Change over recent decades in the world's five Mediterranean Climate Regions (MCRs) of quantities of relevance to water resources, ecosystems and fire are examined for all seasons and placed in the context of changes in large-scale circulation. Near-term future projections are also presented.   It is concluded that, based upon agreement between observational data sets and modeling frameworks, there is strong evidence of radiatively-driven drying of the Chilean MCR in all seasons and southwest Australia in winter.  Observed drying trends in California in fall, southwest southern Africa in fall, the Pacific Northwest in summer and the Mediterranean in summer agree with radiatively-forced models but are not reproduced in a model that also includes historical sea surface temperature (SST) forcing, raising doubt about the human-origin of these trends. Observed drying in the Mediterranean in winter is stronger than can be accounted for by radiative forcing alone and is also outside the range of the SST-forced ensemble. It is shown that near surface vapor pressure deficit (VPD) is increasing almost everywhere but that, surprisingly, this is contributed to in the southern hemisphere subtropics to mid-latitudes by a decline in low level specific humidity.  The southern hemisphere drying, in terms of precipitation and specific humidity, is related to a poleward shift and strengthening of the westerlies with eddy-driven subsidence on the equatorward side. Model projections indicate continued drying of southern hemisphere MCRs in winter and spring, despite ozone recovery and year-round drying in the Mediterranean.  Projections for the North American MCR are uncertain, with a large contribution from internal variability, with the exception of drying in the Pacific Northwest in summer.  Overall the results indicate continued aridification of MCRs other than in North America with important implications for water resources, agriculture and ecosystems. 

How to cite: Seager, R., Wu, Y., Cherchi, A., Simpson, I., Osborn, T., Kushnir, Y., Lukovic, J., Liu, H., and Nakamura, J.: Recent and near-term future changes in impacts-relevant seasonal hydroclimate in the world's Mediterranean climate regions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4782, https://doi.org/10.5194/egusphere-egu24-4782, 2024.

Changes in the hydroclimate of the Mediterranean region by the end of the 21^st century are studied using phase 6 of the Coupled Model Intercomparison Project (CMIP6) projections. More specifically, we examine how changes in the different terms of the atmospheric moisture budget in this region, namely the moisture flux convergence due to the zonally averaged flow, and stationary and transient eddies, contribute to changes in the climatological net precipitation (precipitation minus evaporation, P – E), in the annual, seasonal, and zonal mean over land and sea.

According to the ensemble-mean of ten CMIP6 models, the climatological annual mean P – E is projected to decrease drastically by the end of the 21^st century over northern Mediterranean land regions as well as the sea. The drying is predominantly due to increased total stationary-eddy moisture flux divergence, which arises from increased divergence of the zonally averaged moisture by the zonally-anomalous circulation. For both land and sea, the annual mean pure stationary eddy term is projected to bring wetter conditions within the Mediterranean, except for northwestern Africa and the Iberian Peninsula. This wettening tendency is, however, not large enough to offset the drying caused by the zonally-anomalous circulation.

By the end of the 21^st century, the annual mean transient eddies are projected to cause increased drying over the northern Mediterranean land regions and the western Mediterranean Sea, and increased moistening over the eastern Mediterranean. The drying due to the annually and zonally averaged circulation, associated with the descending branch of the Hadley cell, is very small, and appears to be a weaker signal with respect to the others.

While increased moisture divergence due to transient eddies during winter is a contributing factor to the Mediterranean drying, it is not the main cause of year-round drying by the end of the 21^st century. In fact, there are slight increases of moisture convergence over Portugal, Spain, and northern Turkey. Rather, it is the increase in the divergent stationary eddies during summer and winter that drives the aridification phenomenon in the Mediterranean. Recent studies using CMIP5 models have reported similar results (Seager et al. 2014; Seager et al. 2019), pointing to the robustness of the projected signal.

References:

• Seager, R., Liu, H., Henderson, N., Simpson, I., Kelley, C., Shaw, T., Kushnir, Y., & Ting, M. (2014). Causes of increasing aridification of the mediterranean region in response to rising greenhouse gases. Journal of Climate, 27(12), 4655–4676. https://doi.org/10.1175/JCLI-D-13-00446.1
• Seager, R., Osborn, T. J., Kushnir, Y., Simpson, I. R., Nakamura, J., & Liu, H. (2019). Climate Variability and Change of Mediterranean-Type Climates. Journal of Climate, 32(10), 2887–2915. https://doi.org/10.1175/JCLI-D-180472.1

How to cite: Tootoonchi, R., Bordoni, S., and D'Agostino, R.: Climate Change in the Mediterranean: Assessing Changes in Different Circulations and the Impacts on the Mediterranean Hydroclimate, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6769, https://doi.org/10.5194/egusphere-egu24-6769, 2024.

