CL4.2

In the Mediterranean region climate and other environmental changes have become major threats to both ecosystems and human wellbeing. Climate change is expected to be the most important threat to biodiversity in the Mediterranean over the next 10 years, followed by habitat degradation, exploitation, pollution, eutrophication and invasion of species and the loss of biodiversity. Climate change interacts with other environmental problems in the Mediterranean Basin, resulting from land use, pollution and biodiversity loss. The nature of the semi-enclosed Mediterranean Sea implies unique physiographic and ecological features. The Mediterranean Sea is considered as one of the hotspots of global biodiversity where the impact of climate change associated with other anthropogenic pressures could be the most destructive. Although it represents only 0.8% of the world's ocean surface, it is home to between 4 and 18% of the world's marine species.

The Mediterranean region is particularly vulnerable because it cumulates environmental risks, including strong warming and drying, accelerating sea-level, rapid urbanization, increasing pollution of the air and the water, and the impacts of mass tourism. Ecosystems suffer from land degradation including the loss of half of the wetlands, overfishing (20% of fish species are at risk of extinction by 2050), non-sustainable agriculture, wildfires (burnt area may double by 2100) and the invasion of non-indigenous species (‘tropicalization’). These factors strongly impact water resources, biodiversity on land and in the ocean, human health and security.

The effects of climate change in the Mediterranean basin are asymmetric. In the northern and western part of the Mediterranean, situation is heterogeneous, but historical responsibility of greenhouse emissions since industrial revolution is objectively higher than in southern and eastern part. The EU counties are facing impacts of climate change but societies are less vulnerable.  Most countries located in the Southern and Eastern Mediterranean suffer the consequences of climate change with greater effects. Climate change can be an added challenge, when a country is already facing structural issues of poverty rate, weakness of infrastructure and social services, critical demographic changes, high unemployment, economic informality and emigration, political instability, corruption and spatial inequality with fast urbanization. All Mediterranean countries are nevertheless facing cross-cutting common issues, such as biodiversity preservation, sustainable development of tourism, commercial links related to food production and consumption, stock of fishes, blue carbon, energy production, political stability, migrations and security. Their interests are linked, because their share a common resource.

The adaptive capacity of ecosystems and humans is expected to be progressively challenged due to the effects of droughts, heat waves, sea-level rise and ocean warming and acidification. Progress towards achievement of the UN Sustainable Development Goals differs strongly between Mediterranean sub-regions, with north-western countries having stronger resilience than southern and eastern countries.

Our objective is to present the threats and vulnerabilities of the Mediterranean region. Then we will see the impacts on ecosystems, economic sectors and human well-being. Finally, we will present the different adaptation options, their limits and climate-resilient development pathways. 

Disclaimer : the content of IPCC reports are pre-decisional and confidential until they are formally accepted by member governments.

How to cite: Hilmi, N., Ali, E., Carnicer Cols, J., Cramer, W., Georgopoulou, E., Le Cozannet, G., and Tirado, C.: IPCC AR6 WGII Cross-Chapter Paper 4: Mediterranean Region, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10590, https://doi.org/10.5194/egusphere-egu22-10590, 2022.

Eddy-resolving projections of the physical and biogeochemical state of the Mediterranean Sea under the Representative Concentration Pathway (RCP) 4.5 and 8.5 are here analyzed to assess the impacts of climate change on the Mediterranean marine ecosystems in the middle and at the end of the 21st century. The projections were produced through the offline coupling between the physical model MFS16 and the transport-biogeochemical reactor OGSTM-BFM. The analysis shows during the 21st century an overall warming and an increase in the stratification of the water column, resulting in a weakening of the thermohaline circulation of the basin. The biogeochemical projections show a decline in the dissolved nutrients content and organic matter stock of the euphotic and intermediate layers of the basin and an increase in the net primary production and phytoplankton respiration. Moreover, the projected warming of the water column and the increase in the respiration community will drive a quite uniform surface and subsurface reduction in the oxygen concentration. Finally an acidification of the upper and intermediate layers of the basin driven by the CO₂ absorption from the atmosphere is projected. All the projected changes are found to be stronger in the eastern part of the Mediterranean basin. 

How to cite: Reale, M., Cossarini, G., Lazzari, P., Lovato, T., Bolzon, G., Masina, S., Solidoro, C., and Salon, S.: Mediterranean Sea warming, nutrient decline, primary production increase, deoxygenation and acidification during the 21st century from high resolution physical and biogeochemical projections under emission scenarios RCP4.5 and RCP8.5, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12013, https://doi.org/10.5194/egusphere-egu22-12013, 2022.

