Early Holocene greening of the Sahara requires Mediterranean winter rainfall

The greening of the Sahara, associated with the African Humid Period (AHP) between ca. 14,500 and 5,000 y ago, is arguably the largest climate-induced environmental change in the Holocene; it is usually explained by the strengthening and northward expansion of the African monsoon in response to orbital forcing. However, the strengthened monsoon in Early to Middle Holocene climate model simulations cannot sustain vegetation in the Sahara or account for the increased humidity in the Mediterranean region. Here, we present an 18,500-y pollen and leaf-wax δD record from Lake Tislit (32° N) in Morocco, which provides quantitative reconstruction of winter and summer precipitation in northern Africa. The record from Lake Tislit shows that the northern Sahara and the Mediterranean region were wetter in the AHP because of increased winter precipitation and were not influenced by the monsoon. The increased seasonal contrast of insolation led to an intensification and southward shift of the Mediterranean winter precipitation system in addition to the intensified summer monsoon. Therefore, a winter rainfall zone must have met and possibly overlapped the monsoonal zone in the Sahara. Using a mechanistic vegetation model in Early Holocene conditions, we show that this seasonal distribution of rainfall is more efficient than the increased monsoon alone in generating a green Sahara vegetation cover, in agreement with observed vegetation. This conceptual framework should be taken into consideration in Earth system paleoclimate simulations used to explore the mechanisms of African climatic and environmental sensitivity.

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The climate of the Mediterranean basin during the Holocene from terrestrial and marine pollen records: A model/data comparison

10.5194/cp-2016-65 ◽

2016 ◽

Cited By ~ 1

Author(s):

Odile Peyron ◽

Nathalie Combourieu-Nebout ◽

David Brayshaw ◽

Simon Goring ◽

Valérie Andrieu-Ponel ◽

...

Keyword(s):

Mediterranean Region ◽

Late Holocene ◽

Eastern Mediterranean ◽

Summer Precipitation ◽

Early Holocene ◽

Climate Information ◽

The Holocene ◽

Precipitation Estimates ◽

The Mediterranean ◽

The Mediterranean Basin

Abstract. Climate evolution of the Mediterranean region during the Holocene exhibits strong spatial and temporal variability. The spatial differentiation and temporal variability, as evident from different climate proxy datasets, has remained notoriously difficult for models to reproduce. In light of this complexity, we examine the previously described evidence for (i) opposing northern and southern precipitation regimes during the Holocene across the Mediterranean basin, and (ii) an east-to-west precipitation gradient or dipole during the early Holocene, from a wet eastern Mediterranean to dry western Mediterranean. Using quantitative climate information from marine and terrestrial pollen archives, we focus on two key time intervals, the early to mid-Holocene (8000 to 6000 cal yrs BP) and the late Holocene (4000 to 2000 yrs BP), in order to test the above mentioned hypotheses on a Mediterranean-wide scale. Palynologically derived climate information is compared with the output of regional-scale climate-model simulations for the same time intervals. Quantitative pollen-based precipitation estimates were generated along a longitudinal gradient from the Alboran (West) to the Aegean Sea (East); they are derived from terrestrial pollen records from Greece, Italy and Malta as well as from pollen records obtained from marine cores. Because seasonality represents a key parameter in Mediterranean climates, special attention was given to the reconstruction of season-specific climate information, notably summer and winter precipitation. The reconstructed climatic trends corroborate a previously described north-south partition of precipitation regimes during the Holocene. During the early Holocene, relatively wet conditions occurred in the south-central and eastern Mediterranean region, while drier conditions prevailed from 45° N northwards. These patterns reversed during the late Holocene, with a wetter northern Mediterranean region and drier conditions in the east and south. More sites from the northern part of the Mediterranean basin are needed to further substantiate these observations. With regard to the existence of a west-east precipitation dipole during the Holocene, our pollen-based climate data show that the strength of this dipole is strongly linked to the seasonal parameter reconstructed: Early Holocene summers show a clear east-to-west gradient, with summer precipitation having been highest in the central and eastern Mediterranean and lowest over the western Mediterranean. In contrast, winter precipitation signals are less spatially coherent. A general drying trend occurred from the early to the late Holocene; particularly in the central and eastern Mediterranean. However, summer precipitation in the east remained above modern values, even during the late Holocene interval. Pollen-inferred precipitation estimates were compared to regional-scale climate modelling simulations based on the HadAM3 GCM coupled to the dynamic HadSM3 and the high-resolution regional HadRM3 models. Climate model outputs and pollen-inferred precipitation estimates show remarkably good overall correspondence, although many simulated patterns are of marginal statistical significance. Nevertheless, models weakly support an east to west division in summer precipitation and there are suggestions that the eastern Mediterranean experienced wetter summer and winter conditions during the early Holocene and wetter summer conditions during the late Holocene. The extent to which summer monsoonal precipitation may have existed in the southern and eastern Mediterranean during the mid-Holocene remains an outstanding question; our model, consistent with other global models, does not suggest an extension of the African monsoon into the Mediterranean. Given the difficulty in modelling future climate change in Southern Europe, more simulations based on high resolution global models and very high resolution regional downscaling, perhaps even including transient simulations, are required to fully understand the patterns of change in winter and summer circulation patterns over the Mediterranean region

