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Taking advantage of a large ensemble of Convection Permitting‐Regional Climate Models on a pan‐Alpine domain and of an object‐oriented dedicated analysis, this study aims to investigate future changes in high‐impact fall Mediterranean Heavy Precipitation Events at high warming levels. We identify a robust multi‐model agreement for an increased frequency from central Italy to the northern Balkans combined with a substantial extension of the affected areas, for a dominant influence of the driving Global Climate Models for projecting changes in the frequency, and for an increase in intensity, area, volume and severity over the French Mediterranean. However, large quantitative uncertainties persist despite the use of convection‐permitting models, with no clear agreement in frequency changes over southeastern France and a large range of plausible changes in events' properties, including for the most intense events. Model diversity and international coordination are still needed to provide policy‐relevant climate information regarding precipitation extremes. Plain Language Summary: Despite growing computational resources and multiple model developments, projecting future changes in the high‐impact Mediterranean Heavy Precipitation Events remains both a numerical and scientific challenge. The present study takes advantage of the recent availability of a relatively large ensemble of high resolution Regional Climate Models (2–3 km), which represent a step change in the simulation of precipitation extremes, and of an object‐oriented approach, allowing us to track the convective precipitating systems on an hourly basis. Looking at future changes in fall Mediterranean Heavy Precipitation Events at high warming levels, we identify a robust multi‐model agreement for an increased frequency from central Italy to the northern Balkans combined with a substantial expansion of the affected areas, and an increase in intensity, area, volume and severity over the French Mediterranean. However, considerable uncertainties remain in terms of frequency over parts of the domain arising from uncertainty in changes in large scale weather patterns, and in terms of degree of intensification for the most intense events. It suggests the need for model diversity and for more coordinated high resolution climate projections with careful selection of different driving global models in order to provide policy‐relevant climate information regarding precipitation extremes. Key Points: High‐resolution ensemble and object‐oriented approach offer a unique opportunity to study changes in Mediterranean extreme precipitationRobust agreement is found for an increase in intensity, volume and severity for future French Mediterranean Heavy Precipitation EventsEven at convection‐permitting scale, considerable uncertainty remains regarding the degree of intensification of the most extreme events [ABSTRACT FROM AUTHOR]

Providing reliable information on climate change at local scale remains a challenge of first importance for impact studies and policymakers. Here, we propose a novel hybrid downscaling method combining the strengths of both empirical statistical downscaling methods and Regional Climate Models (RCMs). In the longer term, the final aim of this tool is to enlarge the high-resolution RCM simulation ensembles at low cost to explore better the various sources of projection uncertainty at local scale. Using a neural network, we build a statistical RCM-emulator by estimating the downscaling function included in the RCM. This framework allows us to learn the relationship between large-scale predictors and a local surface variable of interest over the RCM domain in present and future climate. The RCM-emulator developed in this study is trained to produce daily maps of the near-surface temperature at the RCM resolution (12 km). The emulator demonstrates an excellent ability to reproduce the complex spatial structure and daily variability simulated by the RCM, particularly how the RCM refines the low-resolution climate patterns. Training in future climate appears to be a key feature of our emulator. Moreover, there is a substantial computational benefit of running the emulator rather than the RCM, since training the emulator takes about 2 h on GPU, and the prediction takes less than a minute. However, further work is needed to improve the reproduction of some temperature extremes, the climate change intensity and extend the proposed methodology to different regions, GCMs, RCMs, and variables of interest. [ABSTRACT FROM AUTHOR]

17 Spatial distribution of the annual mean number of cells per year above the 10 mm threshold during the extended fall (SOND) for CNRM-AROME and COMEPHORE on the tracking domain for several time periods The original article has been corrected. 11 Spatial distribution of the annual mean number of cells per year above the 10 mm threshold during the extended fall (SOND) between 1997-2016 for CNRM-AROME and COMEPHORE on the tracking domain Graph: Fig. [Extracted from the article]

Large multiscenario multimodel ensembles (MMEs) of regional climate model (RCM) experiments driven by global climate models (GCMs) are made available worldwide and aim at providing robust estimates of climate changes and associated uncertainties. Due to many missing combinations of emission scenarios and climate models leading to sparse scenario–GCM–RCM matrices, these large ensembles, however, are very unbalanced, which makes uncertainty analyses impossible with standard approaches. In this paper, the uncertainty assessment is carried out by applying an advanced statistical approach, called QUALYPSO, to a very large ensemble of 87 EURO-CORDEX climate projections, the largest MME based on regional climate models ever produced in Europe. This analysis provides a detailed description of this MME, including (i) balanced estimates of mean changes for near-surface temperature and precipitation in Europe, (ii) the total uncertainty of projections and its partition as a function of time, and (iii) the list of the most important contributors to the model uncertainty. For changes in total precipitation and mean temperature in winter (DJF) and summer (JJA), the uncertainty due to RCMs can be as large as the uncertainty due to GCMs at the end of the century (2071–2099). Both uncertainty sources are mainly due to a small number of individual models clearly identified. Due to the highly unbalanced character of the MME, mean estimated changes can drastically differ from standard average estimates based on the raw ensemble of opportunity. For the RCP4.5 emission scenario in central–eastern Europe for instance, the difference between balanced and direct estimates is up to 0.8 ∘ C for summer temperature changes and up to 20 % for summer precipitation changes at the end of the century. [ABSTRACT FROM AUTHOR]

Large Multiscenarios Multimodel Ensembles (MMEs) of regional climate model (RCM) experiments driven by Global Climate Models (GCM) are made available worldwide, and aim at providing robust estimates of climate changes and associated uncertainties. Due to many missing combinations of emission scenarios and climate models leading to sparse Scenario-GCM-RCM matrices, these large ensembles are however very unbalanced, which makes uncertainty analyses impossible with standard approaches. In this paper, the uncertainty assessment is carried out by applying an advanced statistical approach, called QUALYPSO, to a very large ensemble of 87 EURO-CORDEX climate projections, the largest ensemble ever produced for regional projections in Europe. This analysis provides i) the most up-to-date and balanced estimates of mean changes for near-surface temperature and precipitation in Europe, ii) the total uncertainty of projections and its partition as a function of time, and iii) the list of the most important contributors to the model uncertainty. For changes of total precipitation and mean temperature in winter (DJF) and summer (JJA), the uncertainty due to RCMs can be as large as the uncertainty due to GCMs at the end of the century (2071-2099). Both uncertainty sources are mainly due to a small number of individual models clearly identified. Due to the highly unbalanced character of the MME, mean estimated changes can drastically differ from standard average estimates based on the raw ensemble of opportunity. For the RCP4.5 emission scenario in Central-Eastern Europe for instance, the difference between balanced and direct estimates are up to 0.8°C for summer temperature changes and up to 20% for summer precipitation changes at the end of the century. [ABSTRACT FROM AUTHOR]

Modelling the rare but high-impact Mediterranean Heavy Precipitation Events (HPEs) at climate scale remains a largely open scientific challenge. The issue is adressed here by running a 38-year-long continuous simulation of the CNRM-AROME Convection-Permitting Regional Climate Model (CP-RCM) at a 2.5 km horizontal resolution and over a large pan-Alpine domain. First, the simulation is evaluated through a basic Eulerian statistical approach via a comparison with selected high spatial and temporal resolution observational datasets. Northwestern Mediterranean fall extreme precipitation is correctly represented by CNRM-AROME at a daily scale and even better at an hourly scale, in terms of location, intensity, frequency and interannual variability, despite an underestimation of daily and hourly highest intensities above 200 mm/day and 40 mm/h, respectively. A comparison of the CP-RCM with its forcing convection-parameterised 12.5 km Regional Climate Model (RCM) demonstrates a clear added value for the CP-RCM, confirming previous studies. Secondly, an object-oriented Lagrangian approach is proposed with the implementation of a precipitating system detection and tracking algorithm, applied to the model and the reference COMEPHORE precipitation dataset for twenty fall seasons. Using French Mediterranean HPEs as objects, CNRM-AROME's ability to represent the main characteristics of fall convective systems and tracks is highlighted in terms of number, intensity, area, duration, velocity and severity. Further, the model is able to simulate long-lasting and severe extreme fall events similar to observations. However, it fails to reproduce the precipitating systems and tracks with the highest intensities (maximum intensities above 40 mm/h) well, and the model's tendency to overestimate the cell size increases with intensity. [ABSTRACT FROM AUTHOR]