Here, we present an updated assessment of projected climate change over Greece in the near future and at the end of the 21^st century. The analysis is based on an ensemble of 11 high-resolution EURO-CORDEX simulations based on historical emission data and three different greenhouse gas concentration scenarios, namely, RCP2.6, RCP4.5, and RCP8.5. Our results strongly point towards a warmer future under all the examined RCPs. Under the extreme RCP8.5 scenario, temperature is expected to increase on average by 1.6 ^oC (12%) in the near future and 4.3 ^oC (33%) at the end of the century. The number of hot days and tropical nights per year is expected to increase significantly and the number of frost days to decrease. Also, the future will be possibly drier, with statistically robust results for the end-of-the-century period under RCP8.5 only. On average, precipitation is  expected to decrease under RCP8.5 by -0.4 mm day^-1 (-16%) and the number of consecutive dry days per year to increase by 15.4 days (30%) at the end of the century.

The authors acknowledge funding from the Action titled "National Νetwork on Climate Change and its Impacts - CLIMPACT" which is implemented under the sub-project 3 of the project "Infrastructure of national research networks in the fields of Precision Medicine, Quantum Technology and Climate Change", funded by the Public Investment Program of Greece, General Secretary of Research and Technology/Ministry of Development and Investments.

How to cite: Akritidis, D., Georgoulias, A. K., Kalisoras, A., Kapsomenakis, J., Melas, D., Zerefos, C. S., and Zanis, P.: Climate change projections for Greece in the 21st century , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11972, https://doi.org/10.5194/egusphere-egu22-11972, 2022.

Global warming is anticipated to intensify the hydrological cycle. However, this is neither expected to be globally uniform nor is the relationship between temperature increase and rainfall intensities expected to be linear. The objective of this study is to assess changes in annual rainfall extremes, total annual precipitation, and their relationship in the larger Mediterranean region. We use an ensemble of 33 regional climate simulations from the EURO-CORDEX initiative at a spatial resolution of 0.11°. We analyse the significance of trends for two periods (1951–2000 and 2001–2100) under a ‘business-as-usual’ pathway (RCP8.5). Our future projections indicate a strong north/south gradient, with significant, decreasing trends in the magnitude of daily precipitation extremes in the south and the Maghreb region (up to − 10 mm/decade) and less profound, increasing trends in the north parts of the Mediterranean. Despite the contrasting future trends, the 50-year daily precipitation extremes are projected to strongly increase throughout the region. The 100-year extremes, derived with traditional extreme value approaches from the 1951–2000 simulations, underestimate the magnitude of these extreme events in the 2001–2100 projections by 30% for the drier areas of the Mediterranean (200–500 mm average annual rainfall) and by up to 20–30% for the wetter parts of the region. These 100-year extremes can occur at any time in any Mediterranean location. The contribution of the wettest day per year to the annual total precipitation is expected to increase (5–30%) throughout the region. The projected increase in extremes and the strong reductions in mean annual precipitation in the drier, southern and eastern Mediterranean will amplify the challenges for water resource management. These results have been published in Zittis et al. (2021).

References

Zittis, G., Bruggeman, A., Lelieveld, J., 2021. Revisiting future extreme precipitation trends in the Mediterranean. Weather and Climate Extremes. 34, 100380. https://doi.org/10.1016/j.wace.2021.100380

How to cite: Zitttis, G., Bruggeman, A., and Lelieveld, J.: Extreme daily precipitation trends in the Mediterranean region under a business-as-usual pathway , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2837, https://doi.org/10.5194/egusphere-egu22-2837, 2022.

Sandy beaches have a paramount importance as natural barrier for coastal protection (Vousdoukas et al., 2020) and a valued socioeconomical asset for touristic activities (Enríquez & Bujosa Bestard, 2020). The unprecedented population expansion along with the sea level rise put the coastal areas under a high risk for the coming decades. An accurate estimate of the future evolution of sandy beaches is a key step for the development of effective adaptation strategies.

In this work, we estimate the potential loss of sandy beaches due to climate change under different scenarios of greenhouse gas (GHG) emissions. We focus on the Balearic Islands beaches as a case study representative of the Mediterranean sandy beaches. We combine a high-resolution nearshore total water level (TWL) with the detailed characteristics (area, granulometry and slope) of the 869 beaches of the Islands. TWL is obtained combining the contribution of mean sea level, storm surge and wave runup. In particular, a cost-effective methodology that combines numerical modelling and statistical techniques has been developed to  explicitly obtain wave runup on beaches.

An additional important point to be considered is that, in the Mediterranean Sea, seagrass meadows are commonly present at shallow depths (Marbà et al., 1996; Ruíz, Boudouresque, & Enríquez, 2009). This presence of vegetation plays a relevant role in the dissipation of the incident wave energy against the coast (Infantes et al., 2012) and, consequently, induces a reduction in the coastal flooding during extreme events.  So, in this work we consider the wave attenuation due to bottom flow and seagrass interaction in the wave propagation to the coast using a specific parametrization (Mendez & Losada, 2004).