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Assessment of gridded observations used for climate model validation in the Mediterranean region: the HyMeX and MED-CORDEX framework

Environmental Research Letters ◽

10.1088/1748-9326/7/2/024017 ◽

2012 ◽

Vol 7 (2) ◽

pp. 024017 ◽

Cited By ~ 18

Author(s):

Emmanouil Flaounas ◽

Philippe Drobinski ◽

Marco Borga ◽

Jean-Christophe Calvet ◽

Guy Delrieu ◽

...

Keyword(s):

Model Validation ◽

Mediterranean Region ◽

Climate Model ◽

The Mediterranean

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Investigation of the Climate Change Effects on the Mediterranean Region with the Hypothetical inclusion of the Istanbul Isthmus

10.5194/egusphere-egu2020-22217 ◽

2020 ◽

Author(s):

Elcin Tan

Keyword(s):

Climate Change ◽

Land Surface ◽

Mediterranean Region ◽

Climate Model ◽

Wrf Model ◽

Ocean Model ◽

Atmospheric Conditions ◽

Sea Level Changes ◽

The Mediterranean ◽

The Impact

A debate on the probable Istanbul Isthmus Project that may have catastrophic impacts on our ecosystem has been recently accelerated in public, due to the fact that the approved environmental impact assessment (EIA) report of the hypothetical Istanbul Isthmus (HII) Project has recently been announced. The EIA report indicates that the assessment covers only the current conditions and the conditions that may arise during the construction of the HII. Unfortunately, The EIA report did not evaluate the climate change impact on either the Istanbul Area or Mediterranean Region after the inclusion of the HII, only the current conditions were evaluated. Therefore, the aim of this study is to investigate the impact of HII on the climate of the Mediterranean Region. The climate version of the WRF Model is utilized with 9 km resolution for the Region 12: Mediterranean (CORDEX) for the historical conditions and RCP8.5 scenarios of available climate model results from CMIP5 and CMIP6 projects. Land surface and land use maps are prepared by following the EIA report if the necessary information is included, otherwise, the current conditions are applied. The atmospheric conditions were not coupled to an Ocean Model, only the Sea Surface Temperature (SST) values of the Ocean Models are coupled to the WRF model during both historical and future simulations. The model results are evaluated in terms of temperature, precipitation, and sea-level changes. Consequently, the results indicate that the HII may decrease the resilience of the Mediterranean Region to Climate Change.

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Impacts of model spatial resolution on intense and heavy precipitation events over the Mediterranean region.

10.5194/egusphere-egu2020-2712 ◽

2020 ◽

Cited By ~ 1

Author(s):

Dario Conte ◽

Piero Lionello ◽

Silvio Gualdi

Keyword(s):

