Yannis N. Krestenitis | Aristotle University of Thessaloniki (original) (raw)
Papers by Yannis N. Krestenitis
Journal of Marine Science and Engineering, 2024
The summer of 2024 witnessed record-high sea surface temperatures (SST) across the Aegean, Ionian... more The summer of 2024 witnessed record-high sea surface temperatures (SST) across the Aegean, Ionian, and Cretan Seas (AICS), following unprecedented air heatwaves over the sea under a long-term warming trend of 0.46 °C/decade for the mean atmospheric temperature (1982–2024). The respective mean SST trend for the same period is even steeper, increasing by 0.59 °C/decade. With mean summer surface waters surpassing 28 °C, particularly in the Ionian Sea, the southern Cretan, and northern Aegean basins, this summer marked the warmest ocean conditions over the past four decades. Despite a relatively lower number of marine heatwaves (MHWs) compared to previous warm years, the duration and cumulative intensity of these events in 2024 were the highest on record, reaching nearly twice the levels seen in 2018, which was the warmest until now. Intense MHWs were recorded, especially in the northern Aegean, with extensive biological consequences to ecosystems like the Thermaikos Gulf, a recognized MHW hotspot. The strong downward atmospheric heat fluxes in the summer of 2024, following an interannual increasing four-decade trend, contributed to the extreme warming of the water masses together with other met-ocean conditions such as lateral exchanges and vertical processes. The high temperatures were not limited to the surface but extended to depths of 50 m in some regions, indicating a deep and widespread warming of the upper ocean. Mechanisms typically mitigating SST rises, such as the Black Sea water (BSW) inflow and coastal upwelling over the eastern Aegean Sea, were weaker in 2024. Cooler water influx from the BSW decreased, as indicated by satellite-derived chlorophyll-a concentrations, while upwelled waters from depths of 40 to 80 m at certain areas showed elevated temperatures, likely limiting their cooling effects on the surface. Prolonged warming of ocean waters in a semi-enclosed basin such as the Mediterranean and its marginal sea sub-basins can have substantial physical, biological, and socioeconomic impacts on the AICS. This research highlights the urgent need for targeted monitoring and mitigation strategies to address the growing impact of MHWs in the region.
5th International Congress on Applied Ichthyology, Oceanography, and Aquatic Environment (HydroMediT) , 2024
Thermaikos Gulf is an environmentally fragile coastal environment characterized by numerous anthr... more Thermaikos Gulf is an environmentally fragile coastal environment characterized by numerous anthropogenic and natural pressures. The environmentally protected areas along its western coasts and the large number of inhabitants that live over its northern and eastern coasts raise the need for systematic monitoring and prediction of the marine environment concerning the ocean circulation, weather conditions, sea level and wave characteristics, pollution events, coastal flooding, and freshwater input. Herein, we present recent advances of the Wave4Us operational platform that provides short-term forecasts of all the above conditions, freely accessed by local authorities, the research community, and the broader audience on a daily basis. Specified marine predictions (e.g., about pollution, flooding, and heatwaves) provide useful real-time information to first-level responders and managerial stakeholders during hazardous events that may threaten the quality of the coastal environment and the safety of the population residing on Thermaikos Gulf's littorals.
Annales Geophysicae, 1994
Hydrology
Storm surges due to severe weather events threaten low-land littoral areas by increasing the risk... more Storm surges due to severe weather events threaten low-land littoral areas by increasing the risk of seawater inundation of coastal floodplains. In this paper, we present recent developments of a numerical modelling system for coastal inundation induced by sea level elevation due to storm surges enhanced by astronomical tides. The proposed numerical code (CoastFLOOD) performs high-resolution (5 m × 5 m) raster-based, storage-cell modelling of coastal inundation by Manning-type equations in decoupled 2-D formulation at local-scale (20 km × 20 km) lowland littoral floodplains. It is fed either by outputs of either regional-scale storm surge simulations or satellite altimetry data for the sea level anomaly. The presented case studies refer to model applications at 10 selected coastal sites of the Ionian Sea (east-central Mediterranean Sea). The implemented regular Cartesian grids (up to 5 m) are based on Digital Elevation/Surface Models (DEM/DSM) of the Hellenic Cadastre. New updated f...
Natural Hazards
The IANOS Medicane was one of the most severe storms that have formed in the Mediterranean Sea wi... more The IANOS Medicane was one of the most severe storms that have formed in the Mediterranean Sea with Category 2 Hurricane characteristics. The storm induced a significant increase in sea-level elevation along its pathway and caused storm surges at the central Ionian Sea with consequent impacts on coastal regions of the Ionian Islands and western Greece. An integrated approach, based on hydrodynamic ocean simulations, coupled to meteorological and coastal flooding simulations, is used in combination with field and satellite observations to analyze the marine weather conditions, the storm surge characteristics, and the coastal inundation characteristics due to the impact of IANOS Medicane in September 2020. The evolution of the Medicane and the respective storm surge in the ocean have been successfully recorded by the met-ocean simulations, part of an active public-access operational forecast system. Both wind and atmospheric pressure patterns affected the storm surge variability over the Ionian Sea. The direct intrusion of the Medicane from the central Mediterranean Sea toward the Ionian Sea formed storm surges over several coastal areas, even before the storm's landfall, due to the accompanying onshore currents. Storm surges in the order of 30 cm generated extensive flooding over lowland coastal areas, as confirmed by both satellite (Normalized Difference Water Index, NDWI) and numerical (coastal inundation modeling) data. Satellite-derived and simulated estimations showed that, in specific coastal regions, the run-up of seawater extended up to 200 m inland, depending on the hydraulic connectivity between the lowland areas, which determined the inundation extents during the storm surge.
Continental Shelf Research, 2021
Thermaikos Gulf is a typical, river-fed, microtidal, semi-enclosed, coastal inlet of the east-cen... more Thermaikos Gulf is a typical, river-fed, microtidal, semi-enclosed, coastal inlet of the east-central Mediterranean Sea. It is an important coastal ecosystem susceptible to several anthropogenic pressures, strong river discharges and variable meteorological and ocean (met-ocean) conditions. One of the most significant environmental problems of the region is the occasional formation of extended eutrophication phenomena (red tides, mucilaginous aggregates), especially over the Northern Thermaikos Gulf (NTG). Herein, we investigate the contribution of hydrodynamic processes on the formation of such events, under the effects of different meteorological and river discharge conditions during the annual cycle. We conducted field observations (physical-chemical measurements), microscopy analysis of phytoplankton samples, satellite ocean color image analysis, and implemented high-resolution numerical hydrodynamic simulations with updated river discharge outflows to detect eutrophication events and correlate them with the prevailing physical processes and ocean circulation patterns. The eutrophication events were mainly associated with the dominance of southerly winds, which affect the ocean circulation over the NTG in three ways: i) they confined the surface waters in the northern parts of the NTG separating the waters masses between the northern and southern regions, ii) they contribute on the northward spreading of nutrient-rich brackish waters towards the northern parts of the Gulf, and iii) they impose an anticyclonic circulation, especially in the inner- and central-Gulf weakening its renewal process. Northerly winds contribute on the renewal of the Gulf imposing a two-layer flow, especially along the eastern coasts. The seasonal observational campaigns of the 2017–2018 period captured three eutrophication events (June–July 2017, December 2017, and May 2018) and two renewal periods (late-July 2017 and October 2017) that were favoured by the two aforementioned types of met-ocean synergy. New insight is provided on the mesoscale ocean circulation and sub-mesoscale local effects on eutrophication events in a typical microtidal coastal system of the east-central Mediterranean, where freshwater discharges by a multi-river inlet.
