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Guide Complètement cramé ! : chapitres offerts ! (French Edition)

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In polar records, RCCs that start abruptly within a decade or two at the most and most often concern a period of to years, are often considered among the main environmental factors causing socio-economic and cultural changes, migrations, and even collapses. According to such climatic determinism, an RCC would be much harder if not impossible , for a human society to adapt to, thus leading to radical societal transformations e. Weiss et al.

Butzer, Starting from this perspective, we have developed a new research project ArcheoMed- Paleomex in the framework of the MISTRAls initiative to respond to the following questions: 1 What is a natural forcing timing, nature, origin? Methods We have conducted new archaeological and palaeoenvironmental investigations on an intermediate scale, enabling the cross-comparison of social and environmental data e.

Carozza et al. Like Flohr et al. We have developed a multi-scalar approach from the local site continental natural archive near archaeological sites to the regional scale. It will then be possible to develop more general conclusions on interactions between nature and society from the local scale to the regional scale — which is also that of the cultural areas — to the entire Mediterranean area. In practical terms, we have developed research in various areas from the south-western to the northeastern part of the Mediterranean basin.

Three main transects are organized in different investigation windows fig. In each window, we develop multi-proxy palaeoenvironmental analyses geomorphology, sedimentology, geochemistry, micromorphology, palynology, non-pollen palynomorphs, fire signature, phytoliths, etc. To present our investigations, we briefly summarize results the obtained on the regional scale in 4 RCC periods from the Early Holocene and the Neolithization process to the Late Holocene. The research demonstrates the reality of hydrogeomorphological responses to early Holocene RCCs in valleys and alluvial fans and lake-marsh systems Berger et al.

It highlights the importance of Holocene sedimentation and post- depositional disturbances on reading the Mesolithic-Early Neolithic transition and attests to the first true levels of Neolithic occupation in SE Europe. Terrestrial records still reflect heterogeneities in palaeoclimatic restitution across the north- eastern Mediterranean during RCC events.

They suggest a probable tripartite timing for the 8.

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These issues are crucial if we are to reach a clearer assessment of climate impact on coastal and continental environments, in major societal disruptions such as the Neolithization of the Mediterranean. The probable tripartite timing of the 8. Our hypothesis of an early Neolithic colonization of the NorthAegean around 8. BP , prior to the assertion of the second and more marked part of the 8.

Wenninger et al. We must keep in mind that the geographical setting of the Mediterranean results in physically very contrasting environments in which it is often sufficient to move over very short distances to find different environmental conditions Lespez et al. In fact, a dry period could imply a move closer to water resources or, on the contrary, as observed in Dikili Tash, a rise of water table and flood hazards might imply leaving the floodplain to settle higher on the alluvial fans or lower slopes in the surrounding areas.

Only new research, closely interlinked with the multidisciplinary analyses of intra-archaeological sites will optimize our perception of forms of socioenvironmental resilience. At the end of the Late Neolithic, the period between 6. High-resolution paleoenvironmental proxy data obtained in northern Greece enables an examination of the societal responses to rapid climatic change Lespez et al.

The development of a lasting fluvio-lacustrine environment followed by enhanced fluvial activity is evident from 6 ka cal BP c. Palaeoecological data show a succession of three dry events at —, and — cal yr BP. By comparison with the available regional data, it appears that these events correspond to the incursion of cold air masses to the eastern Mediterranean, confirming the climatic instability of the middle Holocene climate transition.

Two periods with farming and pastoral activities during the Late to Final Neolithic 6. The intervening period is marked by environmental changes, but the continuous occurrence of anthropogenic taxa and fire signatures suggests the persistence of human activities and in particular, pastoralism, despite the lack of archaeological sites dated to this period and the weakness of archaeological evidence of continuity, raising the question of changes in settlement patterns. The populations moved to cope with environmental change, but although they moved away from areas most affected by the rising water table, they probably settled in the foothills.

The permanence, even slightly diminished, of anthropogenic indicators confirms the continuity of settlement in the LowerAngitis and Strymon Valley. As in other Eastern Mediterranean areas e. Ghilardi et al. Archaeological surveys must be developed at the micro-regional scale in order to better understand the changes in the settlement patterns.

This study highlights the high capacity for adaptation of Neolithic and Bronze age societies during climatic stress periods. A short period of drought in the Mediterranean may correspond to the establishment of the Mediterranean climate under orbital forcing Magny et al. In lowland areas, after maximal concentration, the number of settlements decreased significantly along the river systems during a period of very high hydrosedimentary discharges, dryness, and fire activity fig. Red minus signs — depopulated areas; blue plus signs — densely populated area; red arrows — direction of possible mobility of people around the 4.

Blue arrows — sharp decline; red arrows — growth. From Carozza et al. Indeed, from 2. The exploitation of intermediate areas from foothills to moderately mountainous regions in the Basque Country took the form of temporary habitations pastoralism. The period between 2. In the same period, the effects of millennial-scale Rapid Climate Change RCC lasting three to four centuries around the 4.

It still seems to present a temporal tripartite structure with two wet periods in Southern France Magny et al. The socio-economic modifications show a decrease in lowland area occupation and an increase of settlement in mountainous areas and may have resulted in a spatial reorganization at a regional level, but not in a global societal collapse. It is characterized by complementary productions fruits, cereals, trees, vineyards, olives, animals etc.

It lasted until the Early Byzantium, ending at places between AD and 1. While the end of the BOP is well correlated in central Anatolia with the Arab raids, its end in other areas seems to be more or less related to a contraction in rural settlement with no clear cause, mainly because it varies so significantly from region to region. In spite of the limits in 14 C dating inducing a c. From Kuzucuoglu, Here, the 2nd half of the 2nd mill.

BP and the start of the 1st mill. BC BP were characterized by several dry periods and drought spikes recorded by indicators in marsh, lake, river and slope sediments. Here several facts contradict the deterministic view of the climate role in history which assumes that climate causes both an irreversible decline of agriculture during increasing periods of dryness, and political destabilization resulting from migrations and wars motivated by resource depletion.

In fact, at the end of the 2nd mill. BC, neither the droughts nor the vanishing of the Hittite Empire, impacted the BOP at sites where it had started before 1. This example shows also that the degree of cultural sensibility to climate change is not obviously related to the intensity or nature of that change, but to the internal factors of vulnerability with regard to change: rigidity of social structures, centralization of decision, transmission networks, unbalanced distribution of resources and means for productions e.

Where archaeological and local palaeoenvironmental data are still unexploited, our understanding of land use and historical dynamics is hindered, with many surprises still in store. Climate of the Past in press.

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Part II. Palaeohistoria Proceedings of the National Academy of Sciences , Quaternary International, , Science , Journal of Archaeological Science 39, Environmental Archaeology, 20 2 , In: J-F. Berger Ed. In: O. Henry, D. Beyer, A. Quaternary Research 85, 2, In: Going West? Climate of the Past 9, Past 9, Quaternary Science Reviews , Documenta Praehistorica 41, The Mediterranean Region under Climate Change 48 to centennial time scales.

Some of these abrupt cold climate regimes would have been synchronous with societal collapses, such as that of Akkadian cultures Weiss and Bradley, With the recent rise in global temperatures, more rapid and intense events including floods, droughts or heat waves have been observed and are likely to be more frequent with climate change and to have more severe societal impacts.

Understanding natural climate variability and the role of human activities in current climate change requires long pre-instrumental records. Indeed, direct observations of climate variables i. The shortness of instrumental records also limits our understanding of low frequency climate variability as well as of gradual trends or sustained periods of floods, droughts and storms. Reconstructions of the pre-industrial climate rely on indirect information based on climate sensitive bio-indicators and geochemical tracers, called proxies.

The improvement of sampling techniques, the development of new proxies and more robust calibrations has indisputably led to major advances and produced high quality reconstructions of the recent past climate. Proxies have been commonly measured in continental archives such as tree-rings, speleothems or ice cores to estimate past temperatures and precipitation but it is only recently that marine sediments have been explored to produce decadal time scale records of the temperature of the surface ocean, the primary heat reservoir of the Earth McGregor et al.

Yet accurate dating to assess rates of changes or the synchronicity between records is still problematic. The study of the last millennium climate is of particular interest because this period encompasses the most recent pre-industrial warm climate interval known as the Medieval Climate Anomaly followed by the coldest centuries of the Little Ice Age interrupted around by the industrial era.

In parallel with major progress in generating proxy signals, model simulations of the last millennium climate using state-of-the-art coupled ocean-atmosphere models within the Coupled Model Intercomparison Project CMIP allow cross- analyses between proxy and model data to explore the physical mechanisms at play and the role of external factors like solar activity, volcanism, land use and greenhouse gases in climate variability. Nevertheless, comparison of proxy data with GCM model simulations is still a critical first step in linking global climate and regional signals with the information collected across site s reflecting the impact of climate change on ecosystems and the response of human societies.

Sea level rise and the expected increase in extreme climatic events such as coastal flooding and storm surges are major concerns for populations living in the coastal regions of the Mediterranean. Understanding the frequency of intense storms in the past several centuries to millennia is important to better predict future vulnerability and economic loss.