Climate Change ◽

Spatial Pattern ◽

Mediterranean Region ◽

Heavy Rainfall ◽

Climate Model ◽

Regional Climate ◽

Geographic Area ◽

Fine Scale ◽

The Mediterranean ◽

Precipitation Events

Dynamical downscaling through coupled regional climate model plays an important role to improve climate information at regional fine-scale, since it modulates information produced by GCM, combining planetary scale processes with regional scale processes. &#160;This study describes the impact of climate change &#160;on rainfall over the Mediterranean region, downscaling, at two different horizontal grid resolutions (0.44 and 0.11 degs), a Global Climate Model (GCM at 0.75 degs) by means of a coupled Regional Climate System Models (RCSM). We analyze the effect of adopting model version with different horizontal resolutions (0.11, 0.44 e 0.75 degs), considering &#160;two climate representative concentration pathways (rcp4.5 and rcp8.5). The spatial pattern on different aspects of precipitation climatology are investigated such as increase/decrease in the intensity of precipitation events, extremes and annual amount of wet days. Moreover, since the grid models cover a wide and complex climate geographic area, the rainfall probability over six sub-regions are calculated: (1) Alps, (2) North-Western coast, (2) South Italy, (3) central part of the Mediterranean sea, (4) Greece Anatolia peninsula and Levantine basin. Although, the evaluation of RCSM downscaling is complex and depends on several factors such as: variables considered, geographic area, topography, model configuration and so on, the results show that it produces an significant improvement, adding information with regards to fine-scale spatial pattern, respect to that provided by GCM.ACKNOWLEDGEMENT: This contribution is based on work conducted by the authors within the SOCLIMPACT project, that has received funding from the European Union&#8217;s Horizon 2020 research and innovation programme under grant agreement No 776661. The fullname of the project is "DownScaling CLImate ImPACTs and decarbonisation pathways in EU islands, and enhancing socioeconomic and non-market evaluation of Climate Change for Europe, for 2050 and Beyond". The opinions expressed are those of the author(s) only and should not be considered as representative of the European Commission&#8217;s official position.Keywords: &#160;widespread heavy rainfall, coupled numerical models, daily rainfall, climate scenarios, climatology of heavy rainfall.&#160;

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Deglacial and Holocene vegetation and climatic changes in the southern Central Mediterranean from a direct land–sea correlation

Climate of the Past ◽

10.5194/cp-9-767-2013 ◽

2013 ◽

Vol 9 (2) ◽

pp. 767-787 ◽

Cited By ~ 54

Author(s):

S. Desprat ◽

N. Combourieu-Nebout ◽

L. Essallami ◽

M. A. Sicre ◽

I. Dormoy ◽

...

Keyword(s):

Winter Precipitation ◽

Climatic Changes ◽

Early Holocene ◽

Last Deglaciation ◽

Central Mediterranean ◽

The Holocene ◽

Southern Central ◽

The Last Deglaciation ◽

The Mediterranean ◽

Trees And Shrubs

Abstract. Despite a large number of studies, the long-term and millennial to centennial-scale climatic variability in the Mediterranean region during the last deglaciation and the Holocene is still debated, including in the southern Central Mediterranean. In this paper, we present a new marine pollen sequence (core MD04-2797CQ) from the Siculo-Tunisian Strait documenting the regional vegetation and climatic changes in the southern Central Mediterranean during the last deglaciation and the Holocene. The MD04-2797CQ marine pollen sequence shows that semi-desert plants dominated the vegetal cover in the southern Central Mediterranean between 18.2 and 12.3 ka cal BP, indicating prevailing dry conditions during the deglaciation, even during the Greenland Interstadial (GI)-1. Across the transition Greenland Stadial (GS)-1 – Holocene, Asteraceae-Poaceae steppe became dominant till 10.1 ka cal BP. This record underlines with no chronological ambiguity that even though temperatures increased, deficiency in moisture availability persisted into the early Holocene. Temperate trees and shrubs with heath underbrush or maquis expanded between 10.1 and 6.6 ka, corresponding to Sapropel 1 (S1) interval, while Mediterranean plants only developed from 6.6 ka onwards. These changes in vegetal cover show that the regional climate in southern Central Mediterranean was wetter during S1 and became drier during the mid- to late Holocene. Wetter conditions during S1 were likely due to increased winter precipitation while summers remained dry. We suggest, in agreement with published modeling experiments, that the early Holocene increased melting of the Laurentide Ice Sheet in conjunction with weak winter insolation played a major role in the development of winter precipitation maxima in the Mediterranean region in controlling the strength and position of the North Atlantic storm track. Finally, our data provide evidence for centennial-scale vegetation and climatic changes in the southern Central Mediterranean. During the wet early Holocene, alkenone-derived cooling episodes are synchronous with herbaceous composition changes that indicate muted changes in precipitation. In contrast, enhanced aridity episodes, as detected by strong reduction in trees and shrubs, are recorded during the mid- to late Holocene. We show that the impact of the Holocene cooling events on the Mediterranean hydroclimate depend on baseline climate states, i.e. insolation and ice sheet extent, shaping the response of the mid-latitude atmospheric circulation.