Applied Mathematical Modelling, 2021
The structure of the "Amphioxus sand" community in Thermaikos Bay was studied over a two-year per... more The structure of the "Amphioxus sand" community in Thermaikos Bay was studied over a two-year period. The examination of the collected 4,767 specimens revealed the presence of 141 species. Gastropoda and Polychaeta were the dominant taxa. Multivariate analyses showed high similarity, whereas samples discriminated according to sediment granulometry. The degradation of this community was evident in its structure as most of the recorded macrobenthic species characterizes the organically enriched sediments.
ΥΔΡΟΤΕΧΝΙΚΑ, Apr 6, 2017
Διερευνάται η επίδραση της κλιματικής αλλαγής στην εξέλιξη των μετεωρολογικών παλιρροιών στο Αιγα... more Διερευνάται η επίδραση της κλιματικής αλλαγής στην εξέλιξη των μετεωρολογικών παλιρροιών στο Αιγαίο και το Ιόνιο Πέλαγος και την παράκτια ζώνη της Ελλάδας. Η ανάλυση καλύπτει την περίοδο 1951-2100 (κλιματικό σενάριο Α1Β για τoν 21 ο αιώνα) και στηρίζεται σε προσομοιώσεις με ένα διδιάστατο υδροδυναμικό μοντέλο υψηλής χωρικής ανάλυση (GreCSSM). Η σύγκριση των προσομοιωμένων αποτελεσμάτων έναντι επί τόπου παρατηρήσεων με βάση στατιστικά μέτρα και δείκτες είναι ικανοποιητική. Παρουσιάζονται επίσης οι μελλοντικές τάσεις, η μεταβλητότητα και η συχνότητα εμφάνισης έντονων γεγονότων μετεωρολογικής παλίρροιας στις ελληνικές θάλασσες και την ελληνική παράκτια ζώνη. Δίνονται επίσης εκτιμήσεις για την τάση της πιθανής κλιματικής αλλαγής μέχρι το 2100, μαζί τις μέσες, ετήσιες και υπερετήσιες μέγιστες τιμές της θυελλογενούς ανύψωσης της θαλάσσιας στάθμης στο Αιγαίο και το Ιόνιο Πέλαγος.
Environmental Modeling & Assessment
Modern concepts in water resources management and related risk assessment necessitate participato... more Modern concepts in water resources management and related risk assessment necessitate participatory approaches with stakeholders having a key role in the respective processes. The objective of the article is to (i) integrate stakeholders’ opinions and preferences on identified hazards, i.e., coastal flooding, water scarcity, and heat stress, derived by physically based numerical modeling under current and future climate change conditions and attributed in the form of an Integrated deltaic risk index (IDRI) at a specific case study area, and (ii) investigate whether and how the stakeholders’ opinions differentiate the initial outputs coming from the mathematical models. Doing so, stakeholders’ mapping was conducted in tandem with interviews for the detection of responsibilities, tasks, importance, and influence, followed by a structured questionnaire for registering the stakeholders’ perception on climate change impacts and relevant estimated hazards at the same deltaic case study ar...
Ocean Modelling
This study aims to systematically assess the impacts of projected climate change on episodic even... more This study aims to systematically assess the impacts of projected climate change on episodic events of sea level elevation in coastal areas of the Mediterranean, induced by severe weather conditions identified as deep depressions. We try to add new insight into the long-term, climatic timescale, and identification of affected parts of the Mediterranean coastal zone correlated to low atmospheric pressure systems, indicative of the Mediterranean basin during the 21st century. To achieve this goal, an integrated quantitative assessment is proposed by combining projections from available and established, greenhouse gasses emission/concentration scenarios (based on Representative Concentration Pathways; RCP 4.5 and 8.5) with advanced numerical modelling and statistical post-processing for the definition of cyclonic weather impacts on characteristic coastal zone hotspots. To this end, climate projections and outputs from three Regional Climate Models (RCMs) of the Med-CORDEX initiative at the Mediterranean basin scale are used and extensively evaluated against re-analysis data. These atmospheric datasets feed a robust storm surge model (MeCSS) for the simulation of barotropic hydrodynamics (sea level elevation and currents) thoroughly validated against in situ sea level observations by tide gauges. Our results corroborate a projected storminess attenuation for the end of the 21st century, yet local differentiations in storm surge maxima around the Mediterranean coastal zone are pinpointed. Moreover, a slight reduction of average storm-induced Mean Sea Level (MSL; component attributed solely to the meteorological residual of sea level elevation) is also apparent towards the end of the 21st century.
Journal of Marine Science and Engineering, 2021
In the present work, a methodological framework, based on nonstationary extreme value analysis of... more In the present work, a methodological framework, based on nonstationary extreme value analysis of nearshore sea-state parameters, is proposed for the identification of climate change impacts on coastal zone and port defense structures. The applications refer to the estimation of coastal hazards on characteristic Mediterranean microtidal littoral zones and the calculation of failure probabilities of typical rubble mound breakwaters in Greek ports. The proposed methodology hinges on the extraction of extreme wave characteristics and sea levels due to storm events affecting the coast, a nonstationary extreme value analysis of sea-state parameters and coastal responses using moving time windows, a fitting of parametric trends to nonstationary parameter estimates of the extreme value models, and an assessment of nonstationary failure probabilities on engineered port protection. The analysis includes estimation of extreme total water level (TWL) on several Greek coasts to approximate the ...
Journal of Marine Research, 2017
Oil spills in the ocean are a matter of concern due to the damaging effect they can have on coast... more Oil spills in the ocean are a matter of concern due to the damaging effect they can have on coastal and offshore resources. This work presents a review of present-day modeling techniques used in the mitigation of oil spills by booms, skimmers, chemical dispersants, and other equipment and the importance of the controlling parameters of these techniques. Three basic questions need to be addressed by oil spill models: (1) where the spill will move, (2) when will the spill get to the modeled endpoints, and (3) what will be its state when it arrives. The first two questions are relatively urgent, as far as response measures are concerned, and depend closely on the use of accurate data on winds, sea currents, and wave action as oil spill accidents evolve. Obtaining a reasonable answer to the third question lies in the use of reliable fate algorithms. Oil spill models can be divided in two types: Euleurian and Langragian. Adding to information regarding the oil type and its initial location, all oil spill models require data for the wind fields, sea state, sea-surface temperature, and currents, as well as other environmental parameters, if available. Such reliable data suit the needs of oil spill modeling predictions and are available daily at global, regional, and coastal scales within the broader scope of operational oceanography. Advanced oil spill models available at present use satellite synthetic aperture radar (SAR) images/data to detect possible oil slicks and assimilate slick and drifter observations to correct slick predictions. The emphasis of research and governmental institutions has been on improving 4D predictions obtained through simulation of oil spills backward in time to track the slicks back to their source. Such backward simulations, when integrated with ships' Automatic Identification Systems (AIS), will be used to locate the sources of oil slicks around the world's oceans and seas.