Because extreme events are rare and therefore difficult to observe in a human lifetime, proxy reconstructions are essential to trace their recent history and place them in a longer temporal context. Proxy data have shown that during the Little Ice Age from ca. In lagoons in southern France, stratigraphic data revealed an increase in catastrophic category 3 or more storms during the second half of the Little Ice Age Dezileau et al.

Longer records covering the past thousand years indicate that enhanced storminess in the western Mediterranean coastal region was coeval with known cold periods in the North Atlantic Ocean and in Europe. During the past years, no major intense storm has directly struck the western Mediterranean area, a situation that has resulted in inadequate policies plus the subsequent construction of buildings and infrastructure dams, recent harbors well within the zone of possible storm tide flooding.

The population residing on the coast has increased by a factor of 10 since with a dramatic rise since the s Figure 1C and the number of residential or business buildings now threatened by flooding has been rising and will continue to rise. The last few centuries, and notably the abrupt termination of the Little Ice Age and onset of industrial era warming saw a regime shift in the occurrence of storms along the coast of the western Mediterranean Sea. While we acknowledge that the Little Ice Age climate is different from the climate we are experiencing today, little is known about the future of extreme events in the context of sea level rise and warming Mediterranean surface waters.

The mechanisms that cause regime shifts are still not sufficiently well understood to allow accurate predictions of extreme events, or to assess the risk of exposure of human populations in the context of rapidly increasing urbanization and tourism along the Mediterranean coast. Aerial photograph of washover fans Palavasian lagoons, France. The Uwitec platform used in the different lagoons to collect sediment cores. The resident population on the coast of the French part of the Mediterranean area has increased by a factor of 15 since with a dramatic increase since the s.

Today, people live on the sandy barrier all year round. The area had a 0. The last few centuries have seen a regime shift in the occurrences of storms crossing the coast in the northwestern Mediterranean area Dezileau et al. The occurrence of the severe conditions is thought to be linked to North Atlantic blocking regimes leading to intensified cold Mistral winds blowing in southern France and the NW Mediterranean Sea.

Figure 2 A. Changes in the sea surface temperature in the north-western Mediterranean Sea Gulf of Lion over the last 2, years derived from alkenones as a temperature proxy. Comparison between the proxy reconstruction and instrumental data over the last century. This rate of warming is higher than the 0.

The post-industrial warming reversal of the pre-industrial long-term cooling, which is also observed in the global ocean surface temperature McGregor et al. The ROV is maneuvered from the research vessel down to the seafloor, where it searches for samples of coral that preserve the history of climate change. Increasing CO2 emissions do not only result in global warming. Penetration of CO2 into the ocean through gas exchange with the atmosphere causes the progressive acidification of both surface and deeper waters.

This finding confirms the ability of corals to assess changes in the pH of the ocean since the increase in CO emissions needed to estimate the beginning of acidification of the Mediterranean Sea, which represents a major threat for marine calcifying organisms. Hydroclimate and vegetation changes in the Mediterranean region Vegetation is closely linked to regional climate and the pollen produced by plants and tree species has been used by palynologists to reconstruct past air temperature and precipitation. Pollen records have shown that forests recolonized the whole of Europe including the Mediterranean about 10, years ago.

Over the last 5, years, temperate forest progressively retreated northwards or upwards in altitude with the overall increase in dryness over the northern Mediterranean as recorded in southern France, Spain and Italy. In southern France, recurrent swings between beech and oak abundances in the Languedoc hinterland characterized this trend. In the same period in southern Tunisia, the desert progressively expanded Figure 4AB.

Map showing the vulnerability of the west Mediterranean region to desertification from the Natural Resources Conservation Service. An Olive tree submerged by desert sands near Sebkha Boujmel southern Tunisia. Examination of changes in vegetation through pollen assemblages preserved in the sediments clearly shows that long term dryness continues today over the western Mediterranean and even more significantly in the southern Mediterranean borderlands. The species composition of the vegetation cover has been impacted by human activity through the deforestation of northern Mediterranean area.

The expansion of desert landscape along the southern rim of the Mediterranean Sea was also notably enhanced by farming, cultivation and grazing from the Bronze Age 4, cal BP to the end of the Iron Age around 2, cal BP , and has further intensified since the beginning of the 20th century Azuara et al.

The hydrological activity of major Mediterranean rivers was also deeply modified, in particular during deforestation phases when high rates of erosion were revealed by sediment fluxes and by the subsequent increase in the occurrence of floods, as evidenced in the Rhone River basin Bassetti et al. Quantifying vegetation changes is critical to evaluate feedback mechanisms on climate and their consequences for the environment.

Information about past continental temperature and precipitation is also provided by speleothems that form in caves from precipitation waters depending on the location and the weathering of the host rocks. The Mediterranean Region under Climate Change 54 climatic factors. In some caves, climate information can be linked to human occupation, for example in Gueldaman cave in northern Algeria, one of the few examples in which it is possible to link human history and climate.

In this cave, archaeological layers contained numerous prehistoric remains including pottery, bones and charcoal dated by radiocarbon dating Kherbouche et al. Stable oxygen isotopes in the stalagmites in the cave revealed a drought that lasted several centuries between 4, and 3, years ago, leading to the abandonment of the cave around 4, years ago after several thousand years of occupation. This study provides an example of the role that climate may have played in societal reorganization.

Several stalagmites that grew in the cave during the Holocene indicate other periods of past climate variations that appear to be synchronous with human occupation. Figure 5 Comparison of evidence of ancient human occupation and past climate change in Gueldaman Cave from Ruan et al.

While the current climate change has encouraged interdisciplinary collaboration to better understand the role that climate may have played in the development of past Mediterranean societies, effective collaboration between disciplines is still a challenge Izdebski et al. Journal of Biogeography, 39 10 , MASI, A. XOPLAKI Realising consilience: how better communication between archaeologists, historians and geoscientists can transform the study of past climate change in the Mediterranean, Quaternary Science Review, , OPPO, M.

WEIS, H. Science, The Mediterranean Region under Climate Change 58 Introduction The challenge is to implement research that can estimate the consequences of climate changes in terms of impact on terrestrial environments and resources. Emphasis should be placed on regions dependent on natural resources and for which demographic pressure is strong.

Simulations obtained from climate model projections using different Representative Concentration Pathways RCPs predict that the Mediterranean basin and its southern periphery are particularly vulnerable to water resources and environmental impact IPCC, AR5, In addition, several studies using regional atmospheric models indicate an increase in the precipitation inter-annual variability with extreme events and a spatial heterogeneous signature, superimposed on a decrease in the total precipitation amount Giorgi and Lionello, ; Raible et al.

Currently, regional climate projections are highly sensitive to the climate model used. In particular, spatial resolution as well as local climate conditions seem to impact significantly on the simulations Jacob et al. The Mediterranean region, at the interface between arid and temperate climates with several mountainous areas, is a complex climate system affected by the interactions between mid-latitude and sub-tropical processes. In this context, Morocco, located at the transition between a temperate climate to the North and a tropical climate to the south constitutes a key area for an impact and sensitivity study to global climate changes.

The climate is influenced by the Atlantic Ocean, the Mediterranean Sea and the Sahara, together with a very steep orography in the Atlas region. The precipitation distribution is therefore characterised by great spatial variability, and exhibits a marked seasonality, a strong inter-annual variability Ouda et al. At a broader scale, Morocco is located on the subtropical subsidence path and between the Acores High and the Saharan Low Agoussine, Several studies have also identified strong links with inter-annual precipitation variability and NAO index Knippertz, as well as remote climate modes Esper et al.

Meteorological stations in Morocco provide climatic data mainly for the last 40 years with only a few stations located in the mountainous region Tramblay et al. Besides the poor coverage of instrumented areas, lacustrine systems can provide a climatic data set that offers access to short and long-term time series of climate parameters when knowledge of modern lake water balance is combined with lacustrine sedimentary-climate records.

This time interval corresponding to the Holocene is a key period to investigate short and long-term climate variability and to improve prediction in a warming climate. In this study we present an integrated approach focusing on a mountainous lake Aguelmam Azigza. The modern lake system study is based on site monitoring and available regional hydro-climatic data. These data show that lake level changes during the instrumented period were mainly driven by precipitation following the high inter-annual variability.

These data are then compared with accurately dated short sediment cores retrieved in the same lake. Micro-scale geochemical and sedimentological analyses of these sequences enable us to identify various sedimentary facies that can be linked with periods of high low lake levels over the past decades. Study area The Moroccan Middle Atlas is an intra-continental mountain range belonging to the Atlasic system Choubert and Marcais, It comprises two morpho- structural units: the tabular Middle Atlas in the Northwest and the folded Middle Atlas in the southeast separated by the Northern Middle Atlas fault Martin, The study area is located in the Ajdir plateau of the tabular Middle Atlas.

Its structure consists of landscapes of elevated Jurassic limestone and dolomite lying over Triassic argilites and Paleozoic basement units Lepoutre and Martin, The climate in the Middle Atlas is of a Mediterranean sub-humid type, characterised by wet winters and dry summers Martin, This particular climate results essentially from its altitudinal position, its geographical position and its exposure to marine influences Atlantic and Mediterranean. Most of these stations were installed during the sixties. Data are expressed as standard deviation to the mean calculated for the whole period, Symbols red indicate lake levels observed at the study site Lake Azigza compared to our reference level of The data are available every 3 hours and cover the period from January to the present with a projected horizontal resolution grid of 0.