The Mediterranean Climate Regions (MCRs) share similarities in terms of experienced temperatures and precipitation patterns, resulting in similar vegetation, i.e. farms and agricultural approaches/strategies. Recent findings suggest that groundwater levels in the Euro-Mediterranean may experiencing negative trends, resulting from decreasing precipitation, increasing evapotransipration and/or increasing withdrawal. This suggests a potential dry transition in MCRs, affecting biodiversity and ecosystems. By focusing on the Euro-Mediterranean and California, this work characterizes the dry transition through soil water content analysis from observation. The Total Water Storage (TWS) variable provided by the GRACE/GRACE-FO mission is utilized, carrying information about groundwater, soil moisture, surface water, snow water equivalent, and water stored in biomass. Furthermore, the contribution related to the variability of TWS due to associated drivers, precipitation, and potential evapotranspiration (PET) is quantified. The methodology framework relies on Empirical Orthogonal Function (EOF) analysis and a Multivariate Linear Regression model (MLR) to characterize, respectively, the modes of variability of TWS and the relative influence of the drivers to the total variance of the field. Our results highlight a general drying trend for both regions; furthermore, they suggest that in certain domains, variations in TWS are more sensitive to specific drivers than others: the western Euro-Mediterranean (Spain, Portugal, and parts of North Africa) is more susceptible to precipitation variability than PET, as it is more influenced by Atlantic flows and the effects of the North Atlantic Oscillation; in contrast, the TWS in the eastern Euro-Mediterranean (Greece and Turkey) is predominantly affected by the increase in PET due to the temperature increase; on the other hand he central EuroMed (Italy and Tunisia) exhibit a mixed behaviour with influences of both precipitation and PET on TWS. Regarding California, similar to the Euro-Mediterranean, there is a negative trend in TWS in equatorward regions, where PET is the major source of variability. Conversely, starting from 43°N in the poleward regions, there is a positive trend in TWS, mostly due to the increase in precipitation in that area.

How to cite: Senigalliesi, V., Alessandri, A., Di Carlo, E., and Cherchi, A.: Decline of water resources in Northern Hemisphere Mediterranean Climate Regions based on satellite observations., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-699, https://doi.org/10.5194/egusphere-egu24-699, 2024.

How to cite: Lukovic, J., Chiang, J., Blagojevic, D., and Sekulic, A.: A Later Onset of the Rainy Season in California, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18437, https://doi.org/10.5194/egusphere-egu24-18437, 2024.

In this study, the impacts of a specific class of extreme weather systems in the Mediterranean region (Medicanes) on the physical and biogeochemical parameters of the marine environment are thoroughly investigated. A comprehensive analysis based on 14 systems that occurred between 2007 and 2021 was carried out, with a specific focus on the impact on the different regions of the Mediterranean Sea (MS). The analysis showed some consistent patterns in the response of the marine environment to the passage of the system: surface concentrations of Chlorophyll-a (Chl-a), phytoplankton, nutrients, and oxygen tend to increase above the MLD, while temperature tends to decrease. Significant increments of these parameters were observed in the presence of Warm Core Eddies (WCEs) and Cold Core Eddies (CCEs). The interaction with WCEs enhanced the intensity of the weather system and related mixing and upwelling in the upper layer, leading to the increase in Chl-a, phytoplankton, and oxygen concentrations .. Cyclone-induced local mixing injects nutrients into the ocean’s upper layer that can drive significant phytoplankton blooms. Moreover, strong winds frequently lead to a drop in sea surface temperature (SST), which is a key factor in primary productivity. The analysis of mean sea level pressure (MSLP) and wind speed (WS) along the path of the cyclones revealed a sudden drop (rise) in MSLP and rise (drop) in WS at WCEs (CCEs) locations. It is observed that a few medicanes, such as Zissi, Anton, and Xandra, show exceptional behavior. Among them, Zissi exhibited an exceptionally high translational speed. The fast evolution of Zissi resulted in limited interaction with the underlying ocean, which is responsible for its unique characteristics during the event.