We assess the differences of future climate changes over Europe in summer as projected by state-of-the-art regional climate models (RCM, from the EURO-Coordinated Regional Downscaling Experiment) and by their forcing global climate models (GCM, from the Coupled Model Intercomparison Project Phase 5) and study the associated physical mechanisms. We show that important discrepancies at large-scales exist between global and regional projections. The RCMs project at the end of the 21st century over a large area of Europe a summer warming 1.5–2 K colder, and a much smaller decrease of precipitation of 5%, versus 20% in their driving GCMs. The RCMs generally simulate a much smaller increase in shortwave radiation at surface, which directly impacts surface temperature. In addition to differences in cloud cover changes, the absence of time-varying anthropogenic aerosols in most regional simulations plays a major role in the differences of solar radiation changes. We confirm this result with twin regional simulations with and without time-varying anthropogenic aerosols. Additionally, the RCMs simulate larger increases in evapotranspiration over the Mediterranean sea and larger increases/smaller decreases over land, which contribute to smaller changes in relative humidity, with likely impacts on clouds and precipitation changes. Several potential causes of these differences in evapotranspiration changes are discussed. Overall, this work suggests that the current EURO-CORDEX RCM ensemble does not capture the upper part of the climate change uncertainty range, with important implications for impact studies and the adaptation policies that they inform. [ABSTRACT FROM AUTHOR]

Marine heatwaves (MHWs) are episodes of anomalous warming in the ocean, responsible for widespread impacts on marine ecosystems. For the first time summer MHW variability at surface and three ecosystem‐relevant depths of the upper Mediterranean Sea are assessed here for 1982–2017. We apply a MHW detection algorithm on a hindcast simulation, performed with a high‐resolution, fully coupled regional climate system model. Identified surface events last, on average, 15 days with a mean intensity of 0.6 °C above threshold and a maximum sea surface coverage of around 39%. Subsurface events are seasonally shifted and appear, on average, longer and more intense but less frequent and less extended in space than surface MHWs. We also find significant trends of increase in most MHW properties throughout the period, with severe surface MHWs detected for the first time in 2012, 2015, and 2017. However, MHW spatial ≪ hot spots ≫ are inhomogeneously distributed in surface and deeper layers. Plain Language Summary: Marine heatwaves (MHWs) are episodes of prolonged and extended anomalous warming in the ocean, responsible for widespread impacts on marine ecosystems and related fisheries. Here, we identify for the first time all the MHWs that have occurred at surface and three ecosystem‐relevant depths of the Mediterranean Sea between 1982 and 2017. To do this, we use the output from the latest version of a regional, high‐resolution climate system model and a consistent detection framework. We find that past surface events, on average, last around 2 weeks and cover almost half the basin with above‐normal temperatures by more than half a degree. Subsurface events appear seasonally shifted and on average, longer and more intense but less frequent and less extended in space than surface MHWs. Following an increase of extremes temperatures with time, surface MHWs appear to have become longer, more severe and spatially extended, while record‐breaking MHWs are identified for the first time in 2012, 2015, and 2017 in addition to the well‐documented 2003 event. However, spatial distribution of MHW ≪ hot spots ≫ differs at surface and depth. Key Points: First time significant past trends of (sub)surface Mediterranean Marine heatwave characteristics are detected using a consistent frameworkSubsurface events are seasonally shifted and on average longer and more severe than surface ones with different spatial hot spotsRecord‐breaking events are identified for the first time in 2012 and 2015 using a high‐resolution coupled regional climate system model [ABSTRACT FROM AUTHOR]

Extreme ocean warming events, known as marine heatwaves (MHWs), have been observed to perturb significantly marine ecosystems and fisheries around the world. Here, we propose a detection method for long-lasting and large-scale summer MHWs, using a local, climatological 99th percentile threshold, based on present-climate (1976–2005) daily SST. To assess their future evolution in the Mediterranean Sea we use, for the first time, a dedicated ensemble of fully-coupled Regional Climate System Models from the Med-CORDEX initiative and a multi-scenario approach. The models appear to simulate well MHW properties during historical period, despite biases in mean and extreme SST. In response to increasing greenhouse gas forcing, the events become stronger and more intense under RCP4.5 and RCP8.5 than RCP2.6. By 2100 and under RCP8.5, simulations project at least one long-lasting MHW every year, up to three months longer, about 4 times more intense and 42 times more severe than present-day events. They are expected to occur from June-October and to affect at peak the entire basin. Their evolution is found to occur mainly due to an increase in the mean SST, but increased daily SST variability also plays a noticeable role. Until the mid-21st century, MHW characteristics rise independently of the choice of the emission scenario, the influence of which becomes more evident by the end of the period. Further analysis reveals different climate change responses in certain configurations, more likely linked to their driving global climate model rather than to the individual model biases. [ABSTRACT FROM AUTHOR]

Mediterranean basins can be impacted by severe floods caused by extreme rainfall, and there is a growing awareness about the possible increase in these heavy rainfall events due to climate change. In this study, the climate change impacts on extreme daily precipitation in 102 catchments covering the whole Mediterranean basin are investigated using nonstationary extreme value model applied to annual maximum precipitation in an ensemble of high-resolution regional climate model (RCM) simulations from the Euro-CORDEX experiment. Results indicate contrasted trends, with significant increasing trends in Northern catchments and conversely decreasing trends in Southern catchments. For most cases, the time of signal emergence for these trends is before the year 2000. The same spatial pattern is obtained under the two climate scenarios considered (RCP4.5 and RCP8.5) and in most RCM simulations, suggesting a robust climate change signal. The strongest multi-model agreement concerns the positive trends, which can exceed + 20% by the end of the twenty-first century in some simulations, impacting South France, North Italy, and the Balkans. For these areas, society-relevant strong impacts of such Mediterranean extreme precipitation changes could be expected in particular concerning flood-related damages. [ABSTRACT FROM AUTHOR]

Highlights • Evaluation of the role of aerosols in the spatiotemporal variability of photovoltaic productivity in a large area. • Evaluation of regional climate model simulations for photovoltaic energy modeling. • Different tracking systems for the photovoltaic generators are considered. • The results show a non-negligible effect of aerosols in photovoltaic production. Abstract The increase in the photovoltaic energy installed capacity over the world leads to the need of a better understanding of solar resource and its variability. The aim of this work is to assess the influence of aerosols on photovoltaic energy production from seasonal to multi-decadal time scales. For this purpose we use various coupled aerosol-climate simulations that take into account the complex spatial and temporal patterns of natural and anthropogenic aerosols over the Euro-Mediterranean domain. The results show that aerosols strongly influence the spatial pattern, seasonal cycle and long-term trend of PV production. The most affected area is Central Europe where sensitivity of PV production to aerosols is higher. The annual production loss due to aerosols ranges from no impact to - 16 % in The Netherlands, with variation depending on the area and on the typology of the tracking system. The summer production loss can even reach - 20 % over regions of Africa and Syria-Iraq. We conclude that aerosols cannot be neglected in the assessment of PV production at large time scales over the Euro-Mediterranean area. Besides, the potential increase in energy due to reduction in the anthropogenic aerosols is shown in the simulation of the brightening period over Europe, with an increase of 2000 kW h kWp in a PV lifetime for the most affected areas. It illustrates the evolution that PV potential could follow in highly polluted areas through the effective implementation of pollution control measures. [ABSTRACT FROM AUTHOR]

Regional climate models (RCMs) constitute a powerful tool to study and understand climate variability and change at local scales. Nevertheless, to correctly interpret regional climate simulations, a number of uncertainties need to be considered. In this study, we investigate the so-called Internal Variability (IV) of an RCM. The IV can be defined as the degree of irreproducibility in an RCM solution observed when it is conducted by the same lateral boundary conditions (LBCs) but initialised from different initial states. The main goal of this work is to investigate how the IV affects the cyclone tracks simulated by an RCM over a Mediterranean domain. For standard variables such as sea level pressure, 2 m temperature and precipitation, our results over the Mediterranean region are consistent with studies conducted over other geographical domains: the IV is stronger at the easternmost part of the domain, where the control exerted by the LBCs is weaker; the IV shows a strong seasonal dependence, reaching larger values in summer than in winter. We show here that the IV values associated with the density of cyclone tracks are much stronger than for the other documented variables, reaching more than 50 % of the estimated total variability. Concerning the cyclone characteristics, long travelling tracks are associated to a greatest IV. Within the latter cyclone category, the fast moving cyclones seems to exhibit also larger IV values. A secondary IV maximum is observed for static cyclones with short travelling distances (thermal lows) during the warm season. [ABSTRACT FROM AUTHOR]

