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Dr. Anastasios Papadopoulos
Hellenic Centre for Marine Research, Athens, Greece

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0 Numerical Weather Prediction
0 flash floods
0 model evaluation
0 Operational meteorology and hydrometeorology
0 Water and energy cycle

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Numerical Weather Prediction
flash floods
model evaluation

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Journal article
Published: 13 July 2021 in Atmosphere
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A hydrometeorological forecasting system has been operating at the Institute of Marine Biological Resources and Inland Waters (IMBRIW) of the Hellenic Centre for Marine Research (HCMR) since September 2015. The system consists of the Advanced Weather Research and Forecasting (WRF-ARW) model, the WRF-Hydro hydrological model, and the HEC-RAS hydraulic–hydrodynamic model. The system provides daily 120 h weather forecasts focusing on Greece (4 km horizontal resolution) and hydrological forecasts for the Spercheios and Evrotas rivers in Greece (100 m horizontal resolution), also providing flash flood inundation forecasts when needed (5 m horizontal resolution). The main aim of this study is to evaluate precipitation forecasts produced in a 4-year period (September 2015–August 2019) using measurements from meteorological stations across Greece. Water level forecasts for the Evrotas and Spercheios rivers were also evaluated using measurements from hydrological stations operated by the IMBRIW. Moreover, the forecast skill of the chained meteorological–hydrological–hydraulic operation of the system was investigated during a catastrophic flash flood in the Evrotas river. The results indicated that the system provided skillful precipitation and water level forecasts. The best evaluation results were yielded during rainy periods. They also demonstrated that timely flash flood forecasting products could benefit flood warning and emergency responses due to their efficiency and increased lead time.

ACS Style

George Varlas; Anastasios Papadopoulos; George Papaioannou; Elias Dimitriou. Evaluating the Forecast Skill of a Hydrometeorological Modelling System in Greece. Atmosphere 2021, 12, 902 .

AMA Style

George Varlas, Anastasios Papadopoulos, George Papaioannou, Elias Dimitriou. Evaluating the Forecast Skill of a Hydrometeorological Modelling System in Greece. Atmosphere. 2021; 12 (7):902.

Chicago/Turabian Style

George Varlas; Anastasios Papadopoulos; George Papaioannou; Elias Dimitriou. 2021. "Evaluating the Forecast Skill of a Hydrometeorological Modelling System in Greece." Atmosphere 12, no. 7: 902.

Journal article
Published: 08 July 2021 in Sensors
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The monitoring of the water stage in streams and rivers is essential for the sustainable management of water resources, particularly for the estimation of river discharges, the protection against floods and the design of hydraulic works. The Institute of Marine Biological Resources and Inland Waters of the Hellenic Centre for Marine Research (HCMR) has developed and operates automatic stations in rivers of Greece, which, apart from their monitoring role, offer opportunities for testing new monitoring equipment. This paper compares the performance of a new ultrasonic sensor, a non-contact water stage monitoring instrument, against a pressure transducer, both installed at the same location in an urban stream of the metropolitan area of Athens. The statistical and graph analysis of the almost one-year concurrent measurements from the two sensors revealed that stage differences never exceeded 7%, while the ultrasonic measurements were most of the time higher than the respective pressure transducer ones during the low flow conditions of the dry period and lower during the wet period of the year, when high flow events occurred. It is also remarkable that diurnal air temperature variations under stable hydrologic conditions had an impact on the measured stage from the ultrasonic sensor, which varied its stage measurements within a small but non-negligible range, while the pressure transducer did not practically fluctuate. Despite a slightly increased sensitivity of the ultrasonic sensor to meteorological conditions, the paper concludes that non-contact sensors for the monitoring of the water stage in rivers can be useful, especially where danger for possible damage of submersible instruments is increased.

ACS Style

Yiannis Panagopoulos; Anastasios Papadopoulos; Georgios Poulis; Emmanouil Nikiforakis; Elias Dimitriou. Assessment of an Ultrasonic Water Stage Monitoring Sensor Operating in an Urban Stream. Sensors 2021, 21, 4689 .

AMA Style

Yiannis Panagopoulos, Anastasios Papadopoulos, Georgios Poulis, Emmanouil Nikiforakis, Elias Dimitriou. Assessment of an Ultrasonic Water Stage Monitoring Sensor Operating in an Urban Stream. Sensors. 2021; 21 (14):4689.

Chicago/Turabian Style

Yiannis Panagopoulos; Anastasios Papadopoulos; Georgios Poulis; Emmanouil Nikiforakis; Elias Dimitriou. 2021. "Assessment of an Ultrasonic Water Stage Monitoring Sensor Operating in an Urban Stream." Sensors 21, no. 14: 4689.

Journal article
Published: 31 May 2021 in Hydrology
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Water resources, especially riverine ecosystems, are globally under qualitative and quantitative degradation due to human-imposed pressures. High-temporal-resolution data obtained from automatic stations can provide insights into the processes that link catchment hydrology and streamwater chemistry. The scope of this paper was to investigate the statistical behavior of high-frequency measurements at sites with known hydromorphological and pollution pressures. For this purpose, hourly time series of water levels and key water quality indicators (temperature, electric conductivity, and dissolved oxygen concentrations) collected from four automatic monitoring stations under different hydromorphological conditions and pollution pressures were statistically elaborated. Based on the results, the hydromorphological conditions and pollution pressures of each station were confirmed to be reflected in the results of the statistical analysis performed. It was proven that the comparative use of the statistics and patterns of the water level and quality high-frequency time series could be used in the interpretation of the current site status as well as allowing the detection of possible changes. This approach can be used as a tool for the definition of thresholds, and will contribute to the design of management and restoration measures for the most impacted areas.

ACS Style

Angeliki Mentzafou; George Varlas; Anastasios Papadopoulos; Georgios Poulis; Elias Dimitriou. Assessment of Automatically Monitored Water Levels and Water Quality Indicators in Rivers with Different Hydromorphological Conditions and Pollution Levels in Greece. Hydrology 2021, 8, 86 .