The mean annual air temperature series obtained close to the study site between and is about Higher average precipitation is recorded at Tamchachate, linked to the orographic influence. The precipitation variability is also marked by extreme hydrological events. Some of them had a large regional impact like in violent flood episode in the Ourika valley. The lake has been studied intermittently since Previous works noticed the relative pristine nature of the lake environment particularly the Cedar forest and the low level of human activity in the catchment area.

The local vegetation is dominated by Cedar Cedrus Atlantica and Oak Quercus woodland formed on calcareous red soils. Physical parameter measurements temperature profiles have shown that the lake is monomictic with a winter overturning period Gayral et Panouse, This has been confirmed with recent temperature profiles indicating a thermocline at about 8 m water depth during stratification periods spring, summer and autumn.

The lake is fed by diverse springs and sub-surface inflows. Despite the absence of surface outflows, chemical and isotopic signatures of water samples suggest an open system, with a short residence time and diluted water Benkaddour et al. Ample evidence of significant lake level changes have been observed Gayral et Panouse, ; Flower et al. It was suggested that variation in annual rainfall significantly affects the magnitude of water level fluctuations Flower et al.

Precise information about the timing and causes of these variations is still missing, mainly due to poor data availability. For this study, a high resolution digital elevation model DEM of the lake and its watershed was produced Adallal, Thesis Figure 2a. The morphometry of the lake shows a mean depth of 26 m and a maximum depth of 42 m in the eastern part of the basin characterised by steep slopes compared to the western part Figure 2a. Today, the lake has no surface outflow but evidence for a former outlet has been observed on the NW shore, probably linked to past high lake level periods.

In April , monthly measurements of Azigza lake level have been manually measured using a reference gauge Figure 2b. After November , the installation of a data logger and a meteorological station at Lake Azigza enabled us to collect daily measurements. The data logger was anchored in the eastern part of the basin in order to measure water pressure, temperature and conductivity at 2. Lake level is obtained by correcting the water pressure data from the atmospheric pressure measured at the same place.

Other atmospheric parameters were measured with the meteorological station precipitation, temperature, evaporation, humidity, solar radiation and wind speed Figure 2b. The daily data reveal a strong link between precipitation and lake level over an annual cycle, which increases during the rainy season November to February and decreases during the dry period, with an annual amplitude of 0.

In addition, the lake level responds rapidly to precipitation events with, for example, a mean increase of about 0. Over and above these changes, we also observed a long-term trend with a lake level decline of about 3 m since April As already mentioned, lake level fluctuations of several meters have been documented from the survey of former lake level terraces.

Historical aerial photographs obtained from Direction de Cartographie, Rabat, Morocco and historical lake level observations Flower et al. The data suggest that the lake level fluctuations follow inter-annual variations of precipitation Figure 1b. It is noticeable that the high lake level reported in Figure 1b follows a rainy period in , and as recorded at Tamchachate Station not shown. Our monthly monitoring of the physico- chemical properties of the lake system lake, wells, springs indicate a significant contribution of groundwater flows in the lake water budget.

For example, conductivity data not shown do not record any trend apart from the seasonal variability despite the lake level decline. Indeed, the lake water remains fresh even in the absence of surface outflow, in line with previous results Benkaddour et al. However, the contribution of this groundwater outflow to the long-term lake level fluctuations still needs to be estimated.

The Mediterranean Region under Climate Change 64 depth and deep water 30 m water depth locations were obtained Figure 2a. The cores were split longitudinally into two halves and after lithological description were used for multi proxy analyses. In general, the sedimentary sequences were composed of unconsolidated light-brown to dark, partly laminated clastic sediments and endogenic carbonates and few transition metal oxides. Using a Molybdenum X-ray source, a suite a chemical element was semi-quantitatively determined at 40 kV, 30 mA, and an exposure time of 15s.

Thin sections performed at CEREGE for core AZA allow for micro- scale observations of the sedimentary facies using a microscopic approach and semi-quantitative analysis of elements using energy dispersive technique EDS coupled with a scanning electron microscope SEM. The elemental mapping of each facies is then linked to the mineralogy and sedimentary characteristics of the sample in order to improve interpretation of XRF signals Jouve et al. The chronological framework of core AZA was derived using the Pb and Cs activity- depth profiles.

Concentration of Cs clearly identifies the AD peak due to atmospheric nuclear tests and the associated radionuclides fallout Cambray et al. Considering a continuous sedimentation rate we tentatively estimate that the deep basin sedimentary sequences cover approximately the last years, given that the age model needs to be improved.

Micro-scale analyses of thin section of sediments revealed three main facies in core AZA The first is a mixing of clastic quartz and authigenic calcite sediments with thin laminations of calcitic shells of ostracods and bivalves, and wood fragments Facies 1 Figure 3b.

The second is composed of a mixing of clastic and authigenic sediments with few millimetric calcitic shells of ostracods and bivalves without wood fragments Facies 2. Facies 1 and 2 repeated several times along the sequence while Facies 3 is only present in the upper part of the sequence. It is composed of a mixing of clastic and authigenic sediments that integrate a critical amount of authigenic minerals, such as gypsum, pyrite and phosphates, inconsistently deposited on Facies 1.

Facies 1 is interpreted as a proxy of higher superficial runoff during high lake levels. During increased runoff activity, and when the shoreline is close to the cedar forest, calcitic shells and wood fragments can be mobilized from the littoral zone. Facies 2 reflects reduced runoff activity associated with low lake levels.

The Mediterranean Region under Climate Change 66 calcitic shells can be moved from the littoral zone to the deep basin. In this case, less intense superficial runoff prevents the transport of wood fragments to the basin. In agreement with the sedimentation rate derived from the age model, Facies 3 is interpreted as the sedimentary deposit derived from the refilling period of the shallow basin in , following a period of low rainfall Figure 1b. When the lake level was rising, the superficial runoff carried authigenic particles from the shallow to the deep basin throughout small rivers visible in the bathymetry, Figure 2a and Jouve et al.

Conclusion and perspectives Several studies have already highlighted the significant impact of human and climatic factors in the Middle Atlas lake systems at various spatio-temporal scales Lamb et al. These approaches, while indicating the vulnerability and sensitivity of these lakes suffer from poor current characterisation of these hydro-systems needed for a better interpretation of sedimentary records in term of past hydrological variability.

Long-term site survey is essential to conduct research dealing with the environmental impact of global climate change in vulnerable remote areas. At Lake Azigza, our site monitoring confirmed the strong link between lake level fluctuations and precipitation variability at daily, monthly and annual steps. This data set will definitively help to understand the long-term decreasing trend of the lake level as observed during the instrumented period. Indeed, the understanding of the hydrological behaviour of the lake requires the quantification of the groundwater contribution to the lake water balance.

This is an ongoing study in which a water balance model is coupled with water isotopes Adallal et al. Finally, our approach has the potential to provide quantitative past lake level reconstructions using the hydrological model forced by historical precipitation times series. The same approach should be tested with precipitation simulations obtained from high resolution regional climate model projections. The micro-scale studies of the sedimentary lake deposits revealed that sed- imentary structures and geochemical composition can be interpreted as a proxy for runoff intensity.

The improvement of the dating of the cores will allow for the extension of the sedimentary record over the last years. A calibration of the proxy with the climatic data will be tested and used to reconstruct runoff intensity changes linked to precipitation extreme events over the last years, beyond the instrumental period. Interestingly, Flower et al. The approach conducted in this project shows that micro-scale observations can bring valuable additional sedimentary information linked to the hydro-sedimentary behaviour of the lake.

The integration of modern lake system knowledge through site instrumentation and modelling with lacustrine sedimentary climate records from the same site will provide new insights into the study of continental hydrological variability at various time scales. It will enable us to evaluate the imprint of human activities vs climate factors at decadal scale for the last millennia and provide keys to future environmental management and preservation purposes.

Actes de la 4e rencontre des quaternaristes marocains RQM4, , 1, Climate Dynamics, 14 12 , DEE, D. Quarterly Journal of the Royal Meteorological Society, , Global and Planetary Change, 72 1 , Geophysical Research Letters, 34 Global and Planetary Change, 63 2 , Regional Environmental Change, 14 2 , TEAM, T.

Quaternary Science Reviews, 71, Meteorology and Atmospheric Physics, 83 , LAMB, H. Nature, , Les cahiers de la recherche agronomique, 24, Climate of the Past, 9 4 , Comptes Rendus Acad. Geosciences, 9 , OUDA, O. Climate Dynamics, 35 , Journal of arid environments, 74 7 , Contribution of working group I to the fifth assessment report of the intergovernmental panel on climate change. Global and Planetary Change, 82, Earth Syst. Sci, 17 10 , The high sensitivity of the hydrological cycle to climate change is a consequence of both the location of the region in a transition zone between a temperate climate in the mid-latitudes and the hotter-drier North African climate and its specific physiographic features, i.

These climatic, topographical and anthropogenic factors also explain the marked spatial and temporal variability of the atmospheric, oceanic and hydrological conditions in the Mediterranean region. Analyses of observation-based data show that the Mediterranean region has tended to be warmer and drier during the last half century, associated with an increase in evaporation and a decrease in runoff.