How to cite: Jangir, B., Reale, M., Menna, M., Mishra, A. K., Martellucci, R., Cossarini, G., Salon, S., Mauri, E., and Strobach, E.: Assessing the interactions between extreme weather systems and the marine environment in the Mediterranean Sea     , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1072, https://doi.org/10.5194/egusphere-egu24-1072, 2024.

In a global warming scenario, there is a growing need to understand why the Euro-Mediterranean region is a hotspot for both warming and drying signals and the seasonal and regional details, thus providing improved climate information required by decision makers. This work focuses on the design of an evaluation framework for climate simulations based on a classification of synoptic circulation patterns (CPs). A set of 30 CMIP6 global climate models (GCMs) is evaluated in terms of how well they reproduce the spatio-temporal variability of a CPs classification within the region. CPs are constructed through a hierarchical clustering procedure, using daily mean sea level pressure (SLP) during 1950-2014 against the ERA5 reanalysis. The link with surface variables -including precipitation, minimum and maximum temperatures- is also studied. Model performance is quantified based on different metrics for the spatial and temporal representation of the SLP patterns and the associated surface conditions, allowing a ranking of the best-performing GCMs.

GCMs adequately reproduce the annual cycle of the CPs frequency, with a dominant synoptic structure during summertime enhancing warm and dry conditions. Best-performing models in this regard include MPI-ESM1-2-LR, EC-Earth3-CC and MRI-ESM2-0. However, the correct timing of this CP and the transitional patterns are often misrepresented, such as in GFDL-ESM4 and NorESM2-LM. The analysis of the surface patterns associated with each CP show good model skills, better for the extreme temperatures than for rainfall and particularly during the transition seasons, for which the GCMs spread also increases. In this sense, the models EC-Earth3-Veg, EC-Earth3-CC and GFDL-CM4 present the best scores, whereas INM-CM5-0, KIOT-ESM and NorESM2-LM show the lower skills. By blending both the spatial and temporal features of the CPs, the EC-Earth3-CC, EC-Earth3-Veg, GFDL-CM4 and MRI-ESM2-0 arise as the best-performing GCMs over the Euro-Mediterranean region.

Overall, it is highlighted that not all models perform best in all the aspects considered, emphasizing the need of a complete process-based model evaluation. This is a way to constrain the future projections in order to reduce uncertainty and come up with coherent climate information at a regional scale.

How to cite: Olmo, M., Campos, D., Pep, C., Ángel, M., Albert, S., and Francisco, D.-R.: A synoptic circulation patterns evaluation framework for CMIP6 GCMs over the Euro-Mediterranean region, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2544, https://doi.org/10.5194/egusphere-egu24-2544, 2024.

Increasingly frequent and intense drought events at a global scale emphasize the heightened vulnerability and exposure of ecosystems and human populations. In Southern Europe, identified as a significant climate change 'hotspot', particularly within the Iberian Peninsula (IP), droughts are a recurring and impactful type of extreme weather events. Anticipated shifts in climate patterns and the occurrence of extreme weather events are expected to cause profound environmental and socio-economic consequences. This study investigates the impacts of 1.5ᵒ and 2ᵒC Global Warming Levels (GWL) at the end of the 21st century on drought events and population exposure to dry extreme events in the IP.

For this research, EURO-CORDEX experiments (13 simulations) were considered and aggregated as a weighted multi-variable multi-model ensemble, encompassing different time periods, namely the historical period from 1971 to 2000, 30-year periods centred on the 1.5ᵒ and 2ᵒC GWL years, and the projected end of the century period spanning 2066 to 2095. Two drought indicators, the Standardized Precipitation Index (SPI) and the Standardized Precipitation-Evapotranspiration Index (SPEI) are used to characterize droughts. Three representative scenarios are employed to delineate distinct greenhouse gas emission trajectories. This study uses Eurostat's demographic projections covering the period up to 2100 with 5-year intervals starting in 2020 for Portugal and Spain. The study supplements historical population values with The World Bank data until 2011.

For the RCP8.5 scenario, changes in the number of moderate, severe, and extreme droughts are projected to grow throughout the century, with 24 to 33 % (58 to 69 %) in the case of SPI (SPEI). This escalation reflects an overwhelming growth of drought occurrences in the IP because of the 0.5°C additional warming. Population exposure to extreme droughts is higher under the 2ᵒC scenario than under the 1.5ᵒC scenario, particularly as measured by SPEI, reflecting again the importance of the expected increase of the temperature in the IP. Population exposure to extreme droughts in the end of the century can vary between an increase of 50 % and more than 600 % for SPEI with timescales of 3 to 12-months under RCPs 4.5 and 8.5.

