecting their future evolution using regional climate models (RCMs) remains a key modelling challenge. This study evaluates the impact of model configuration on the representation of extreme daily precipitation in an RCM at climatological (1979–2012) and event scales (HPEs). Additionally, the impact of the spectral nudging (SN) technique is analysed. We compare two CNRM-ALADIN model configurations, and perform several sensitivity tests on specific parameters within a configuration. All simulations are driven by the ERA-Interim re-analysis over the Med-CORDEX domain at 0.11° horizontal resolution. On all examined time scales, model configuration shows a considerable impact on the mean and extreme daily precipitation. The new physical parameterizations of moist processes show improvement at the climatological (precipitation intensity, extreme precipitation and frequency of light precipitation) and event (the occurrence, spatial pattern and structure of HPEs) scales. Extreme precipitation shows limited sensitivity to specific parameters and is highly dependent on HPE. The use of SN improves the temporal variability at climatological scales and the location and occurrence of HPEs. We conclude that extreme precipitation representation in CNRM- ALADIN is more sensitive to change in the model configuration, particularly in the physical parameterizations, than to the application of SN. This study shows that the development and advancement of physical parameterizations can improve the model representation of extreme precipitation at several time scales and can therefore be considered as a means to reduce uncertainties in future climate projections.

Flooding of the Adriatic coastline is predominantly caused by storm surges induced by winds from the south-eastern sector. This phenomenon in Venice is known as acqua alta. We present a study of wind fields favouring storm-surge setups in the Adriatic, including their characteristics in the present climate and their expected characteristics in future scenarios. Analysis is based on (i) measured sea levels in Venice and Bakar (1984–2014), (ii) near-surface wind from ERA5 reanalysis, and (iii) simulations of wind fields with three regional climate models (ALADIN52, RCA4, and RegCM4) forced with several global models (CNRM-CM, MPI-ESM-MR/LR, HadGEM2-ES, EC-EARTH, and IPSL-CM5). For future climates, we considered two scenarios (RCP4.5 and RCP8.5) and two future periods (2041–2070 and 2071–2100) with respect to the historical 1971–2000 period. It was found that the probability that the frequency, intensity, annual cycle, and spatial structure of the wind inducing the Adriatic storm surges will change in future climates is small. The result is robust and consistent according to all considered criteria—it does not depend on the analysed regional climate models, boundary conditions, climate scenarios, or future time interval.

We investigate the impact of horizontal resolution, convection parameterization and lateral boundary conditions on the ability of a regional climate model ‐ RegCM4 to simulate the observed temperature and precipitation climatology over Croatia and surrounding regions. An ensemble of RegCM4 simulations over Europe has been generated including two resolutions (50 and 12.5 km), two different deep convection schemes and different boundary conditions (a reanalysis and four global climate models). Using two observational data sets (with and without the undercatch correction) shows that the magnitude of RegCM4 errors in winter precipitation also depends on observational uncertainty. While the mean precipitation amounts in high‐resolution simulations are generally overestimated in the cold part of the year, low‐resolution RegCM4 simulations are comparable to most of other EURO‐CORDEX models. When forced by ERA‐Interim, RegCM4 performs relatively poorly in reproducing temporal correlations against observations, but performs well in terms of spatial correlation. Whereas precipitation amounts from high‐resolution simulations need further improvements, the RegCM4 skill in simulating near‐surface temperature is high and well suited for impact studies.

Introduction: Last IPCC AR6 reported with very high confidence that more frequent hot extremes will increase for the severity of heatwaves all-round the globe. It is known that heat and hot weather that can last for several days (so called heatwaves) can significantly influence human health as well as rise in heat-related deaths.Design and methods: In this work, climate simulations obtained by regional climate model RegCM4 over Croatia are used. RegCM4 was forced by four different global climate models on 12.5 km horizontal resolution. Historical climate simulated by model is compared with observed daily data measured at Croatian meteorological stations in order to evaluate simulations. Future climate is considered by three different IPCC scenarios: the lowest RCP2.6, the middle RCP4.5 and the highest RCP8.5 emission scenario. We considered three future time slices: 2021-2050 (P1), 2031-2060 (P2) and 2041-2070 (P3).Results: The range of climate change for maximum temperature during summer will be examined in the future time slices. We will also look into duration and number of heat waves in different parts of Croatia. Knowledge of the current situation as well as possible change in the future can help in the planning future adaptation and mitigation measures.