Global and regional climate model projections indicate that warming and drying will likely continue, with the amplitude of the changes after being highly dependent on the emission scenario. The climate models also predict a general increase in temperature extremes for the end of the 21st century. However, the exact spatial distribution of changes in temperature and much more in precipitation remains uncertain.

The Mediterranean Region under Climate Change 72 Both global and regional climate models clearly predict warming of the Mediterranean Sea surface propagating towards the deeper layers. The thermohaline circulation is expected to change under the influence of warming as well as with the uncertain changes in salinity, an issue which is still under debate. In any case, these future changes will influence the exchange of water and heat at the Strait of Gibraltar and consequently heat and salinity in the deep layers of the North Atlantic Ocean, whose source is the Mediterranean Sea.

However the models do not agree on the future thermohaline circulation or on exchanges between the Mediterranean Sea and the Atlantic Ocean. Because of the latitude range it covers, the Mediterranean region is a transition area under the influence of both the temperate mid-latitude climate and the hotter-drier North-African climate. In addition, the region features a nearly enclosed sea surrounded by highly urbanized littorals and mountains in which numerous rivers have their source.

This results in interactions and feedback between ocean- atmosphere-land processes that play a prominent role in the climate and hydrological cycle, including in the high-impact weather events that frequently affect the region. The hydrological Mediterranean basin is also characterized by a strong coastal component.

The remaining part of the hydrological Mediterranean basin is made up of many small to medium size watersheds. The Mediterranean Region under Climate Change 74 can become powerful torrential rivers during flash-flooding episodes in fall and winter. The water resource is a major concern for a large part of the Mediterranean basin.

Freshwater is rare and unevenly distributed in time and space, and the current situation is worsening due to increasing water demands related to population growth and economic development as well as to climate change. The Mediterranean region in fact concentrates all the main natural risks linked with the water cycle, including heavy precipitation leading to flash floods, strong winds and associated large swells and storm surges, heatwaves and droughts accompanied by forest fires.

Such natural hazards affect the populations living in the area. Accurate forecasting of such high-impact weather events is still challenging and there are large uncertainties in the prediction of their evolution under climate change, especially precipitation extremes. The hydrological cycle in the Mediterranean region is thus a key scientific, environmental and socio-economic issue in a large region that includes southern Europe, North Africa and the Middle East, which motivated the launch of the year HyMeX experimental research program dedicated to the hydrological cycle in the Mediterranean region see Box 1.

The following sections of this sub-chapter describe the main characteristics of the Mediterranean climate, of the Mediterranean Sea, and of the continental hydrology, their variability and trends over recent decades. Sub-chapters 1. The variability, trends and future changes in hydrometeorological extremes under climate change are discussed in Chapter 1. Box 1 HyMeX — A research program on the water cycle in the Mediterranean The overarching objectives of the Hydrological Cycle in Mediterranean Experiment HyMeX program are to improve our understanding of the water cycle, with emphasis on the predictability and frequency of high-impact weather events, and to evaluate the social and economic vulnerability and capacity of the Mediterranean territories and citizens to adapt to these extreme events www.

HyMeX is an international and interdisciplinary program involving about scientists from about 20 countries. The HyMeX observation component includes i heavily instrumented special observation periods of a few months to provide detailed and specific observations to analyze key processes and ii longer observation periods repetitively or routinely collecting observations to monitor long-term water cycle processes and rare events such as flash-floods over a few specific instrumented watersheds.

The exploitation of the rich database more than datasets obtained thanks to successful field campaigns, and the modelling components, has already produced numerous results, with more than peer-reviewed articles published in international scientific journals. The outcomes of the program include the improvement of the numerical weather forecasting systems, the forecasting of flash-floods and the production of MED-CORDEX regional climate projections for the Mediterranean area for impact studies Ruti et al. Figure 1 Some examples of research instruments deployed in the fall, in France, Spain, and Italy.

Bottom row: Non-contact discharge radar left , CTD rosette deployment at sea right. The Mediterranean Region under Climate Change 76 Mediterranean climate Temperature and precipitation variability The climatology of the Mediterranean region is characterized by dry summers frequently associated with very long drought periods, followed by fall and winter rainfall events that are mostly very intense.

It is not rare that total monthly precipitation at a specific location falls in only few hours during thunderstorms. Summer in southern Mediterranean regions is characterized by high temperatures and lack of rain, leading to drought and marked arid conditions. Total precipitation values show high spatial and temporal variability. The high spatial and temporal variability of the seasonal mean temperature and total precipitation is explained by several features. First, the Mediterranean region is located at the southeastern limit of the North Atlantic storm tracks, and is thus particularly sensitive to interannual displacement of the paths of mid-latitude cyclones that can affect precipitation over the region.

The Mediterranean climate is also influenced by tropical and subtropical systems tropical cyclones, Asian summer monsoon, etc. All these influences result in marked variability. In addition, the complex morphology of the Mediterranean region, including high mountain ridges surrounding the coast and sharp orographic features, islands and peninsulas, leads to much sharper and smaller- scale climatic features than over other ocean basins. The Mediterranean Sea is also a source of moisture and heat for the mesoscale atmospheric circulation that can evolve into high-impact weather systems such as heavy precipitation thunderstorms, cyclogenesis and wind storms.

Observed trends Observed trends indicate a general tendency for annual mean conditions to become warmer and drier. Indeed, observations and the CMIP5 global climate simulations show progressive warming of the land surface air temperature since the s. The trend for the summer months is higher, over 0. The annual mean precipitation trend has been estimated to be about These observed long term trends are combined with marked decadal and interannual variability. The surrounding orography tends to produce cold dry northern regional winds Mistral, Tramontane, Bora, etc.

These specific features strongly influence the water budget and the thermohaline circulation of the Mediterranean Sea. Indeed, the Mediterranean Sea has a negative water budget over a multi-year period: the loss to the atmosphere by evaporation is larger than gains due to precipitation and runoff from the rivers. This freshwater deficit is offset by exchanges through the narrow and shallow Strait of Gibraltar, where the inflow is composed of relatively warm and low-salinity upper water, while the outflow to the Atlantic Ocean is relatively cooler and saltier.

Light low salinity water from theAtlantic is transformed into denser water through interaction with the low-level atmosphere and deep ocean convection that renew Mediterranean waters at intermediate and deep levels, and generate the thermohaline circulation in the Mediterranean Sea. The formation of deep ocean convection takes place preferentially in the Gulf of Lion, the Adriatic, the south Aegean and the north- east Levantine, regions under the influence of regional winds like the Mistral in the Gulf of Lion.

Ocean convection produces deep vertical mixing processes that provide oxygen to the deepest part of the water column and consequently have major impacts on marine ecosystems. Observed trends Estimation of trends using observations of the ocean is much less certain than estimation of trends over land, as series of observations are fewer and not always sufficiently reliable due to sampling errors or temporal homogeneity issues.

This justified the setting up of additional long-term ocean observatories such as the MOOSE research observatory see Box 2. Still, analyses of the trends observed in the Mediterranean Sea in recent decades tend to show a marked increase in the temperature of the deep layer from the mids as well an increase in salinity. Observations of sea surface temperatures show an increase over the last half-century Sevault et al. Concerning surface salinity, which displays decadal variability, no significant change was observed in the eastern basin, with possibly a small increase in the western Mediterranean Ulbrich et al.

Sanchez-Gomez et al. The Mediterranean Region under Climate Change 78 the mids followed by an increase, thereafter associated with the increase in sea surface temperature Mariotti, Observed precipitation estimates over the Mediterranean Sea are very uncertain, which makes it difficult to produce evidence for robust trends. Yet these estimates have shown no significant trend over the whole Mediterranean Sea in recent decades.

Box 2 MOOSE - An example of research observatories Despite intensive research efforts in the Mediterranean Sea over more than a century, an integrated view of its evolution, in the framework of climate change and anthropogenic pressures is still lacking. In this context, a Mediterranean Ocean Observing System for the Environment MOOSE was set up as an interactive, distributed and integrated observatory of the north-western Mediterranean Sea to detect and identify long-term changes in the Mediterranean Sea and its ecosystems.

MOOSE, built as a multi-scale observation network, is based on a multisite system of continental-shelf and deep-sea fixed stations as well as Lagrangian and mobile platforms to observe the spatio-temporal variability of interactions between the coastal-open ocean and the ocean-atmosphere components. The long term aims of the observatory Fig. In deep water, a significant increase was observed in the nitrogen:phosphorus ratio, together with a clear decrease in the concentration of oxygen 1. The MOOSE network is a solid observation service for research into the environment, which is able to provide operational service for the timely, continuous and sustainable delivery of high quality environmental data and information products, related to the northwestern Mediterranean environment.

Continental hydrological cycle Characteristics Hydrological processes are highly variable in time and space, due to the high variability of the rainfall regime, the complexity of the topography, and the geological, soil and land use characteristics. Most Mediterranean rivers have maximum discharges between February and May and minimum discharges in summer, due to reduced precipitation, elevated temperatures and the associated evapotranspiration in the summer season.

The differences between low and high water discharge can be extreme, in particular in the numerous small to medium watersheds most of whose water is collected during short-duration floods. In space, hydrological regimes depend on geographical and anthropogenic factors such as basin size, topographic position mountainous versus plain , the hydrogeological and aquifer systems e.