AMA Style

Angeliki Mentzafou, George Varlas, Anastasios Papadopoulos, Georgios Poulis, Elias Dimitriou. Assessment of Automatically Monitored Water Levels and Water Quality Indicators in Rivers with Different Hydromorphological Conditions and Pollution Levels in Greece. Hydrology. 2021; 8 (2):86.

Chicago/Turabian Style

Angeliki Mentzafou; George Varlas; Anastasios Papadopoulos; Georgios Poulis; Elias Dimitriou. 2021. "Assessment of Automatically Monitored Water Levels and Water Quality Indicators in Rivers with Different Hydromorphological Conditions and Pollution Levels in Greece." Hydrology 8, no. 2: 86.

Journal article
Published: 01 April 2021 in Sustainability
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Nature-based solutions (NBS) are being deployed around the world in order to address hydrometeorological hazards, including flooding, droughts, landslides and many others. The term refers to techniques inspired, supported and copied from nature, avoiding large constructions and other harmful interventions. In this work the development and evaluation of an NBS applied to the Spercheios river basin in Central Greece is presented. The river is susceptible to heavy rainfall and bank overflow, therefore the intervention selected is a natural water retention measure that aims to moderate the impact of flooding and drought in the area. After the deployment of the NBS, we examine the benefits under current and future climate conditions, using various climate change scenarios. Even though the NBS deployed is small compared to the rest of the river, its presence leads to a decrease in the maximum depth of flooding, maximum velocity and smaller flooded areas. Regarding the subsurface/groundwater storage under current and future climate change and weather conditions, the NBS construction seems to favor long-term groundwater recharge.

ACS Style

Christos Spyrou; Michael Loupis; Νikos Charizopoulos; Ilektra Apostolidou; Angeliki Mentzafou; George Varlas; Anastasios Papadopoulos; Elias Dimitriou; Depy Panga; Lamprini Gkeka; Paul Bowyer; Susanne Pfeifer; Sisay Debele; Prashant Kumar. Evaluating Nature-Based Solution for Flood Reduction in Spercheios River Basin under Current and Future Climate Conditions. Sustainability 2021, 13, 3885 .

AMA Style

Christos Spyrou, Michael Loupis, Νikos Charizopoulos, Ilektra Apostolidou, Angeliki Mentzafou, George Varlas, Anastasios Papadopoulos, Elias Dimitriou, Depy Panga, Lamprini Gkeka, Paul Bowyer, Susanne Pfeifer, Sisay Debele, Prashant Kumar. Evaluating Nature-Based Solution for Flood Reduction in Spercheios River Basin under Current and Future Climate Conditions. Sustainability. 2021; 13 (7):3885.

Chicago/Turabian Style

Christos Spyrou; Michael Loupis; Νikos Charizopoulos; Ilektra Apostolidou; Angeliki Mentzafou; George Varlas; Anastasios Papadopoulos; Elias Dimitriou; Depy Panga; Lamprini Gkeka; Paul Bowyer; Susanne Pfeifer; Sisay Debele; Prashant Kumar. 2021. "Evaluating Nature-Based Solution for Flood Reduction in Spercheios River Basin under Current and Future Climate Conditions." Sustainability 13, no. 7: 3885.

Special issue paper
Published: 29 March 2021 in Hydrological Processes
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A common source of uncertainty in flood inundation forecasting is the hydrograph used. Given the role of sea‐air‐hydro‐land chain processes on the water cycle, flood hydrographs in coastal areas can be indirectly affected by sea state. This study investigates sea‐state effects on precipitation, discharge, and flood inundation forecasting implementing atmospheric, ocean wave, hydrological, and hydraulic‐hydrodynamic coupled models. The Chemical Hydrological Atmospheric Ocean wave System (CHAOS) was used for coupled hydro‐meteorological‐wave simulations “accounting” or “not accounting” the impact of sea state on precipitation and, subsequently, on flood hydrograph. CHAOS includes the WRF‐Hydro hydrological model and the WRF‐ARW meteorological model two‐way coupled with the WAM wave model through the OASIS3‐MCT coupler. Subsequently, the 2D HEC‐RAS hydraulic‐hydrodynamic model was forced by the flood hydrographs and map the inundated areas. A flash flood event occurred on 15 November 2017 in Mandra, Attica, Greece, causing 24 fatalities, and damages was selected as case study. The calibration of models was performed exploiting historical flood records and previous studies. Human interventions such as hydraulic works and the urban areas were included in the hydraulic modeling geometry domain. The representation of the resistance caused by buildings was based on Unmanned Aerial System (UAS) data while the local elevation rise method was used in the urban‐flood simulation. The flood extent results were assessed using the Critical Success Index (CSI), and CSI penalize. Integrating sea‐state affected the forecast of precipitation and discharge peaks, causing up to +24% and from ‐8% to +36% differences, respectively, improving inundation forecast by 4.5% and flooding additional ~70 building blocks. The precipitation forcing time step was also highlighted as significant factor in such a small‐scale flash flood. The integrated multidisciplinary methodological approach could be adopted in operational forecasting for civil protection applications facilitating the protection of socio‐economic activities and human lives during similar future events.

ACS Style

George Papaioannou; George Varlas; Anastasios Papadopoulos; Athanasios Loukas; Petros Katsafados; Elias Dimitriou. Investigating sea‐state effects on flash flood hydrograph and inundation forecasting. Hydrological Processes 2021, 35, 1 .

AMA Style

George Papaioannou, George Varlas, Anastasios Papadopoulos, Athanasios Loukas, Petros Katsafados, Elias Dimitriou. Investigating sea‐state effects on flash flood hydrograph and inundation forecasting. Hydrological Processes. 2021; 35 (4):1.

Chicago/Turabian Style

George Papaioannou; George Varlas; Anastasios Papadopoulos; Athanasios Loukas; Petros Katsafados; Elias Dimitriou. 2021. "Investigating sea‐state effects on flash flood hydrograph and inundation forecasting." Hydrological Processes 35, no. 4: 1.