Since changes in temperature and precipitation have different effects on (i) all developmental stages of grapevines in most of the wine regions worldwide (i.e., on their phenological characteristics) and (ii) different varieties, a comprehensive database of bioclimatic indices has been calculated and analyzed for Croatian wine producing regions. The database consists of theaverage growing season temperature, Growing degree-days, Huglin index, Dryness index, and Cool night index that are based on all available meteorological measurements as well as the outputs of regional climate models (RCMs) from the EURO-CORDEX database. The horizontal grid spacing of 0.11° from the RCM ensembles enabled a fine-scale determination of bioclimatic indices for the present and future climate in Croatia. In addition, statistical analyses (standard statistical parameters and Bayesian method) were done to examine trends in sugar content, total acidity and date of harvest. Calculations were performed for the present and future climate on the basis of data from seven selected vineyards/wineries and four varieties (‘ Graševina’, ‘Plavac mali’, ‘Chardonnay’, and ‘Merlot’). The results show whether the part of Croatia that is suitable for grape cultivation in the present climate will continue to be favorable in the future within the Mediterranean area. In general, projections suggest further warming and drying of the climate in Croatia and an earlier harvest, with some variations among varieties that show latitude dependence. Projections for the future climate also suggest that the existing viticultural zoningwill be much less adequate for the Croatian territory because it reduces the economically sustainable production of wine in certain areas.

The topographically complex coastal-mountainous region of the eastern Adriatic and Dinaric Alps is one of the rainiest areas in the Mediterranean and particularly vulnerable to climate change. The aim is to estimate the future climate change of precipitation over this region over which research on this subject is still limited. We use the climate projections from the latest EURO-CORDEX ensemble at 0.11° resolution. The ensemble is comprised of 14 regional climate models (RCMs) driven by eight CMIP5 global climate models (GCMs), a total of 68 members. The climate change signal is examined for the far future period (2071-2100) with respect to the historical period (1971-2000) for one greenhouse gases concentration scenario, particularly for RCP8.5. Total precipitation shows a considerable reduction in summer months, while in winter it is projected to increase in the northern part of the region and to decrease in southern parts, displaying the known south-north gradients. Accordingly, the number of rainy days is projected to decrease by the end of the century, especially during summer over the entire region and in winter over the southern parts. However, the precipitation intensity increase can be expected by the end of the century, especially during the winter months, while in the summer there is no clear consensus between different models. Also, an increase in extreme precipitation is projected during the winter months, while during summer months a similar south-north gradient is shown as for total precipitation. A more detailed analysis for multiple future periods and greenhouse gases concentration scenarios, with an emphasis on extreme precipitation, is planned.

The almost closed structure of the Pannonian Basin makes it an exceptional natural laboratory for the study of the water and energy cycles, focusing on the physical processes of relevance. The Pannonian Basin Experiment, under the umbrella of the Global Energy and Water Exchanges project of the World Climate Research Programme, aims to achieve a better understanding of the Earth System components and their interactions in the Pannonian Basin. The scientific basis of the PannEx supports research that can better translate and deliver relevant climate data, information and knowledge for societal decision making through the national hydro-meteorological and climate services, research institutes and universities. We outline the framework for the development of the PannEx in the light of international efforts to provide scientific support and involve international research community in integrated approach towards identifying and increasing adaptation capacity in the face of climate change in the Pannonian Basin. As such, PannEx dedicated observational and modeling efforts also strive to reach results with the global impact. Keywords: Pannonian Basin, Pannonian Basin Experiment (PannEx), Earth System, Integrated modeling, GEWEX, Adaptation, Mitigation

The lower Neretva river basin includes a fertile valley at the estuary into the Adriatic Sea, where intense agricultural production occurs, and the higher terrain where drinking water resources exist. To provide input for the further assessment of crop-yield production and hydrological risks, climate and climate change were analysed using the Opuzen station air temperature and total precipitation data for the 1961–2015 period. Both historical and future climates (2021–2050) were assessed based on simulations of three regional climate models (RCMs). The RCMs were forced by the observed concentrations of greenhouse gases (GHGs) from 1951 to 2000, and the IPCC A1B scenario of the GHG emissions was applied from 2001 onwards. The models were compared with the observations, and two bias adjustment methods were evaluated. The results generally showed a significant increase in the mean annual and seasonal temperature and a weak decreasing trend in annual and seasonal precipitation. Projections revealed a predominant increase in the mean temperature by the mid-21st century for all three RCMs (between 0.5 and 3.5 °C). The precipitation changed by between −60 and +60% throughout the year for the different models, although the changes generally were not statistically significant.