Asswan , lakes e.

This decrease is mainly due to the reduction in annual precipitation associated with climate change, and the construction of dams, which may have further reduced discharge. The biggest decrease is indeed observed in rivers that have been affected by the construction of dams such as the River Ebro in Spain and the Moulouya River in Morocco. Lespisnas et al. As they found no clear trend in annual precipitation over the region, the decrease in water discharge is likely to be the result of the rise in temperature causing the switch from snowfall to rainfall at high altitudes and from the drop in groundwater levels, which are also partly explained by the rise in temperature.

In a recent study Zampieri et al. This shift in the river discharge of these two largest rivers might, in turn, have implications for the hydrological cycle of the whole region, or at least a large part of it. Conclusion Analyses of long-term trends in the Mediterranean region show that annual mean conditions tend to be warmer and drier, with an increase in evaporation and a decrease in runoff.

However, there is high spatial and temporal variability of the atmospheric, ocean and hydrological conditions due to the climate, topographical and anthropogenic factors that are specific to the Mediterranean. Bulletin of the American Meteorological Society, Climatic Change, Progress in oceanography. It will enable us to evaluate the imprint of human activities vs climate factors at decadal scale for the last millennia and provide keys to future environmental management and preservation purposes.

Actes de la 4e rencontre des quaternaristes marocains RQM4, , 1, Climate Dynamics, 14 12 , DEE, D. Quarterly Journal of the Royal Meteorological Society, , Global and Planetary Change, 72 1 , Geophysical Research Letters, 34 Global and Planetary Change, 63 2 , Regional Environmental Change, 14 2 , TEAM, T. Quaternary Science Reviews, 71, Meteorology and Atmospheric Physics, 83 , LAMB, H.

Nature, , Les cahiers de la recherche agronomique, 24, Climate of the Past, 9 4 , Comptes Rendus Acad. Geosciences, 9 , OUDA, O. Climate Dynamics, 35 , Journal of arid environments, 74 7 , Contribution of working group I to the fifth assessment report of the intergovernmental panel on climate change. Global and Planetary Change, 82, Earth Syst. Sci, 17 10 , The high sensitivity of the hydrological cycle to climate change is a consequence of both the location of the region in a transition zone between a temperate climate in the mid-latitudes and the hotter-drier North African climate and its specific physiographic features, i.

These climatic, topographical and anthropogenic factors also explain the marked spatial and temporal variability of the atmospheric, oceanic and hydrological conditions in the Mediterranean region. Analyses of observation-based data show that the Mediterranean region has tended to be warmer and drier during the last half century, associated with an increase in evaporation and a decrease in runoff. Global and regional climate model projections indicate that warming and drying will likely continue, with the amplitude of the changes after being highly dependent on the emission scenario.

The climate models also predict a general increase in temperature extremes for the end of the 21st century. However, the exact spatial distribution of changes in temperature and much more in precipitation remains uncertain. The Mediterranean Region under Climate Change 72 Both global and regional climate models clearly predict warming of the Mediterranean Sea surface propagating towards the deeper layers.

The thermohaline circulation is expected to change under the influence of warming as well as with the uncertain changes in salinity, an issue which is still under debate. In any case, these future changes will influence the exchange of water and heat at the Strait of Gibraltar and consequently heat and salinity in the deep layers of the North Atlantic Ocean, whose source is the Mediterranean Sea.


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However the models do not agree on the future thermohaline circulation or on exchanges between the Mediterranean Sea and the Atlantic Ocean. Because of the latitude range it covers, the Mediterranean region is a transition area under the influence of both the temperate mid-latitude climate and the hotter-drier North-African climate. In addition, the region features a nearly enclosed sea surrounded by highly urbanized littorals and mountains in which numerous rivers have their source.

This results in interactions and feedback between ocean- atmosphere-land processes that play a prominent role in the climate and hydrological cycle, including in the high-impact weather events that frequently affect the region. The hydrological Mediterranean basin is also characterized by a strong coastal component.

The remaining part of the hydrological Mediterranean basin is made up of many small to medium size watersheds. The Mediterranean Region under Climate Change 74 can become powerful torrential rivers during flash-flooding episodes in fall and winter. The water resource is a major concern for a large part of the Mediterranean basin. Freshwater is rare and unevenly distributed in time and space, and the current situation is worsening due to increasing water demands related to population growth and economic development as well as to climate change.

The Mediterranean region in fact concentrates all the main natural risks linked with the water cycle, including heavy precipitation leading to flash floods, strong winds and associated large swells and storm surges, heatwaves and droughts accompanied by forest fires. Such natural hazards affect the populations living in the area. Accurate forecasting of such high-impact weather events is still challenging and there are large uncertainties in the prediction of their evolution under climate change, especially precipitation extremes.

The hydrological cycle in the Mediterranean region is thus a key scientific, environmental and socio-economic issue in a large region that includes southern Europe, North Africa and the Middle East, which motivated the launch of the year HyMeX experimental research program dedicated to the hydrological cycle in the Mediterranean region see Box 1. The following sections of this sub-chapter describe the main characteristics of the Mediterranean climate, of the Mediterranean Sea, and of the continental hydrology, their variability and trends over recent decades.

Sub-chapters 1. The variability, trends and future changes in hydrometeorological extremes under climate change are discussed in Chapter 1. Box 1 HyMeX — A research program on the water cycle in the Mediterranean The overarching objectives of the Hydrological Cycle in Mediterranean Experiment HyMeX program are to improve our understanding of the water cycle, with emphasis on the predictability and frequency of high-impact weather events, and to evaluate the social and economic vulnerability and capacity of the Mediterranean territories and citizens to adapt to these extreme events www.

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HyMeX is an international and interdisciplinary program involving about scientists from about 20 countries. The HyMeX observation component includes i heavily instrumented special observation periods of a few months to provide detailed and specific observations to analyze key processes and ii longer observation periods repetitively or routinely collecting observations to monitor long-term water cycle processes and rare events such as flash-floods over a few specific instrumented watersheds.

The exploitation of the rich database more than datasets obtained thanks to successful field campaigns, and the modelling components, has already produced numerous results, with more than peer-reviewed articles published in international scientific journals. The outcomes of the program include the improvement of the numerical weather forecasting systems, the forecasting of flash-floods and the production of MED-CORDEX regional climate projections for the Mediterranean area for impact studies Ruti et al.

Figure 1 Some examples of research instruments deployed in the fall, in France, Spain, and Italy. Bottom row: Non-contact discharge radar left , CTD rosette deployment at sea right. The Mediterranean Region under Climate Change 76 Mediterranean climate Temperature and precipitation variability The climatology of the Mediterranean region is characterized by dry summers frequently associated with very long drought periods, followed by fall and winter rainfall events that are mostly very intense. It is not rare that total monthly precipitation at a specific location falls in only few hours during thunderstorms.

Summer in southern Mediterranean regions is characterized by high temperatures and lack of rain, leading to drought and marked arid conditions. Total precipitation values show high spatial and temporal variability. The high spatial and temporal variability of the seasonal mean temperature and total precipitation is explained by several features. First, the Mediterranean region is located at the southeastern limit of the North Atlantic storm tracks, and is thus particularly sensitive to interannual displacement of the paths of mid-latitude cyclones that can affect precipitation over the region.

Mars 1944 : le parachutage d'armes de La Plagne

The Mediterranean climate is also influenced by tropical and subtropical systems tropical cyclones, Asian summer monsoon, etc. All these influences result in marked variability. In addition, the complex morphology of the Mediterranean region, including high mountain ridges surrounding the coast and sharp orographic features, islands and peninsulas, leads to much sharper and smaller- scale climatic features than over other ocean basins.

The Mediterranean Sea is also a source of moisture and heat for the mesoscale atmospheric circulation that can evolve into high-impact weather systems such as heavy precipitation thunderstorms, cyclogenesis and wind storms. Observed trends Observed trends indicate a general tendency for annual mean conditions to become warmer and drier.

Indeed, observations and the CMIP5 global climate simulations show progressive warming of the land surface air temperature since the s. The trend for the summer months is higher, over 0. The annual mean precipitation trend has been estimated to be about These observed long term trends are combined with marked decadal and interannual variability.

The surrounding orography tends to produce cold dry northern regional winds Mistral, Tramontane, Bora, etc. These specific features strongly influence the water budget and the thermohaline circulation of the Mediterranean Sea. Indeed, the Mediterranean Sea has a negative water budget over a multi-year period: the loss to the atmosphere by evaporation is larger than gains due to precipitation and runoff from the rivers.

This freshwater deficit is offset by exchanges through the narrow and shallow Strait of Gibraltar, where the inflow is composed of relatively warm and low-salinity upper water, while the outflow to the Atlantic Ocean is relatively cooler and saltier. Light low salinity water from theAtlantic is transformed into denser water through interaction with the low-level atmosphere and deep ocean convection that renew Mediterranean waters at intermediate and deep levels, and generate the thermohaline circulation in the Mediterranean Sea. The formation of deep ocean convection takes place preferentially in the Gulf of Lion, the Adriatic, the south Aegean and the north- east Levantine, regions under the influence of regional winds like the Mistral in the Gulf of Lion.