Journal article
Published: 15 March 2021 in Water Research
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Understanding the climatic drivers of eutrophication is critical for lake management under the prism of the global change. Yet the complex interplay between climatic variables and lake processes makes prediction of phytoplankton biomass a rather difficult task. Quantifying the relative influence of climate-related variables on the regulation of phytoplankton biomass requires modelling approaches that use extensive field measurements paired with accurate meteorological observations. In this study we used climate and lake related variables obtained from the ERA5-Land reanalysis dataset combined with a large dataset of in-situ measurements of chlorophyll-a and phytoplankton biomass from 50 water bodies to develop models of phytoplankton related responses as functions of the climate reanalysis data. We used chlorophyll-a and phytoplankton biomass as response metrics of phytoplankton growth and we employed two different modelling techniques, boosted regression trees (BRT) and generalized additive models for location scale and shape (GAMLSS). According to our results, the fitted models had a relatively high explanatory power and predictive performance. Boosted regression trees had a high pseudo R2 with the type of the lake, the total layer temperature, and the mix-layer depth being the three predictors with the higher relative influence. The best GAMLSS model retained mix-layer depth, mix-layer temperature, total layer temperature, total runoff and 10-m wind speed as significant predictors (p<0.001). Regarding the phytoplankton biomass both modelling approaches had less explanatory power than those for chlorophyll-a. Concerning the predictive performance of the models both the BRT and GAMLSS models for chlorophyll-a outperformed those for phytoplankton biomass. Overall, we consider these findings promising for future limnological studies as they bring forth new perspectives in modelling ecosystem responses to a wide range of climate and lake variables. As a concluding remark, climate reanalysis can be an extremely useful asset for lake research and management.

ACS Style

Konstantinos Stefanidis; George Varlas; Aikaterini Vourka; Anastasios Papadopoulos; Elias Dimitriou. Delineating the relative contribution of climate related variables to chlorophyll-a and phytoplankton biomass in lakes using the ERA5-Land climate reanalysis data. Water Research 2021, 196, 117053 .

AMA Style

Konstantinos Stefanidis, George Varlas, Aikaterini Vourka, Anastasios Papadopoulos, Elias Dimitriou. Delineating the relative contribution of climate related variables to chlorophyll-a and phytoplankton biomass in lakes using the ERA5-Land climate reanalysis data. Water Research. 2021; 196 ():117053.

Chicago/Turabian Style

Konstantinos Stefanidis; George Varlas; Aikaterini Vourka; Anastasios Papadopoulos; Elias Dimitriou. 2021. "Delineating the relative contribution of climate related variables to chlorophyll-a and phytoplankton biomass in lakes using the ERA5-Land climate reanalysis data." Water Research 196, no. : 117053.

Technical note
Published: 20 February 2021 in Hydrology
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The monitoring of surface waters is of fundamental importance for their preservation under good quantitative and qualitative conditions, as it can facilitate the understanding of the actual status of water and indicate suitable management actions. Taking advantage of the experience gained from the coordination of the national water monitoring program in Greece and the available funding from two ongoing infrastructure projects, the Institute of Inland Waters of the Hellenic Centre for Marine Research has developed the first homogeneous real-time network of automatic water monitoring across many Greek rivers. In this paper, its installation and maintenance procedures are presented with emphasis on the data quality checks, based on values range and variability tests, before their online publication and dissemination to end-users. Preliminary analyses revealed that the water pH and dissolved oxygen (DO) sensors and produced data need increased maintenance and quality checks respectively, compared to the more reliably recorded water stage, temperature (T) and electrical conductivity (EC). Moreover, the data dissemination platform and selected data visualization options are demonstrated and the need for both this platform and the monitoring network to be maintained and potentially expanded after the termination of the funding projects is highlighted.

ACS Style

Yiannis Panagopoulos; Anna Konstantinidou; Konstantinos Lazogiannis; Anastasios Papadopoulos; Elias Dimitriou. A New Automatic Monitoring Network of Surface Waters in Greece: Preliminary Data Quality Checks and Visualization. Hydrology 2021, 8, 33 .

AMA Style

Yiannis Panagopoulos, Anna Konstantinidou, Konstantinos Lazogiannis, Anastasios Papadopoulos, Elias Dimitriou. A New Automatic Monitoring Network of Surface Waters in Greece: Preliminary Data Quality Checks and Visualization. Hydrology. 2021; 8 (1):33.

Chicago/Turabian Style

Yiannis Panagopoulos; Anna Konstantinidou; Konstantinos Lazogiannis; Anastasios Papadopoulos; Elias Dimitriou. 2021. "A New Automatic Monitoring Network of Surface Waters in Greece: Preliminary Data Quality Checks and Visualization." Hydrology 8, no. 1: 33.

Journal article
Published: 09 February 2021 in Remote Sensing
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Atmospheric-chemical coupled models usually parameterize sea-salt aerosol (SSA) emissions using whitecap fraction estimated considering only wind speed and ignoring sea state. This approach may introduce inaccuracies in SSA simulation. This study aims to assess the impact of sea state on SSA modeling, applying a new parameterization for whitecap fraction estimation based on wave age, calculated by the ratio between wave phase velocity and wind speed. To this end, the new parameterization was incorporated in the coupled Chemical Hydrological Atmospheric Ocean wave modeling System (CHAOS). CHAOS encompasses the wave model (WAM) two-way coupled through the OASIS3-MCT coupler with the Advanced Weather Research and Forecasting model coupled with Chemistry (WRF-ARW-Chem) and, thus, enabling the concurrent simulation of SSAs, wind speed and wave phase velocity. The simulation results were evaluated against in-situ and lidar measurements at 2 stations in Greece (Finokalia on 4 and 15 July 2014 and Antikythera-PANGEA on 15 September 2018). The results reveal significant differences between the parameterizations with the new one offering a more realistic representation of SSA levels in some layers of the lower atmosphere. This is attributed to the enhancement of the bubble-bursting mechanism representation with air-sea processes controlling whitecap fraction. Our findings also highlight the contribution of fresh wind-generated waves to SSA modeling.

