Modelling the tides on the North West European Shelf

Tides are a key process in the dynamics of the North West European Shelf. A GETM model has been developed for the region and this report describes the model performance. Measured harmonic constituents are compared with model outputs and these results are put into context with other shelf sea models of the region. Most of the differences between the model and observations are within the errors that are expected for a shelf sea model, and the overall statistics are skewed by poor performance in a few places. The major constituents are not represented particularly well in the Irish Sea, Celtic Sea and English Channel regions, but overall this model performs reasonably well, and better than many other shelf sea models of the region.JRC.H.1-Water Resource

Decadal trends in 50-year biogeochemical model simulations of the North Aegean Sea

This study examines 50 years (from 1960 to 2009) of physical- biogeochemical simulations of the North Aegean Sea in order to detect the past variability and decadal changes in the surface fields. We examine the decadal trend and variations at surface of the physical variables of the North Aegean Sea, as well as the bloom/no bloom occurrences. Furthermore we apply novel statistical methods to distinguish between linear trends and breakpoints (change points) in the time series. The identification of concurrent breakpoints in many different variables will provide supporting evidence for the detection of potential regime shifts. We select 3 sub-domains of the North Aegean Sea which have very distinct dynamics from each other. The first is the area of main impact of the Dardanelles discharge where waters originally from the Black Sea enter the Aegean Sea. The second area is a riverine discharge area in the west Aegean (Greek) coast (River Strymonas). The third sub-domain is located offshore in the south in an area with neither rivers nor Dardanelles-discharge direct and immediate interaction. The decadal mean of the simulated chlorophyll of the first and the last decade are respectively the lowest and the highest value found and the difference is significant.JRC.H.3-Global environment monitorin

Modelling the influence of Major Baltic Inflows on near-bottom conditions at the entrance of the Gulf of Finland

A coupled hydrodynamic-biogeochemical model was implemented in order to estimate the effects of Major Baltic Inflows on the near-bottom hydrophysical and biogeochemical conditions in the northern Baltic Proper and the western Gulf of Finland during the period 1991-2009. We compared results of a realistic reference run to the results of an experimental run where Major Baltic Inflows were suppressed. Further to the expected overall decrease in bottom salinity, this modelling experiment confirms that in the absence of strong saltwater inflows the deep areas of the Baltic Proper would become more anoxic, while in the shallower areas (western Gulf of Finland) near-bottom average conditions improve. Our experiment revealed that typical estuarine circulation results in the sporadic emergence of short-lasting events of near- bottom anoxia in the western Gulf of Finland due to transport of water masses from the Baltic Proper. Extrapolating our results beyond the modelled period, we speculate that the further deepening of the halocline in the Baltic Proper is likely to prevent inflows of anoxic water to the Gulf of Finland and in the longer term would lead to improvement in near-bottom conditions in the Baltic Proper. Our results reaffirm the importance of accurate representation of salinity dynamics in coupled Baltic Sea models serving as a basis for credible hindcast and future projection simulations of biogeochemical conditions.JRC.H.1-Water Resource

Understanding The Causes of Recent Warming of Mediterranean Waters. How Much Could be Attributed to Climate Change?

During the past two decades Mediterranean waters have been warming at a quite high rate (De Madron et al., 2011) with the consequent scientific and social concern. This warming trend is observed in satellite data, in field sampling and in modeling simulations affecting surface and deep waters in the whole Mediterranean basin (Bethoux and Gentil, 1996; Nykjaer, 2009). The warming rate is, however, regionally different and also seems to change with time (Lelieveld et al., 2002) which has led to questioning what are the underlying causes of observed trends (Vargas-Yanez, 2008). Here we analyze available satellite information on sea surface temperature (SST) during the last 25 years with spectral techniques and find that more than half of the warming tendency during this period is due to a non-linear, wave-like tendency. Using a state of the art hydrodynamic model we perform a hindcast simulation and we obtain the SST evolution on the Mediterranean basin for the last 52 years. These SST results show clear sinusoidal tendency that follows the Atlantic Multidecadal Oscillation (AMO) during the simulation period. The acceleration of water warming during the 90’s seems, thus, to be caused by a superimposition of global warming with the positive phase of the AMO, while recent slow-down of the tendency is likely due to a shift in the AMO phase (Keenlyside et al., 2008). This change in AMO phase has been proposed to mask the effect of global warming in the forthcoming decades (Faurshou-Knudsen et al., 2011) and our results indicate that the same could be applicable to the Mediterranean Sea. Henceforth, natural multidecadal temperature oscillations should be taken into account to avoid an underestimation of anthropogenic-induced warming of the Mediterranean basin in the next future.JRC.H.1-Water Resource