The results show that the beach surface in the Balearic Island (~310ha) would be significantly reduced at mid and long term under the most likely scenarios of future GHG emissions (RCP4.5 and RCP8.5). In particular, at mid-century, around 35-45% of the beach area would permanently disappear under mean conditions, mainly due to the contribution of the mean sea level rise. Under storm conditions, the beach loss would increase up to 75-78% due to the wave runup effect. At the end of the century, around 55-65% of the beach area will be permanently flooded and around 85% under storm conditions. These results could be safely extrapolated to most regions in the Mediterranean as they share similar beach and hydrodynamic characteristics. Finally, some results on the potential of climate-based solutions to reduce the impact of storms will be presented.

How to cite: Agulles, M. and Jordà, G.: Flooding of sandy beaches in a changing climate and the potential of nature based solution for impact mitigation., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4959, https://doi.org/10.5194/egusphere-egu22-4959, 2022.

Climate and weather are significant factors in planning to visit a touristic destination, especially taking into consideration the global warming. In this respect, touristic areas will be significantly affected by the potential adverse effects of climate change. This is the case of the Mediterranean which is considered one of the most vulnerable regions in global climate change, regarding the observed but also the expected future thermal risk. The goal of this study is to highlight the bioclimatic conditions anticipated to prevail in the eastern Mediterranean, studying five touristic destinations; namely, Heraklion, Crete Island (Greece), Antalya (Turkey), Limassol (Cyprus), Valletta (Malta) and Cairo (Egypt).

One of the most popular and widely applied human thermal index, the Physiologically Equivalent Temperature (PET), based on human energy balance, is utilized to quantify the regime of present and simulated future bioclimatic conditions. Air temperature, humidity, wind speed and global solar radiation (estimated at 1.1m where is the gravity center of the human body and builds the reference level for human biometeorological studies) are the parameters needed for the assessment of PET, using the RayMan model. The meteorological datasets concern 3-hour data from the SMHI RCA4 regional climate model (Rossby Center, Swedish Meteorological and Hydrological Institute, Norrkoping Sweden, spatial analysis 11 km), for the historical period 1971-2000 (reference period), as well as for the periods 2021-2050 and 2071-2100 under the two Representative Concentration Pathways, RCP4.5 (intermediate) and RCP8.5 (extreme).

As far as the historical period is concerned, the findings of the analysis showed that Heraklion, Crete Island, appears the most favorable bioclimatic conditions at midday (UTC 12:00), followed by Limassol and Malta, while Cairo and Antalya show high frequency and duration of strong/extreme heat stress within the year. Regarding evening hours (UTC 21:00) during summertime, there is a slight cold stress/thermal comfort in Heraklion and Malta, followed by Limassol, Antalya and Cairo with worse bioclimatic conditions.

Based on climate model simulations for 2021-2050 (near future) and 2071-2100 (far future) under RCP4.5 and RCP8.5, for midday (UTC 12:00), Heraklion, Crete Island depicts the best bioclimatic conditions, which can be attributed to the increased frequency and intensity of the Etesians winds, blowing during the summer period of the year contributing to the mitigation of the strong/extreme heat stress. The frequency and the duration of thermal comfort in the evening (UTC 21:00) is expected to increase for both RCPs. Malta shows similar bioclimatic behavior to Heraklion during evening hours, followed by Limassol, Antalya and Cairo, where the light/moderate heat stress occurs with increasing frequency and seasonality.

The results of the bioclimatic analysis will help in the management/dissemination of climate information for tourism purposes. In addition, the methodology used, based on bioclimatic (PET) diagrams, can provide detailed information in order to assess and quantify the climate change impacts on the tourism potential in the eastern Mediterranean.

How to cite: Nastos, P. T., Polychroni, I. D., Kapsomenakis, J., Solomos, S., and Zerefos, C. S.: Climate change impacts on bioclimatic conditions in the Eastern Mediterranean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6579, https://doi.org/10.5194/egusphere-egu22-6579, 2022.

Climate and environmental changes as drivers of human migration likely reach back to the rise and decline of ancient civilizations in the Mediterranean Basin. At present, there is evidence of such changes and their impacts to cause risks for human security in the Mediterranean region particularly in its southern and eastern rim countries. Discussions on the relationships between climate change, conflicts, and human migration include framing these as potential threat multipliers, e.g., climate change-induced water shortages, which will lead to food insecurity and may thereby intensify conflicts and ultimately internal and cross-border migration. Most accounts anticipate these threat multipliers to occur in countries that are particularly vulnerable to climate change, lack adequate adaptive capacity, and be exposed to multiple socio-ecological stressors. Against the background of existing socio-political and armed conflicts in the Eastern and Southern Mediterranean, this risk deserves further scholarly attention. Inadequate or missing political instruments or agreements to deal with conflicts, insufficient cross-border collaboration, and limited links to international frameworks exacerbate the challenges faced by local communities in this region. These factors have likely contributed to the internal and cross-border migration of large groups of populations in war-torn countries in the Mediterranean Basin and elsewhere.