Over the past few decades the horizontal resolution of regional climate models (RCMs) has steadily increased, leading to a better representation of small-scale topographic features and more details in simulating dynamical aspects, especially in coastal regions and over complex terrain. Due to its complex terrain, the broader Adriatic region represents a major challenge to state-of-the- art RCMs in simulating local wind systems realistically. The objective of this study is to identify the added value in near-surface wind due to the refined grid spacing of RCMs. For this purpose, we use a multi-model ensemble composed of CORDEX regional climate simulations at 0.11° and 0.44° grid spacing, forced by the ERA-Interim reanalysis, a COSMO convection- parameterizing simulation at 0.11° and a COSMO convection-resolving simulation at 0.02° grid spacing. Surface station observations from this region and satellite QuikSCAT data over the Adriatic Sea have been compared against daily output obtained from the available simulations. Both day-to-day wind and its frequency distribution are examined. The results indicate that the 0.44° RCMs rarely outperform ERA- Interim reanalysis, while the performance of the high- resolution simulations surpasses that of ERA- Interim. We also disclose that refining the grid spacing to a few km is needed to properly capture the small-scale wind systems. Finally, we show that the simulations frequently yield the accurate angle of local wind regimes, such as for the Bora flow, but overestimate the associated wind magnitude. Finally, spectral analysis shows good agreement between measurements and simulations, indicating the correct temporal variability of the wind speed.

In the original version of this article the authors unfortunately failed to state the source of sea-level data at Venice.

This paper is a contribution to the special issue on Advances in Convection-Permitting Climate Modeling, consisting of papers that focus on the evaluation, climate change assessment, and feedback processes in kilometer-scale simulations and observations., A recently launched project under the auspices of the World Climate Research Program’s (WCRP) Coordinated Regional Downscaling Experiments Flagship Pilot Studies program (CORDEX-FPS) is presented. This initiative aims to build first-of-its-kind ensemble climate experiments of convection permitting models to investigate present and future convective processes and related extremes over Europe and the Mediterranean. In this manuscript the rationale, scientific aims and approaches are presented along with some preliminary results from the testing phase of the project. Three test cases were selected in order to obtain a first look at the ensemble performance. The test cases covered a summertime extreme precipitation event over Austria, a fall Foehn event over the Swiss Alps and an intensively documented fall event along the Mediterranean coast. The test cases were run in both “weather-like” (WL, initialized just before the event in question) and “climate” (CM, initialized 1 month before the event) modes. Ensembles of 18–21 members, representing six different modeling systems with different physics and modelling chain options, was generated for the test cases (27 modeling teams have committed to perform the longer climate simulations). Results indicate that, when run in WL mode, the ensemble captures all three events quite well with ensemble correlation skill scores of 0.67, 0.82 and 0.91. They suggest that the more the event is driven by large-scale conditions, the closer the agreement between the ensemble members. Even in climate mode the large-scale driven events over the Swiss Alps and the Mediterranean coasts are still captured (ensemble correlation skill scores of 0.90 and 0.62, respectively), but the inter-model spread increases as expected. In the case over Mediterranean the effects of local-scale interactions between flow and orography and land–ocean contrasts are readily apparent. However, there is a much larger, though not surprising, increase in the spread for the Austrian event, which was weakly forced by the large-scale flow. Though the ensemble correlation skill score is still quite high (0.80). The preliminary results illustrate both the promise and the challenges that convection permitting modeling faces and make a strong argument for an ensemble-based approach to investigating high impact convective processes., IG and LS have been supported by the Croatian Science Foundation (HrZZ) project CARE (no. 2831). JF acknowledges support by the Spanish R + D programme through MINECO/FEDER co-funded project INSIGNIA (CGL2016-79210-R). AL-G is supported by the Spanish government though grant BES-2016-078158 and MINECO/FEDER co-funded project MULTI-SDM (CGL2015-66583-R). JM and KW-S gratefully acknowledge the support by the German Science Foundation (DFG) through project FOR 1695. DM, MP, and HT gratefully acknowledge the support received via the Austrian Science Fund (FWF) project NHCM-2 (no. P24758-N29) and the projects HighEnd:Extremes and EASICLIM, funded by the Austrian Climate Research Programme (ACRP) of the Klima- und Energiefonds (nos. KR13AC6K10981 and KR16AC0K13160, respectively). SS and TL acknowledge the support of NOTUR project no. NN9280K and the Research Council of Norway and its basic institute support of their strategic project on Climate Services. RMC and PMMS gratefully acknowledge the support of the SOLAR project (PTDC/GEOMET/7078/2014) financed by the Portuguese Foundation for Science and Technology. EJ Kendon gratefully acknowledges funding from the Joint Department of Energy and Climate Change (DECC) and Department for Environment Food and Rural Affairs (Defra) Met Office Hadley Centre Climate Programme (GA01101). S. Khodayar research is supported by the Bundesministerium für Bildung und Forschung (BMBF; German Federal Ministry of Education and Research). Support of Ministry of Education, Youth and Sports of the Czech Republic for funding the participation in Euro-CORDEX activities via the scheme INTER-TRANSFER under the Grant no. LTT17007. Funding from the Research Council of Norway through the SUPER (Grant no. 250573) and HYPRE (Grant no. 243942) projects.