ACS Style

George Varlas; Eleni Marinou; Anna Gialitaki; Nikolaos Siomos; Konstantinos Tsarpalis; Nikolaos Kalivitis; Stavros Solomos; Alexandra Tsekeri; Christos Spyrou; Maria Tsichla; Anna Kampouri; Vassilis Vervatis; Elina Giannakaki; Vassilis Amiridis; Nikolaos Mihalopoulos; Anastasios Papadopoulos; Petros Katsafados. Assessing Sea-State Effects on Sea-Salt Aerosol Modeling in the Lower Atmosphere Using Lidar and In-Situ Measurements. Remote Sensing 2021, 13, 614 .

AMA Style

George Varlas, Eleni Marinou, Anna Gialitaki, Nikolaos Siomos, Konstantinos Tsarpalis, Nikolaos Kalivitis, Stavros Solomos, Alexandra Tsekeri, Christos Spyrou, Maria Tsichla, Anna Kampouri, Vassilis Vervatis, Elina Giannakaki, Vassilis Amiridis, Nikolaos Mihalopoulos, Anastasios Papadopoulos, Petros Katsafados. Assessing Sea-State Effects on Sea-Salt Aerosol Modeling in the Lower Atmosphere Using Lidar and In-Situ Measurements. Remote Sensing. 2021; 13 (4):614.

Chicago/Turabian Style

George Varlas; Eleni Marinou; Anna Gialitaki; Nikolaos Siomos; Konstantinos Tsarpalis; Nikolaos Kalivitis; Stavros Solomos; Alexandra Tsekeri; Christos Spyrou; Maria Tsichla; Anna Kampouri; Vassilis Vervatis; Elina Giannakaki; Vassilis Amiridis; Nikolaos Mihalopoulos; Anastasios Papadopoulos; Petros Katsafados. 2021. "Assessing Sea-State Effects on Sea-Salt Aerosol Modeling in the Lower Atmosphere Using Lidar and In-Situ Measurements." Remote Sensing 13, no. 4: 614.

Journal article
Published: 22 October 2020 in Remote Sensing
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In this study, the performance and characteristics of the advanced cloud nucleation scheme of Fountoukis and Nenes, embedded in the fully coupled Weather Research and Forecasting/Chemistry (WRF/Chem) model, are investigated. Furthermore, the impact of dust particles on the distribution of the cloud condensation nuclei (CCN) and the way they modify the pattern of the precipitation are also examined. For the simulation of dust particle concentration, the Georgia Tech Goddard Global Ozone Chemistry Aerosol Radiation and Transport of Air Force Weather Agency (GOCART-AFWA) is used as it includes components for the representation of dust emission and transport. The aerosol activation parameterization scheme of Fountoukis and Nenes has been implemented in the six-class WRF double-moment (WDM6) microphysics scheme, which treats the CCN distribution as a prognostic variable, but does not take into account the concentration of dust aerosols. Additionally, the presence of dust particles that may facilitate the activation of CCN into cloud or rain droplets has also been incorporated in the cumulus scheme of Grell and Freitas. The embedded scheme is assessed through a case study of significant dust advection over the Western Mediterranean, characterized by severe rainfall. Inclusion of CCN based on prognostic dust particles leads to the suppression of precipitation over hazy areas. On the contrary, precipitation is enhanced over areas away from the dust event. The new prognostic CCN distribution improves in general the forecasting skill of the model as bias scores, the root mean square error (RMSE), false alarm ratio (FAR) and frequencies of missed forecasts (FOM) are limited when modelled data are compared against satellite, LIDAR and aircraft observations.

ACS Style

Konstantinos Tsarpalis; Petros Katsafados; Anastasios Papadopoulos; Nikolaos Mihalopoulos. Assessing Desert Dust Indirect Effects on Cloud Microphysics through a Cloud Nucleation Scheme: A Case Study over the Western Mediterranean. Remote Sensing 2020, 12, 3473 .

AMA Style

Konstantinos Tsarpalis, Petros Katsafados, Anastasios Papadopoulos, Nikolaos Mihalopoulos. Assessing Desert Dust Indirect Effects on Cloud Microphysics through a Cloud Nucleation Scheme: A Case Study over the Western Mediterranean. Remote Sensing. 2020; 12 (21):3473.

Chicago/Turabian Style

Konstantinos Tsarpalis; Petros Katsafados; Anastasios Papadopoulos; Nikolaos Mihalopoulos. 2020. "Assessing Desert Dust Indirect Effects on Cloud Microphysics through a Cloud Nucleation Scheme: A Case Study over the Western Mediterranean." Remote Sensing 12, no. 21: 3473.

Chapter
Published: 12 September 2020 in The Handbook of Environmental Chemistry
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The meteorological conditions over the Aegean Sea are subjected to strong influences from the large-scale patterns of the general atmospheric circulation, the surrounding continents, the almost enclosed Mediterranean Sea, the complex topography and coastline, as well as the mesoscale and local phenomena imposed on the synoptic-scale atmospheric circulation. This chapter discusses the most important circulation patterns that affect the area determining not only the weather conditions but also the climatic characteristics. The discussion unravels seasonal and spatial characteristics of the weather and climate patterns giving also a particular emphasis on the formation of cyclones (cyclogenesis). The role of upper-air conditions and air-sea interaction is highlighted, especially demonstrating the remarkable patterns of explosive cyclones and Mediterranean tropical-like cyclones (medicanes). This chapter also provides a preliminary analysis of air temperature and precipitation over the Aegean Sea unveiling spatiotemporal variabilities and trends.

ACS Style

Anastasios Papadopoulos; George Varlas. Weather Systems Affecting the Meteorological Conditions over the Aegean Sea. The Handbook of Environmental Chemistry 2020, 1 -25.