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Future Changes in Euro-Mediterranean Daytime Severe Thunderstorm Environments Based on an RCP8.5 Med-CORDEX Simulation

Atmosphere ◽

10.3390/atmos11080822 ◽

2020 ◽

Vol 11 (8) ◽

pp. 822

Author(s):

Abdullah Kahraman ◽

Deniz Ural ◽

Barış Önol

Keyword(s):

Climate Models ◽

Climate Model ◽

Regional Climate ◽

Warm Season ◽

Regional Climate Models ◽

Severe Thunderstorm ◽

Convective Scale ◽

Thermodynamic Conditions ◽

The Mediterranean ◽

Climate Model Simulations

Convective scale processes and, therefore, thunderstorm-related hazards cannot be simulated using regional climate models with horizontal grid spacing in the order of 10 km. However, larger-scale environmental conditions of these local high-impact phenomena can be diagnosed to assess their frequency in current and future climates. In this study, we present a daytime climatology of severe thunderstorm environments and its evolution for a wide Euro-Mediterranean domain through the 21st century, using regional climate model simulations forced by Representative Concentration Pathway (RCP) 8.5 scenario. Currently, severe convective weather is more frequently favored around Central Europe and the Mediterranean Sea. Our results suggest that with a steady progress until the end of the century, Mediterranean coasts are projected to experience a significantly higher frequency of severe thunderstorm environments, while a slight decrease over parts of continental Europe is evaluated. The increase across the Mediterranean is mostly owed to the warming sea surface, which strengthens thermodynamic conditions in the wintertime, while local factors arguably keep the shear frequency relatively higher than the entire region. On the other hand, future northward extension of the subtropical belt over Europe in the warm season reduces the number of days with severe thunderstorm environments.

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Long term precipitation trends and variability within the Mediterranean region

Natural Hazards and Earth System Science ◽

10.5194/nhess-11-3235-2011 ◽

2011 ◽

Vol 11 (12) ◽

pp. 3235-3250 ◽

Cited By ~ 112

Author(s):

C. M. Philandras ◽

P. T. Nastos ◽

J. Kapsomenakis ◽

K. C. Douvis ◽

G. Tselioudis ◽

...

Keyword(s):

Confidence Level ◽

Mediterranean Region ◽

Climate Model ◽

Future Climate ◽

Annual Precipitation ◽

Climatic Research Unit ◽

Rain Season ◽

The World ◽

The Mediterranean

Abstract. In this study, the trends and variability of annual precipitation totals and annual rain days over land within the Mediterranean region are analyzed. Long term ground-based observations concerning, on one hand, monthly precipitation totals (1900–2010) and rain days (1965–2010) from 40 meteorological stations within the Mediterranean region were obtained from the Hellenic National Meteorological Service and the World Climate Data and Monitoring Programme (WCDMP) of the World Meteorological Organization. On the other hand, high spatial resolution (0.5° × 0.5°) gridded monthly data CRU TS 3.1 were acquired from the Climatic Research Unit, University of East Anglia, for the period 1901–2009. The two datasets were compared by means of trends and variability, while the influence of the North Atlantic Oscillation (NAO) in the Mediterranean precipitation was examined. In the process, the climatic changes in the precipitation regime between the period 1961–1990 (reference period) and the period 2071–2100 (future climate) were presented using climate model simulations (RACMO2.1/KNMI). The future climate projections were based on SRES A1B. The findings of the analysis showed that statistically significant (95% confidence level) negative trends of the annual precipitation totals exist in the majority of Mediterranean regions during the period 1901–2009, with an exception of northern Africa, southern Italy and western Iberian peninsula, where slight positive trends (not statistically significant at 95% CL) appear. Concerning the annual number of rain days, a pronounced decrease of 20 %, statistically significant (95% confidence level), appears in representative meteorological stations of east Mediterranean, while the trends are insignificant for west and central Mediterranean. Additionally, NAO index was found to be anticorrelated with the precipitation totals and the number of rain days mainly in Spain, southern France, Italy and Greece. These correlations are higher within the rain season (October–March) than the entire year. Based on the results of regional climate model RACMO2.1/KNMI, precipitation is very likely to decrease almost 20% in the period 2071–2100 compared to 1961–1990, under SRES A1B.

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Greenhouse Gas–Induced Changes in Summer Precipitation over Colorado in NARCCAP Regional Climate Models*

Journal of Climate ◽

10.1175/jcli-d-13-00088.1 ◽

2013 ◽

Vol 26 (21) ◽

pp. 8690-8697 ◽

Cited By ~ 12

Author(s):

Michael A. Alexander ◽

James D. Scott ◽

Kelly Mahoney ◽

Joseph Barsugli

Keyword(s):

Climate Models ◽

Climate Model ◽

Regional Climate ◽

Summer Precipitation ◽

Regional Climate Change ◽

Regional Climate Models ◽

Specific Humidity ◽

The North ◽

Climate Model Simulations ◽

Climate Change Assessment

Abstract Precipitation changes between 32-yr periods in the late twentieth and mid-twenty-first centuries are investigated using regional climate model simulations provided by the North American Regional Climate Change Assessment Program (NARCCAP). The simulations generally indicate drier summers in the future over most of Colorado and the border regions of the adjoining states. The decrease in precipitation occurs despite an increase in the surface specific humidity. The domain-averaged decrease in daily summer precipitation occurs in all of the models from the 50th through the 95th percentile, but without a clear agreement on the sign of change for the most extreme (top 1% of) events.