Despite strong evidence for links between climate change and its consequences for water, food, and economic security, there is still significant debate as to the relative importance of them for individual decisions to migrate. Equally contested are propositions addressing a possible direct causal relationship between climate change impacts or climate variability and violent conflict. In addressing these issues, it quickly becomes clear that the relationships between climate and environmental changes, conflicts, and human migration are multi-causal and are characterized by complex interactions and feedbacks. Key determinants likely include the social, political, cultural, and economic conditions of a specific country or region as well as their historical trajectory.

The Mediterranean Expert Group on Environmental and Climate Change (MedECC) has embarked on addressing these challenging issues through a Special Report that follows the First Mediterranean Assessment Report of MedECC (MAR1; 2019). Major issues to be addressed include:

(i) how can we identify current “hot spots” of climate change impacts and ongoing or emerging conflicts;

(ii) how can we shed light on understanding the roles of different determinants on internal and cross-border migration, particularly with regard to a) migration linked directly and/or indirectly to environmental change and conflicts, b) migration linked to other determinants, and c) understanding the relationships and interdependencies of different determinants;

(iii) what are major knowledge gaps and what approaches should be followed to address them?

While the “Task Force on Migration” of the Eastern Mediterranean and the Middle East - Cyprus Climate Change Initiative has already discussed strategies and policy instruments to enhance adaptation to climate change, the MedECC Special Report will refine and complete such assessment by considering the links between climate change, conflicts, and migration based on existing adaptation measures.

This paper will provide background and rationale for the MedECC Special Report, its present state, and perspectives on its continued development.

How to cite: Lange, M., Cramer, W., Turhan, E., and Jarraud, N.: Environmental Change, Conflict and Human Migration in the Mediterranean: Challenges and Open Issues, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5882, https://doi.org/10.5194/egusphere-egu22-5882, 2022.

We present a variety of applications of the climate component of the coupled atmosphere-ocean kilometer-scale Adriatic Sea and Coast (AdriSC) modelling suite.  The AdriSC modelling suite has been implemented to represent both atmospheric and oceanic dynamics in the Adriatic Sea region and, in particular, to reproduce processes at the mesoscale (i.e. at the kilometer-scale or higher resolutions) like meteotsunamis (atmospherically-generated long-ocean waves in the tsunami frequency band) or orographically-driven winds. For that reason, two different modules have been developed conjointly in the AdriSC model. First, the basic module provides the kilometer-scale atmospheric and oceanic Adriatic baroclinic circulation with the Weather Research and Forecast (WRF) model at up to 3 km resolution in the atmosphere and the Regional Ocean Modelling System (ROMS) in the ocean, coupled with the Simulating WAves Nearshore (SWAN) model for surface waves at up to 1 km resolution. Second, the dedicated nearshore module is used to better reproduce atmospherically driven extreme sea level events, and couples offline the WRF 1.5 km grid in the atmosphere with the ADCIRC-SWAN unstructured mesh down to 10 m resolution along the Adriatic coastline.

Two different approaches – based on Pseudo-Global Warming (PGW) methodology – have been implemented to assess the impact of climate change in the Adriatic Sea: (1) short-term event-oriented simulations to represent the dynamics of extreme events with the nearshore module, and (2) long-term simulations (31-years), based solely on the basic module, to derive statistics of present (1987-2017) and future (2070-2100) climates. More precisely, the numerically unexpansive short-term simulations were used (1) to verify the implementation of the PGW methodology in the ocean and (2) to derive the impact of climate change on the bora wind dynamics and the associated wintertime cooling in the northern Adriatic Sea, as well as on the surface wave dynamics generated by dominant winds (sirocco, bora) and meteotsunamis. Concerning the expansive 31-year long simulations, they each took 18 months of run on the European Centre for Middle-range Weather Forecast (ECMWF) supercomputer to provide, for the very first time, a reliable kilometer-scale coupled atmosphere-ocean dataset – fully evaluated against observations in both atmosphere and ocean. Consequently, kilometer-scale coastal hazards under extreme climate changes can now be fully assessed by researchers, but also environmental agencies in the Adriatic region.

The research was supported by the Croatian Science Foundation (projects BivACME and ADIOS).

How to cite: Vilibić, I., Denamiel, C., Tojčić, I., and Pranić, P.: The Adriatic Sea and Coast (AdriSC) modelling suite: coupled atmosphere-ocean kilometer-scale assessments of present and future climates, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-723, https://doi.org/10.5194/egusphere-egu22-723, 2022.

Med-CORDEX is an international initiative that aims at developing fully coupled high resolution Regional Climate System Models (RCSMs) for the Mediterranean basin.  After 11 years of work an ensemble of more than 25 multi-model and multi–scenario climatic simulations is now available. In this study, we analyze the impact of the high-resolution representation of the Mediterranean Sea and of the interaction between ocean and atmosphere, explicitly resolved in the Med-CORDEX simulations, in the projected evolution of the most relevant climatic variables for the Mediterranean basin and the adjacent regions during the 21^st century. The final goal is to quantify up to what extent including the explicit and high-resolution representation of the ocean-atmosphere coupling is relevant for regional climate projections. The preliminary results show that, in general, higher resolution coupled simulations project a lower increase in the Sea Surface Temperature (SST) than lower resolution runs. This translates in a smaller input of heat and humidity to the atmosphere that, in turn, affect the cloud cover and precipitation over the basin and the adjacent continental areas. These changes are the result of a better representation of the Mediterranean Sea functioning in the Med-CORDEX RCSMs. In particular, they resolve better the mesoscale processes of the basin, which are partly responsible of the heat transport from the surface to deeper layers, and the ocean-atmosphere feedback that regulates the heat exchange.