Near-surface wind over the Adriatic region are examined under present-day and future climate conditions for two greenhouse gas scenarios (RCP4.5 and RCP8.5) with an ensemble of high- resolution (0.11˚) CORDEX simulations. The influence of particular combinations of regional climate models (RCMs) and global climate models (GCMs) and emission scenarios on the future changes in the near-surface wind field has been explored in more detail. Starting with the seasonal climate change signal in large-scale flow over the entire CORDEX domain, we focus to regional daily wind fields over the Adriatic domain and subdaily features of well-known regional winds (Bora and Sirocco winds). The analysis reveals the strong sensitivity of the climate change signal in the simulated wind flow to (i) the choice of the GCM that provides the boundary conditions and (ii) the analyzed locations across the Adriatic region. The results of the 21st century projections indicate that the changes in synoptic activity have an impact on the wind field at the (sub)daily time scale. We found a reduction in the number of Bora events and increase in the number of Sirocco events in northern Adriatic during the winter season, with an increase in pressure in the middle of the 21st century. Overall, the mean wind speed during Bora and Sirocco events is reduced, except for Bora in northern Adriatic. For the summer season, we found a large increase in the number of thermally induced flows, which is probably caused by the weakening of the Azores High.

The hydrostatic regional climate model RCA, version 3 (RCA3), of the Swedish Meteorological and Hydrological Institute was used to dynamically downscale ERA-40 and the ECMWF operational analysis over a 22-yr period. Downscaling was performed at four horizontal resolutions—50, 25, 12.5, and 6.25 km—over an identical European domain. The model-simulated precipitation is evaluated against high-resolution gridded observational precipitation datasets over Switzerland and southern Norway, regions that are characterized by complex orography and distinct climate regimes. RCA3 generally overestimates precipitation over high mountains: during winter and summer over Switzerland and during summer over central-southern Norway. In the summer, this is linked with a substantial contribution of convective precipitation to the total precipitation errors, especially at the coarser resolutions (50 and 25 km). A general improvement in spatial correlation coefficients between simulated and observed precipitation is observed when the horizontal resolution is increased from 50 to 6 km. The 95th percentile spatial correlation coefficients during winter are much higher for southern Norway than for Switzerland, indicating that RCA3 is more successful at reproducing a relatively simple west-to-east precipitation gradient over southern Norway than a much more complex and variable precipitation distribution over Switzerland. The 6-km simulation is not always superior to the other simulations, possibly indicating that the model dynamical and physical configuration at this resolution may not have been optimal. However, a general improvement in simulated precipitation with increasing resolution supports further use and application of high spatial resolutions in RCA3.

International audience; In this study we investigate the scaling of precipitation extremes with temperature in the Mediterranean region by assessing against observations the present day and future regional climate simulations performed in the frame of the HyMeX and MED-CORDEX programs. Over the 1979–2008 period, despite differences in quantitative precipitation simulation across the various models, the change in precipitation extremes with respect to temperature is robust and consistent. The spatial variability of the temperature–precipitation extremes relationship displays a hook shape across the Mediterranean, with negative slope at high temperatures and a slope following Clausius–Clapeyron (CC)-scaling at low temperatures. The temperature at which the slope of the temperature–precipitation extreme relation sharply changes (or temperature break), ranges from about 20 °C in the western Mediterranean to

In the original article, there were mistakes in Figures 2, 4, 6 as published. The interaction term [last right-hand side term in Equation (3) of our published paper] was erroneously multiplied by the average heat conductivity constant. The corrected Figures 2A–C, Figures 4A–C, and Figure 6 appear in the correction article.