Ocean Modelling, 2016
Abstract The wave breaking of weak plungers over a relatively mild slope is investigated in this ... more Abstract The wave breaking of weak plungers over a relatively mild slope is investigated in this paper. Numerical modeling aspects are studied, concerning the propagation and breaking of shore-normal, nonlinear and regular waves. The two-dimensional (2-D) kinematics and dynamics (fluctuating flow features and large 2-D eddies) of the wave-induced flow on a vertical cross-section over the entire surf zone are simulated with the use of Smoothed Particle Hydrodynamics (SPH). The academic ‘open source’ code SPHysics v.2 is employed and the viscosity treatment is based on a Sub-Particle Scale (SPS) approach, similarly to the Large Eddy Simulations (LES) concept. Thorough analysis of the turbulent flow scales determines the necessary refinement of the spatial resolution. The initial particle discretization reaches down to the demarcation point between integral turbulence length scales and Taylor micro-scales. A convolution-type integration method is implemented for the transformation of scattered Lagrangian particle data to Eulerian values at fixed gauges. A heuristic technique of ensemble-averaging is used for the discrimination of the fluctuating flow components from coherent structures and ordered wave motion. Comparisons between numerical and experimental data give encouraging results for several wave features. The wave-induced mean flows are simulated plausibly, and even the ‘streaming’ effect near the bed is reproduced. The recurring vorticity patterns are derived, and coherent 2-D structures inside the surf zone are identified. Fourier spectral analysis of velocities reveals isotropy of 2-D fluctuating dynamics up to rather high frequencies in shear intensified regions. The simulated Reynolds stresses follow patterns that define the characteristic mechanism of wave breaking for weak plungers. Persisting discrepancies at the incipient breaking region confirm the need for fine, massively ‘parallel’ 3-D SPS-SPH simulations.
<p&amp... more <p>Thermaikos Gulf, located in the Northwestern Aegean Sea (Greece), is a marine ecosystem of major importance, not only environmentally (as an area of the deep water formation with contribution to the renewal of the North Aegean deep waters), but also due to the various socioeconomic activities associated with the area. Observational and simulated data are used to investigate the evolution of eutrophication events during the last two years in order to evaluate the current (2017-2019) quality state of the seawater in the Gulf. The quality of the marine environment of Thermaikos Gulf was appraised by measuring physical, chemical and biological parameters. Specific physical-chemical characteristics (temperature, salinity, density along with pH and dissolved oxygen) and biological parameters (chl-a and phytoplankton biomass) throughout the water column were evaluated by conducting in situ measurements during the sampling campaigns. Current fields, derived from a high-resolution 3-D ocean model, together with ADCP measurements, are used to describe the major circulation patterns, the river plume dynamics and the renewal pathways of the Gulf. The obtained results are discussed with regards to seasonal and spatial variability, and the water column stratification. Satellite ocean color data were also used to discuss the in-situ findings and confirm “Dirty” Sea and Red Tide phenomena, that were detected and analyzed based on the physical dynamics and especially the renewal patterns of the Gulf. Moreover, we compare these recent findings to respective observations from a previous period (1997 to 2007) to evaluate potential changes in the quality state of the Gulf with respect to meteorological and river discharge conditions.     </p>
Ocean Dynamics, 2024
Sea surface temperature (SST) is a key indicator of the global climate system and is directly rel... more Sea surface temperature (SST) is a key indicator of the global climate system and is directly related to marine and coastal ecosystems, weather conditions, and atmospheric events. Marine heat waves (MHWs), characterized by prolonged periods of high SST, affect significantly the oceanic water quality and thus, the local ecosystem, and marine and coastal activities. Given the anticipated increase of MHWs occurrences due to climate change, developing targeted strategies is needed to mitigate their impact. Accurate SST forecasting can significantly contribute to this cause and thus it comprises a crucial, yet challenging, task for the scientific community. Despite the wide variety of existing methods in the literature, the majority of them focus either on providing near-future SST forecasts (a few days until 1 month) or long-term predictions (decades to century) in climate scales based on hypothetical scenarios that need to be proven. In this work, we introduce a robust deep learning-based method for efficient SST forecasting of the interim future (1 year ahead) using high-resolution satellite-derived SST data. Our approach processes daily SST sequences lasting 1 year, along with five other relevant atmospheric variables, to predict the corresponding daily SST timeseries for the subsequent year. The novel method was deployed to accurately forecast SST over the northeastern Mediterranean Seas (Aegean, Ionian, Cretan Seas: AICS). Utilizing the effectiveness of well-established deep learning architectures, our method can provide accurate spatiotemporal predictions for multiple areas at once, without the need to be deployed separately at each sub-region. The modular design of the framework allows customization for different spatial and temporal resolutions according to use case requirements. The proposed model was trained and evaluated using available data from the AICS region over a 15-year time period (2008–2022). The results demonstrate the efficiency of our method in predicting SST variability, even for previously unseen data that are over 2 years in advance, in respect to the training set. The proposed methodology is a valuable tool that also can contribute to MHWs prediction.
Natural Hazards
The IANOS Medicane was one of the most severe storms that have formed in the Mediterranean Sea wi... more The IANOS Medicane was one of the most severe storms that have formed in the Mediterranean Sea with Category 2 Hurricane characteristics. The storm induced a significant increase in sea-level elevation along its pathway and caused storm surges at the central Ionian Sea with consequent impacts on coastal regions of the Ionian Islands and western Greece. An integrated approach, based on hydrodynamic ocean simulations, coupled to meteorological and coastal flooding simulations, is used in combination with field and satellite observations to analyze the marine weather conditions, the storm surge characteristics, and the coastal inundation characteristics due to the impact of IANOS Medicane in September 2020. The evolution of the Medicane and the respective storm surge in the ocean have been successfully recorded by the met-ocean simulations, part of an active public-access operational forecast system. Both wind and atmospheric pressure patterns affected the storm surge variability over the Ionian Sea. The direct intrusion of the Medicane from the central Mediterranean Sea toward the Ionian Sea formed storm surges over several coastal areas, even before the storm's landfall, due to the accompanying onshore currents. Storm surges in the order of 30 cm generated extensive flooding over lowland coastal areas, as confirmed by both satellite (Normalized Difference Water Index, NDWI) and numerical (coastal inundation modeling) data. Satellite-derived and simulated estimations showed that, in specific coastal regions, the run-up of seawater extended up to 200 m inland, depending on the hydraulic connectivity between the lowland areas, which determined the inundation extents during the storm surge.
2nd International Conference on Design and Management of Port, Coastal and Offshore Works (DMPCO), 2023
The Northern Thermaikos Gulf (NTG) is a semi-enclosed coastal region of the Aegean Sea facing sev... more The Northern Thermaikos Gulf (NTG) is a semi-enclosed coastal region of the Aegean Sea facing severe pollution events, characterized by anthropogenic and natural stresses such as intense industrial and agricultural activities, urban outflows, and several nutrient-rich river discharges. The hydrography and the hydrodynamic circulation patterns of NTG are revisited in this paper based on the findings of an integrated observational-modeling study, conducted during an annual cycle from June 2021 until May 2022. The main goal of the study is to investigate the environmental conditions that determine the renewal and water quality of the semi-enclosed basin. An operational system for predictions of ocean circulation and Lagrangian pathways to support search and rescue and first responders during pollution accidents over NTG was also developed providing daily 3-day forecasts.