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CHANGES IN PARAMETERIZATIONS OF REGIONAL CLIMATE MODEL REGCM4.4.5: THE ROLE OF LAND COVER ON REGIONAL CLIMATE OVER MEDITERRANEAN

Bulletin of the Geological Society of Greece ◽

10.12681/bgsg.11811 ◽

2017 ◽

Vol 50 (2) ◽

pp. 1062

Author(s):

K. Velikou ◽

K. Tolika ◽

Ch. Anagnostopoulou

Keyword(s):

Land Use ◽

Land Cover ◽

Regional Climate Model ◽

Mediterranean Region ◽

Climate Model ◽

Heat Waves ◽

Regional Climate ◽

Land Use Changes ◽

Mediterranean Forests ◽

The Mediterranean

A parameter that affects significantly the local, regional and global climate system is land cover and the changes that may occur to it. During winter season, heavy precipitation assists vegetation growth of Mediterranean forests and woodlands, whereas during summer, absence of precipitation and severe heat waves result to arid and semiarid vegetation. For that reason, it was quite interesting to track the changes that may occur in the climate of the Mediterranean region due to land cover/land use changes on regional climate over the Mediterranean region. The main objective of the study is the assessment of the impacts of land cover/land use changes on regional climate over the Mediterranean region. The examined regional climate model used in the study is RegCM4.4.5. Its spatial resolution is 25x25km and different simulations were performed with changes in land cover/land use for the time period 1981-1990. The different simulated data were compared in order to examine the modifications that occur from land cover/land use changes in evapotranspiration and surface albedo to direct and diffuse radiation in the domain of study.

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Future Holiday Climate Index (HCI) Performances of Urban and Beach Destinations in the Mediterranean

10.5194/egusphere-egu21-13217 ◽

2021 ◽

Author(s):

F. Sibel Saygili Araci ◽

O. Cenk Demiroglu ◽

Aytac Pacal ◽

C. Michael Hall ◽

M. Levent Kurnaz

Keyword(s):

Mediterranean Region ◽

Climate Model ◽

Geographical Information ◽

Lapse Rate ◽

Climate Index ◽

Macro Scale ◽

The Mediterranean ◽

Elevation Model ◽

Almost All ◽

The Web

Tourism is a major socioeconomic contributor to established and emerging destinations in the Mediterranean region. Recent studies introducing the Holiday Climate Index (HCI) highlight the significance of climate as a factor in sustaining the competitiveness of coastal and urban destinations. The aim of this study is to assess the future HCI performances of urban and beach destinations in the greater Mediterranean region. For this purpose, HCI scores for the reference (1971-2000) and future (2021-2050, 2070-2099) periods were computed with the use of two latest greenhouse gas concentration trajectories, RCP 4.5 and 8.5, based on the Middle East North Africa (MENA) Coordinated Regional Downscaling Experiment (CORDEX) domain and data. The outputs were adjusted to a 500 m resolution via the use of lapse rate corrections that extrapolate the climate model topography against a resampled digital elevation model. All periodic results were seasonally aggregated and visualized on a (web) geographical information system (GIS). The web version of the GIS also allowed for a basic climate service where any user can search her/his place of interest overlaid with index ratings. Exposure levels are revealed at the macro scale while sensitivity is discussed through a validation of the climatic outputs against visitation data for one of Mediterranean's leading destinations, Antalya. HCI:Urban results showed that Canary Islands hold suitable conditions for tourism during almost all four seasons and all five periods which will have certain implications when other core Mediterranean competitors lose their relative climatic attractiveness. HCI:Beach results for the summer season showed that Las Canteras, Alicate, Pampelonne, Myrtos, Golden Sands and Edremit all pose Very Good to Excellent conditions without any Humidex risks for the extreme future scenario (2070-2099 RCP8.5). Much detailed outputs of the study can be viewed from the web service at: http://climatechange.boun.edu.tr/en/holiday-climatology-of-the-mediterranean/.

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