The Prandtl model couples, probably in the most succinct way, basic boundary-layer dynamics andthermodynamics for pure anabaticand katabaticflowsoverinclined surfaces by assuming a one-dimensional steady-state balance between buoyancy and turbulent friction. Although the classic Prandtl model is linear, having an a priori assigned vertically constanteddydiffusivityandheatconductivity,K,inthisanalyticworkwepartlyrelaxboth of these restrictions. The first restriction is loosened by using a weakly nonlinear approach where a small parameter, e, controls feeding of the flow-induced potential temperature gradient back to the environmental potential temperature gradient, because the former, belowthekatabaticjet,canbe20‐50timesstrongerthanthelatter,backgroundorfree-flow gradient. An appropriate range of values for e, controlling the weak nonlinearity for pure katabatic flow, is provided. In this way, the near-surface potential temperature gradient becomes stronger and the corresponding katabatic jet somewhat weaker (at a slightly lower height) than that in the classic Prandtl solution. The second restriction is partly relaxed by usingaprescribed,graduallyvaryingK withdistancefromtheunderlyingsurface,allwithin the usual validity of the zero-order Wentzel‐Kramers‐Brillouin approximation to solve the coupled differential equations. The new model is compared with the glacier wind data from the Pasterze experiment (PASTEX-94), Austria. Further discussion includes gradient Richardson number consideration and an application to simple anabatic flows. The model may be applied for estimation and interpretation of the wind affecting glacier mass balance and air pollution.

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.

The Prandtl model succinctly combines the 1D stationary boundary-layer dynamics and thermodynamics of simple anabatic and katabatic flows over uniformly inclined surfaces. It assumes a balance between the along-the-slope buoyancy component and adiabatic warming/cooling, and the turbulent mixing of momentum and heat. In this study, energetics of the Prandtl model is addressed in terms of the total energy (TE) concept. Furthermore, since the authors recently developed a weakly nonlinear version of the Prandtl model, the TE approach is also exercised on this extended model version, which includes an additional nonlinear term in the thermodynamic equation. Hence, interplay among diffusion, dissipation, and temperature-wind interaction of the mean slope flow is further explored. The TE of the nonlinear Prandtl model is assessed in an ensemble of solutions where the Prandtl number, the slope angle and the nonlinearity parameter are perturbed. It is shown that nonlinear effects have the lowest impact on variability in the ensemble of solutions of the weakly nonlinear Prandtl model when compared to the other two governing parameters. The general behavior of the nonlinear solution is similar to the linear solution, except that the maximum of the along- the-slope wind speed in the nonlinear solution reduces for larger slopes. Also, the dominance of PE near the sloped surface, and the elevated maximum of KE in the linear and nonlinear energetics of the extended Prandtl model are found in the PASTEX-94 measurements. The corresponding level where KE>PE most likely marks the bottom of the sublayer subject to shear- driven instabilities. Finally, possible limitations of the weakly nonlinear solutions of the extended Prandtl model are raised. In linear solutions, the local storage of TE term is zero, reflecting the stationarity of solutions by definition. However, in nonlinear solutions, the diffusion, dissipation and interaction terms (where the height of the maximum interaction is proportional to the height of the low-level jet by the factor ≈4/9) do not balance and the local storage of TE attains nonzero values. In order to examine the issue of non- stationarity, the inclusion of velocity- pressure covariance in the momentum equation is suggested for future development of the extended Prandtl model.

Observed and expected changes in the global climate system due to the increasing concentrations of the greenhouse gasses (GHG), mostly carbon dioxide (CO2) are the main motivation for research on how application of new technology can help in reducing GHG emissions. This paper focuses on climate change analysis, transition of energy and transportation sector towards low carbon paradigm. As one of the most critical barriers to achieve 100 % renewable energy system is intermittent nature of renewable energy sources such as solar and wind, demand for energy storage becomes important. At this point hydrogen technology can be applied. Given the intermittence of the weather conditions at the short term- scales, energy peaks from wind and solar energy can be used for the hydrogen production and stored for later use, e.g. hydrogen utilization in transport sector. This also provides more flexibility in power system network to offset production peaks to energy that can be spent later. Hydrogen technologies and their applications are investigated worldwide, from the aspect of sustainable development, cleaner technologies, energy efficiency and energy savings. Here the focus is positioned to the transport sector as highest energy consumer and polluter. Three different future scenarios were analyzed - estimated cases of 10 %, 50 % and 75 % shift to the hydrogen fuel cells powered vehicles in Croatia until 2030. It is important to note that hydrogen as the fuel is clean as much as energy and processes used for its production are clean. To satisfy this claim the use of renewable energy sources for hydrogen production via water electrolysis is strongly suggested. In Croatia there are approximately 1.9 million registered vehicles, including approximately 1.5 million passenger cars. To accomplish clean and environmentally friendly hydrogen production, calculations have been performed for the systems that include the use of solar and/or wind energy, i.e. photovoltaic cells and/or wind turbines. Given results represent directions in system development based on installed power of wind and solar energy, taking into account demands for hydrogen amounts in the transport sector. In order to understand the scale of future importance of hydrogen and its connection to renewable energy, an amount of installed solar and wind power plants will be estimated in order to satisfy 75 % shift to hydrogen fuel cells powered vehicles in Croatia until 2030. Results are discussed, especially in the context of hydrogen serving as an energy carrier. Paper conclusions can help in rethinking and shaping transportation, energy policies and energy strategies either in Croatia or in any country worldwide.

