Éditeur(s) : HAL CCSD
Résumé : International audience
The challenge is to implement research that can estimate the consequences ofclimate changes in terms of impact on terrestrial environments and resources.Emphasis should be placed on regions dependent on natural resources and forwhich demographic pressure is strong. Simulations obtained from climate modelprojections (using different Representative Concentration Pathways (RCPs))predict that the Mediterranean basin and its southern periphery are particularlyvulnerable to water resources and environmental impact (IPCC, AR5, 2013).An annual rainfall decrease by 30% is found for the projection period 2070-2099(IPCC, AR5, 2013) associated with a decrease in water resources by 30 to 50%(Milano, 2012). In addition, several studies using regional atmospheric modelsindicate an increase in the precipitation inter-annual variability with extremeevents and a spatial heterogeneous signature, superimposed on a decrease in thetotal precipitation amount (Giorgi and Lionello, 2008; Raible et al. 2010).Currently, regional climate projections are highly sensitive to the climate modelused. In particular, spatial resolution as well as local climate conditions seemto impact significantly on the simulations (Jacob et al. 2014).The Mediterranean region, at the interface between arid and temperate climateswith several mountainous areas, is a complex climate system affected by theinteractions between mid-latitude and sub-tropical processes. In this context,Morocco, located at the transition between a temperate climate to the North anda tropical climate to the south constitutes a key area for an impact and sensitivitystudy to global climate changes. The climate is influenced by the Atlantic Ocean,the Mediterranean Sea and the Sahara, together with a very steep orography inthe Atlas region. The precipitation distribution is therefore characterised by greatspatial variability, and exhibits a marked seasonality, a strong inter-annualvariability (Ouda et al. 2005) and in general a pronounced gradient from northto south and west to east. At a broader scale, Morocco is located on the subtropicalsubsidence path and between the Acores High and the Saharan Low (Agoussine,2003). Several studies have also identified strong links with inter-annualprecipitation variability and NAO index (Knippertz, 2003) as well as remoteclimate modes (Esper et al. 2007).Continental climate variability at a local/regional scale, if it is to be integratedin climate predictions, needs to be supported by long-term observation.Meteorological stations in Morocco provide climatic data mainly for the last40 years with only a few stations located in the mountainous region (Tramblayet al. 2012; 2013; Driouech et al. 2010). This climate database is also supportedby the IAEA network providing stations for which isotope tracers have beenapplied to daily/monthly rain and water vapour samples over 2 to 3 years between2000 and 2004. Besides the poor coverage of instrumented areas, lacustrinesystems can provide a climatic data set that offers access to short and long-termtime series of climate parameters when knowledge of modern lake water balanceis combined with lacustrine sedimentary-climate records. Lake sediment recordsideally provide high resolution climate/environmental information of the last10,000 years (Magny et al. 2013). This time interval (corresponding to theHolocene) is a key period to investigate short and long-term climate variabilityand 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(2012-2016) and available regional hydro-climatic data. These data show thatlake level changes during the instrumented period were mainly driven byprecipitation following the high inter-annual variability. These data are thencompared with accurately dated short sediment cores retrieved in the same lake.Micro-scale geochemical and sedimentological analyses of these sequencesenable us to identify various sedimentary facies that can be linked with periodsof high (low) lake levels over the past decades.
The Mediterranean Region under Climate ChangeLa méditerranée face au changement climatique

insu-01394690
https://hal-insu.archives-ouvertes.fr/insu-01394690
https://hal-insu.archives-ouvertes.fr/insu-01394690/document
https://hal-insu.archives-ouvertes.fr/insu-01394690/file/Vidaletal.2016-COP22-Chap1.pdf

Éditeur(s) : HAL CCSD Wiley-Blackwell Wiley
Résumé : A new record from the heart of the Moroccan Middle Atlas cedar forests spans the last 18 000 years and provides valuable insight into our understanding of the natural vegetation and environmental changes. The approach is based on the study of pollen content, geochemical elements and grain size analysis. The pollen data indicate that the vegetation was dominated by herbaceous plants until 9000 BP. Such open landscape allowed greater soil erosion and an input of chemical elements from the watershed. After 9000 BP, tree cover, mainly oak, increased slightly and was accompanied by a higher taxonomic diversity. However, several steppe elements remain well represented in the area until 5000 BP, which suggests that the climate was rather dry during the first part of the Holocene. After 6000 BP, the climate became more favourable to expansion of the forest ecosystems, including Cedrus atlantica, thereby reducing erosion. A strong reduction of the tree pollen percentages is recorded after 2000 BP, which may be related to increasing human activities during the Roman period. These forest changes are concomitant with an increase of lead and copper concentrations in the record, probably related to Roman metalworking activities.
ISSN: 0267-8179

hal-01122848
https://hal.archives-ouvertes.fr/hal-01122848
DOI : 10.1002/jqs.2708