Captures d’écran

Ocean convection produces deep vertical mixing processes that provide oxygen to the deepest part of the water column and consequently have major impacts on marine ecosystems. Observed trends Estimation of trends using observations of the ocean is much less certain than estimation of trends over land, as series of observations are fewer and not always sufficiently reliable due to sampling errors or temporal homogeneity issues. This justified the setting up of additional long-term ocean observatories such as the MOOSE research observatory see Box 2.

Still, analyses of the trends observed in the Mediterranean Sea in recent decades tend to show a marked increase in the temperature of the deep layer from the mids as well an increase in salinity. Observations of sea surface temperatures show an increase over the last half-century Sevault et al. Concerning surface salinity, which displays decadal variability, no significant change was observed in the eastern basin, with possibly a small increase in the western Mediterranean Ulbrich et al.

Sanchez-Gomez et al. The Mediterranean Region under Climate Change 78 the mids followed by an increase, thereafter associated with the increase in sea surface temperature Mariotti, Observed precipitation estimates over the Mediterranean Sea are very uncertain, which makes it difficult to produce evidence for robust trends. Yet these estimates have shown no significant trend over the whole Mediterranean Sea in recent decades.

Box 2 MOOSE - An example of research observatories Despite intensive research efforts in the Mediterranean Sea over more than a century, an integrated view of its evolution, in the framework of climate change and anthropogenic pressures is still lacking. In this context, a Mediterranean Ocean Observing System for the Environment MOOSE was set up as an interactive, distributed and integrated observatory of the north-western Mediterranean Sea to detect and identify long-term changes in the Mediterranean Sea and its ecosystems.

MOOSE, built as a multi-scale observation network, is based on a multisite system of continental-shelf and deep-sea fixed stations as well as Lagrangian and mobile platforms to observe the spatio-temporal variability of interactions between the coastal-open ocean and the ocean-atmosphere components. The long term aims of the observatory Fig. In deep water, a significant increase was observed in the nitrogen:phosphorus ratio, together with a clear decrease in the concentration of oxygen 1. The MOOSE network is a solid observation service for research into the environment, which is able to provide operational service for the timely, continuous and sustainable delivery of high quality environmental data and information products, related to the northwestern Mediterranean environment.

Continental hydrological cycle Characteristics Hydrological processes are highly variable in time and space, due to the high variability of the rainfall regime, the complexity of the topography, and the geological, soil and land use characteristics. Most Mediterranean rivers have maximum discharges between February and May and minimum discharges in summer, due to reduced precipitation, elevated temperatures and the associated evapotranspiration in the summer season. The differences between low and high water discharge can be extreme, in particular in the numerous small to medium watersheds most of whose water is collected during short-duration floods.

In space, hydrological regimes depend on geographical and anthropogenic factors such as basin size, topographic position mountainous versus plain , the hydrogeological and aquifer systems e. Asswan , lakes e. This decrease is mainly due to the reduction in annual precipitation associated with climate change, and the construction of dams, which may have further reduced discharge.

The biggest decrease is indeed observed in rivers that have been affected by the construction of dams such as the River Ebro in Spain and the Moulouya River in Morocco. Lespisnas et al. As they found no clear trend in annual precipitation over the region, the decrease in water discharge is likely to be the result of the rise in temperature causing the switch from snowfall to rainfall at high altitudes and from the drop in groundwater levels, which are also partly explained by the rise in temperature.

In a recent study Zampieri et al. This shift in the river discharge of these two largest rivers might, in turn, have implications for the hydrological cycle of the whole region, or at least a large part of it. Conclusion Analyses of long-term trends in the Mediterranean region show that annual mean conditions tend to be warmer and drier, with an increase in evaporation and a decrease in runoff.

However, there is high spatial and temporal variability of the atmospheric, ocean and hydrological conditions due to the climate, topographical and anthropogenic factors that are specific to the Mediterranean. Bulletin of the American Meteorological Society, Climatic Change, Progress in oceanography. Journal of Climate. Climate Dynamics, RUTI P. Bulletin of the American Meteorological Society. Tellus A, Navarra A. Springer Netherlands. Climate Dynamics.

On the basis of a regional climate change index RCCI calculated from temperature and precipitation projections, the Mediterranean region was revealed to be one of the most prominent hot-spots over the globe. Considering the last global climate change projections in the Fifth Assessment Report of the Intergovernmental Panel on Climate Change IPCC, , the singularity of the region, particularly for a future large reduction of precipitation, was confirmed, as illustrated in figure 1. This figure reproduces the projected average percentage change in precipitation in winter December-January-February and in summer June-July-August , under the conditions of the high emission RCP8.

The Mediterranean Region under Climate Change 84 the middle and at the end of this century compared to the period It clearly shows that the Mediterranean region could be affected by a decrease in precipitation in both seasons, becoming more significant with time. This could occur while other regions, particularly those at the same latitude, do not undergo a change that is distinguishable from climate variability due to internal processes of the climate system. This great sensitivity to climate change can be understood as a consequence of the location of the region in a transition zone between the arid climate of North Africa and the temperate and rainy climate of central Europe, making it vulnerable to climate shifts caused by climate change Lionello et al.

Moreover, there is great consistency between models concerning the main characteristics of these projections over the region. Mean temperature and precipitation Giorgi and Lionello reviewed climate change projections over the Mediterranean region based on a large ensemble of 17 global climate model GCM simulations, part of the ensemble of simulations analyzed in the fourth assessment report AR4 IPCC, With respect to a median emission scenario A1B , robust and large warming is projected at the end of this century compared to the end of 20th century , with a maximum in the summer season.

Changes would be about half a degree higher under the scenario with the highest emissions A2 similar to the RCP8. Climate change affects land areas more than the sea with differences between the Mediterranean Sea and the surrounding land regions of between 0. In most model simulations, the reduction in mean annual precipitation, when averaged over the whole basin, is larger over sea than over land, except in winter. Like changes in temperature, changes in precipitation in the lower higher emission scenarios are smaller larger than in the median emission scenario.

Figure 1 Multi-model CMIP5 average percentage change in seasonal mean precipitation relative to the reference period — averaged over the periods — and — under the RCP8. Hatching indicates regions where the multi-model mean is less than one standard deviation of internal variability. From fig. However, according to the lower emission scenario RCP2. In this case, mean warming would not exceed 1. In addition, in this scenario, mean precipitation change would never exceed one standard deviation of internal climate variability.

These orders of magnitude are also consistent with the results of climate change scenarios run using regional climate models RCMs. The Mediterranean Region under Climate Change 86 better representation of the orography thanks to the improved resolution of the calculation, but they only cover a limited geographical area. They consist in climate change projections over the Mediterranean region based on an ensemble of six regional climate change simulations with a resolution of about 25 km.

Here we reproduce the simulated temperature and precipitation changes between and Precipitation changes simulated by RCMs fig. The amplitude of these changes after depend to a great extent on the emission scenario concerned when the full range of the AR5 emission hypotheses is considered. However, actual values and the detailed spatial distribution of changes in precipitation, remain uncertain as they are strongly model dependent Paeth et al. Figure 3 Same as fig. Mean hydrological cycle Mariotti et al. The Mediterranean Region under Climate Change 88 century precipitation decrease would be followed by rapid drying from onwards precipitation decrease is —0.

Since the multi model ensemble average has internal variability with reduced amplitude, actual variability would be larger than that depicted by the model ensemble mean. As precipitation is the main driver of the land surface hydrological cycle, other major hydrological indicators would also change similarly see chapter 2. Concerning land surfaces, evapotranspiration would also decrease because of the drier soils, but, as increased surface temperature favors higher evaporation, the rate would be half that of precipitation.

By —, the projected difference between precipitation and evaporation decreases over land would be —0. Some specific results concerning the future hydrological budget of the Mediterranean Sea are presented in sub-chapter 1. The amplitude of the mean precipitation anomaly foreseen by — about 0. The Mediterranean region is indeed subject to climatic variability at a decadal time scale resulting partly from teleconnection with other regions Ulbrich et al. Warm spells In addition to changes in mean values, climate projections also include significant changes in variability. Temperature and precipitation distributions would be subject to both a considerable shift and deformation, becoming broader in future climate scenarios.

Increased interannual variability, especially in summer, along with the increase in mean warming, would lead to more frequent occurrence of extremely high temperature events. Like for precipitation, the decrease in mean precipitation and the increased frequency of large negative anomalies would increase the intensity and frequency of drought events Giorgi and Coppola, The detailed impacts of climate change on extremes linked to the water cycle heavy precipitation, strong winds, drought events, flash floods are described in chapter 1.

For example, dry years e. In the context of climate change, it is important to assess possible future changes in precipitation and temperature, two aspects of climate that directly influence agriculture, water resources and many other sectors. The main result obtained with the RCM is a quasi-general decrease in annual and winter rainfall amounts and an increase in temperature in all seasons, in both scenarios and at different time horizons.

The number of high precipitation events is projected to decrease at both annual and winter scales whereas the amount of precipitation during this type of event should increase slightly, indicating fewer but more severe episodes. When future precipitation and temperature changes are combined, soil moisture is expected to be negatively impacted see chapter 2.