Journal of Marine Science and Engineering, 2024
The summer of 2024 witnessed record-high sea surface temperatures (SST) across the Aegean, Ionian... more The summer of 2024 witnessed record-high sea surface temperatures (SST) across the Aegean, Ionian, and Cretan Seas (AICS), following unprecedented air heatwaves over the sea under a long-term warming trend of 0.46 °C/decade for the mean atmospheric temperature (1982–2024). The respective mean SST trend for the same period is even steeper, increasing by 0.59 °C/decade. With mean summer surface waters surpassing 28 °C, particularly in the Ionian Sea, the southern Cretan, and northern Aegean basins, this summer marked the warmest ocean conditions over the past four decades. Despite a relatively lower number of marine heatwaves (MHWs) compared to previous warm years, the duration and cumulative intensity of these events in 2024 were the highest on record, reaching nearly twice the levels seen in 2018, which was the warmest until now. Intense MHWs were recorded, especially in the northern Aegean, with extensive biological consequences to ecosystems like the Thermaikos Gulf, a recognized MHW hotspot. The strong downward atmospheric heat fluxes in the summer of 2024, following an interannual increasing four-decade trend, contributed to the extreme warming of the water masses together with other met-ocean conditions such as lateral exchanges and vertical processes. The high temperatures were not limited to the surface but extended to depths of 50 m in some regions, indicating a deep and widespread warming of the upper ocean. Mechanisms typically mitigating SST rises, such as the Black Sea water (BSW) inflow and coastal upwelling over the eastern Aegean Sea, were weaker in 2024. Cooler water influx from the BSW decreased, as indicated by satellite-derived chlorophyll-a concentrations, while upwelled waters from depths of 40 to 80 m at certain areas showed elevated temperatures, likely limiting their cooling effects on the surface. Prolonged warming of ocean waters in a semi-enclosed basin such as the Mediterranean and its marginal sea sub-basins can have substantial physical, biological, and socioeconomic impacts on the AICS. This research highlights the urgent need for targeted monitoring and mitigation strategies to address the growing impact of MHWs in the region.
5th International Congress on Applied Ichthyology, Oceanography, and Aquatic Environment (HydroMediT) , 2024
Thermaikos Gulf is an environmentally fragile coastal environment characterized by numerous anthr... more Thermaikos Gulf is an environmentally fragile coastal environment characterized by numerous anthropogenic and natural pressures. The environmentally protected areas along its western coasts and the large number of inhabitants that live over its northern and eastern coasts raise the need for systematic monitoring and prediction of the marine environment concerning the ocean circulation, weather conditions, sea level and wave characteristics, pollution events, coastal flooding, and freshwater input. Herein, we present recent advances of the Wave4Us operational platform that provides short-term forecasts of all the above conditions, freely accessed by local authorities, the research community, and the broader audience on a daily basis. Specified marine predictions (e.g., about pollution, flooding, and heatwaves) provide useful real-time information to first-level responders and managerial stakeholders during hazardous events that may threaten the quality of the coastal environment and the safety of the population residing on Thermaikos Gulf's littorals.
Annales Geophysicae, 1994
Hydrology
Storm surges due to severe weather events threaten low-land littoral areas by increasing the risk... more Storm surges due to severe weather events threaten low-land littoral areas by increasing the risk of seawater inundation of coastal floodplains. In this paper, we present recent developments of a numerical modelling system for coastal inundation induced by sea level elevation due to storm surges enhanced by astronomical tides. The proposed numerical code (CoastFLOOD) performs high-resolution (5 m × 5 m) raster-based, storage-cell modelling of coastal inundation by Manning-type equations in decoupled 2-D formulation at local-scale (20 km × 20 km) lowland littoral floodplains. It is fed either by outputs of either regional-scale storm surge simulations or satellite altimetry data for the sea level anomaly. The presented case studies refer to model applications at 10 selected coastal sites of the Ionian Sea (east-central Mediterranean Sea). The implemented regular Cartesian grids (up to 5 m) are based on Digital Elevation/Surface Models (DEM/DSM) of the Hellenic Cadastre. New updated f...
Natural Hazards
The IANOS Medicane was one of the most severe storms that have formed in the Mediterranean Sea wi... more The IANOS Medicane was one of the most severe storms that have formed in the Mediterranean Sea with Category 2 Hurricane characteristics. The storm induced a significant increase in sea-level elevation along its pathway and caused storm surges at the central Ionian Sea with consequent impacts on coastal regions of the Ionian Islands and western Greece. An integrated approach, based on hydrodynamic ocean simulations, coupled to meteorological and coastal flooding simulations, is used in combination with field and satellite observations to analyze the marine weather conditions, the storm surge characteristics, and the coastal inundation characteristics due to the impact of IANOS Medicane in September 2020. The evolution of the Medicane and the respective storm surge in the ocean have been successfully recorded by the met-ocean simulations, part of an active public-access operational forecast system. Both wind and atmospheric pressure patterns affected the storm surge variability over the Ionian Sea. The direct intrusion of the Medicane from the central Mediterranean Sea toward the Ionian Sea formed storm surges over several coastal areas, even before the storm's landfall, due to the accompanying onshore currents. Storm surges in the order of 30 cm generated extensive flooding over lowland coastal areas, as confirmed by both satellite (Normalized Difference Water Index, NDWI) and numerical (coastal inundation modeling) data. Satellite-derived and simulated estimations showed that, in specific coastal regions, the run-up of seawater extended up to 200 m inland, depending on the hydraulic connectivity between the lowland areas, which determined the inundation extents during the storm surge.
Continental Shelf Research, 2021
Thermaikos Gulf is a typical, river-fed, microtidal, semi-enclosed, coastal inlet of the east-cen... more Thermaikos Gulf is a typical, river-fed, microtidal, semi-enclosed, coastal inlet of the east-central Mediterranean Sea. It is an important coastal ecosystem susceptible to several anthropogenic pressures, strong river discharges and variable meteorological and ocean (met-ocean) conditions. One of the most significant environmental problems of the region is the occasional formation of extended eutrophication phenomena (red tides, mucilaginous aggregates), especially over the Northern Thermaikos Gulf (NTG). Herein, we investigate the contribution of hydrodynamic processes on the formation of such events, under the effects of different meteorological and river discharge conditions during the annual cycle. We conducted field observations (physical-chemical measurements), microscopy analysis of phytoplankton samples, satellite ocean color image analysis, and implemented high-resolution numerical hydrodynamic simulations with updated river discharge outflows to detect eutrophication events and correlate them with the prevailing physical processes and ocean circulation patterns. The eutrophication events were mainly associated with the dominance of southerly winds, which affect the ocean circulation over the NTG in three ways: i) they confined the surface waters in the northern parts of the NTG separating the waters masses between the northern and southern regions, ii) they contribute on the northward spreading of nutrient-rich brackish waters towards the northern parts of the Gulf, and iii) they impose an anticyclonic circulation, especially in the inner- and central-Gulf weakening its renewal process. Northerly winds contribute on the renewal of the Gulf imposing a two-layer flow, especially along the eastern coasts. The seasonal observational campaigns of the 2017–2018 period captured three eutrophication events (June–July 2017, December 2017, and May 2018) and two renewal periods (late-July 2017 and October 2017) that were favoured by the two aforementioned types of met-ocean synergy. New insight is provided on the mesoscale ocean circulation and sub-mesoscale local effects on eutrophication events in a typical microtidal coastal system of the east-central Mediterranean, where freshwater discharges by a multi-river inlet.