How to cite: Soto-Navarro, J., Jordà, G., Somot, S., and Sevault, F.: Impact of the ocean-atmosphere coupling on high-resolution future projections for the Mediterranean Sea and surrounding climate from the Med-CORDEX ensemble, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4074, https://doi.org/10.5194/egusphere-egu22-4074, 2022.

Present day Mediterranean Sea (MedSea) is an oligotrophic semi-enclosed basin.  Nutrient supply by rivers, net nutrient export through the Strait of the Gibraltar and the basin-wide circulation create a biological desert. Sediment core records, however, indicate periods of higher production during paleo times.

To gain insight into biogeochemical conditions during the Last Glacial Maximum (LGM), we apply a regional ocean-biogeochemistry model of the Mediterranean Sea.  A consistent forcing is available from a transient simulation with an Earth System Model (ESM) over 22,000 years based, among others, on an ice sheet reconstruction.  The ESM run provides atmospheric forcing fields, being downscaled to the regional setup, temperature and salinity conditions at the open western boundary in the Atlantic, and river runoff.  Nutrient concentrations of river discharge and at the Atlantic boundary are set to present-day estimates.  The automatic bathymetry adjustment to account for sea level variations due to meltwater fluxes is adopted from the ESM simulation. The LGM simulation starts at 22 ka to allow for a 1000 yr spinup run with transient forcing. The LGM period results are compared to a present-day simulation based on the same consistent ESM forcing.  

Colder temperatures and thus lower basin-wide evaporation, as well as a shallower sill depth at the Strait of Gibraltar, lead to lower baroclinic watermass exchange between the MedSea and the Atlantic. The zonal overturning circulation is more sluggish during the LGM than present day.  River discharge to the MedSea increases by 35% during the LGM, causing an increased net primary production near the river mouths.  Despite a higher nutrient inventory of the MedSea at the LGM, net primary production of the entire MedSea is lower than present day. Colder LGM temperatures reduce phytoplankton growth rates and increase the remineralisation length scale.

More characteristics of LGM biogeochemistry are presented and their drivers will be disentangled, also including additional sensitivity studies on changes in bathymetry.        

How to cite: Six, K. and Mikolajewicz, U.: Modeling Ocean Biogeochemistry of the Mediterranean Sea at the Last Glacial Maximum, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8530, https://doi.org/10.5194/egusphere-egu22-8530, 2022.

Proxy-based hydro-climatic reconstructions over the Levant suggest enhanced water availability during the Last Glacial Maximum (LGM) compared to present-day conditions. To date, the governing hypothesis is that additional water availability may be directly linked to increased Cyprus Low frequency and intensity over the region. However, this paradigm has not been tested in a modelling framework. With this aim, we analyzed results from a
weather type classification algorithm and regional climate simulations. The weather type classification is applied to ERA5 Reanalysis data for present-day (1979-2018) and two PMIP3/PMIP4 pre-industrial and LGM model runs. Dynamical downscaling of the two models with the regional WRF model shows that the present hydro-climate can largely be reproduced. Our simulations suggest that both evaporation and precipitation were lower in the LGM compared to pre-industrial conditions, and that their relative changes can thus most likely explain the additional water availability during that time. Indeed, evaporation in the eastern Mediterranean is reduced to a higher degree (~-33%) as compared to precipitation (~-20%) during the LGM. Particularly, lower evaporation during LGM summer may have sustained the year-round wetter conditions in the Levant. In addition, we find significant changes in Cyprus Low characteristics for the LGM. The simulated daily precipitation associated with Cyprus Lows is significantly lower than pre-industrial values (reduction of 26 - 29%), whereas the wind intensity is stronger (increase of 7 - 8%). Finally, a significant increase in Cyprus Low frequency during LGM winter is likely (+22%). Indeed, our findings are in line with a plethora of proxy-based reconstructions, and provide a reinterpretation of the driving mechanism of water availability, i.e., strong changes in evaporation rather than precipitation. This study places projected hydro-climatic drying of the Levant in a long timescale perspective. As such, it improves our understanding of the physical processes influencing the hydrological cycle in this vulnerable region, situated on the border between sub-tropical and mid-latitude climatic zones.

How to cite: Ludwig, P. and Hochman, A.: Last Glacial Maximum Hydro-climate and Cyclone Characteristics in the Levant: A Regional Modelling Perspective, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5066, https://doi.org/10.5194/egusphere-egu22-5066, 2022.