Observing, modelling and understanding the climate-scale variability of the deep water formation (DWF) in the North-Western Mediterranean Sea remains today very challenging. In this study, we first characterize the interannual variability of this phenomenon by a thorough reanalysis of observations in order to establish reference time series. These quantitative indicators include 31 observed years for the yearly maximum mixed layer depth over the period 1980-2013 and a detailed multi-indicator description of the period 2007-2013. Then a 1980-2013 hindcast simulation is performed with a fully-coupled regional climate system model including the high-resolution representation of the regional atmosphere, ocean, land-surface and rivers. The simulation reproduces quantitatively well the mean behaviour and the large interannual variability of the DWF phenomenon. The model shows convection deeper than 1000 m in 2/3 of the modelled winters, a mean DWF rate equal to 0.35 Sv with maximum values of 1.7 (resp. 1.6) Sv in 2013 (resp. 2005). Using the model results, the winter-integrated buoyancy loss over the Gulf of Lions is identified as the primary driving factor of the DWF interannual variability and explains, alone, around 50 % of its variance. It is itself explained by the occurrence of few stormy days during winter. At daily scale, the Atlantic ridge weather regime is identified as favourable to strong buoyancy losses and therefore DWF, whereas the positive phase of the North Atlantic oscillation is unfavourable. The driving role of the vertical stratification in autumn, a measure of the water column inhibition to mixing, has also been analyzed. Combining both driving factors allows to explain more than 70 % of the interannual variance of the phenomenon and in particular the occurrence of the five strongest convective years of the model (1981, 1999, 2005, 2009, 2013). The model simulates qualitatively well the trends in the deep waters (warming, saltening, increase in the dense water volume, increase in the bottom water density) despite an underestimation of the salinity and density trends. These deep trends come from a heat and salt accumulation during the 1980s and the 1990s in the surface and intermediate layers of the Gulf of Lions before being transferred stepwise towards the deep layers when very convective years occur in 1999 and later. The salinity increase in the near Atlantic Ocean surface layers seems to be the external forcing that finally leads to these deep trends. In the future, our results may allow to better understand the behaviour of the DWF phenomenon in Mediterranean Sea simulations in hindcast, forecast, reanalysis or future climate change scenario modes. The robustness of the obtained results must be however confirmed in multi-model studies. [ABSTRACT FROM AUTHOR]

Abstract: Chaotic intrinsic variability is a fundamental driver of the oceanic variability. Its understanding is key to interpret observations, evaluate numerical models, and predict the future ocean and climate. Here we study intrinsic variability of deep convection in the northwestern Mediterranean Sea using an ensemble eddy‐resolving hindcast simulation over the period 1979–2013. We find that the variability of deep convection is mostly forced but also, to a considerable extent, intrinsic. The intrinsic variability can dominate the total convection variability locally and over a single winter. It also makes up a significant fraction of its interannual variability but has only modest impacts on the long‐term mean state. We find that the occurrence of deep convection is random 18% of years at the basin scale, and 29% locally at the LION observational site. Spatially, the intrinsic variability is highest far from the continental shelf. We relate this pattern to baroclinic instability theory that takes bottom stabilization into account. [ABSTRACT FROM AUTHOR]

Important discrepancies in the large-scale summer climate change projections were recently detected between the global and regional climate models (RCM/GCM) in the EURO-CORDEX ensemble for several variables including surface temperature, total precipitation, and surface solar radiation. In this study, we use a new experimental framework inspired by the Big-Brother–Little-Brother protocol to explore the mechanisms responsible for generating large-scale discrepancies in future projections between GCM/RCM pairs over Europe in summer. Starting from past and future simulations with a perfect GCM/RCM pair (same resolution, same physics, same forcings), we then disentangle the role of potential sources of GCM/RCM inconsistency by carrying out targeted sensitivity studies. We show that by following such a perfect approach, it is possible to obtain a GCM/RCM pair without statistically significant inconsistencies in projected climate change. Such discrepancies are mainly generated by differences in aerosols representation and atmospheric physics. The role of plant physiology is limited and unlikely to be the dominant factor in the detected discrepancies. Finally, it is unlikely that the discrepancies in the EURO-CORDEX ensemble projections are a result of the upscaled added value, as we show that the effect of increased resolution is not strong enough and mostly limited to areas with complex topography. These findings raise important questions about the current practices in regional climate modelling. In the short term, implementing RCM external forcings consistent with the driving GCM can significantly improve the situation at low cost. In the long term, adopting a seamless strategy in developing the GCM/RCM models should be questioned. [ABSTRACT FROM AUTHOR]

The Mediterranean climate is expected to become warmer and drier during the twenty-first century. Mediterranean Sea response to climate change could be modulated by the choice of the socio-economic scenario as well as the choice of the boundary conditions mainly the Atlantic hydrography, the river runoff and the atmospheric fluxes. To assess and quantify the sensitivity of the Mediterranean Sea to the twenty-first century climate change, a set of numerical experiments was carried out with the regional ocean model NEMOMED8 set up for the Mediterranean Sea. The model is forced by air-sea fluxes derived from the regional climate model ARPEGE-Climate at a 50-km horizontal resolution. Historical simulations representing the climate of the period 1961-2000 were run to obtain a reference state. From this baseline, various sensitivity experiments were performed for the period 2001-2099, following different socio-economic scenarios based on the Special Report on Emissions Scenarios. For the A2 scenario, the main three boundary forcings (river runoff, near-Atlantic water hydrography and air-sea fluxes) were changed one by one to better identify the role of each forcing in the way the ocean responds to climate change. In two additional simulations (A1B, B1), the scenario is changed, allowing to quantify the socio-economic uncertainty. Our 6-member scenario simulations display a warming and saltening of the Mediterranean. For the 2070-2099 period compared to 1961-1990, the sea surface temperature anomalies range from +1.73 to +2.97 °C and the SSS anomalies spread from +0.48 to +0.89. In most of the cases, we found that the future Mediterranean thermohaline circulation (MTHC) tends to reach a situation similar to the eastern Mediterranean Transient. However, this response is varying depending on the chosen boundary conditions and socio-economic scenarios. Our numerical experiments suggest that the choice of the near-Atlantic surface water evolution, which is very uncertain in General Circulation Models, has the largest impact on the evolution of the Mediterranean water masses, followed by the choice of the socio-economic scenario. The choice of river runoff and atmospheric forcing both have a smaller impact. The state of the MTHC during the historical period is found to have a large influence on the transfer of surface anomalies toward depth. Besides, subsurface currents are substantially modified in the Ionian Sea and the Balearic region. Finally, the response of thermosteric sea level ranges from +34 to +49 cm (2070-2099 vs. 1961-1990), mainly depending on the Atlantic forcing. [ABSTRACT FROM AUTHOR]

A set of simulations from different configurations of the NEMOMED8, NEMOMED12 and NEMOMED36 ocean regional circulation models for the Mediterranean Sea has been studied in order to assess the accuracy of their representation of the exchange through the Strait of Gibraltar. The model volume transport and thermohaline properties of the Mediterranean outflow have been compared with observational data collected at Espartel sill, the westernmost sill of the strait, by a permanent station moored since October 2004 in the frame of the INGRES projects. Results show that, in terms of volume transport, NEMOMED8 simulations perform a better representation of the exchange, while NEMOMED12/36 underestimate both the mean inflow and outflow. The reason for this underestimation is a too low velocity of the flow, which could be consequence of an enhanced roughness effect due the flow-bathymetry interaction. An important improvement in the representation of the exchange seasonality is achieved by the simulations including sea surface height variability of the Atlantic area of the domain. The results for the themohaline characteristics of the Mediterranean outflow are better for NEMOMED12 and NEMOMED36, as a consequence of their better representation of the local dynamical processes that leads to a more realistic composition of the Mediterranean waters comprising the flow. [ABSTRACT FROM AUTHOR]

A fully coupled regional climate system model (CNRM-RCSM4) has been used over the Mediterranean region to investigate the direct and semi-direct effects of aerosols, but also their role in the radiation-atmosphere-ocean interactions through multi-annual ensemble simulations (2003-2009) with and without aerosols and ocean-atmosphere coupling. Aerosols have been taken into account in CNRM-RCSM4 through realistic interannual monthly AOD climatologies. An evaluation of the model has been achieved, against various observations for meteorological parameters, and has shown the ability of CNRM-RCSM4 to reproduce the main patterns of the Mediterranean climate despite some biases in sea surface temperature (SST), radiation and cloud cover. The results concerning the aerosol radiative effects show a negative surface forcing on average because of the absorption and scattering of the incident radiation. The SW surface direct effect is on average −20.9 Wm over the Mediterranean Sea, −14.7 Wm over Europe and −19.7 Wm over northern Africa. The LW surface direct effect is weaker as only dust aerosols contribute (+4.8 Wm over northern Africa). This direct effect is partly counterbalanced by a positive semi-direct radiative effect over the Mediterranean Sea (+5.7 Wm on average) and Europe (+5.0 Wm) due to changes in cloud cover and atmospheric circulation. The total aerosol effect is consequently negative at the surface and responsible for a decrease in land (on average −0.4 °C over Europe, and −0.5 °C over northern Africa) and sea surface temperature (on average −0.5 °C for the Mediterranean SST). In addition, the latent heat loss is shown to be weaker (−11.0 Wm) in the presence of aerosols, resulting in a decrease in specific humidity in the lower troposphere, and a reduction in cloud cover and precipitation. Simulations also indicate that dust aerosols warm the troposphere by absorbing solar radiation, and prevent radiation from reaching the surface, thus stabilizing the troposphere. The comparison with the model response in atmosphere-only simulations shows that these feedbacks are attenuated if SST cannot be modified by aerosols, highlighting the importance of using coupled regional models over the Mediterranean. Oceanic convection is also strengthened by aerosols, which tends to reinforce the Mediterranean thermohaline circulation. In parallel, two case studies are presented to illustrate positive feedbacks between dust aerosols and regional climate. First, the eastern Mediterranean was subject to high dust aerosol loads in June 2007 which reduce land and sea surface temperature, as well as air-sea humidity fluxes. Because of northern wind over the eastern Mediterranean, drier and cooler air has been consequently advected from the sea to the African continent, reinforcing the direct dust effect over land. On the contrary, during the western European heat wave in June 2006, dust aerosols have contributed to reinforcing an important ridge responsible for dry and warm air advection over western Europe, and thus to increasing lower troposphere (+0.8 °C) and surface temperature (+0.5 °C), namely about 15 % of this heat wave. [ABSTRACT FROM AUTHOR]