Taking into account the dependence of many vital sectors on climate and projected future changes, it is easy to deduce that adaptation is unavoidable to limit the negative impacts of climate change on the country to the greatest possible extent. The Mediterranean Region under Climate Change 90 extremes projected for the end of the 21st century in different emission scenarios Planton et al. Using a statistical downscaling approach Hertig et al. In general, the results indicate that changes in temperature extremes do not follow a simple shift of the whole temperature distribution to higher values but also due to a broadening of the frequency distributions of Mediterranean temperatures.

In more quantitative terms, Barriopedro et al. By the end of the 21st century, such extreme weekly heat spells are expected to occur about every 4 years, whereas some models show like anomalies about every second summer. Projections of extreme temperature changes always show regional variability that can be partly attributed to mechanisms involving coupling between the surface and the atmosphere. For instance, a study by Zittis et al. This mechanism has been shown to play a role in particular in Italy, the Balkans and Turkey, but this result remains to some extent model dependent.

Science, , doi: Change, 1—10, doi: Chap9, In: M. Sivakumar, R.

Lettre Actu

Lal, R. Selvaraju, I. Conferences, 1: , doi: Hazards Earth Sys. Solomon, S. Qin, G. Plattner, M. Tignor, S. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P. Midgley eds. Reg Environ Change, 14 : —, doi : The contrast between the fresher hence lighter waters west of the Strait of Gibraltar compared to the saltier hence heavier Mediterranean waters east of it, is the principal forcing of the outflowing water vein and the compensating inflow of light Atlantic waters floating as a surface layer.

The entire thermohaline circulation has a time scale of 75 to years. How the circulation of the Mediterranean Sea will evolve under a changed climate is a major issue. Other key questions concern changes in the surface characteristics: sea surface temperature and salinity SST, SSS , surface currents, sea level and waves.

An overview of the projected future state of the Mediterranean Sea and associated uncertainties are presented in the following. The various modeling approaches used up to now should be considered as complementary as they all have their advantages and drawbacks and none has been demonstrated to be better than the others in assessing the effect of climate change on the Mediterranean Sea. The specific climate,topographical and anthropogenic factors that characterize the Mediterranean region make it a good candidate for regional climate modelling and the region was indeed chosen as a CORDEX sub-domain leading to the Med-CORDEX initiative www.

The Med-CORDEX initiative is a voluntary-based approach and was proposed by the Mediterranean climate research community as a continuation of previous initiatives. It takes advantage of new very high resolution regional climate models RCMs, up to 10 km and of new fully coupled regional climate system models RCSMs , coupling the various components of the regional climate.

Med-CORDEX is a unique framework in which the research community will make use of these new modelling tools to increase the reliability of past and future regional climate information and to better understand the processes responsible for the Mediterranean climate variability and trends. Future evolution of the Mediterranean Sea forcings As mentioned in the previous sub-chapter, there is a wide consensus that the future Mediterranean climate will be characterized by drier and warmer conditions.

In line with these changes, the components of the Mediterranean Sea surface freshwater budget, evaporation, precipitation, rivers and Black Sea freshwater inputs, will also change Mariotti et al. The latter value implies that, according to some future projections, the Black Sea will become an evaporative basin and as a consequence, the net water flow through the Dardanelles Strait would reverse from the Mediterranean to the Black Sea.

Changes in the components of the water budget depend to a great extent on the socio-economic scenario chosen Adloff et al. However, changes in the Mediterranean Sea water budget are not expected to emerge from natural variability before the middle of the 21st century. It is worth noting that the future change in the Nile River discharge is a challenging issue due to the considerable influence of the management of this river, which has not been correctly tackled up to now see Somot et al.

Future changes in the components of the Mediterranean Sea surface heat budget: shortwave and longwave radiation, latent and sensible heat fluxes, have been less frequently studied Somot et al. These studies show that in all available climate projections, the surface heat loss from the Mediterranean will decrease. The changes in surface heat fluxes are tightly correlated with the GHG concentrations in the scenarios.

The Mediterranean Region under Climate Change 96 Few studies have assessed changes in the speed and direction of the wind over the Mediterranean Sea Somot et al. From these RCM-based studies, changes are not expected before the middle of the 21st century but a decrease in wind speed is projected for the end of the 21st century. The only sub-basin where an increase in wind speed is expected is the Aegean Sea Somot et al.

Concerning the heat and salt transport from the near-Atlantic Ocean into the Mediterranean Sea, the global temperature increase will certainly lead to an increase in the temperatures of the incoming waters through the Strait of Gibraltar. This, together with the change in the surface heat budget, would increase the heat content of the Mediterranean Sea. In addition, an increase in water lost through the sea surface would increase the net water transport at the Strait and probably increase salinization of the basin, since more salty water will enter the basin to compensate for the increase in the fresh water deficit.

Some global models project an increase in salinity in the northeast, whereas other models suggest freshening. In the latter case, the waters entering the Mediterranean through the Strait of Gibraltar could be fresher and could at least partially compensate for the effects of increased water transport. The evolution of salinity forcing coming from the Atlantic Ocean is today probably one of the main uncertainties of future projections concerning the Mediterranean Sea. Future evolution of sea circulation, temperature and salinity Sea surface temperature and salinity In the climate change scenarios, GCMs and RCMs clearly predict warming of the Mediterranean Sea surface, with a significant, nearly homogenous increase of up to 1.

Somot et al. The warming rate depends at the first order on both the time horizon and the greenhouse gas emission scenario Shaltout et al. However, warming will always remain below than that of the air due to ocean thermal inertia. Some studies indicate greater warming in summer compared to winter. Even if there is still no clear consensus on the spatial variability of the increase in SST, Adloff et al.

This leads to non- homogeneous, geographically and seasonally dependent projected changes for SSS. A progressively higher SSS is however generally projected with values ranging from 0. Changes in SSS often remain undetectable until the middle of the 21st century and more pronounced salinization is identified in the Aegean and the Adriatic, possibly driven by a marked decrease in Black Sea and Po river runoff Planton et al , Adloff et al.

Pessimistic scenarios project a decrease in surface density due to the marked increase in temperature whereas some optimistic scenarios project an increase in density related to a moderate increase in temperature and sometimes major changes in SSS in the near Atlantic Ocean. The Mediterranean Region under Climate Change 98 Deep layer characteristics The surface climate change signal is propagated efficiently towards the deeper layers through the Mediterranean thermohaline circulation and more particularly through deep convection and dense water formation processes.

For the total salt content of the seawater, no significant signal is projected for the middle of the 21st century Carillo et al. This means the socio- economic scenario is not the main source of uncertainty in future changes in salinity. Sea circulation Although sea surface circulation is difficult to assess from the published literature only one study , it is projected to undergo some modifications with a northward shift of the eastward moving surface water veins in both the western and eastern basins.

For example in Figure 1, the areas with a decrease in salinity in the Balearic area and in the northern Ionian Sea are signatures of these changes in surface circulation Adloff et al. All published studies agree on a weakening of the open-sea deep convection, the winter deep water formation and the related branch of the thermohaline circulation for the western Mediterranean Sea Thorpe and Bigg , Somot et al.

The picture in the eastern Mediterranean Sea is more contrasted with weakening in some simulations Somot et al. This EMT-like situation is attributed to stronger winds over this area and to a drastic reduction in the flow of freshwater from the Black Sea into the Aegean Sea. The results concerning future changes in the Mediterranean thermohaline circulation should to be interpreted with caution as the models still have difficulty representing the current climate thermohaline circulation. Adloff et al. The Atlantic Ocean is therefore projected to increase its supply of mass, salt, and heat to the Mediterranean Sea.

These changes reflect changes in the hydrographic characteristics of the Mediterranean Sea but also probably in those of the eastern Atlantic Ocean. However the projected changes vary among models, with some models showing a reduction in the net heat gain and in the salt loss at the Strait of Gibraltar Somot et al. The model simulations underline the complexity of the expected changes in water transport through the Strait of Gibraltar as they are the result of competing changes in temperature and salinity.


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Mean sea level, storm surge and wind waves Mean sea level Modeling mean sea level variability in the Mediterranean Sea is not straightforward. On one hand, GCMs do not have enough spatial resolution to reproduce the main mechanisms that control regional dynamics. For instance, the redistribution of heat inside the basin is strongly biased if the resolution is too coarse. This has a major impact on the reliability of temperature projections in the Mediterranean, and consequently on thermal expansion. On the other hand, at low frequencies, the variability of Mediterranean sea level is strongly influenced by changes in the nearbyAtlantic, which are usually not included in regional climate models RCMs thus making it impossible for them to estimate long term trends of total sea level.

Up to now, studies on the projections of sea level in the Mediterranean have focused on one of the components of sea level variability, the steric component i. This is only a part of the story as long as the projected sea level changes in the nearby Atlantic i. The Mediterranean Region under Climate Change in the amount of salt and using only the steric component to characterize the total sea level can lead to false conclusions in the Mediterranean. In particular, the steric component is equal to total sea level only in those cases where the mass in the water column is preserved.

However, major changes in salt content are expected in the Mediterranean Sea that would not only increase the density of the water column but also change the mass. In other words, an increase in salinity in the basin would not imply a contraction of the water column, even if the steric component were negative. Therefore, projections based only on the steric component should be interpreted with caution. Using the simulated evolution of the steric component in the Mediterranean, Carillo et al.