The “Teleconnection” term in climate studies was defined primarily for widely separated regions. This stems from the basic idea that a physical process, such as an advection or a particular synoptic system, cannot simply explain a relation or a correlation in large distances. Also, in modern times, models more often fail in predicting these remote patterns, particularly with regional models, such as in the hurricane example and its effect on Mediterranean precipitation, explored here. Several teleconnection relations are reviewed, with particular focus on Mediterranean rainfall. It is argued that even with a clear physical process of advection and for a short horizontal scale, ‘teleconnection’ is often not well understood, if the physical mechanism involved is complex, such as in the sub-synoptic scales of aerosol-rainfall interaction or megacities and their potential effects on precipitation. Thus, a broader look at the horizontal scale of teleconnection is proposed where the word TELE is still representing the word ‘far’, as in its Greek origin, but it also includes our limitation in understanding of complex atmospheric relations in various distances.

Furthermore, the hidden assumption that ancients were not able to observe teleconnections is contradicted by an example from ~1800 years ago. In this example, a claim was made in the Talmud that the Euphrates flow is strongly related to the rainfall over the greater Israel region, located at ~700-900 km westward. However, the understanding of this ancient teleconnection was only possible at the 2^nd half of the 19^th century when the role of synoptic systems in weather, has emerged. 

Keywords: Teleconnection, Rainfall, synoptic system, Euphrates discharge, Middle East, Levant, Talmud

REFERENCE:

P. Alpert and H. Saaroni, “Historical and New Insights into Atmospheric Teleconnection” Oxford Research Encyclopedia of Climate Science (eds von Storch, H. et al.)  (Oxford Univ. Press, Oxford, 2021).(accepted Aug. 2021)

How to cite: Alpert, P. and saaroni, H.: Historical and New Insights into Atmospheric Teleconnection , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3567, https://doi.org/10.5194/egusphere-egu22-3567, 2022.

During boreal summer, large scale subsidence and a persistent northerly flow, known as the Etesians, characterize the tropospheric circulation over the eastern Mediterranean, respectively bringing clear skies and mitigating the emergence of heat waves. Atmospheric drivers over both South Asia and the North Atlantic have been proposed to influence the intraseasonal variability of subsidence and Etesians over the eastern Mediterranean. Here, we employ Causal Effect Networks, obtained by applying the Peter and Clark Momentary Conditional Independence (PCMCI) causal discovery algorithm, to identify causal precursors of subsidence and Etesians in a set of atmospheric fields. We find that both wave train activity over the North Atlantic/North American region and convective activity over the northern Indian Ocean are causally related to the 3-day average 850 hPa meridional wind variations over the eastern Mediterranean at a lag of 3-to-6 days. For 3-day average 500 hPa vertical wind velocity, causal precursors over the Middle East and Arabian Sea similar to those identified for the Etesian are found. We further explore in detail the different nature of the causal precursors to the Etesians and subsidence over the eastern Mediterranean by applying varying averaging in the variables representing the involved phenomena.

How to cite: Tyrlis, E., Di Capua, G., Matei, D., Coumou, D., and Donner, R.: Causal drivers of eastern Mediterranean tropospheric circulation during boreal summer, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8913, https://doi.org/10.5194/egusphere-egu22-8913, 2022.

Moisture transport over the northeastern Atlantic Ocean is one of the processes governing precipitation distribution and variability over Southern Europe. This moisture transport mainly occurs in the so-called Atmospheric Rivers (ARs). ARs are relatively narrow and elongated filaments of high-water vapor transport, which are associated with tropical moisture exports and often occur in combination with the passage of strong extratropical cyclones. Such structures transport more than 90% of the total mid-latitude vertically integrated water vapor, that on landfall, produce precipitation which can be both beneficial and destructive due to its interaction with topography or ascent in the Warm Conveyor Belt.

Understanding how AR characteristics will respond to a warming climate is, therefore, critical to mitigate changes in the intensity of AR-related precipitation and related hydrological extremes.

ARs reaching Southern Europe are analyzed using CMIP5 and CMIP6 simulations and on a high resolution transient simulation between 850 CE to 2100. The projected IVT for 2070–99 significantly exceeds the range given by interannual–interdecadal variability of the last millennium. Changes in IVT are in line with significant increases in tropospheric moisture content, driven by the concurrent rise in surface temperatures associated with the anthropogenic climate trend. On regional scales, recent and projected precipitation changes over the British Isles follow the global positive IVT trend, whereas a robust precipitation decrease over Iberia is identified in the twenty-first century, particularly during autumn. This indicates a possible extension of stable and dry summer conditions and a decoupling between moisture availability and dynamical forcing. The investigation of circulation features reveals a mean poleward shift of moisture corridors and associated atmospheric rivers.

Acknowledgments

The financial support for this work was possible through the following FCT project: HOLMODRIVE—North Atlantic Atmospheric Patterns Influence on Western Iberia Climate: From the Late Glacial to the Present (PTDC/CTA-GEO/29029/2017).