In this study, an ensemble of four multi-year climate simulations is performed with the regional climate model ALADIN to evaluate its ability to simulate the climate over North America in the CORDEX framework. The simulations differ in their driving fields (ERA-40 or ERA-Interim) and the nudging technique (with or without large-scale nudging). The validation of the simulated 2-m temperature and precipitation with observationally-based gridded data sets shows that ALADIN performs similarly to other regional climate models that are commonly used over North America. Large-scale nudging improves the temporal correlation of the atmospheric circulation between ALADIN and its driving field, and also reduces the warm and dry summer biases in central North America. The differences between the simulations driven with different reanalyses are small and are likely related to the regional climate model's induced internal variability. In general, the impact of different driving fields on ALADIN is smaller than that of large-scale nudging. The analysis of the multi-year simulations over the prairie and the east taiga indicates that the ALADIN 2-m temperature and precipitation interannual variability is similar or larger than that observed. Finally, a comparison of the simulations with observations for the summer 1993 shows that ALADIN underestimates the flood in central North America mainly due to its systematic dry bias in this region. Overall, the results indicate that ALADIN can produce a valuable contribution to CORDEX over North America. [ABSTRACT FROM AUTHOR]

One of the Mediterranean hotspots for extreme precipitation is the coastal mountainous easternAdriatic andDinaric 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. [ABSTRACT FROM AUTHOR]

Croatian Adriatic coast is often affected by extreme precipitation that leads to flash-floods with severe damage, both human and material. The added value of high-resolution regional climate model (RCM) simulations of mean and extreme precipitation has already been proven, but RCMs' skill over complex terrain, such as coastal mountains in Croatia, still poses some challenges and open questions. We evaluate the daily precipitation simulations of high-resolution (0.11°) RCM ALADIN-Climate versions 5.2 (ALD5) and 6.3 (ALD6) driven by the ERA-Interim reanalysis over the Med-CORDEX domain. The spectral nudging technique (SN) was applied on both model versions (AD5SN, ALD6SN). Reference datasets used are precipitation analysis system MESCAN, available on 5.5 km resolution every 6 h, and 24 h accumulated precipitation data from the Croatian raingauge network. To assess the agreement between model and reference we perform statistical analysis in terms of multi year spatial bias for the mean annual and seasonal precipitation, the number of wet days, the 99.9th quantile, and the quantile-quantile plots for the period 1979-2012. ALD6SN outperforms the previous versions by diminishing the drizzling effect, with notably less wet days than ALD5 and ALD5SN, and with significantly improved lower precipitation quantiles. All model versions show an underestimation of higher-order quantiles. The spectral nudging in ALD5SN causes an overestimation of the lower quantiles, with minimum difference in higher quantiles compared to ALD5. [ABSTRACT FROM AUTHOR]

The Mediterranean region of France are regularly affected by extreme precipitation that often lead to devastating flash-floods, often associated with both human and material damages. The evolution of such events in terms of occurrence and severity with climate change remains an open question.The purpose of the current study is to characterize the future evolution of these heavy precipitating events in terms of occurrence and intensity. A historical simulation (1976 – 2005) will be compare to a future simulation (2071 – 2100) for the RCP8,5 scenario. The CNRM-CM5 global climate is used as driver model. The study also compare climate change simulations from a convection parametrized convection model (ALADIN-Climate) and a convection permitting reginal climate model (AROME-Climate). These simulations were carried out on the domain defined by the CORDEX Flagship Pilot Study "Convective phenomena at high resolution over Europe and the Mediterranean". It is centered on the Alps. This domain allows a good representation of the large scale circulation over the Mediterranean sea that causes convective phenomena in the Southeastern France. The study of changes in spatial distribution and cumulative precipitation will be based on daily and hourly averages and quantiles of precipitation.I would like to share my knowledge on convection permitting regional climate model with interested people. This workshop would be a great opportunity and I hope, I will have the opportunity to exchange with people from this community. [ABSTRACT FROM AUTHOR]

The evolution of different renewable energy resources under different climate change scenarios is a key factor for the energy industry and for the energy transition. The possible changes with respect to present conditions for the operating plants and the projected resources can affect the financial frame and viability of the projects.Over Europe, climate models give a robust answer in terms of global warming and other important climate variables. However, GCMs and RCMs disagree in the projected changes of surface solar radiation (SSR) over Europe. Whereas global climate models, GCMs, present a clear positive signal for the end of XXI century, some studies show a negative anomaly for the same period in RCMs from EURO-CORDEX ensemble. This discrepancy is of special interest for photovoltaic (PV) power plants, whose resource is precisely solar radiation reaching earth's surface.In this work, which is a contribution to the CORDEX FPS-aerosols, we try to explain the reasons of the difference in anomalies focusing on the representation of aerosols in the scenario simulations of RCMs. We use regional climate models simulations from the EURO-CORDEX ensemble grouped together by its forcing GCM. Different families of runs are analysed with only one simulation with evolving aerosols per group. We focus on RCP8.5 emissions scenario. In addition, a detailed PV model is used to estimate future PV potential over Europe, which has not been considered in previous approaches.Results of this study will lead to the obtention of more accurate PV projections over Europe, demanded by policymakers and the energy sector. [ABSTRACT FROM AUTHOR]

For now, the question about future sea level change in the Mediterranean remains a challenge. Previous climate modelling attempts to estimate future sea level change in the Mediterranean did not meet a consensus. The low resolution of CMIP-type models prevents an accurate representation of important small scales processes acting over the Mediterranean region. For this reason among others, the use of high resolution regional ocean modelling has been recommended in literature to address the question of ongoing and future Mediterranean sea level change in response to climate change or greenhouse gases emissions. Also, it has been shown that east Atlantic sea level variability is the dominant driver of the Mediterranean variability at interannual and interdecadal scales. However, up to now, long-term regional simulations of the Mediterranean Sea do not integrate the full sea level information from the Atlantic, which is a substantial shortcoming when analysing Mediterranean sea level response. In the present study we analyse different approaches followed by state-of-the-art regional climate models to simulate Mediterranean sea level variability. Additionally we present a new simulation which incorporates improved information of Atlantic sea level forcing at the lateral boundary. We evaluate the skills of the different simulations in the frame of long-term hindcast simulations spanning from 1980 to 2012 analysing sea level variability from seasonal to multidecadal scales. Results from the new simulation show a substantial improvement in the modelled Mediterranean sea level signal. This confirms that Mediterranean mean sea level is strongly influenced by the Atlantic conditions, and thus suggests that the quality of the information in the lateral boundary conditions (LBCs) is crucial for the good modelling of Mediterranean sea level. We also found that the regional differences inside the basin, that are induced by circulation changes, are model-dependent and thus not affected by the LBCs. Finally, we argue that a correct configuration of LBCs in the Atlantic should be used for future Mediterranean simulations, which cover hindcast period, but also for scenarios. [ABSTRACT FROM AUTHOR]

The characteristics of the mesoscale Mistral and Tramontane winds under changing climate conditions are of great interest for risk assessments. In this study, a classification algorithm is applied to identify Mistral and Tramontane-permitting sea-level pressure patterns, thus allowing for estimates of their future characteristics. Five simulations with three regional climate models on a 0.44 $$^\circ$$ grid and five global circulation models are assessed for the representative concentration pathways (RCPs) 4.5 and 8.5. Regional climate simulations driven by ERA-Interim are used to test the classification algorithm and to estimate its accuracy. The derived Mistral and Tramontane time series are discussed. The results for the ERA-Interim period show that the classification algorithm and the regional climate models work well in terms of the number of Mistral and Tramontane days per year, but the results overestimate the average length of such events. For both the RCPs, only small changes in Mistral frequency were found in both regional and global climate simulations. Most simulations show a decrease in Tramontane frequencies and average period lengths during the 21st century. Regional climate simulations using RCP8.5 show fewer Tramontane events than those using RCP4.5. [ABSTRACT FROM AUTHOR]