Applied Mathematical Modelling, 2021
The structure of the "Amphioxus sand" community in Thermaikos Bay was studied over a two-year per... more The structure of the "Amphioxus sand" community in Thermaikos Bay was studied over a two-year period. The examination of the collected 4,767 specimens revealed the presence of 141 species. Gastropoda and Polychaeta were the dominant taxa. Multivariate analyses showed high similarity, whereas samples discriminated according to sediment granulometry. The degradation of this community was evident in its structure as most of the recorded macrobenthic species characterizes the organically enriched sediments.
ΥΔΡΟΤΕΧΝΙΚΑ, Apr 6, 2017
Διερευνάται η επίδραση της κλιματικής αλλαγής στην εξέλιξη των μετεωρολογικών παλιρροιών στο Αιγα... more Διερευνάται η επίδραση της κλιματικής αλλαγής στην εξέλιξη των μετεωρολογικών παλιρροιών στο Αιγαίο και το Ιόνιο Πέλαγος και την παράκτια ζώνη της Ελλάδας. Η ανάλυση καλύπτει την περίοδο 1951-2100 (κλιματικό σενάριο Α1Β για τoν 21 ο αιώνα) και στηρίζεται σε προσομοιώσεις με ένα διδιάστατο υδροδυναμικό μοντέλο υψηλής χωρικής ανάλυση (GreCSSM). Η σύγκριση των προσομοιωμένων αποτελεσμάτων έναντι επί τόπου παρατηρήσεων με βάση στατιστικά μέτρα και δείκτες είναι ικανοποιητική. Παρουσιάζονται επίσης οι μελλοντικές τάσεις, η μεταβλητότητα και η συχνότητα εμφάνισης έντονων γεγονότων μετεωρολογικής παλίρροιας στις ελληνικές θάλασσες και την ελληνική παράκτια ζώνη. Δίνονται επίσης εκτιμήσεις για την τάση της πιθανής κλιματικής αλλαγής μέχρι το 2100, μαζί τις μέσες, ετήσιες και υπερετήσιες μέγιστες τιμές της θυελλογενούς ανύψωσης της θαλάσσιας στάθμης στο Αιγαίο και το Ιόνιο Πέλαγος.
Environmental Modeling & Assessment
Modern concepts in water resources management and related risk assessment necessitate participato... more Modern concepts in water resources management and related risk assessment necessitate participatory approaches with stakeholders having a key role in the respective processes. The objective of the article is to (i) integrate stakeholders’ opinions and preferences on identified hazards, i.e., coastal flooding, water scarcity, and heat stress, derived by physically based numerical modeling under current and future climate change conditions and attributed in the form of an Integrated deltaic risk index (IDRI) at a specific case study area, and (ii) investigate whether and how the stakeholders’ opinions differentiate the initial outputs coming from the mathematical models. Doing so, stakeholders’ mapping was conducted in tandem with interviews for the detection of responsibilities, tasks, importance, and influence, followed by a structured questionnaire for registering the stakeholders’ perception on climate change impacts and relevant estimated hazards at the same deltaic case study ar...
Ocean Modelling
This study aims to systematically assess the impacts of projected climate change on episodic even... more This study aims to systematically assess the impacts of projected climate change on episodic events of sea level elevation in coastal areas of the Mediterranean, induced by severe weather conditions identified as deep depressions. We try to add new insight into the long-term, climatic timescale, and identification of affected parts of the Mediterranean coastal zone correlated to low atmospheric pressure systems, indicative of the Mediterranean basin during the 21st century. To achieve this goal, an integrated quantitative assessment is proposed by combining projections from available and established, greenhouse gasses emission/concentration scenarios (based on Representative Concentration Pathways; RCP 4.5 and 8.5) with advanced numerical modelling and statistical post-processing for the definition of cyclonic weather impacts on characteristic coastal zone hotspots. To this end, climate projections and outputs from three Regional Climate Models (RCMs) of the Med-CORDEX initiative at the Mediterranean basin scale are used and extensively evaluated against re-analysis data. These atmospheric datasets feed a robust storm surge model (MeCSS) for the simulation of barotropic hydrodynamics (sea level elevation and currents) thoroughly validated against in situ sea level observations by tide gauges. Our results corroborate a projected storminess attenuation for the end of the 21st century, yet local differentiations in storm surge maxima around the Mediterranean coastal zone are pinpointed. Moreover, a slight reduction of average storm-induced Mean Sea Level (MSL; component attributed solely to the meteorological residual of sea level elevation) is also apparent towards the end of the 21st century.
Journal of Marine Science and Engineering, 2021
In the present work, a methodological framework, based on nonstationary extreme value analysis of... more In the present work, a methodological framework, based on nonstationary extreme value analysis of nearshore sea-state parameters, is proposed for the identification of climate change impacts on coastal zone and port defense structures. The applications refer to the estimation of coastal hazards on characteristic Mediterranean microtidal littoral zones and the calculation of failure probabilities of typical rubble mound breakwaters in Greek ports. The proposed methodology hinges on the extraction of extreme wave characteristics and sea levels due to storm events affecting the coast, a nonstationary extreme value analysis of sea-state parameters and coastal responses using moving time windows, a fitting of parametric trends to nonstationary parameter estimates of the extreme value models, and an assessment of nonstationary failure probabilities on engineered port protection. The analysis includes estimation of extreme total water level (TWL) on several Greek coasts to approximate the ...
Journal of Marine Research, 2017
Oil spills in the ocean are a matter of concern due to the damaging effect they can have on coast... more Oil spills in the ocean are a matter of concern due to the damaging effect they can have on coastal and offshore resources. This work presents a review of present-day modeling techniques used in the mitigation of oil spills by booms, skimmers, chemical dispersants, and other equipment and the importance of the controlling parameters of these techniques. Three basic questions need to be addressed by oil spill models: (1) where the spill will move, (2) when will the spill get to the modeled endpoints, and (3) what will be its state when it arrives. The first two questions are relatively urgent, as far as response measures are concerned, and depend closely on the use of accurate data on winds, sea currents, and wave action as oil spill accidents evolve. Obtaining a reasonable answer to the third question lies in the use of reliable fate algorithms. Oil spill models can be divided in two types: Euleurian and Langragian. Adding to information regarding the oil type and its initial location, all oil spill models require data for the wind fields, sea state, sea-surface temperature, and currents, as well as other environmental parameters, if available. Such reliable data suit the needs of oil spill modeling predictions and are available daily at global, regional, and coastal scales within the broader scope of operational oceanography. Advanced oil spill models available at present use satellite synthetic aperture radar (SAR) images/data to detect possible oil slicks and assimilate slick and drifter observations to correct slick predictions. The emphasis of research and governmental institutions has been on improving 4D predictions obtained through simulation of oil spills backward in time to track the slicks back to their source. Such backward simulations, when integrated with ships' Automatic Identification Systems (AIS), will be used to locate the sources of oil slicks around the world's oceans and seas.