The findings of this study reveal a notable projected surge in population exposure to droughts throughout the entire IP, particularly by the end of the century, with climate change identified as the predominant factor for this escalation. The findings underscore the urgency for regional authorities, policymakers, and society to prioritize adaptation planning and develop a comprehensive understanding of the vulnerabilities and potential strategies to cope with the challenges posed by dry extreme events.

This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds (PIDDAC) – UIDB/50019/2020 (https://doi.org/10.54499/UIDB/50019/2020), UIDP/50019/2020 (https://doi.org/10.54499/UIDP/50019/2020) and LA/P/0068/2020 (https://doi.org/10.54499/LA/P/0068/2020). This work was performed under the scope of project https://doi.org/10.54499/2022.09185.PTDC (DHEFEUS) and supported by national funds through FCT. DL and AR acknowledge FCT I.P./MCTES (Fundação para a Ciência e a Tecnologia) for the FCT, 2022.03183.CEECIND/CP1715/CT0004 (https://doi.org/10.54499/2022.03183.CEECIND/CP1715/CT0004) and (https://doi.org/10.54499/2022.01167.CEECIND/CP1722/CT0006 (Complex), respectively.

How to cite: Russo, A., Bento, V. A., Ribeiro, A., Lima, D. C. A., Careto, J. A., Soares, P. M. M., Libonati, R., Trigo, R. M., and Gouveia, C. M.: Projected Increases in Population Exposure to Droughts in the Iberian Peninsula under 1.5ᵒ and 2ᵒC Global Warming Levels, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18396, https://doi.org/10.5194/egusphere-egu24-18396, 2024.

The Mediterranean region is recognized as a climate change hotspot, where temperatures increase faster than the global average. Modelling experiments suggest that such rapid and drastic changes will induce droughts and extreme rainfall events in this vulnerable region. Records of past climatic changes are useful to determine the speed and mode of regional responses and climatic sensitivities. We examine here the response of southern European hydroclimate to large-scale oceanic disturbances and rapid climatic changes during the Younger Dryas (YD) interval (e.g., 14-11 ka BP).

We present new results from Lago Grande di Monticchio (Italy) that allow us to explore the dynamics of precipitation at high temporal resolution. By combining multiple tracers (hydrogen isotope ratios of leaf waxes, X-ray fluorescence scanning, microfacies analyses, tephrochronology), we were able to determine both rainfall dynamics and sedimentary and environmental responses. We identified a pronounced positive shift in hydrogen isotope ratios (expressed as δD values) during the YD cold period of ca. 20 ‰ between 12.6 and 11.5 ka BP. We interpret this to reflect to a decrease in the input of north Atlantic moisture (a significant contributor to annual rainfall at present) and lower overall precipitation amount. This coincides with an increase in the varve thickness and occurrence of organic-clastic microfacies. The presence of marker tephra layers in the record (esp. the Neapolitan Yellow Tuff and Pomici Principali) provides important temporal tie-points that enable us to compare local hydroclimatic responses across the wider region. In particular, the observed drying trend at Monticchio is in striking contrast to more humid conditions north of the Alps in western, central and eastern Europe, potentially reflecting the southward migration of synoptic climatic systems (westerlies) and the presence of sea-ice in the moisture source region.

How to cite: Blanchet, C., Cormier, M.-A., Liang, Z., Zhao, X., Rik, T., Ramisch, A., Wulf, S., Schwab, M., Brauer, A., and Sachse, D.: Large-scale atmospheric circulation changes in the northern Mediterranean realm during the Younger Dryas: new insights from Lago Grande di Monticchio (Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17746, https://doi.org/10.5194/egusphere-egu24-17746, 2024.