AMA Style

Anastasios Papadopoulos, George Varlas. Weather Systems Affecting the Meteorological Conditions over the Aegean Sea. The Handbook of Environmental Chemistry. 2020; ():1-25.

Chicago/Turabian Style

Anastasios Papadopoulos; George Varlas. 2020. "Weather Systems Affecting the Meteorological Conditions over the Aegean Sea." The Handbook of Environmental Chemistry , no. : 1-25.

Journal article
Published: 27 August 2020 in Remote Sensing
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Severe hydrometeorological hazards such as floods, droughts, and thunderstorms are expected to increase in the future due to climate change. Due to the significant impacts of these phenomena, it is essential to develop new and advanced early warning systems for advance preparation of the population and local authorities (civil protection, government agencies, etc.). Therefore, reliable forecasts of extreme events, with high spatial and temporal resolution and a very short time horizon are needed, due to the very fast development and localized nature of these events. In very short time-periods (up to 6 h), small-scale phenomena can be described accurately by adopting a “nowcasting” approach, providing reliable short-term forecasts and warnings. To this end, a novel nowcasting system was developed and presented in this study, combining a data assimilation system (LAPS), a large amount of observed data, including XPOL radar precipitation measurements, the Chemical Hydrological Atmospheric Ocean wave System (CHAOS), and the WRF-Hydro model. The system was evaluated on the catastrophic flash flood event that occurred in the sub-urban area of Mandra in Western Attica, Greece, on 15 November 2017. The event was one of the most catastrophic flash floods with human fatalities (24 people died) and extensive infrastructure damage. The update of the simulations with assimilated radar data improved the initial precipitation description and led to an improved simulation of the evolution of the phenomenon. Statistical evaluation and comparison with flood data from the FloodHub showed that the nowcasting system could have provided reliable early warning of the flood event 1, 2, and even to 3 h in advance, giving vital time to the local authorities to mobilize and even prevent fatalities and injuries to the local population.

ACS Style

Christos Spyrou; George Varlas; Aikaterini Pappa; Angeliki Mentzafou; Petros Katsafados; Anastasios Papadopoulos; Marios Anagnostou; John Kalogiros. Implementation of a Nowcasting Hydrometeorological System for Studying Flash Flood Events: The Case of Mandra, Greece. Remote Sensing 2020, 12, 2784 .

AMA Style

Christos Spyrou, George Varlas, Aikaterini Pappa, Angeliki Mentzafou, Petros Katsafados, Anastasios Papadopoulos, Marios Anagnostou, John Kalogiros. Implementation of a Nowcasting Hydrometeorological System for Studying Flash Flood Events: The Case of Mandra, Greece. Remote Sensing. 2020; 12 (17):2784.

Chicago/Turabian Style

Christos Spyrou; George Varlas; Aikaterini Pappa; Angeliki Mentzafou; Petros Katsafados; Anastasios Papadopoulos; Marios Anagnostou; John Kalogiros. 2020. "Implementation of a Nowcasting Hydrometeorological System for Studying Flash Flood Events: The Case of Mandra, Greece." Remote Sensing 12, no. 17: 2784.

Journal article
Published: 28 March 2020 in Mediterranean Marine Science
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Nowadays, it has become clear that atmosphere and ocean should be simulated by integrated modeling systems resolving interconnected physical factors which determine Earth’s energy balance. Waves play a key role on the interfacial interaction between atmosphere and ocean regulating momentum, heat and moisture exchange. This study aims to evaluate the two-way coupled atmosphere-ocean wave system CHAOS (Chemical Hydrological Atmosphere Ocean wave System) over the Mediterranean and Black Seas. The evaluation is performed against in-situ and remote sensing data for the period from 1 December 2013 to 1 December 2014. CHAOS includes the Weather Research Forecasting (WRF) model version 3.8 as atmospheric component and the Wave model (WAM) cycle 4.5.4 as ocean wave component, coupled through the OASIS3-MCT coupler version 3.0. In order to assess the impact of the atmosphere-ocean waves coupling, two approaches of continuous model simulations are followed. In the first approach (1-way coupling mode) the ocean wave component uses the winds produced by the atmospheric component while in the second approach (2-way coupling mode) the atmospheric component additionally uses the sea state information estimated by the ocean wave component through wave-dependent Charnock parameter computations. In the 2-way coupling mode, the attenuation of the atmospheric flow has a damping effect on wind-generated waves. The simulations in 2-way coupling mode produce more realistic results yielding statistical improvements. Against buoys observations, 2-way reduces root mean square error (RMSE) per 1.2% and 6.3% for wind speed and significant wave height, respectively, while against Jason-2 satellite retrievals per 0.5% and 2.4%, respectively. Additionally, the 2-way outperforms the 1-way coupling mode under intense wind and wave conditions during this one-year period.

ACS Style

George Varlas; Christos Spyrou; Anastasios Papadopoulos; Gerasimos Korres; Petros Katsafados. One-year assessment of the two-way coupled atmosphere-ocean wave modeling system CHAOS over the Mediterranean and Black Seas. Mediterranean Marine Science 2020, 1 .

AMA Style

George Varlas, Christos Spyrou, Anastasios Papadopoulos, Gerasimos Korres, Petros Katsafados. One-year assessment of the two-way coupled atmosphere-ocean wave modeling system CHAOS over the Mediterranean and Black Seas. Mediterranean Marine Science. 2020; ():1.

Chicago/Turabian Style

George Varlas; Christos Spyrou; Anastasios Papadopoulos; Gerasimos Korres; Petros Katsafados. 2020. "One-year assessment of the two-way coupled atmosphere-ocean wave modeling system CHAOS over the Mediterranean and Black Seas." Mediterranean Marine Science , no. : 1.