Ocean Modelling, 2016
Abstract The wave breaking of weak plungers over a relatively mild slope is investigated in this ... more Abstract The wave breaking of weak plungers over a relatively mild slope is investigated in this paper. Numerical modeling aspects are studied, concerning the propagation and breaking of shore-normal, nonlinear and regular waves. The two-dimensional (2-D) kinematics and dynamics (fluctuating flow features and large 2-D eddies) of the wave-induced flow on a vertical cross-section over the entire surf zone are simulated with the use of Smoothed Particle Hydrodynamics (SPH). The academic ‘open source’ code SPHysics v.2 is employed and the viscosity treatment is based on a Sub-Particle Scale (SPS) approach, similarly to the Large Eddy Simulations (LES) concept. Thorough analysis of the turbulent flow scales determines the necessary refinement of the spatial resolution. The initial particle discretization reaches down to the demarcation point between integral turbulence length scales and Taylor micro-scales. A convolution-type integration method is implemented for the transformation of scattered Lagrangian particle data to Eulerian values at fixed gauges. A heuristic technique of ensemble-averaging is used for the discrimination of the fluctuating flow components from coherent structures and ordered wave motion. Comparisons between numerical and experimental data give encouraging results for several wave features. The wave-induced mean flows are simulated plausibly, and even the ‘streaming’ effect near the bed is reproduced. The recurring vorticity patterns are derived, and coherent 2-D structures inside the surf zone are identified. Fourier spectral analysis of velocities reveals isotropy of 2-D fluctuating dynamics up to rather high frequencies in shear intensified regions. The simulated Reynolds stresses follow patterns that define the characteristic mechanism of wave breaking for weak plungers. Persisting discrepancies at the incipient breaking region confirm the need for fine, massively ‘parallel’ 3-D SPS-SPH simulations.
<p&amp... more <p>Thermaikos Gulf, located in the Northwestern Aegean Sea (Greece), is a marine ecosystem of major importance, not only environmentally (as an area of the deep water formation with contribution to the renewal of the North Aegean deep waters), but also due to the various socioeconomic activities associated with the area. Observational and simulated data are used to investigate the evolution of eutrophication events during the last two years in order to evaluate the current (2017-2019) quality state of the seawater in the Gulf. The quality of the marine environment of Thermaikos Gulf was appraised by measuring physical, chemical and biological parameters. Specific physical-chemical characteristics (temperature, salinity, density along with pH and dissolved oxygen) and biological parameters (chl-a and phytoplankton biomass) throughout the water column were evaluated by conducting in situ measurements during the sampling campaigns. Current fields, derived from a high-resolution 3-D ocean model, together with ADCP measurements, are used to describe the major circulation patterns, the river plume dynamics and the renewal pathways of the Gulf. The obtained results are discussed with regards to seasonal and spatial variability, and the water column stratification. Satellite ocean color data were also used to discuss the in-situ findings and confirm “Dirty” Sea and Red Tide phenomena, that were detected and analyzed based on the physical dynamics and especially the renewal patterns of the Gulf. Moreover, we compare these recent findings to respective observations from a previous period (1997 to 2007) to evaluate potential changes in the quality state of the Gulf with respect to meteorological and river discharge conditions.     </p>
Ocean Dynamics, 2024
Sea surface temperature (SST) is a key indicator of the global climate system and is directly rel... more Sea surface temperature (SST) is a key indicator of the global climate system and is directly related to marine and coastal ecosystems, weather conditions, and atmospheric events. Marine heat waves (MHWs), characterized by prolonged periods of high SST, affect significantly the oceanic water quality and thus, the local ecosystem, and marine and coastal activities. Given the anticipated increase of MHWs occurrences due to climate change, developing targeted strategies is needed to mitigate their impact. Accurate SST forecasting can significantly contribute to this cause and thus it comprises a crucial, yet challenging, task for the scientific community. Despite the wide variety of existing methods in the literature, the majority of them focus either on providing near-future SST forecasts (a few days until 1 month) or long-term predictions (decades to century) in climate scales based on hypothetical scenarios that need to be proven. In this work, we introduce a robust deep learning-based method for efficient SST forecasting of the interim future (1 year ahead) using high-resolution satellite-derived SST data. Our approach processes daily SST sequences lasting 1 year, along with five other relevant atmospheric variables, to predict the corresponding daily SST timeseries for the subsequent year. The novel method was deployed to accurately forecast SST over the northeastern Mediterranean Seas (Aegean, Ionian, Cretan Seas: AICS). Utilizing the effectiveness of well-established deep learning architectures, our method can provide accurate spatiotemporal predictions for multiple areas at once, without the need to be deployed separately at each sub-region. The modular design of the framework allows customization for different spatial and temporal resolutions according to use case requirements. The proposed model was trained and evaluated using available data from the AICS region over a 15-year time period (2008–2022). The results demonstrate the efficiency of our method in predicting SST variability, even for previously unseen data that are over 2 years in advance, in respect to the training set. The proposed methodology is a valuable tool that also can contribute to MHWs prediction.
Natural Hazards
The IANOS Medicane was one of the most severe storms that have formed in the Mediterranean Sea wi... more The IANOS Medicane was one of the most severe storms that have formed in the Mediterranean Sea with Category 2 Hurricane characteristics. The storm induced a significant increase in sea-level elevation along its pathway and caused storm surges at the central Ionian Sea with consequent impacts on coastal regions of the Ionian Islands and western Greece. An integrated approach, based on hydrodynamic ocean simulations, coupled to meteorological and coastal flooding simulations, is used in combination with field and satellite observations to analyze the marine weather conditions, the storm surge characteristics, and the coastal inundation characteristics due to the impact of IANOS Medicane in September 2020. The evolution of the Medicane and the respective storm surge in the ocean have been successfully recorded by the met-ocean simulations, part of an active public-access operational forecast system. Both wind and atmospheric pressure patterns affected the storm surge variability over the Ionian Sea. The direct intrusion of the Medicane from the central Mediterranean Sea toward the Ionian Sea formed storm surges over several coastal areas, even before the storm's landfall, due to the accompanying onshore currents. Storm surges in the order of 30 cm generated extensive flooding over lowland coastal areas, as confirmed by both satellite (Normalized Difference Water Index, NDWI) and numerical (coastal inundation modeling) data. Satellite-derived and simulated estimations showed that, in specific coastal regions, the run-up of seawater extended up to 200 m inland, depending on the hydraulic connectivity between the lowland areas, which determined the inundation extents during the storm surge.