How to cite: Ramos, A. M., Sousa, P. M., and Trigo, R. M.: Atmospheric rivers responses to climate change in the Mediterranean Region, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4163, https://doi.org/10.5194/egusphere-egu22-4163, 2022.

Climate changes have been invoked to explain recent changes in wildfire regimes in Mediterranean regions, and climate projections suggest that there will be an increase in fire weather during the 21st century. However, humans influence natural fire regimes today directly by supressing or igniting fires, and indirectly by changing fuel types and fuel structure through land use changes. Recent observations provide only a limited basis for determining the relative importance of climate and human activities for fire. The diachronous introduction of agriculture during the Neolithic provides an opportunity to examine the potential impact of human activities on fire regimes. We reconstruct fire history using sedimentary charcoal records and population change based on summed probability distributions of radiocarbon dates on archaeological material, focusing on the interval between 10,000 and 3,500 cal. BP. The archaeological radiocarbon dates are also used to map the onset of agriculture through time across the region. For Iberia as a whole, we identify two periods of rapid population growth, centred on ca. 7,400 and ca. 5,400 cal. BP. However, these periods of rapid population growth are not synchronous with changes in charcoal accumulation. Changes in charcoal accumulation are not aligned with the time-transgressive dates for the introduction of agriculture across the region; charcoal accumulation was already increasing ca. 400 years prior to the onset of agriculture and continues to increase for ca. 200 years afterwards. There is also no consistent correlative relationship between population and fire across the period of analysis.  Our analyses show that there are no direct links between the introduction of agriculture or subsequent increases in population and changes to fire regimes in Iberia in the early to mid-Holocene, suggesting that changes in fire regimes were largely driven by climate changes.

How to cite: Sweeney, L., Harrison, S. P., and Vander Linden, M.: The drivers of changing fire regimes: an assessment of anthropogenic influence on fire history in the Iberian Peninsula during the Holocene, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-884, https://doi.org/10.5194/egusphere-egu22-884, 2022.

The Mediterranean basin is one of the most thermally vulnerable regions of the planet, already affected by frequent extreme heat events, which are projected to increase in the future. Using multiple extreme climate indices and daily temperature observations from over 50 meteorological stations in the region (NOAA Global Historical Climatology Network daily database) the dates of past heatwave events were identified from 1961 to 2020. While derived heatwave metrics from threshold-based indices generally differed from more complex, calendar day percentile-based indices (e.g., CTX90PCT), findings confirmed a statistically significant positive trend for the frequency, intensity, and duration of heatwave events for the majority of stations (Mann-Kendall test). Next, long-term (years: 2002-2020) daily satellite-derived Land Surface Temperature (LST) from the MODIS Aqua platform was used to compute surface thermal anomalies at the station locations. The dates and the summary metrics of the maximum anomalies were compared to the previously derived air temperature heatwave events to assess the feasibility of using LST estimates as a heatwave proxy for areas with a scarce station network. Finally, a physical understanding of the mechanisms behind heatwave trends for Athens, Greece was attempted through the use of large-scale synoptic data. Daily 500 hPa geopotential height anomalies were computed from ERA5 reanalysis data (1979-2020); then, an automated classification scheme was modified and applied to detect the circulation types for all past heatwave events for this period in Athens. Results indicated an evolving mixture of circulation types through the decades, associated with different intensities and durations of heatwave events.

How to cite: Agathangelidis, I., Cartalis, C., Tzanis, C., Kourtesiotis, C., and Philippopoulos, K.: A multi-faceted, long-term analysis of Mediterranean heatwaves using in-situ temperature observations, remote sensing imagery and large-scale circulation types., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12089, https://doi.org/10.5194/egusphere-egu22-12089, 2022.

The Mediterranean Sea is very sensitive to climatic changes due to its semi-enclosed nature and is defined as one of the hotspots in future climate change projections. In this study we use Argo float data to describe spatial variabilities and trends in Ocean Heat Content (OHC) within the entire Mediterranean Sea and for specified sub-basins (e.g. Western and Eastern Mediterranean, Gulf of Lion, South Adriatic). The amount of the OHC, spatially averaged in bins of 1 °x1 ° over the period 2001-2020, increases from west to east in the Mediterranean Sea.
Time series of temperature and OHC from 2005 to 2020, estimated in the upper and intermediate layers (5-700 m) and deeper layer (700-2000 m), reveal significant warming trends and an increase of OHC: the upper 700 m of the Mediterranean Sea show a warming trend of 0.041±0.012 °Cyr^-1, corresponding to a yearly increase in OHC of 3.59±1.02 Wm^-2. The upper 700 m of the Western Mediterranean Sea are warming fastest with an increase in temperature at a rate of 0.070±0.015 °Cyr^-1, corresponding to a yearly increase in OHC of 5.72±1.28 Wm^-2.