Here, we analyze future projections of cyclone activity in the Mediterranean region at the end of the twenty-first century based on an ensemble of state-of-the-art fully-coupled Regional Climate System Models (RCSMs) from the Med-CORDEX initiative under the Representative Concentration Pathway (RCP) 8.5. Despite some noticeable biases, all the RCSMs capture spatial patterns and cyclone activity key characteristics in the region and thus all of them can be considered as plausible representations of the future evolution of Mediterranean cyclones. In general, the RCSMs show at the end of the twenty-first century a decrease in the number and an overall weakening of cyclones moving across the Mediterranean. Five out of seven RCSMs simulate also a decrease of the mean size of the systems. Moreover, in agreement with what already observed in CMIP5 projections for the area, the models suggest an increase in the Central part of the Mediterranean region and a decrease in the South-eastern part of the region in the cyclone-related wind speed and precipitation rate. These rather two opposite tendencies observed in the precipitation should compensate and amplify, respectively, the effect of the overall reduction of the frequency of cyclones on the water budget over the Central and South-eastern part of the region. A pronounced inter-model spread among the RCSMs emerges for the projected changes in the cyclone adjusted deepening rate, seasonal cycle occurrence and associated precipitation and wind patterns over some areas of the basin such as Ionian Sea and Iberian Peninsula. The differences observed appear to be determined by the driving Global Circulation Model (GCM) and influenced by the RCSM physics and internal variability. These results point to the importance of (1) better characterizing the range of plausible futures by relying on ensembles of models that explore well the existing diversity of GCMs and RCSMs as well as the climate natural variability and (2) better understanding the driving mechanisms of the future evolution of Mediterranean cyclones properties. [ABSTRACT FROM AUTHOR]

Climate simulations made with two regional climate models (RCMs), the French Aire Limitée Adaptation Dynamique Développement International (ALADIN) and the Canadian Regional Climate Model, version 5 (CRCM5), operating on 10-km meshes for the period 1989-2011, and the Hydro-Québec hydrological model (HSAMI), are used to reconstruct the spring 2011 Richelieu River flood in the southern region of the province of Québec, Canada. The analysis shows that the simulated fields of 2-m air temperature, precipitation, and snow water equivalent by the RCMs closely match the observations with similar multiyear means and a high correlation of the monthly anomalies. The climatic conditions responsible for the 2011 flood are generally well simulated by the RCMs. The use of multidecadal RCM simulations facilitates the identification of anomalies that contributed to the flood. The flood was linked to a combination of factors: the 2010/11 winter was cold and snowy, the snowmelt in spring was fast, and there was a record amount of precipitation in April and May. Driven by outputs from the RCMs, HSAMI was able to reproduce the mean hydrograph of the Richelieu River, but it underestimated the peak of the 2011 flood. HSAMI adequately computes the water transport from the mountains to the river mouth and the storage effect of Lake Champlain, which dampens the flood over a long period. Overall, the results suggest that RCM simulations can be useful for reconstructing high-resolution climate information and providing new variables that can help better understand the causes of extreme climatic events. [ABSTRACT FROM AUTHOR]

Aim To study the combined effects of climate change on connectivity between marine protected areas ( MPAs) and larval supply to the continental shelf. Location The Mediterranean Sea, where sea surface temperatures are expected to strongly increase by the end of the 21st century, represents an archetypal situation with a dense MPA network but resource overexploitation outside. Methods Using an individual-based mechanistic model of larval transport, forced with an emission-driven regional climate change scenario for the Mediterranean Sea, we explored the combined effects of changes in hydrodynamics, adult reproductive timing and larval dispersal on the connectivity among MPAs and their ability to seed fished areas with larvae. Results We show that, over the period 1970-2099, larval dispersal distances would decrease by 10%, the continental shelf area seeded with larvae would decrease by 3% and the larval retention fraction would increase by 5%, resulting in higher concentration of larvae in smaller areas of the continental shelf. However, connectance within the MPA network would increase by 5% as more northern MPAs would become suitable for reproduction with increasing temperatures. We also show that the effects of changes in adult reproductive timing and larval dispersal on connectivity patterns are additive. Main conclusions Climate change will influence connectivity and the effectiveness of MPA networks, and should receive more attention in future conservation planning and large-scale population dynamics. [ABSTRACT FROM AUTHOR]

Results obtained with two versions of the Limited Area Model (LAM) ALADIN over differently sized integration domains (large, intermediate and small) in the European area are presented in order to investigate both the general model performance and the influence of domain choice on the quality of obtained results. The aim is also to illustrate the issues related to the strategy of selection of the optimal integration domain. Each of these studies has been performed with two versions of the ALADIN model: the first one is ALADIN-CLIMATE developed at CNRM/Météo-France, the second one is ALADIN-CLIMATE/CZ prepared at the Czech Hydrometeorological Institute (CHMI). This leaves us with total of six experiments forced by the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-40 reanalysis data. The west Balkan domain covering Bulgaria is used as an evaluation region for investigation of the temporal and spatial properties of simulated precipitation and temperature fields. This region has been selected for its challenging orography making the results obtained here a valuable source for studies leading to further developments in climate modeling. It was found that size of the domain strongly affects the quality of obtained results. We have found that the largest domain reproduces the spatial characteristics of climate (such as bias) very well, but its use results in a poor representation of temporal aspects, which are however captured very well in experiments over both smaller domains. Our findings suggest that there is no optimal choice of domain size, securing the best results for both spatial and temporal evaluation. Our study also proves that model ALADIN can be efficiently used for climate research purposes, which together with its modest computational demands should make it as an attractive modeling choice for the Central and Eastern European climate research community. [ABSTRACT FROM AUTHOR]

Spectral nudging, a dynamic downscaling method, has been used as a suitable approach to force a regional model to adopt prescribed large-scales over the entire domain, not just at the lateral boundaries, while developing realistic detailed regional features consistent with the large-scales. The aim of this study is to compare a global spectral climate model at high resolution (50 km) and a driven spectral regional climate model over Europe by using the so-called perfect model approach. The spectral nudging method is applied in order to achieve a better representation of large-scale climate over a limited domain. The results show that the regional model driven only at its lateral boundaries presents a summer warm bias in the middle of the domain. This bias disappears when spectral nudging is applied. On the other hand, the smallest scales which are not driven by the spectral nudging are not significantly affected by scale interaction. The only detrimental impact of spectral nudging is a slight precipitation increase in the upper quantiles of precipitation, which can be resolved by large-scale nudging of specific humidity. [ABSTRACT FROM AUTHOR]

Abstract: Sea level trends and inter-annual variability in the Mediterranean Sea for the period 1960–2000 is explored by comparing observations from tide gauges with sea level hindcasts from a barotropic 2D circulation model, and two full primitive equation 3D ocean circulation models, a regional one and the Mediterranean component of a global one,. In the 2D model, 50% of the sea level variance was found to result from the wind and atmospheric pressure forcing. In the 3D models, 20% of the sea level variance was explained by the steric effects. The sea level residuals at the tide gauges locations, calculated by subtraction of the 2D model output from the sea level observations are significantly correlated (r =0.4) with the steric signals from the 3D models. After the removal of the atmospheric and the steric contributions the tide-gauge sea level records indicate a period where sea level was stable (1960–1975) and a period where sea level was rising (1975–2000) with rates in the range 1.1–1.8 mm/yr. A part of the residual trend can be explained by the contribution of local land movements (0.3 mm/yr) while its major part indicates a global signal, probably mass addition, appearing after 1975. [Copyright &y& Elsevier]

Abstract: An Atmosphere-Ocean Regional Climate Model coupled over the Mediterranean basin and forced by river runoff and influxes from the Atlantic Ocean and the Black Sea is used to obtain estimates of sea level rise in the region during the 21st century. Changes in temperature and salinity under the A2 emission scenario, which corresponds to a high level of anthropogenic gas concentration in the atmosphere, are investigated in the different sub-basins and are used to compute the steric sea level change in the region. Significant spatial variability is observed. This model projects a maximum steric sea level rise of 25 cm. The mean steric sea level rise value predicted is around 13 cm with lower values in the eastern Mediterranean and higher values at the western Mediterranean. Coastal sea level rise values are found to be smaller, although this is partly due to the smaller range of vertical integration in the computation of sea level changes. Warming and salinification of the intermediate waters are also predicted to occur simultaneously thus partly compensating each other. The effects of atmospheric pressure changes are added to the steric sea level obtained from the model giving up to 2 mbars and thus also compensating some of the thermal expansion. Circulation changes will in certain areas also add up to 6 cm of sea level rise. There is no predicted seasonal bias in the sea level rise indicating that the seasonal cycles will remain unaffected. These results are derived from a single model and therefore can only been seen as part of a methodological study. Similar investigations should be applied to a range of models and scenarios in order to obtain a range of the future sea level change in the Mediterranean basin and its associated uncertainties. [Copyright &y& Elsevier]