The seasonal cycle of the Atlantic Jet dynamics in the Alboran Sea: direct atmospheric forcing versus Mediterranean thermohaline circulation

TThe Atlantic Jet (AJ) is the inflow of Atlantic sur- face waters into the Mediterranean Sea. This geostrophically adjusted jet fluctuates in a wide range of temporal scales from tidal to subinertial, seasonal, and interannual modifying its velocity and direction within the Alboran Sea. At seasonal scale, a clearly defined cycle has been previously described, with the jet being stronger and flowing towards the northeast during the first half of the year and weakening and flowing more southwardly towards the end of the year. Different hy- pothesis have been proposed to explain this fluctuation pattern but, up to now, no quantitative assessment of the importance of the different forcings for this seasonality has been provided. Here, we use a 3D hydrodynamic model of the entire Medi- terranean Sea forced at the surface with realistic atmospheric conditions to study and quantify the importance of the differ- ent meteorological forcings on the velocity and direction of the AJ at seasonal time scale. We find that the direct effects of local zonal wind variations are much more important to ex- plain extreme collapse events when the jet dramatically veers southward than to the seasonal cycle itself while sea level pressure variations over the Mediterranean seem to have very little direct effect on the AJ behavior at monthly and longer time scales. Further model results indicate that the annual cycle of the thermohaline circulation is the main driver of the seasonality of the AJ dynamics in the model simulations.JRC.H.1-Water Resource

Multi-year simulations of future socio-economic and climate scenarios in the Mediterranean Sea

The Modelling Framework for European regional seas developed at unit D02 of the JRC is applied to explore plausible consequences for the Mediterranean Sea marine ecosystems of a set of climate and socio-economic scenarios for the 2030 horizon. The main objective of this work is to test the capability of the Modelling Framework to perform scenario forecasts. Therefore an ensemble of two different regional climate models under two selected emissions scenarios are combined with two socio-economic pathways to force a single hydrodynamic-biogeochemical ocean model. Socio-economic alternatives are reflected in the modelling system through changes in the river water quality (nutrient levels) that are flowing into the ocean basin. A step-wise approach allows to compare the different scenarios (combination of climate and socio-economic changes) and to quantify the induced changes in the marine ecosystem status. The model performance and the achieved results are strongly influenced by the reliability of the applied hydro-meteorological forcings. The applicability of the Modelling Framework to this type of scenario investigations could be successfully demonstrated.JRC.D.2-Water and Marine Resource

Application of the Singular Spectrum Analysis Technique to Study the Recent Hiatus on the Global Surface Temperature Record

Global mean surface temperature has been increasing since the beginning of the 20th century but with a highly variable warming rate, and the alternation of rapid warming periods with ‘hiatus’ decades is a constant throughout the series. The superimposition of a secular warming trend with natural multidecadal variability is the most accepted explanation for such a pattern. Since the start of the 21st century, the surface global mean temperature has not risen at the same rate as the top-of-atmosphere radiative energy input or greenhouse gas emissions, provoking scientific and social interest in determining the causes of this apparent discrepancy. Again, multidecadal natural variability is the most commonly proposed cause for the present hiatus period. Here, we analyze the longest and most up-to-date surface temperature database (HadCRUT4) with spectral techniques to separate a multidecadal oscillation (MDV) from a secular trend (ST). Both signals combined account for nearly 88% of the total variability of the temperature series showing the main acceleration/deceleration periods already described elsewhere. Three stalling periods with very little warming could be found within the series, from 1878 to 1907, from 1945 to 1969 and from 2001 to the end of the series. All of them coincided with a cooling phase of the MDV while the ST has shown a quasi-permanent warming trend from the beginning of the 20th century. Henceforth, MDV seems to be the main cause of the different hiatus periods shown by the global surface temperature records. However, and contrary to the two previous events, during the current hiatus period (2001–2013), the ST shows a strong fluctuation on the warming rate, with a large acceleration (from 0.0085°C year-1 to 0.017°C year-1) during 1992 – 2001 a and sharp deceleration (from 0.017°C year-1 to 0.003°C year-1) from 2002 onwards. This is the first time in the observational record that the ST shows such a drastic variability, so determining the causes and consequences of this change of behavior needs to be addressed by the scientific community.JRC.H.1-Water Resource