An ensemble of regional climate model (RegCM4) simulations applied over the EURO-CORDEX domain is used to estimate model performance for historical climate. Earlier experiments at the 12.5 km and 50 km, when RegCM4 was forced by ERA-Interim, showed strong sensitivity of simulated near-surface temperature, total cloud cover and total precipitation to horizontal resolution. In this study, we assess an enlarged set of experiments when RegCM4 was forced by global climate models (GCMs) HadGEM2-ES, EC-EARTH, MPI-ESM-LR and CNRM- CM5 for the period 1970–2005 at the 50-km resolution and for the period 1970–1974 at the 12.5-km resolution. Model performance is evaluated against the E-OBS gridded temperature, precipitation and the mean sea-level pressure data and also compared with the results from forcing GCMs. In order to estimate potential impact of reduced time step on the RegCM 12.5-km simulations, an additional set of 50-km simulations is performed with the same time step as in the 12.5-km simulations. We explore how the RegCM4 time stepping relates to overestimation of the total cloud cover when large time step is used in model integrations.

The surface energy budget components from two simulations of the regional climate model RegCM4.2 over the European/North African domain during the period 1989–2005 are analysed. The simulations differ in specified boundary forcings which were obtained from ERA-Interim reanalysis and the HadGEM2-ES Earth system model. Surface radiative and turbulent fluxes are compared against ERA-Interim. Errors in surface radiative fluxes are derived with respect to the Global Energy and Water Cycle Experiment/Surface Radiation Budget satellite-based products. In both space and time, we find a high degree of realism in the RegCM surface energy budget components, but some substantial errors and differences between the two simulations are also present. The most prominent error is an overestimation of the net surface shortwave radiation flux of more than 50 W/m2 over central and southeastern Europe during summer months. This error strongly correlates with errors in the representation of total cloud cover, and less strongly with errors in surface albedo. During other seasons, the amplitude of the surface energy budget components is more in line with reference datasets. The errors may limit the usefulness of RegCM simulations in applications (e.g. high-quality simulation-driven impact studies). However, by using a simple diagnostic model for error interpretation, we suggest potential sensitivity studies aiming to reduce the underestimation of cloud cover and overestimation of shortwave radiation flux.

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., The EURO-CORDEX simulations and analysis were carried out in several groups within the framework of the IMPACT2C FP7 project (Grant FP7-ENV.2011.1.1.6-1). The BTU Cottbus offered an exchange ftp site for sharing all model simulation files. The contribution from CRP-GL was funded by the Luxembourg National Research Fund (FNR) through Grant FNR C09/SR/16 (CLIMPACT). We acknowledge financial support from the Spanish R&D program through Grants CGL2010-21869 (EXTREMBLES) and CGL2010-22158-C02-01 (CORWES). Charles University runs were supported partially in framework of the Research Plan of MSMT (No. MSM 0021620860) and GACR project No. P209/11/2405. The contribution from UHOH was funded by the German Science Foundation (DFG) through project FOR 1695. The REMO simulations were supported by CSC, MPI, as well as BMBF and performed under the ‘‘Konsortial’’ share at the German Climate Computing Centre (DKRZ), as well as the CCLM simulations carried out by BTU, which we are further thankful for their various support. We are thankful to the French CCRT/TGCC supercomputing center support and the CEA and GENCI computing resource allocation agency for the WRF-IPSL-INERIS runs. The development of the modeling chain at INERIS and IPSL was carried out in part within the French national project SALUT’AIR (PRIMEQUAL research program). Part of SMHI contribution was done in the ECLISE projects that receive funding from the European Union Seventh Framework Programme (FP7/2007–2013) under Grant agreement 265240 and in the Swedish Mistra-SWECIA programme founded by Mistra (the Foundation for Strategic Environmental Research). DHMZ contribution was partially supported by the Croatian Ministry of Science, Education and Sports (Grant No. 004-1193086-3035).