Journal article
Published: 07 November 2019 in Climate
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In this study, the physically-based hydrological model MIKE SHE was employed to investigate the effects of anthropogenic land cover changes to the hydrological cycle components of a regional watershed in Central Greece. Three case studies based on the land cover of the years 1960, 1990, and 2018 were examined. Copernicus Climate Change Service E-OBS gridded meteorological data for 45 hydrological years were used as forcing for the model. Evaluation against observational data yielded sufficient quality for daily air temperature and precipitation. Simulation results demonstrated that the climatic variabilities primarily in precipitation and secondarily in air temperature affected basin-averaged annual actual evapotranspiration and average annual river discharge. Nevertheless, land cover effects can locally outflank the impact of climatic variability as indicated by the low interannual variabilities of differences in annual actual evapotranspiration among case studies. The transition from forest to pastures or agricultural land reduced annual actual evapotranspiration and increased average annual river discharge while intensifying the vulnerability to hydrometeorological-related hazards such as droughts or floods. Hence, the quantitative assessment of land cover effects presented in this study can contribute to the design and implementation of successful land cover and climate change mitigation and adaptation policies.

ACS Style

Angeliki Mentzafou; George Varlas; Elias Dimitriou; Anastasios Papadopoulos; Ioannis Pytharoulis; Petros Katsafados. Modeling the Effects of Anthropogenic Land Cover Changes to the Main Hydrometeorological Factors in a Regional Watershed, Central Greece. Climate 2019, 7, 129 .

AMA Style

Angeliki Mentzafou, George Varlas, Elias Dimitriou, Anastasios Papadopoulos, Ioannis Pytharoulis, Petros Katsafados. Modeling the Effects of Anthropogenic Land Cover Changes to the Main Hydrometeorological Factors in a Regional Watershed, Central Greece. Climate. 2019; 7 (11):129.

Chicago/Turabian Style

Angeliki Mentzafou; George Varlas; Elias Dimitriou; Anastasios Papadopoulos; Ioannis Pytharoulis; Petros Katsafados. 2019. "Modeling the Effects of Anthropogenic Land Cover Changes to the Main Hydrometeorological Factors in a Regional Watershed, Central Greece." Climate 7, no. 11: 129.

Journal article
Published: 07 November 2019 in Water
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Nowadays, as extreme weather increasingly threatens human health and economy, early warning system approaches are critical for timely preparedness and response. Towards the implementation of a multi-model forecasting system for flood hazards, this study presents a coupled application of three (3) models: The WRF-ARW weather model, the WRF-Hydro hydrological model, and the HEC-RAS 2D hydraulic model. A flash flood event that occurred on 9 October 2006 in Volos city, Greece, is used as a case study to assess the accuracy of the integrated modelling approach to simulate the flood hydrograph and flood extent in Xerias ungauged catchment. The hydrometeorological simulation results indicated a severe persistent storm over Pelion mountain at the northeast of Volos, as the main factor of the major flash flood and extensive impacts. Historical flood records retrieved by several conventional and non-conventional sources are used to validate the flooded area. Compared to the collected data and prior studies, the generated inundation map of Xerias river is found to realistically capture highly impacted areas which experienced infrastructure damage and human rescues from inundated roads and buildings. Results from our analyses show that the proposed physically-based modelling approach can give reliable inputs into flood risk management.

ACS Style

George Papaioannou; George Varlas; Galateia Terti; Anastasios Papadopoulos; Athanasios Loukas; Yiannis Panagopoulos; Elias Dimitriou. Flood Inundation Mapping at Ungauged Basins Using Coupled Hydrometeorological–Hydraulic Modelling: The Catastrophic Case of the 2006 Flash Flood in Volos City, Greece. Water 2019, 11, 2328 .

AMA Style

George Papaioannou, George Varlas, Galateia Terti, Anastasios Papadopoulos, Athanasios Loukas, Yiannis Panagopoulos, Elias Dimitriou. Flood Inundation Mapping at Ungauged Basins Using Coupled Hydrometeorological–Hydraulic Modelling: The Catastrophic Case of the 2006 Flash Flood in Volos City, Greece. Water. 2019; 11 (11):2328.

Chicago/Turabian Style

George Papaioannou; George Varlas; Galateia Terti; Anastasios Papadopoulos; Athanasios Loukas; Yiannis Panagopoulos; Elias Dimitriou. 2019. "Flood Inundation Mapping at Ungauged Basins Using Coupled Hydrometeorological–Hydraulic Modelling: The Catastrophic Case of the 2006 Flash Flood in Volos City, Greece." Water 11, no. 11: 2328.

Journal article
Published: 17 May 2019 in Mediterranean Marine Science
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The forecast skill of numerical weather prediction (NWP) models relies, among other factors such as the prediction itself and the assimilation scheme, on the accuracy of the observations utilized in the assimilation systems for the production of initial and boundary conditions. One of the most crucial parameters in weather forecasting is the sea surface temperature (SST). In the majority of NWP models, the initial and lower boundary conditions involve gridded (SST) analyses which consist of data obtained by buoys, ships and satellites. The main aim of this study is to integrate Argo temperature measurements in gridded SST analyses and to assess their impact on the forecast skill of a limited area atmospheric model. Argo floats are “state-of-the-art” oceanographic instruments producing high-quality temperature profiles for the ice-free ocean. In this study, Argo temperatures are incorporated into gridded SST fields without applying any smoothing method in order to directly assess the impact of Argo temperatures on numerical weather prediction. Their impact is assessed under intense weather cyclonic conditions at the Mediterranean Sea by performing two sensitivity simulations either incorporating or not Argo temperatures into gridded SST fields used in the generation of the initial and lower boundary conditions. The results indicate that the inclusion of Argo-measured near-surface temperatures in the lower boundary condition modifies the surface heat fluxes, thus affecting mean sea level pressure and precipitation. In particular, an overall improvement of the precipitation forecast skill up to 3% has been demonstrated. Moreover, the incorporation of Argo temperatures affects the simulated track and intensity of the cyclone over the Balkan Peninsula.

ACS Style

George Varlas; Petros Katsafados; Gerasimos Korres; Anastasios Papadopoulos. Assessing the impact of Argo floats temperature measurements on the numerical weather prediction forecast skill. Mediterranean Marine Science 2019, 20, 331 -341.