Mixing and convection events transport and disperse the temperature and OHC changes: significant warming trends are evident in the deeper layers (700-2000 m) of the two deep convection sites in the Mediterranean Sea (Gulf of Lion, South Adriatic), with an exceptionally strong warming trend in the South Adriatic from 2013 to 2020 of  0.058±0.005 °Cyr^-1, corresponding to a yearly increase in OHC of 9.43±0.85 Wm^-2. 

The warming of different water masses will show its feedback on ocean dynamics and the atmosphere (air-sea fluxes) in the next years, decades or even centuries when these warming waters spread or re-emerge. This will stress ecosystems and accelerate the extinction of several marine species. This study contributes to a better understanding of climate change in the Mediterranean region and should be another wake-up call for policy makers and society.

How to cite: Kubin, E., Menna, M., Mauri, E., Notarstefano, G., and Poulain, P.-M.: Heat content and temperature trends in the Mediterranean Sea as derived by Argo float data (2005 – 2020), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4899, https://doi.org/10.5194/egusphere-egu22-4899, 2022.

The Eastern Mediterranean-Black Sea Caspian Corridor (EMBSeCBIO) region (33°–49°N, 20°–60°E ), is characterized by strong temperature and precipitation gradients and topographic heterogeneity, resulting in the clear patterns in biome distribution within a relatively limited geographic space. The complexity of this area is a challenge for reconstructing the dynamics of the vegetation throughout the Holocene. In this study, we apply a recently developed method to reconstruct past vegetation changes. The method uses a large dataset of modern pollen samples assigned to biomes based on potential natural vegetation cover data to characterize biomes according to the means and standard deviations of the abundances of each taxon. We use this characterization to calculate an index of dissimilarity between any given pollen sample and each biome, and thus evaluate the probability that a pollen sample belongs to a particular biome. The method also allows us to identify non-analogue vegetation types, when the scores for fossil samples are outside the range of modern scores. The vegetation reconstructions were used to produce point-to-area interpolated maps for 300 years windows. We identify periods of relative ecological stability for mapping, and also periods of rapid environmental change, by analysing high resolution (=<200 years) fossil records using a breakpoint regression approach. For quantifying ecological change, we used ordination analysis to characterize the major gradient of compositional variation in pollen records. Preliminary results indicate the presence of non-analogue vegetation at several sites during the late glacial. They document a rapid expansion of forest and semi-open forest vegetation after the late glacial period in the Black Sea region, the Balkans, the Aegean and the Carpathians, but the persistence of open vegetation types in the mountains of south-eastern Anatolia (Zagros Mountains). The reconstructions indicate the maximum expansion of temperate forest at ~6000 calibrated years BP, where it reaches the south-eastern part of Anatolia and the mountains at the south of the Aegean Peninsula. A replacement of forest vegetation by open or semi-open vegetation types occurred in the Aegean Peninsula from ~7 to 5 ky. The middle to late-Holocene transition from forest vegetation to more open vegetation types was observed across the central Aegean area, Anatolia and the Caucasus.

How to cite: Cruz-Silva, E., P. Harrison, S., Prentice, C., and Marinova, E.: Vegetation history of the Eastern Mediterranean–Black Sea–Caspian-Corridor during the last 12500 years, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4939, https://doi.org/10.5194/egusphere-egu22-4939, 2022.

We investigate the impact of rapid climate changes during the Dansgaard-Oeschger cycles of the last glacial on the climate of the Mediterranean region. We reconstructed the temperature of the coldest and warmest months, growing season warmth, and plant-available moisture (MI) from 20 published pollen cores from Iberia to Iran, using frequency corrected tolerance-weighted weighted average partial least squares (fxTWA-PLS) method. We corrected the MI reconstructions to account for the direct physiological impact of changing CO₂ levels on plant water-use efficiency. We found warm intervals – probable GIs - by identifying potential D-O warmings using their signature asymmetrical rise and fall. Cold climate intervals – considered as the most extreme expression of the GSs - were defined as periods when growing season warmth was below the long-term average value for each individual record.

Warm intervals are characterised by a decrease in moisture in the western Mediterranean compared to the preceding cold interval. Sites in the eastern Mediterranean show either no change in moisture between the two states or are characterised by a slight increase in moisture during the warm intervals compared to the cold intervals. There is also a marked west-east difference in temperature seasonality, with warmer intervals showing increased seasonality in the western and northwestern region compared to the eastern Mediterranean. The increased seasonality is largely driven by changes in summer temperature since the degree of winter warming during warm intervals is similar across the whole region. Changes in all of the bioclimatic variables between cold and warm intervals show a strong relationship with latitude: the latitudinal gradient is steeper in cold climates than in warm climates. The relative homogeneity of changes during the cold intervals is consistent with a more zonal circulation pattern than during warm intervals. This change in circulation patterns could help to explain the west-east patterns in the changes in moisture between cold and warm intervals.

How to cite: Turner, M. and Harrison, S. P.: Mediterranean climates during Dansgaard-Oechger cycles in the last glacial period, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4968, https://doi.org/10.5194/egusphere-egu22-4968, 2022.