Report on the Kick-off workshop of the Network of Experts for ReDeveloping Models of the European Marine Environment

The ‘Kick-off workshop of the Network of Experts for ReDeveloping Models of the European Marine Environment. Eutrophication modelling and Descriptor 5 of the Marine Strategy Framework Directive’ was held on 20-21 January 2016 in Brussels, Belgium, jointly organized by DG Environment and DG JRC (IES –Water Resources Unit) within the framework of the Administrative Arrangement NoENV.C.2/2015/070201/705766 (Deliverable 2.2) and the Marine Strategy Framework Directive (MFSD). The aim of this workshop was to learn about existing modelling work and to draw lessons for the build-up of the European modelling effort. In this context, the workshop consisted of 18 presentations on the use of marine ecosystem models to address indicators within the Eutrophication descriptor (D5) of the MFSD in coastal zones and European regional seas, including assessment, indicator development and scenario building. Some other descriptors were also covered by the presentations and discussions. The presentations dealt with (1) South European regional seas (Black and Mediterranean Seas), (2) Atlantic shelf areas, (3) North Sea and Baltic Sea and (4) General lectures. The workshop also served as the inception meeting of the newly created informal network of experts on the Modelling of the European Marine Environment (MEME). The participants were invited to join the network DG Environment and DG JRC emphasizing the added value of a joint effort to further develop modelling capabilities with the objective of providing useful advice for policy makers. This was well received by the attendants. This report summarizes the workshop and provides further detail on the presentations, discussion and conclusions.JRC.H.1-Water Resource

Separating Contributions from Anthropogenic Warming and from Natural Oscillations to Global Warming

During the past five decades, global air temperatures have been warming at a rather high rate (IPCC-2013) resulting in scientific and social concern. This warming trend is observed in field data sampling and model simulations and affects both air temperatures over land and over the ocean. However, the warming rate changes with time and this has led to question the causes underlying the observed trends. Here, we analyze recent measured and modeled data on global mean surface air temperature anomalies (GMTA) covering the last 160 years using spectral techniques. The spectral analysis of the measured data does show a strong secular trend (ST) and a clear multidecadal sinusoidal oscillation (MDV) that resembles the Atlantic Multidecadal Oscillation (AMO). The observed acceleration of the warming during the period from 1970 to 2000 therefore appears to be caused by a superimposition of anthropogenic-induced warming (~60%) with the positive phase of a multidecadal oscillation (~40%), while the recent slowdown (hiatus) of this tendency is likely due to a shift in the MDV phase. It has been proposed that this change in the MDV phase could mask the effect of global warming in the forthcoming decades and our analysis indicates that this is quite likely, the current hiatus being already a manifestation of this phenomenon. Most current generation global circulation models (CMIP5) do not reproduce this MDV and are missing the actual temperature hiatus. Therefore, it is less likely that such models could correctly forecast the temperature evolution during the coming decades. We propose here to use the climate dynamics that is inherent in the GMTA data to forecast temperatures until 2100. These forecasts, based on the analyzed secular trend and the multidecadal oscillations are indeed capable of reproducing the actual hiatus and generally result, in comparison to CMIP5 forecasts, in much lower temperature increases for 2100 of only about 1oC. Global mean air temperatures could be even decreasing for the next 2-3 decades. Henceforth, for a correct assessment of the anthropogenic-induced warming of the global air temperatures in the future natural multidecadal temperature oscillations should be taken into account.JRC.H.1-Water Resource