AMA Style

George Varlas, Petros Katsafados, Gerasimos Korres, Anastasios Papadopoulos. Assessing the impact of Argo floats temperature measurements on the numerical weather prediction forecast skill. Mediterranean Marine Science. 2019; 20 (2):331-341.

Chicago/Turabian Style

George Varlas; Petros Katsafados; Gerasimos Korres; Anastasios Papadopoulos. 2019. "Assessing the impact of Argo floats temperature measurements on the numerical weather prediction forecast skill." Mediterranean Marine Science 20, no. 2: 331-341.

Journal article
Published: 28 December 2018 in Remote Sensing
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Urban areas often experience high precipitation rates and heights associated with flash flood events. Atmospheric and hydrological models in combination with remote-sensing and surface observations are used to analyze these phenomena. This study aims to conduct a hydrometeorological analysis of a flash flood event that took place in the sub-urban area of Mandra, western Attica, Greece, using remote-sensing observations and the Chemical Hydrological Atmospheric Ocean Wave System (CHAOS) modeling system that includes the Advanced Weather Research Forecasting (WRF-ARW) model and the hydrological model (WRF-Hydro). The flash flood was caused by a severe storm during the morning of 15 November 2017 around Mandra area resulting in extensive damages and 24 fatalities. The X-band dual-polarization (XPOL) weather radar of the National Observatory of Athens (NOA) observed precipitation rates reaching 140 mm/h in the core of the storm. CHAOS simulation unveils the persistent orographic convergence of humid southeasterly airflow over Pateras mountain as the dominant parameter for the evolution of the storm. WRF-Hydro simulated the flood using three different precipitation estimations as forcing data, obtained from the CHAOS simulation (CHAOS-hydro), the XPOL weather radar (XPOL-hydro) and the Global Precipitation Measurement (GMP)/Integrated Multi-satellitE Retrievals for GPM (IMERG) satellite dataset (GPM/IMERG-hydro). The findings indicate that GPM/IMERG-hydro underestimated the flood magnitude. On the other hand, XPOL-hydro simulation resulted to discharge about 115 m3/s and water level exceeding 3 m in Soures and Agia Aikaterini streams, which finally inundated. CHAOS-hydro estimated approximately the half water level and even lower discharge compared to XPOL-hydro simulation. Comparing site-detailed post-surveys of flood extent, XPOL-hydro is characterized by overestimation while CHAOS-hydro and GPM/IMERG-hydro present underestimation. However, CHAOS-hydro shows enough skill to simulate the flooded areas despite the forecast inaccuracies of numerical weather prediction. Overall, the simulation results demonstrate the potential benefit of using high-resolution observations from a X-band dual-polarization radar as an additional forcing component in model precipitation simulations.

ACS Style

George Varlas; Marios N. Anagnostou; Christos Spyrou; Anastasios Papadopoulos; John Kalogiros; Angeliki Mentzafou; Silas Michaelides; Evangelos Baltas; Efthimios Karymbalis; Petros Katsafados. A Multi-Platform Hydrometeorological Analysis of the Flash Flood Event of 15 November 2017 in Attica, Greece. Remote Sensing 2018, 11, 45 .

AMA Style

George Varlas, Marios N. Anagnostou, Christos Spyrou, Anastasios Papadopoulos, John Kalogiros, Angeliki Mentzafou, Silas Michaelides, Evangelos Baltas, Efthimios Karymbalis, Petros Katsafados. A Multi-Platform Hydrometeorological Analysis of the Flash Flood Event of 15 November 2017 in Attica, Greece. Remote Sensing. 2018; 11 (1):45.

Chicago/Turabian Style

George Varlas; Marios N. Anagnostou; Christos Spyrou; Anastasios Papadopoulos; John Kalogiros; Angeliki Mentzafou; Silas Michaelides; Evangelos Baltas; Efthimios Karymbalis; Petros Katsafados. 2018. "A Multi-Platform Hydrometeorological Analysis of the Flash Flood Event of 15 November 2017 in Attica, Greece." Remote Sensing 11, no. 1: 45.

Journal article
Published: 01 December 2018 in Progress in Oceanography
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The Samaria and Lithinon canyons at the southern Cretan margin (Eastern Mediterranean) were studied with respect to hydrography, deep currents, particle dynamics and settling fluxes by utilizing: a) current-meter and sediment trap records from May 2005 to May 2006; and b) hydrographic and optical measurements along with particulate matter and particulate organic carbon concentrations (PMC and POC, respectively) in two surveys (May and October 2005). The deep currents were very weak with mean velocity ∼3-4 cm s-1 and their direction was controlled by the local bottom topography. The entire area was characterized by very low PMC and POC, depicted both by transmissometry profiles and discrete bottle data. The fluxes of downward settling particles are comparable with the fluxes measured in the broader Eastern Mediterranean and hence point to an oligotrophic environment with low atmospheric and lateral inputs. A series of relatively high total mass fluxes (>1000 mg m-2 d-1) were recorded near the head of the Samaria canyon, at the trap closest to Crete, and was attributed to: a) high temporal lithogenic inputs (mineral calcite) transferred to the sea by a small, intermittent stream flowing through the Samaria gorge, which was activated by short rainfall events and spring snowmelt; and b) inputs of numerous coccoliths of E. huxleyi and calcite by shallow sediment resuspension generated by wind-induced waves. Apart from this local-scale event, there was very little evidence of matter transfer through the canyons, thus, during the one-year of observations, the canyons were dormant. Because of this lack of down-canyon transport during the study period, open slopes and canyons exhibited roughly similar characteristics in terms both of particle dynamics and fluxes. However, the presence of coarse-grained sediments along the canyon axes point to episodic canyon activity, occurring at unknown time scales and periodicity.

ACS Style

A.P. Karageorgis; H. Kontoyiannis; S. Stavrakakis; Evangelia Krasakopoulou; Alexandra Gogou; Anastasios Papadopoulos; Th.D. Kanellopoulos; G. Rousakis; E. Malinverno; M.V. Triantaphyllou; V. Lykousis. Particle dynamics and fluxes in canyons and open slopes of the southern Cretan margin (Eastern Mediterranean). Progress in Oceanography 2018, 169, 33 -47.