Mediterranean thermohaline circulation is a very sensitive system to changes in regional climate conditions. The current warming conditions have already been transferred into the deep water properties, and future projections indicate an overall weakening of this circulation system. In this context, it becomes extremely relevant understanding the natural range of variability of this system and the interplay between the different basins and sub-basins controlling deep and intermediate convection in the Mediterranean Sea. Here we use the past record as a natural laboratory to learn on the impact that different climate forcings had in this circulation system, and also evaluating its consequences in the Mediterranean Outflow Water (MOW) and thus in the Atlantic oceanography. These are the main results of the ERC-Consolidator grant TIMED, devoted to understanding of past changes in Mediterranean thermohaline circulation. This new data set is based in a variety of proxies that are sensitive to ocean circulation changes such as U/Mn ratios measured in the foraminifera diagenetic coatings, Nd isotopes, absolute dating on deep sea corals, among other geochemical and sedimentological tools applied in sediment cores from both E- and W-Med. The obtained results indicate the deglacial development of an intense minimum oxygen zone in the W-Med associated to the LIW which extended down to at least 950m. These evidences support by the first time, that the formation of the deglacial Organic Rich Layer was also connected to a weakening of E-Med convection, this would indicate a long pre-conditioning prior to the last Sapropel (S1) that would start with last Heinrich event in the North Atlantic and fully develop with the onset of the African humid period. We identify that an intense aridification and cooling of the E-Med driven by the AMOC weakening of the Younger Dryas was responsible of a strong reactivation of E-Med convection that resulted in a stronger MOW, and also triggered enhanced deep intermediate convection in the W-Med. This circulation change pushed out an old water mass previously accumulated in the Med for several centuries with major consequences in deep ecosystems sustained by deep sea corals. The onset of the last S1 in the E-Med led to major changes in deep convection in both E and W-Med, but with opposite sign in their response. These results highlight the tide connection between the AMOC and E-Med convection and rise questions on the potential role that the associate changes in the MOW could have on the AMOC, particularly during weak stages.

How to cite: Cacho, I., Pena, L., Frigola, J., Català, A., de la Fuente, M., Trias, S., Campderrós, S., Selvaggi, M., Torner, J., Margaritelli, G., Pérez-Asensio, J. N., Corbera, G., Evangelinos, D., and Lirer, F.: Learning from past changes in Mediterranean Thermohaline Circulation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20558, https://doi.org/10.5194/egusphere-egu24-20558, 2024.

Mediterranean coastal lagoons play a pivotal role in the environmental, social, and economic facets of the coastal areas.  In general, coastal lagoons serve as biodiversity hotspots, supporting diverse ecosystems, including wetlands, marshes, seagrass beds, and unique fauna. They function as carbon sinks, sequestering substantial amounts of atmospheric carbon dioxide. Coastal lagoons also act as hydrological regulators, serving as natural buffer zones during extreme weather events, regulating hydrological cycles, and minimizing the impacts of flooding.  Mediterranean coastal lagoons hold significant socio-economic value, providing essential fishing grounds and supporting local fishing communities, and as tourist. Finally, coastal lagoons have been integral to Mediterranean cultures for centuries, holding historical and cultural significance. Understanding the impacts of climate change on coastal lagoon is crucial for coastal planning and adaptation strategies. In this study artificial neural networks (ANNs)are applied to estimate the impacts of anthropogenic climate change on water masses characteristics of coastal lagoon. Specifically, ANNs are used to model the associations between climate variables and water mass properties (namely temperature and salinity), which can be used for future projections. The developed ANNs approach can be applied to generic coastal lagoons, if sufficient in situ data of temperature, salinity and sea level are available for developing the model. The driving meteorological variable can be extracted from meteorological reanalysis and model climate projections if their resolution is sufficient to describe the relevant mesoscale features. The method is applied to the Venice Lagoon, the largest Mediterranean lagoon. The Venice lagoon is an ecologically and socio-economically relevant environment with notable susceptibility and a comprehensive description of climate change impacts is essential for its conservation and sustainable management. An advantage of the Venice lagoon is the relative richness of in situ observations, because of extensive past field campaigns. Here we provide and estimate of the expected changes of its temperature and salinity that are produced by low and high climate change scenario, with corresponding uncertainties. The ANN was parameterized using a combination of field data of temperature, salinity, and sea level, along with reanalysis data for ground temperature, wind speed (v and u components), temperature at 2 m, precipitation, evaporation, and humidity. Field data were obtained from a 10-year monitoring campaign, during which 30 stations within the lagoon were sampled. Reanalysis data were downloaded from the Copernicus ERA5 database. The climate scenarios used for projections were obtained from the Med-CORDEX network.

How to cite: Bozzeda, F., Sigovini, M., and Lionello, P.: Application of artificial neural networks for modeling the climate change impacts on Mediterranean coastal lagoons:  the Venice Lagoon example., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12335, https://doi.org/10.5194/egusphere-egu24-12335, 2024.