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.

Oborina iz četiri simulacije regionalnim klimatskim modelom RCA3 na horizontalnim rezolucijama 50, 25, 12.5 i 6.25 km uspoređena je s dostupnim skupovima mjerenja interpoliranim na pravilne mreže iznad Švicarske i Norveške. Ova dva područja karakterizira složena topografija i predstavljaju zahtjevan test za regionalne klimatske modele. Simulirani i analizirani period je 1987.-2008. u kojem je do kolovoza 2002. RCA3 forsiran s reanalizom ERA-40 a nakon toga ECMWF operativnom analizom. Za verifikaciju su korišteni ECAD E-OBS4 i E-OBS5 na rezolucijama 25 km i 50 km za oba područja, RhiresD na rezoluciji 2.2 km za područje Švicarske i KLIMAGRID na rezoluciji 1 km za područje Norveške. Model općenito precijenjuje količinu ukupne oborine u visokim planinskim područjima te podcijenjuje u niskim i obalnim područjima. Pogreške modela se smanjuju u simulacijama do 12.5 km, dok povećanjem rezolucije na 6.25 km nije uočeno smanjenje pogrešaka. Bitno poboljšanje prilikom povećanja horizontalne rezolucije modela uočava se u procjenama raspodjele gustoće vjerojatnosti u dijelu ekstremno visokih količina oborine. Porastom rezolucije mijenja se odnos između simulirane konvektivne oborine i oborine zbog kondenzacije na velikoj skali i to tako da se smanjuje udio konvektivnog doprinosa.

A new version of the RegCM regional climate modeling system, RegCM4, has been recently developed and made available for public use. Compared to previous versions, RegCM4 includes new land surface, planetary boundary layer, and air-sea flux schemes, a mixed convection and tropical band configuration, modifications to the pre-existing radiative transfer and boundary layer schemes, and a full upgrade of the model code towards improved flexibility, portability, and user friendliness. The model can be interactively coupled to a 1D lake model, a simplified aerosol scheme (including organic carbon, black carbon, SO4, dust, and sea spray), and a gas phase chemistry module (CBM-Z). After a general description of the model, a series of test experiments are presented over 4 domains prescribed under the CORDEX framework (Africa, South America, East Asia, and Europe) to provide illustrative examples of the model behavior and sensitivities under different climatic regimes. These experiments indicate that, overall, RegCM4 shows an improved performance in several respects compared to previous versions, although further testing by the user community is needed to fully explore its sensitivities and range of applications.

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.

Previous studies have shown that numerical diffusion plays a crucial role in the ability of mesoscale models to reproduce features similar to sub-meso motions found in observations, particularly in terms of spectral energy distribution. In this study, the impacts of surface heterogeneity and frequency of lateral boundary coupling are investigated as potential factors governing or modulating the occurrence of sub-meso motions. The spectral energy distribution after the reduction of model diffusion is analysed in detail. It is suggested that a combination of physical and numerical mechanisms is responsible for the final spectral shape. Copyright © 2012 Royal Meteorological Society

Temperature and precipitation from five regional climate models (RCMs), all run at 25-km resolution, are compared with point observations for the 50-year period of the 20th century. Climatological stations are located in the eastern Adriatic, either on the islands or at the coast. The stations are under strong maritime influence and the main cause of sub-grid scale variability comes primarily from a very complex coastal configuration and the land-sea contrast ; local orography plays less important role there. All RCMs were driven by the same global climate model (GCM) and such a setup enables an assessment on how different physical parameterisations affect the downscaling process. On average, monthly means of observed temperature are overestimated by models in the colder part of the year and underestimated in the warm period. Precipitation is generally overestimated by models throughout the year, but approaching observations in summer, when normally small amounts prevail. Model errors are not changed much across the stations although some slight differences exist. The overall poorer RCMs simulations in winter than in summer may indicate a stronger impact of the GCM lateral boundary conditions when large- scale circulation is relatively strong. Simulated interannual variability for temperature is generally lower than observed and for precipitation higher than observed, especially during the warm part of the year. When long time-series of individual variables are compared, interannual variability is found to be strikingly similar among the models although they have different systematic errors. This indicates a prevailing impact of the same lateral boundary conditions from the forcing GCM over the regional physics. The analysis of cumulative distribution functions reveals that temperature extremes are, similar to mean values, overestimated by RCMs. Extremes in precipitation are generally overestimated but no uniform picture from model simulations emerges. Climate change and variability, with respect to the 20th century climate, are analysed for three 30-year climate periods of the 21st century for the IPCC A1B scenario. For temperature, a warming in all three periods is statistically significant in all seasons and at all locations. The warming is strongest in summer irrespective of the climate period considered. Later in the 21st century, the warming is accompanied with precipitation deficit during spring and summer, which would make the eastern Adriatic region particularly vulnerable to climate change. Models disagree on the sign of precipitation change in autumn and winter, even towards the end of the century.