2nd International Conference on Design and Management of Port, Coastal and Offshore Works (DMPCO), 2023
The Northern Thermaikos Gulf (NTG) is a semi-enclosed coastal region of the Aegean Sea facing sev... more The Northern Thermaikos Gulf (NTG) is a semi-enclosed coastal region of the Aegean Sea facing severe pollution events, characterized by anthropogenic and natural stresses such as intense industrial and agricultural activities, urban outflows, and several nutrient-rich river discharges. The hydrography and the hydrodynamic circulation patterns of NTG are revisited in this paper based on the findings of an integrated observational-modeling study, conducted during an annual cycle from June 2021 until May 2022. The main goal of the study is to investigate the environmental conditions that determine the renewal and water quality of the semi-enclosed basin. An operational system for predictions of ocean circulation and Lagrangian pathways to support search and rescue and first responders during pollution accidents over NTG was also developed providing daily 3-day forecasts.
Kallipos - Hellenic Academic eBooks, 2015
Το βιβλίο απευθύνεται σε Πολιτικούς Μηχανικούς αλλά και Μηχανικούς ή Επιστήμονες άλλων ειδικοτήτω... more Το βιβλίο απευθύνεται σε Πολιτικούς Μηχανικούς αλλά και Μηχανικούς ή Επιστήμονες άλλων ειδικοτήτων που βρίσκονται στη φάση των προπτυχιακών ή και μεταπτυχιακών τους σπουδών για θέματα Παράκτιας Μηχανικής και Θαλάσσιας Περιβαλλοντικής Υδραυλικής.
Θα περιλαμβάνει έννοιες της παράκτιας φυσικής ωκεανογραφίας (φυσικές παράμετροι του θαλασσίου νερού, μετρήσεις και ανάλυση των παραμέτρων αυτών και χαρακτηρισμός θαλασσίων μαζών).
Θα περιέχει θέματα δυναμικής ωκεανογραφίας (παράκτια ρεύματα, ανεμογενή, αδρανιακά και γεωστροφικά ρεύματα) οι βασικές εξισώσεις περιγραφής των φαινομένων αυτών, απλοποιημένες εξισώσεις υπολογισμού, μεθοδολογίες μετρήσεων αλλά και σύγχρονες τεχνικές άντλησης και επεξεργασίας μετρήσεων (δορυφορικές εικόνες, αλτιμετρία κλπ.).
Θα αναλύονται οι μεταβολές της ελεύθερης στάθμης της θάλασσας και τα φυσικά αίτια που την προκαλούν όπως αστρονομική παλίρροια, σεισμικές μεταβολές του θαλάσσιου πυθμένα (tsounamis), μετεωρολογικά συστήματα - μετεωρολογική παλίρροια (storm surge) και η κλιματική αλλαγή. Θα αναλύονται οι επιπτώσεις από τις παράκτιες πλημμύρες και θα δίδονται στοιχεία για αναλυτικούς απλοποιημένους υπολογισμούς αλλά και υπολογισμούς της τρωτότητας της παράκτιας ζώνης.
Για την κατανόηση των διεργασιών μεταφοράς και διάχυσης ρύπων στο θαλάσσιο περιβάλλον, στο βιβλίο θα παρουσιάζονται οι διεργασίες αυτές και η μαθηματική τους προσομοίωση, αλλά και οι φυσικές, χημικές και βιολογικές παράμετροι και διεργασίες στο θαλάσσιο οικοσύστημα.
Με δεδομένη την αυξανόμενη απαίτηση για περιβαλλοντικά ασφαλή και τεχνικά ορθή διάθεση επεξεργασμένων λυμάτων στο θαλάσσιο περιβάλλον, θα συμπεριλαμβάνεται και κεφάλαιο για τους υδραυλικούς υπολογισμούς υπoβρυχίων συστημάτων διάθεσης λυμάτων αλλά και υπολογισμού της αραίωσης - διάλυσης στο κοντινό και το μακρινό πεδίο.
Τέλος, συμπεριλαμβάνονται μαθηματικά ομοιώματα και μεθοδολογίες αριθμητικής τους επίλυσης για θέματα παράκτιας υδροδυναμικής κυκλοφορίας, μετεωρολογικής παλίρροιας και μεταφοράς-διασποράς ρύπων.
One of the most challenging tasks in modelling marine processes is the description of fine sedime... more One of the most challenging tasks in modelling marine processes is the description of fine sediment dynamics. Cohesive sediments enter the marine environment from physical or anthropogenic sources and affect physical, biochemical and biological processes. Their movement and fate is the result of various physical processes and forces that interact with one another. These processes extend from the scale of the microfloc and the effects of the small-scale forces, like cohesion, to the macroscale of the hydrodynamic field and the effects the local hydrodynamics. The present chapter aims at covering the most significant processes that control the motion and fate of cohesive sediment in microtidal areas, focusing both on the physical and mathematical description of the phenomena.
More specifically, the physical processes that take place in the water column and near the seabed and the corresponding mass-exchanges between them are presented and analyzed. The motion of sediment in suspension is determined by the seawater velocities and local shear, the stratification of the water column and the characteristics of the cohesive flocs that control the processes of advection, dispersion flocculation-deflocculation and settling. Near-bed processes are highly dependant on the prevailing shear stress conditions and the characteristics of the sedimentary matter and control the mass-exchanges between the water column and the seabed; these processes include deposition, self-weight consolidation, resuspension and erosion of the bed.
Modelling results from a three-dimensional sediment transport model, formulated based on the aforementioned considerations, are also presented and discussed; the applications were performed in the domain of Thermaikos, a microtidal gulf in the NW Aegean Sea (Eastern Mediterranean), for different (point or distributed) sources of fine particulate matter, including river-borne matter, physically and mechanically (trawling-induced) eroded sediments and aeolian transported dust.
8th MonGOOS Annual Meeting & Workshop, 2019
Thermaikos Gulf, located in the Northwestern Aegean Sea, is a marine ecosystem of major importanc... more Thermaikos Gulf, located in the Northwestern Aegean Sea, is a marine ecosystem of major importance, not only environmentally, but also due to the various socioeconomic activities associated with the area. The present observational study aims to investigate the current (2017-2019) quality state of seawater and seabed in the Gulf. The quality of the marine environment of Thermaikos Gulf was appraised by measuring physical, chemical and biological parameters. Water and sediment samples were seasonally collected from three sampling stations located at the inner part of Thermaikos Gulf. Specific physical-chemical characteristics (temperature, salinity, density along with pH and dissolved oxygen) throughout the water column were evaluated by conducting in situ measurements during the sampling campaigns. In situ processing of the water density data enabled the determination of the water column stratification. Afterwards, water samples were collected from three levels of the water column (surface, pycnocline and bottom), in order to investigate the variations of the measured parameters over the water column depth. The studied parameters of water samples included chemical parameters, such as ammonium nitrogen, nitrites, nitrates, silicates, phosphates and total phosphorus and biological parameters focusing on phytoplankton and protozooplankton species composition, abundance and biomass. Sediment samples were collected with a standard VanVeen grab from each sampling station. The obtained results are discussed with regards to seasonal and spatial variability, and water column stratification. Satellite ocean color data were also used to discuss the in situ findings and confirm "Dirty" Sea and Red Tide phenomena that were detected and analyzed based on the physical dynamics and especially the renewal of the Gulf.