South-East France is a region often affected by heavy precipitating events the characteristics of which are likely to be significantly impacted in the future climate. In this study, cnrm-arome, a Convection-Permitting Regional Climate Model with a 2.5 km horizontal resolution is compared to its forcing model, the Regional Climate Model aladin-climate at a horizontal resolution of 12.5 km, self-driven by the era-interim reanalysis. An hourly observation dataset with a resolution of 1 km, comephore, is used in order to assess simulated surface precipitation from a seasonal to hourly scale. The representation of the spatial pattern of fall precipitation climatology is improved by cnrm-arome. It also shows a clear added value with respect to aladin-climate through the improvement of the localization and intensity of extreme rainfall on a daily and hourly time scale on both fine and coarse spatial scales (2.5, 12.5 and 50 km). cnrm-arome in particular is able to simulate intense rainfall on lowlands and makes sub-daily rainfall events more intense than aladin-climate. cnrm-arome still underestimates very extreme precipitation from above 30 mm/h or 230 mm/day. [ABSTRACT FROM AUTHOR]

Highlights • Seven multi-decadal ocean simulations have been assessed for the Adriatic Sea. • Analysed simulations differ in resolution, forcing and coupling strategies. • Thermohaline properties and dynamic processes of the Adriatic Sea are better reproduced by coupled models. • All analysed models underrepresent dense water formation on the shelf. • Ocean model resolution and river forcing play a second-order role. Abstract A performance study of seven regional ocean configurations based on NEMO has been carried out for the Adriatic Sea over a common period (1980–2012). Assessed models differ in resolution, model physics, atmospheric forcing (forced vs. coupled models) and river discharges imposed within the Adriatic Sea. Models have been evaluated on the long-term temperature and salinity measurements in all of the Adriatic sub-basins, in particular within dense water collectors (Jabuka Pit and South Adriatic Pit) and dense water formation sites (northern and southern Adriatic). Adriatic-wide salinity content is mostly linked to the proper introduction of the overall water budget, rather than to the local river forcing. Forced models mostly overestimate temperature and salinity values. On average, coupled models better reproduce the thermohaline properties and processes, in particular the Adriatic-Ionian Bimodal Oscillating System (BiOS) reversals and its decadal variability. Wintertime heat losses are playing major role in defining the Adriatic Deep Water (ADW) transport rates in coupled models, while in forced models preconditioning in salinity is the most important factor. Further on, increase of resolution of the atmospheric forcing results in more realistic ocean behaviour, including dense water formation (DWF) in the complex coastal northern Adriatic. However, all models have large temperature biases and lower deep stratification at the dense water collector sites, indicating overall underrepresentation of the Adriatic DWF. Consequently, mixed-layer depth in the southern Adriatic is overestimated, reaching the bottom during some years. Ocean model resolution and river forcing seem to play a second-order role in defining the overall Adriatic-Ionian thermohaline properties, while inclusion of aerosol trend only slightly modified the BiOS reproduction. [ABSTRACT FROM AUTHOR]

We examine long-term trends in the historical record of extreme precipitation events occurring over the French Mediterranean area. Extreme events are considered in terms of their intensity, frequency, extent and precipitated volume. Changes in intensity are analysed via an original statistical approach where the annual maximum rainfall amounts observed at each measurement station are aggregated into a univariate time-series according to their dependence. The mean intensity increase is significant and estimated at + 22% (+ 7 to + 39% at the 90% confidence level) over the 1961-2015 period. Given the observed warming over the considered area, this increase is consistent with a rate of about one to three times that implied by the Clausius-Clapeyron relationship. Changes in frequency and other spatial features are investigated through a Generalised Linear Model. Changes in frequency for events exceeding high thresholds (about 200 mm in 1 day) are found to be significant, typically near a doubling of the frequency, but with large uncertainties in this change ratio. The area affected by severe events and the water volume precipitated during those events also exhibit significant trends, with an increase by a factor of about 4 for a 200 mm threshold, again with large uncertainties. All diagnoses consistently point toward an intensification of the most extreme events over the last decades. We argue that it is difficult to explain the diagnosed trends without invoking the human influence on climate. [ABSTRACT FROM AUTHOR]

Abstract: For more than five decades, the Mediterranean Sea has been identified as a region of so‐called thermohaline circulation, namely, of basin‐scale overturning driven by surface heat and freshwater exchanges. The commonly accepted view is that of an interaction of zonal and meridional conveyor belts that sink at intermediate or deep convection sites. However, the connection between convection and sinking in the overturning circulation remains unclear. Here we use a multidecadal eddy‐permitting numerical simulation and glider transport measurements to diagnose the location and physical drivers of this sinking. We find that most of the net sinking occurs within 50 km of the boundary, away from open sea convection sites. Vorticity dynamics provides the physical rationale for this sinking near topography: only dissipation at the boundary is able to balance the vortex stretching induced by any net sinking, which is hence prevented in the open ocean. These findings corroborate previous idealized studies and conceptually replace the historical offshore conveyor belts by boundary sinking rings. They challenge the respective roles of convection and sinking in shaping the oceanic overturning circulation and confirm the key role of boundary currents in ventilating the interior ocean. [ABSTRACT FROM AUTHOR]

Medicanes are cyclones over the Mediterranean Sea having a tropical-like structure but a rather small size, that can produce significant damage due to the combination of intense winds and heavy precipitation. Future climate projections, performed generally with individual atmospheric climate models, indicate that the intensity of the medicanes could increase under climate change conditions. The availability of large ensembles of high resolution and ocean-atmosphere coupled regional climate model (RCM) simulations, performed in MedCORDEX and EURO-CORDEX projects, represents an opportunity to improve the assessment of the impact of climate change on medicanes. As a first step towards such an improved assessment, we analyze the ability of the RCMs used in these projects to reproduce the observed characteristics of medicanes, and the impact of increased resolution and air-sea coupling on their simulation. In these storms, air-sea interaction plays a fundamental role in their formation and intensification, a different mechanism from that of extra-tropical cyclones, where the baroclinic instability mechanism prevails. An observational database, based on satellite images combined with high resolution simulations (Miglietta et al. in Geophys Res Lett 40:2400-2405, 2013), is used as a reference for evaluating the simulations. In general, the simulated medicanes do not coincide on a case-by-case basis with the observed medicanes. However, observed medicanes with a high intensity and relatively long duration of tropical characteristics are better replicated in simulations. The observed spatial distribution of medicanes is generally well simulated, while the monthly distribution reveals the difficulty of simulating the medicanes that first appear in September after the summer minimum in occurrence. Increasing the horizontal resolution has a systematic and generally positive impact on the frequency of simulated medicanes, while the general underestimation of their intensity is not corrected in most cases. The capacity of a few models to better simulate the medicane intensity suggests that the model formulation is more important than reducing the grid spacing alone. A negative intensity feedback is frequently the result of air-sea interaction for tropical cyclones in other basins. The introduction of air-sea coupling in the present simulations has an overall limited impact on medicane frequency and intensity, but it produces an interesting seasonal shift of the simulated medicanes from autumn to winter. This fact, together with the analysis of two contrasting particular cases, indicates that the negative feedback could be limited or even absent in certain situations. We suggest that the effects of air-sea interaction on medicanes may depend on the oceanic mixed layer depth, thus increasing the applicability of ocean-atmosphere coupled RCMs for climate change analysis of this kind of cyclones. [ABSTRACT FROM AUTHOR]

This study aims to assess the skill of regional climate models (RCMs) at reproducing the climatology of Mediterranean cyclones. Seven RCMs are considered, five of which were also coupled with an oceanic model. All simulations were forced at the lateral boundaries by the ERA-Interim reanalysis for a common 20-year period (1989-2008). Six different cyclone tracking methods have been applied to all twelve RCM simulations and to the ERA-Interim reanalysis in order to assess the RCMs from the perspective of different cyclone definitions. All RCMs reproduce the main areas of high cyclone occurrence in the region south of the Alps, in the Adriatic, Ionian and Aegean Seas, as well as in the areas close to Cyprus and to Atlas mountains. The RCMs tend to underestimate intense cyclone occurrences over the Mediterranean Sea and reproduce 24-40 % of these systems, as identified in the reanalysis. The use of grid nudging in one of the RCMs is shown to be beneficial, reproducing about 60 % of the intense cyclones and keeping a better track of the seasonal cycle of intense cyclogenesis. Finally, the most intense cyclones tend to be similarly reproduced in coupled and uncoupled model simulations, suggesting that modeling atmosphere-ocean coupled processes has only a weak impact on the climatology and intensity of Mediterranean cyclones. [ABSTRACT FROM AUTHOR]