Large warm bias during winter is detected in simulations with RegCM4 over subarctic regions. Similar error is present in several other regional and global climate models. The modifications to reduce warm bias in RegCM4 included the reductions of low-level cloud cover fraction and minimum turbulent mixing in stable planetary boundary layer. The reductions are spatially confined and located at the lower tropospheric levels and do not degrade model’s results in other locations and seasons. The impacts of new land-surface scheme and new PBL scheme are assessed.

U predavanju su prikazani neki problemi u simuliranju klimatologije temperature na području Europe. Diskutirani su pristupi kojima bi se detektirane sustavne pogreške mogle ukloniti ili smanjiti.

The influence of meandering flow on dispersion of pollutants is frequently underrepresented in dispersion models. In terms of measurements, meandering is primarily associated with time-scales between the turbulence and the applied averaging time, which is usually 1 h. The related spatial scales thus range roughly from 10 2 to 10 4 m (referred to here as submesoscales). As the state-of-the-art mesoscale models should be capable of reproducing flow features on scales larger than the turbulence, and as the meandering-generating mechanisms are not fully understood yet, it is useful to examine if the mesoscale models can reproduce meandering. For that purpose, the WRF/Chem model at 1/3 km horizontal resolution is used to simulate a weak-wind night during the CASES99 experiment. The measurements are used for detailed model verification. The model with its typical set-up fails to reproduce the variability at submesoscales and the locus of the under-representation is traced to too-strong horizontal diffusion. Reducing or removing the model diffusion allows the appearance of the submeso variability, whose spectral properties and the resulting plume behaviour agree well with the measurements. The linear correlation between the simulations with reproduced variability and the measurements is low, as is the case between two simulations with only slightly different set-up. The conclusion is that mesoscale models are able to reproduce the strength of variability and the effects of meandering, but only with reduced or removed horizontal diffusion. The question arises whether it is possible to obtain a linear correlation, i.e. to correctly reproduce individual modes at these scales at all. Copyright c � 2010 Royal Meteorological Society

Large warm bias in near-surface temperature during winter was detected over north- eastern Europe in simulations with RegCM4 regional climate model when compared to observational dataset. Modifications to alleviate warm bias included reductions of the low-level cloud cover fraction and the minimum turbulent mixing in stable planetary boundary layer. When implemented, these modifications reduced warm bias up to 50% and did not degrade, or substantially impact, the variables analyzed outside the region and season considered. Valida- tions of the planetary boundary layer and cloud features were limited due to unavailability of appropriate observational data at climatological timescales.

MedECC has published the First Mediterranean Assessment Report (MAR1) on the current state and expected risks of climate and environmental change in the Mediterranean Basin. The Chapter 2 "Drivers of change" describes characteristics and evolution of human-induced and natural factors that cause changes in the Mediterranean Basin ecosystems and human systems. In order to cover most major risks for people and biodiversity, four broad domains of change drivers are considered: climate change and variability, pollution, land and sea use changes and non-indigenous species., Preferred citation: Cherif S, Doblas-Miranda E, Lionello P, Borrego C, Giorgi F, Iglesias A, Jebari S, Mahmoudi E, Moriondo M, Pringault O, Rilov G, Somot S, Tsikliras A, Vila M, Zittis G 2020 Drivers of change. In: Climate and Environmental Change in the Mediterranean Basin – Current Situation and Risks for the Future. First Mediterranean Assessment Report [Cramer W, Guiot J, Marini K (eds.)] Union for the Mediterranean, Plan Bleu, UNEP/MAP, Marseille, France, pp. 59-180, https://doi.org/10.5281/zenodo.7100601.