1st Scientific Conference PANACEA , 2019
Intense storm surge events threaten low-elevation coastal areas with large inundation risk. In th... more Intense storm surge events threaten low-elevation coastal areas with large inundation risk. In the past, storm surges have
been responsible for human casualties, loss of land and property, damages to onshore infrastructure, harbor structures
and coastal defenses. Global climate change is associated with impacts on the regional regime of sea level variations,
i.e. influencing the intensity and frequency of occurrence of extreme storm surges. In the present work, the storm surge
patterns in the coastal zone of the Mediterranean Sea are investigated for a period from 1971 to 2100 covering the
observed past- and estimated future-climate. The future variation trends of the storm-induced extremes of sea level in
the Mediterranean are also explored. The surge-induced sea surface height (SSH) in coastal areas is numerically
simulated with MeCSS (Mediterranean Climatic Storm Surge) model. MeCSS is a 2-DH barotropic model for
hydrodynamic ocean circulation based on the depth-averaged shallow water equations (Androulidakis et al., 2015;
Makris et al., 2016). Simulations cover three 35-year time-windows, i.e. the Reference (1971-2005), short-term Future
(2021-2055) and long-term Future (2066-2100) periods. The atmospheric forcing of the MeCSS model consists of wind
(velocity and direction) and atmospheric pressure fields produced by three Regional Climate Models (RCMs), namely
the CMCC-CCLM, CNRM-ALADIN, GUF-CCLM-NEMO, implemented in the framework of the MED-CORDEX
initiative (https://www.medcordex.eu/; Ruti et al., 2016). Historical climate data by all the RCMs for the Reference
Period are validated against ECMWF reanalyses, based on assimilation system fields produced under CERA-20C
(https://www.ecmwf.int/en/research/projects/cera). Estimations of future climate change projections from the RCMs are
based on two climatic scenarios of the Representative Concentration Pathways, RCP4.5 and RCP8.5 (IPCC, 2014). In
situ SSH observations from tide gauges by national hydrographic services, during the last 50 years, are used to evaluate
the performance skill of MeCSS model in several coastal areas of focus. Appropriate statistical measures (Storm Surge
Index, high-order percentiles, probabilities of exceedance, etc.) of intra- and inter-annual extremes reveal the agreement
between historical sea-level data and simulation outputs. This confirms the ability of MeCSS to estimate the episodic
sea surface response to intense climatic conditions. Our results support that there is a general decreasing trend only in
the averaged patterns of storminess under the considered climate scenarios. However, the magnitudes of SSH maxima
are estimated to increase locally in certain regions of the Mediterranean during the 21st century. Different topographical
characteristics of the regional seas (e.g. northern Adriatic and Aegean Seas, Gulf of Gabes, etc.) in the Mediterranean
basin have a significant influence on the variability of storm surge maxima.
4th International Conference on Advances in Extreme Value Analysis and Application to Natural Hazard (EVAN), 2019
Global climate change is closely associated with extreme marine events of higher intensity and fr... more Global climate change is closely associated with extreme marine events of higher intensity and frequency, and is generally considered as one of the main causes of nonstationarity in marine signals. In the present work the Generalized Extreme Value (GEV) distribution function is used within a nonstationarity framework to assess extreme storm surges for selected coastal regions in the Mediterranean Sea, both for the present and the future climate. The storm surge-induced sea level data in coastal regions result from high-resolution simulations with MeCSS, a 2-DH barotropic model of hydrodynamic ocean circulation (Androulidakis et al., 2015; Makris et al. 2016), and cover the reference (1971-2005), the short-term (2021-2055) and the long-term (2061-2095) future climate. The atmospheric forcing of the model consists of wind (velocity and direction) and atmospheric pressure fields by three high-resolution Regional Climate Models (RCMs), namely CMCC, CNRM and GUF, implemented in the framework of the MED-CORDEX initiative (https://www.medcordex.eu/; Ruti et al., 2016). Historical climate data by all the RCMs for the reference period are validated against ECMWF reanalyses, based on assimilation system fields produced under CERA-20C. Future estimations of RCMs are based on RCP 4.5 and RCP 8.5 climate scenarios (IPCC, 2014). For each study period, the parameters of the nonstationary GEV distribution are specified as functions of time-varying covariates and estimated using Vector Generalized Linear and Additive models (VGLM and VGAM; Yee, 2015), which are semi-parametric regression type models. The nonstationary models use multiple covariates, namely time, teleconnection indices such as the North Atlantic Oscillation (NAO) index, deep depressions, and wind fields. Bayesian model averaging is then used to generate a statistical model accounting for multiple possible storm surge covariates. Time-dependent return levels for reference and future timespans are produced for several return periods of interest and conclusions are extracted regarding the effects of climate change on storm surge extremes.
International Coordination Workshop (ICW4) of the Coastal and Shelf Seas Task Team (COSS-TT) & ARCOM Pilot Workshop, 2015
Proceedings of the 12th Panhellenic Symposium of Oceanography and Fisheries, Jun 2018
Thermaikos Gulf, located in the Northwestern Aegean Sea, is a marine ecosystem of major importanc... more Thermaikos Gulf, located in the Northwestern Aegean Sea, is a marine ecosystem of major importance, not only environmentally, but also due to the various socioeconomic activities associated with area (Krestenitis et al., 2012). A multi-platform observational study was conducted in summer, autumn and winter 2017 to investigate the current quality state of seawater and seabed. Water and sediment samples were seasonally collected from three sampling stations located at the northern part of Thermaikos Gulf: two stations at the outfall areas of the Thessaloniki's Wastewater Treatment Plants (WTP) and one very close to the city's seafront. The measurements include the physical (CTD), chemical and biological characteristics of the water column (phytoplankton and protozooplankton community) and seabed (macro-invertebrates). Satellite data were also used to discuss the in situ findings. Very large temperature and chl-a differences were observed between Thessaloniki (inner) and Aggelohori (outer) Gulf in December. Very high surface concentrations of phosphates and total phosphorus were also measured, especially in Thessaloniki. The phytoplankton biomass was extremely high in the inner Gulf on July after the “dirty” Sea phenomenon and on December when strong Mesodinium rubrum red tide were observed in the inner Gulf. Polychaetes and mollusks prevailed in the sediment fauna. The density of macro-invertebrates was found very increased close to the seafront of Thessaloniki.Significant differences were detected in physical and biochemical characteristics between the inner and outer Gulf. More brackish waters were measured in summer than in fall and winter.
SPHERIC newsletter 15th issue, 2012
Following our previous work (Makris et al., 2010), SPHysics code v.2 (Gómez-Gesteira et al., 2010... more Following our previous work (Makris et al., 2010), SPHysics code v.2 (Gómez-Gesteira et al., 2010) has been thoroughly calibrated and validated against experimental data for wave propagation and weak plunging breaking on a smooth mild sloping beach placed inside a laboratory scale wave flume (Stansby & Feng, 2005). The LES-type Smagorinsky model is used for the viscosity treatment. Spatial resolution is based on the size of expected turbulent eddies. Discretization values dx
approach the demarcation range between integral turbulence length scales (energy-containing eddies) and Taylor micro-scales (inertial sub-range).