A performance analysis of the NEMOMED8 ocean regional circulation model was undertaken for the Adriatic Sea during the period of 1961-2012, focusing on two mechanisms, dense water formation (DWF) and the Adriatic-Ionian Bimodal Oscillating System (BiOS), which drive interannual and decadal variability in the basin. The model was verified based on sea surface temperature and sea surface height satellite measurements and long-term in situ observations from several key areas. The model qualitatively reproduces basin-scale processes: thermohaline-driven cyclonic circulation and freshwater surface outflow along the western Adriatic coast, dense water dynamics, and the inflow of Ionian and Levantine waters to the Adriatic. Positive temperature and salinity biases are reported; the latter are particularly large along the eastern part of the basin, presumably because of the inappropriate introduction of eastern Adriatic rivers into the model. The highest warm temperature biases in the vertical direction were found in dense-water-collecting depressions in the Adriatic, indicating either an inappropriate quantification of DWF processes or temperature overestimation of modelled dense water. The decadal variability in the thermohaline properties is reproduced better than interannual variability, which is considerably underestimated. The DWF rates are qualitatively well reproduced by the model, being larger when preconditioned by higher basin-wide salinities. Anticyclonic circulation in the northern Ionian Sea was modelled only during the Eastern Mediterranean Transient. No other reversals of circulation that could be linked to BiOS-driven changes were modelled. [ABSTRACT FROM AUTHOR]

We investigate European regional climate change for time periods when the global mean temperature has increased by 1.5 and 2 °C compared to pre-industrial conditions. Results are based on regional downscaling of transient climate change simulations for the 21st century with global climate models (GCMs) from the fifth-phase Coupled Model Intercomparison Project (CMIP5). We use an ensemble of EURO-CORDEX highresolution regional climate model (RCM) simulations undertaken at a computational grid of 12.5 km horizontal resolution covering Europe. The ensemble consists of a range of RCMs that have been used for downscaling different GCMs under the RCP8.5 forcing scenario. The results indicate considerable near-surface warming already at the lower 1.5 °C of warming. Regional warming exceeds that of the global mean in most parts of Europe, being the strongest in the northernmost parts of Europe in winter and in the southernmost parts of Europe together with parts of Scandinavia in summer. Changes in precipitation, which are less robust than the ones in temperature, include increases in the north and decreases in the south with a borderline that migrates from a northerly position in summer to a southerly one in winter. Some of these changes are already seen at 1.5 °C of warming but are larger and more robust at 2 °C. Changes in near-surface wind speed are associated with a large spread among individual ensemble members at both warming levels. Relatively large areas over the North Atlantic and some parts of the continent show decreasing wind speed while some ocean areas in the far north show increasing wind speed. The changes in temperature, precipitation and wind speed are shown to be modified by changes in mean sea level pressure, indicating a strong relationship with the large-scale circulation and its internal variability on decade-long timescales. By comparing to a larger ensemble of CMIP5 GCMs we find that the RCMs can alter the results, leading either to attenuation or amplification of the climate change signal in the underlying GCMs. We find that the RCMs tend to produce less warming and more precipitation (or less drying) in many areas in both winter and summer. [ABSTRACT FROM AUTHOR]

The Strait of Gibraltar is a narrow and shallow channel that controls the Mediterranean Sea thermohaline and biogeochemical balances. Strong tidal currents significantly modulate exchanges across this strait and induce an intense vertical mixing, impacting both the Mediterranean Sea and the Atlantic Ocean on a climatic scale. However, the turbulent processes controlling the tidal mixing location, timing, and magnitude remain unclear. To fill this gap, we investigate tidal mixing at the Strait of Gibraltar in yearly twin tidal and non-tidal simulations from a regional configuration of the three-dimensional numerical model MITgcm, using a high spatial resolution around the Strait of Gibraltar (1/200°, 100 vertical levels). More specifically, we investigate the model turbulence closure scheme, based on a turbulent kinetic energy budget, and illustrate that vertical buoyancy fluxes should be preferred to diapycnal diffusivities as mixing indicators. In agreement with previous literature, we find that tides strongly intensify vertical mixing and motions within the Strait of Gibraltar. We then demonstrate that tidal mixing relies on two main ingredients: a sustained vertical shear of horizontal velocities and a local weakening of stratification. In the Mediterranean layer, the former drives diapycnal mixing near the seafloor and the latter in shallower areas above the prominent sills of the strait. We also evidence the frequent but irregular occurrences of static instabilities in the vicinity of these sills. In the Atlantic layer, both vertical shear and stratification are involved in diapycnal mixing that develops along the trail of the eastward internal bore released at the Camarinal sill. At high frequency, the local weakening of stratification results from convergence and divergence patterns in the vicinity of the Camarinal and Espartel sills, feeding recirculation cells between the Atlantic and Mediterranean layers. In addition, we highlight that diapycnal mixing mainly develops during the westward tidal phase in the Mediterranean layer and the eastward tidal phase in the Atlantic layer. We conclude by proposing a revised conceptual view of tidal mixing at the Strait of Gibraltar, where tidally-induced recirculation cells play an instrumental role in transforming the exchanged water masses. Overall, this study emphasizes the relevance of a realistic representation of both tides and abrupt topography to simulate the exchanges through the Strait of Gibraltar and argues for the use of a specific tidal mixing parameterization otherwise. • Tidal mixing mechanisms are investigated in a highresolution simulation of the Strait of Gibraltar. • Tidal convergence and divergence patterns, that feed recirculation cells, play an instrumental role in enhanced mixing at the Strait of Gibraltar. • Tides drive diapycnal mixing by enhancing vertical shear and weakening vertical stratification. • Accurate representation of both tides and abrupt topography is key for representing exchanges through the Strait of Gibraltar. [ABSTRACT FROM AUTHOR]

We investigate European regional climate change for time periods when the global mean temperature has increased by respectively 1.5 °C and 2 °C compared to preindustrial conditions. Results are based on regional downscaling of transient climate change simulations for the 21st century with global climate models (GCMs) from the fifth phase Coupled Model Intercomparison Project (CMIP5). We use an ensemble of EURO-CORDEX high-resolution regional climate model (RCM) simulations undertaken at a computational grid of 12.5 km horizontal resolution covering Europe. The ensemble consists of a range of RCMs that have been used for downscaling different GCMs under different forcing scenarios. The results indicate considerable near-surface warming already at the lower 1.5 °C warming. Regional warming exceeds that of the global mean in most parts of Europe, strongest in northernmost parts of Europe in winter and in southernmost parts of Europe together with parts of Scandinavia in summer. Changes in precipitation, that are less robust than the ones in temperature, include increases in the north and decreases in the south with a borderline that migrates from a northerly position in summer to a southerly one in winter. Some of these changes are seen already at 1.5 °C warming but larger and more robust at 2 °C. Changes in near-surface wind speed are associated with a large spread between individual ensemble members at both warming levels. Relatively large areas over the North Atlantic and some parts of the continent shows decreasing wind speed while some ocean areas in the far north show increasing wind speed. The changes in temperature, precipitation and wind speed are shown to be modified by changes in mean sea level pressure indicating a strong relationship with the large-scale circulation and its internal variability on decade-long timescales. By comparing to a larger ensemble of CMIP5 GCMs we find that the RCMs can alter the results leading either to attenuation of amplification of the climate change signal in the underlying GCMs. We find that the RCMs tend to produce less warming and more precipitation (or less drying) in many areas in both winter and summer. [ABSTRACT FROM AUTHOR]

Heavy precipitation events (HPEs) can be a major cause of damage and casualties in the Mediterranean basin. With the use of atmosphere-ocean coupled regional climate models (AORCMs) and the advantage of 24 years of simulation (1989-2012), we identified regions with potential impact of submonthly air-sea coupling on HPEs from among the regions hit by heavy rain during the Hydrological Cycle in the Mediterranean Experiment (HyMeX) first special observation period (SOP1): Valencia in Spain, the Cévennes in Southern France, Liguria in Northwestern Italy, Calabria in Southern Italy and Northeastern Italy. A first evaluation of the two AORCMs (MORCE and CNRM-RCSM4) against gridded precipitation datasets showed that 70-90% of the 30 most intense HPEs simulated were observed HPEs for most regions. The Cévennes, Valencia and Calabria were the only three regions to show a statistical relationship between rain differences and sea-surface temperature (SST) differences where the low-level jets that feed the events most frequently blow. This sensitivity of precipitation to SST changes is due to low-level wind changes related to changes in surface heat fluxes. Based on the calculation of submonthly variations in these regions during HyMeX, HPEs on 28 September 2012 and 12 October 2012 in Valencia and on 25-26 October 2012 in the Cévennes have most probably been affected by submonthly air-sea coupling. [ABSTRACT FROM AUTHOR]