It can also be concluded from their study that differences in the temperature of the waters flowing into the Mediterranean from the Atlantic will have little effect on the thermal evolution of the basin. Gualdi et al. These authors found that the discrepancies are mainly due to the conditions prescribed for theAtlantic forcing, thus somewhat in disagreement with Carillo et al. In addition to the local thermal expansion, other components will play a role in future changes in sea level in the Mediterranean.

In particular, melting of terrestrial ice due to global warming will be converted into a quasi-homogeneous global signal. This could mean an additional rise of between 10 and 60 cm in the level of the Mediterranean Sea Spada et al. Changes in the northeast Atlantic circulation will also represent an additional cm Bouttes et al. In summary, the projected rise in the average sea level of the Mediterranean basin is estimated to be between 40 cm and cm at the end of the 21st century with respect to the present climate.

The range reflects the uncertainties linked to the GHG emissions scenario and to uncertainties in the modelling system. Finally, it is worth mentioning that changes in circulation within the Mediterranean can also sustain local changes that differ from the basin average Figure 1. Storm surge Concerning the extreme sea level events, studies show that projections of extreme sea level events in the Mediterranean are very sensitive to the choice of atmospheric forcing.

Marcos et al. However, these authors reported marked differences among simulations, and that the results were not spatially coherent. Figure 2 Projection of sea level change for the period with respect to the period Wind waves Future changes in waves will be determined by future changes in the wind field over the Mediterranean Sea. Lionello et al. These authors found that the mean significant wave height field over a large fraction of the Mediterranean Sea would be lower all year round at the end of the 21st century with a greater reduction about cm in winter under scenario A2.

The changes are similar, though smaller and less significant, under the B2 scenario, except during winter in the north-western Mediterranean Sea, where the mean significant wave height is projected to be higher than at present. Concerning extreme events, these authors also found smaller values in future scenarios than in the present climate. They also showed that, in general, changes in significant wave height, wind speed and atmospheric circulation were consistent.

These results are in agreement with the above mentioned work and point to a larger decrease in wave height under higher emission scenarios. The Mediterranean Region under Climate Change Conclusions Several robust and significant conclusions can be drawn such as general warming and an increase in the salinity of Mediterranean waters, as well as the sea level rise due to the propagation of the global signal. However the changes in temperature and salinity have opposite and competing effects on the change in water density and hence on changes in vertical stratification, in the Mediterranean thermohaline circulation, and in the total steric sea level.

Whereas some scenarios project a weakening of the thermohaline circulation especially in the western Mediterranean basin, others predict that the Mediterranean Sea could enter an EMT-like state. As a consequence, future changes in water and heat exchanges at the Strait of Gibraltar, being part of the thermohaline circulation, are less certain but will very likely be an increasing source of heat and salt for the deep layers of the NorthAtlantic Ocean during the course of the 21st century.

Similarly, the uncertainty on the expected sea level rise is as high as that for oceans worldwide. Changes related to the water cycle are not expected to emerge from the natural variability before the middle of the 21st century, whereas changes related to the heat cycle are already being observed. Concerning the end of the 21st century, as expected, the choice of the socio-economic scenario is often the most important source of uncertainty, but future changes in conditions in the Near Atlantic Ocean may outweigh salinity related changes including the Mediterranean thermohaline circulation.

Future changes in river discharges could be the main source of uncertainty in some key sub-basins. Clim Dyn — DOI Climate Dynamics, — Climate Dynamics, 39 Global and Planetary Change — DOI: Climate Dynamics, 39 7—8 — Bull Am Meteorol Soc, 94 1 — Global and Planetary Change, — How much could be attributed to climate change?. PloS one, 8 11 , e Climate Dynamics, in press. J Geophys Res.

Global and Planetary Change, 77 , Climate Dynamics, 44 Geophys Res Lett,L21, Oceanologia, 56, Issue 3, — Clim Dyn 27 7—8 — Global and Planetary Change, 63 , doi Climate dynamics, 16 5 The magnitude and frequency of these hydro- meteorological extremes could be significantly affected by the ongoing climate change. The study of extremes is based on the combination of observations, data analysis and numerical modeling to extrapolate the observations and produce possible future trends.

However, studying extremes is a complex task for several reasons. Extremes are, by definition, rare events and the existing datasets against which scientific theories and models can be calibrated and tested are only progressively enriched. Extreme events are often characterized by large spatial and temporal variability that is hardly captured by existing observation networks. Moreover, measurements of exceptional values may also be affected by significant uncertainties. The Mediterranean Region under Climate Change sometimes contradictory conclusions of scientific studies on past observed and future trends, for instance.

Our knowledge of hydro-meteorological extremes has nevertheless advanced substantially in recent years thanks to the development of databases and dedicated research programs. This chapter presents a state of the art review of extremes around the Mediterranean, their seasonal and geographical patterns, and their observed and projected trends. Remaining questions and uncertainties are also discussed. Itprovides an overview of the state-of-the-art knowledge of past and expected future changes.

The high vulnerability of the Mediterranean area to future anthropogenic climate change has been pointed out since the early s Giorgi based on the consistency of the climate projections made by many atmosphere-ocean general circulation models AOGCM in the successive phases of the Coupled Model Intercomparison Projects CMIP.

Whatever the model types, climate projections are resolved at scales of a few kilometers to hundreds of kilometers. The question of how humans will perceive these projections at the scale of an urban area or a small catchment basin is still open. Behind this is the question of the scaling of rainfall with horizontal resolution and of the processes involved when a physical risk becomes a human hazard. The Mediterranean Region under Climate Change tackle these questions in part by examining how changes in extreme rainfall in the recent past scale between regional and local diagnostics in the following section.

In the second section, we review the main results of regional climate simulations of extreme rainfall. Extreme precipitation trends in the recent past Methods for trend analysis of extreme rainfall Trends in extreme rainfall reported in the literature are examined using a variety of methodologies to which the results are sensitive. Two main approaches exist. The first is based on climate indices. Most indices describe the occurrence and the intensity of moderate extremes that typically occur several times a year.

This broad spectrum of indices is used to cope implicitly with the variety of rainfall. The relevance of the indices can be discussed when comparing their use from a region to another and their partial assessment of the extreme rainfall phenomenon. These approaches have the advantage of being scale independent. Thus the same theoretical framework can be used to analyze precipitation at different scales rain gauges, climate model fields, etc.

Moreover fitting a probability density function onto the data implicitly mixes the intrinsic information of the dataset and the theoretical knowledge behind the statistical model. This leads to implicit filtering of sampling issues in rainfall data. However such an approach is seldom used in the literature.

Most studies assess changes in extreme precipitation by regressing climate indices with time or in the case of the statistical model approach, by capturing the temporal evolution of one or more parameters of the statistical model. Another approach is to consider, rather than time, state parameters of the atmosphere temperature, humidity or a large scale diagnosis of atmospheric circulation North Atlantic oscillation, NAO as covariates either in the climate index regressions or in the statistical model parameters.

This framework is useful to compare past and future climates, however it does not really provide a quantitative assessment of the rate of change. From regional to local trends in the recent past Casanueva et al. Their study was based on the E-OBS data high-resolution gridded data set of daily climate over Europe at a resolution of 0. At this spatial resolution, the trend is either significantly positive at specific points or null for most of the areas, but seldom negative.

Significant positive trends are in the range of 1. None of the local studies in this region Tramblay et al. This is particularly apparent over the Iberian Peninsula, where contrasting rainfall regimes are observed from the ocean shore to inland Spain. The dataset spans the period from to In the western part of the basin, they obtained similar results to those described above, but their results in the eastern part differed, although they were in agreement with those of other local studies.

The quasi-homogeneously positive trend in extreme rainfall in Italy, can become significantly negative moving eastwards toward the Balkans, Peloponnese, Turkey and Cyprus. In Israel, these trends vary from significantly negative to significantly positive passing through zero among sites located only a few tens of kilometers apart. Again it appears that designing a robust method to study extreme rainfall is still a scientific challenge see Box 1.

Regional change in extreme rainfall in future climates Modeling background Most models predict a reduction in annual precipitation, associated with a larger increase in temperature than in the surrounding regions, except in snow covered areas that are subject to strong winter warming due to snow-albedo feedback. The Mediterranean Region under Climate Change Box 1 Trends in extreme rainfall in southern France The Mediterranean region of southern France is prone to heavy rainfall that can have major impacts on humans and society in general.

In the framework of the HyMeX program, a sensitive study was conducted on how the definition of extreme rainfall influences the resulting extreme rainfall trends. The first result is that the statistical extreme value theory is the most efficient framework in the context of extreme rainfall and its possible evolution. Figure 1 shows the relative trend in the annual maxima of daily rainfall computed from both rain gauges and spatialized rainfall data from to the present. Extreme rainfall in the study region was most likely stationary from to From on, we hypothesize a linear evolution in the statistical distribution of extreme rainfall.

The figure below shows that the trend is spatially highly variable over the region and sometimes even at neighboring rain gauges such as over the mountain range delineated by the location of the main mountain peaks triangles. Adapted from Blanchet et al. For these reasons, a concerted strategy of climate simulations at higher resolution has been implemented in the Mediterranean basin. The results confirmed and even amplified the risk of drought over southern Europe.