AMA Style

A.P. Karageorgis, H. Kontoyiannis, S. Stavrakakis, Evangelia Krasakopoulou, Alexandra Gogou, Anastasios Papadopoulos, Th.D. Kanellopoulos, G. Rousakis, E. Malinverno, M.V. Triantaphyllou, V. Lykousis. Particle dynamics and fluxes in canyons and open slopes of the southern Cretan margin (Eastern Mediterranean). Progress in Oceanography. 2018; 169 ():33-47.

Chicago/Turabian Style

A.P. Karageorgis; H. Kontoyiannis; S. Stavrakakis; Evangelia Krasakopoulou; Alexandra Gogou; Anastasios Papadopoulos; Th.D. Kanellopoulos; G. Rousakis; E. Malinverno; M.V. Triantaphyllou; V. Lykousis. 2018. "Particle dynamics and fluxes in canyons and open slopes of the southern Cretan margin (Eastern Mediterranean)." Progress in Oceanography 169, no. : 33-47.

Research letter
Published: 07 November 2018 in Geophysical Research Letters
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One of the most understudied and less understood phenomenon in air‐sea interaction studies is the effect of rain on the sea state and in turn the atmosphere's response to this surface forcing. In order to examine the entire process, a new parameterization scheme for rain‐induced sea surface roughness was incorporated in the two‐way atmosphere‐ocean wave coupled system CHAOS. The simulation of the late October 2012 hurricane Sandy indicates that the complex rain‐on‐ocean effect primarily modifies sea surface roughness and attenuates both the atmospheric flow and the ocean wave growth. The heterogeneity of roughness variations modulates the asymmetry of the hurricane and affects its central pressure and its track as well. Comparing with in‐situ and remotely sensed data, the consideration of rain‐on‐ocean effect reduces the root mean square error up to 8% and 11% for wind speed and significant wave height, respectively, and finally improves Sandy's track offshore eastern US coastline.

ACS Style

P. Katsafados; G. Varlas; A. Papadopoulos; C. Spyrou; G. Korres. Assessing the Implicit Rain Impact on Sea State During Hurricane Sandy (2012). Geophysical Research Letters 2018, 45, 12,015 -12,022.

AMA Style

P. Katsafados, G. Varlas, A. Papadopoulos, C. Spyrou, G. Korres. Assessing the Implicit Rain Impact on Sea State During Hurricane Sandy (2012). Geophysical Research Letters. 2018; 45 (21):12,015-12,022.

Chicago/Turabian Style

P. Katsafados; G. Varlas; A. Papadopoulos; C. Spyrou; G. Korres. 2018. "Assessing the Implicit Rain Impact on Sea State During Hurricane Sandy (2012)." Geophysical Research Letters 45, no. 21: 12,015-12,022.

Journal article
Published: 06 October 2018 in Remote Sensing
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The principal objective of this study is to present and evaluate an advanced dust wet deposition scheme in the Weather and Research Forecasting model coupled with Chemistry (WRF-Chem). As far as the chemistry component is concerned, the Georgia Tech Goddard Global Ozone Chemistry Aerosol Radiation and Transport of the Air Force Weather Agency (GOCART-AFWA) module is applied, as it supports a binary scheme for dust emissions and transport. However, the GOCART-AFWA aerosol module does not incorporate a wet scavenging scheme, nor does it interact with cloud processes. The integration of a dust wet deposition scheme following Seinfeld and Pandis into the WRF-Chem model is assessed through a case study of large-scale Saharan dust transport over the Eastern Mediterranean that is characterized by severe wet deposition over Greece. An acceptable agreement was found between the calculated and measured near surface PM10 concentrations, as well as when model estimated atmospheric optical depth (AOD) was validated against the AERONET measurements, indicating the validity of our dust wet deposition scheme.

ACS Style

Konstantinos Tsarpalis; Anastasios Papadopoulos; Nikolaos Mihalopoulos; Christos Spyrou; Silas Michaelides; Petros Katsafados. The Implementation of a Mineral Dust Wet Deposition Scheme in the GOCART-AFWA Module of the WRF Model. Remote Sensing 2018, 10, 1595 .

AMA Style

Konstantinos Tsarpalis, Anastasios Papadopoulos, Nikolaos Mihalopoulos, Christos Spyrou, Silas Michaelides, Petros Katsafados. The Implementation of a Mineral Dust Wet Deposition Scheme in the GOCART-AFWA Module of the WRF Model. Remote Sensing. 2018; 10 (10):1595.

Chicago/Turabian Style

Konstantinos Tsarpalis; Anastasios Papadopoulos; Nikolaos Mihalopoulos; Christos Spyrou; Silas Michaelides; Petros Katsafados. 2018. "The Implementation of a Mineral Dust Wet Deposition Scheme in the GOCART-AFWA Module of the WRF Model." Remote Sensing 10, no. 10: 1595.

Journal article
Published: 01 August 2018 in Atmospheric Research
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ACS Style

George Varlas; Petros Katsafados; Anastasios Papadopoulos; Gerasimos Korres. Implementation of a two-way coupled atmosphere-ocean wave modeling system for assessing air-sea interaction over the Mediterranean Sea. Atmospheric Research 2018, 208, 201 -217.

AMA Style

George Varlas, Petros Katsafados, Anastasios Papadopoulos, Gerasimos Korres. Implementation of a two-way coupled atmosphere-ocean wave modeling system for assessing air-sea interaction over the Mediterranean Sea. Atmospheric Research. 2018; 208 ():201-217.

Chicago/Turabian Style

George Varlas; Petros Katsafados; Anastasios Papadopoulos; Gerasimos Korres. 2018. "Implementation of a two-way coupled atmosphere-ocean wave modeling system for assessing air-sea interaction over the Mediterranean Sea." Atmospheric Research 208, no. : 201-217.