Aim In this paper, we applied the concept of 'hierarchical filters' in community ecology to model marine species distribution at nested spatial scales. Location Global, Mediterranean Sea and the Gulf of Gabes ( Tunisia). Methods We combined the predictions of bioclimatic envelope models ( BEMs) and habitat models to assess the current distribution of 20 exploited marine species in the Gulf of Gabes. BEMs were first built at a global extent to account for the full range of climatic conditions encountered by a given species. Habitat models were then built using fine-grained habitat variables at the scale of the Gulf of Gabes. We also used this hierarchical filtering approach to project the future distribution of these species under both climate change (the A2 scenario implemented with the Mediterranean climatic model NEMOMED8) and habitat loss (the loss of Posidonia oceanica meadows) scenarios. Results The hierarchical filtering approach predicted current species geographical ranges to be on average 56% smaller than those predicted using the BEMs alone. This pattern was also observed under the climate change scenario. Combining the habitat loss and climate change scenarios indicated that the magnitude of range shifts due to climate change was larger than from the loss of P. oceanica meadows. Main conclusions Our findings emphasize that BEMs may overestimate current and future ranges of marine species if species-habitat relationships are not also considered. A hierarchical filtering approach that accounts for fine-grained habitat variables limits the uncertainty associated with model-based recommendations, thus ensuring their outputs remain applicable within the context of marine resource management. [ABSTRACT FROM AUTHOR]

A hindcast experiment of the Mediterranean present-day climate is performed using a fully-coupled Atmosphere-Ocean Regional Climate Model (AORCM) for the Mediterranean basin. The new model, called LMDz-NEMO-Med, is composed of LMDz4-regional as atmospheric component and of NEMOMED8 as oceanic component. This AORCM equilibrates freely, without any flux adjustment, neither in fresh water nor in heat. At its atmospheric lateral boundary conditions, it is driven by ERA-40 data from 1958 to 2001, after a spin-up of 40 years in coupled configuration. The model performance is assessed and compared with available observational datasets. The model skill in reproducing mean state and inter-annual variability of main atmospheric and oceanic surface fields is in line with that of state-of-the-art AORCMs. Considering the ocean behaviour, the inter-annual variations of the basin-scale heat content are in very good agreement with the observations. The model results concerning salt content could not be adequately validated. High inter-annual variability of deep convection in the Gulf of Lion is simulated, with 53 % of convective winters, representative of the present climate state. The role of different factors influencing the deep convection and its inter-annual variability is examined, including dynamic and hydrostatic ocean preconditioning and atmospheric surface forcing. A conceptual framework is outlined and validated in linking the occurrence of deep convection to the efficiency of the integrated surface buoyancy fluxes along the winter season to mix the initially stratified averaged water column down to the convective threshold depth. This simple framework (based only on 2 independent variables) is able to explain 60 % (resp. 69 %) of inter-annual variability of the deep water formation rate (resp. maximum mixed layer depth) for the West Mediterranean Deep Water (WMDW) formation process. [ABSTRACT FROM AUTHOR]

Abstract: A hindcast simulation in the Aegean–Levantine basins for the years 1960–2000 is performed, using an eddy resolving ocean model (1°/30). The model incorporates a 6-h atmospheric forcing provided by the ARPERA and captures the observed variability of the 40-years. The Eastern Mediterranean Transient (EMT) is the most prominent climatic event of the period. We investigate the impact of the atmospheric versus lateral forcing on the buoyancy content of the Aegean–Levantine basins. During the pre-EMT period, the basins’ buoyancy content is lowered by surface fluxes by about 1.5×10−8 m2 s−3 in the Aegean Sea, mostly related to surface heat loss, and lateral fluxes by about 0.9×10−8 m2 s−3, mostly related to salt flux, with the Levantine changes leading those of the Aegean. Furthermore, while long-term trends of surface and lateral inputs are preconditioning the changes in the Aegean stratification, it is the extreme heat loss pulses, related to the variability of the wind field that is controlling the formation processes by abruptly lowering the buoyancy content. Those events are possibly linked to an eastern Mediterranean bimodal atmospheric oscillation, with the anomalous surface heat fluxes shifting from the Levantine in the 1960s to the Aegean in the 1990s. The central Aegean due to its topography and thermohaline properties trigger events of excessive formation and producing the Aegean’s densest waters. During the EMT winters the central Aegean lower layers contain very dense waters, with σ Θ larger than 29.3kgm−3. These waters form the core of the water mass outflowing in the Eastern Mediterranean, after being mixed with ambient waters along their southward flow. The outflowing layer is characterized by density of 29.21kgm−3. The deepest parts of the NW Levantine is initially filled with the new water mass, which later spreads to the SE parts of the basin, flowing over the Eastern Mediterranean Ridge. [Copyright &y& Elsevier]

Aim To forecast the potential effects of climate change in the Mediterranean Sea on the species richness and mean body size of coastal fish assemblages. Location The Mediterranean Sea. Methods Using an ensemble forecasting approach, we used species distribution modelling to project the potential distribution of 288 coastal fish species by the middle and end of the 21st century based on the IPCC A2 scenario implemented with the Mediterranean climatic model NEMOMED8. Results A mean rise of 1.4 °C was projected for the Mediterranean Sea by the middle of the 21st century and 2.8 °C by the end of the 21st century. Projections for the end of the century suggest that: (1) 54 species are expected to lose their climatically suitable habitat, (2) species richness was predicted to decrease across 70.4% of the continental shelf area, especially in the western Mediterranean Sea and several parts of the Aegean Sea, and (3) mean fish body size would increase over 74.8% of the continental shelf area. Small-bodied species that are not targeted by either commercial or recreational fleets presented, on average, the highest predicted decrease in geographic range size. Main conclusions Projected climate change in the Mediterranean Sea may have deleterious effects on coastal fish diversity, including a significant loss of climatically suitable habitat for endemic fish species. In addition, climate change may contribute to the loss of small and low trophic-level fishes, which may have ecosystem-wide impacts by reducing food supply to larger and higher trophic-level species. Fishing pressure is already selectively removing large-bodied species from marine ecosystems, and so fishing and climatic change might act in tandem to drive both direct and secondary extinctions. [ABSTRACT FROM AUTHOR]

Atmospheric circulation patterns that are conducive to extreme ocean heat loss are investigated at four sites of special interest in the Mediterranean Sea. The Gulf of Lions, the South Adriatic Sea, the Cretan Sea, and the Levantine Sea are areas where anomalously high winter heat loss may lead to deep- or intermediate-water formation. At each of the above sites, the atmospheric circulation during such events is derived by averaging the sea level pressure (SLP) fields during the lower decile of the wintertime series of the net heat exchange. A relatively simple SLP pattern dominated by an anticyclone over northwestern Europe with a weaker cyclone to the southeast is found to be associated with strong heat loss in the selected sites with minor variations in pattern structure depending on the site. The SLP composite pattern reflects the combined effect of different atmospheric modes of variability and the authors consider the impacts on heat loss of a number of these modes (North Atlantic Oscillation, east Atlantic pattern, east Atlantic-west Russia pattern, and Scandinavian pattern), together with the North Sea-Caspian pattern and the Mediterranean index. The extremes in heat loss are strongly connected with the intensity and the positions of the poles of these patterns that modulate, through the necessary SLP gradient and associated northerlies, the transfer of cold and dry air over the areas of dense-water formation. Analysis of air-sea temperature difference, specific humidity, and evaporation anomalies indicates that the extremes of the net heat fluxes are primarily due to the latent and sensible heat flux components. [ABSTRACT FROM AUTHOR]

Abstract: This work proposes a new method to reconstruct and forecast surface Chlorophyll (Chl) from remotely sensed (SeaWiFS) data in the Alboran Sea, based on the correlation between zonal wind velocities and satellite Chl concentrations. First, the spatial and temporal variability of Chl and zonal wind have been characterized using standard statistics. Second, the annual cycle and trends are removed from the original time series and the residuals submitted to an EOF computation scheme. Then, the correlations between the amplitudes of the first temporal modes of Chl-wind couple have been quantified. Using the most highly correlated pair (Chl-zonal wind, with r=0.63), a simple linear relationship is proposed to reconstruct and forecast the Chl field. This forecasting method is more efficient than persistence for forecast horizons longer than 100days, with a mean correlation between original and predicted field of 0.73 as compared to 0.5 for persistence for all the year round. In partic\ular, this new method gives a 0.95 mean correlation for periods from 100 to 290days (while persistence gives 0.5). However, for a constant 8-days prediction horizon the persistence performs marginally better than the proposed method (0.79 vs. 0.68), giving some insight into the temporal scales of the features studied. These results may have significant implications for both short-term operational applications and seasonal forecasts. [Copyright &y& Elsevier]