Publications by Year: 2018

Papalexi C, Hatzaki M, Keramitsoglou I, Sismanidis P, Vassilakis E, Daglis I. The effect of urban landscape on land surface temperature: study of the Athens metropolitan area using very high spatial resolution data. 14th International Conference on Meteorology, Climatology and Atmospheric Physics [Internet]. 2018. PosterAbstract
Urbanization has a significant impact on the surface environment and land surface temperature (LST) can be used as reliable indicator of the Surface Urban Heat Island effect that is caused by it. Here, the relationship between LST and the Athens urban landscape is investigated, using very high resolution airborne nighttime LST image data, obtained during the ESA’s 2009 THERMOPOLIS campaign for three typical summer days (warm day, day with strong Etesian winds and heat wave day). The landscape is represented by the percentage of built-up area coverage per spatial unit provided the European Settlement Map (ESM), spatially averaged on the European Urban Atlas land use map, both provided by Copernicus Land Monitoring Service. It is found that the LSTs exhibit statistically significant differences among the different urban land cover/land use (LCLU) classes, but also among the different days for the same LCLU. A modelled global relationship between LST and landscape can be constructed, though hot and cold spots exist, which indicate clustered areas with higher and lower LSTs. The hotspots coincide with the city centre area of dense fabric and the deviations are maximized with unfavourable meteorological conditions, i.e. heat waves and windless days.
Kourliaftis G, Vandarakis D, Kapsimalis V, Vassilakis E, Poulos S, Petropoulos A. Study of the sedimentological processes and evolution of the coastline of Marathon Bay - Schinias beach. 12th Panhellenic Symposium of Oceanography and Fisheries. 2018.Abstract
The purpose of the study is the determination of the morphodynamical processes and the changes of the shoreline of Marathon Bay, which is located at northeast Attica. The area was lagoon 3.500 years BP (Pavlopoulos et al.2006) and it is characterized by low elevations and smooth slopes. The survey of the coastal and marine geomorphology was carried out by acoustic scanning of the seafloor with an echo sounder and sonar side scan topographical sections perpendicular to the shoreline and collection and analysis of surface sediments. The quantification of long-term shoreline displacements (Thieler et al. 2009) was carried out by comparing historical and recent aerial photographs (1945, 1960, 1969, 1988, 1996, 2001, 2010,), satellite imagery (6/2015, World View 2) and the imprint of the coastline (3/2013) with real time kinematic digital global positioning system (RTK DGPS). The estimation of rate and volume of the sediments transportation was realized by a hydrodynamical model (MIKE 21 Flow Model FM). At the north section of the area, near the estuary of Kainourio stream, and the lagoon’s draining channel, the maximum rates of coastal retreat are noticed (̴0,35m/year). The exposition of the coast to the southern waves, the reduced sediment supply from local rivers, due to the Marathon’s Dam and secondly of the morphology of their riverbeds, they have been filled because of the sea level rise the last 50yrs (IPCC, 2007). The lack of sediment supply, the sediment's composition and the morphological appearance of the submarine basin at the northeast of the Bay are mainly responsible for the coastal retreat along with the sea level rise.
Mavroulis S, Dilalos S, Alexopoulos J, Emm. V, Lekkas E. Multidisciplinary analysis including neotectonic mapping, morphotectonic indices, applied geophysics and remote sensing techniques for studying recently recognized active faults in Northwestern Peloponnese (Greece). 10 years after the 2008 Movri Mtn M6.5 Earthquake; An earthquake increasing our knowledge for the deformation in a foreland area. 2018.Abstract
A multidisciplinary analysis comprising neotectonic mapping, morphotectonic indices, applied geophysics and remote sensing techniques was applied in the area affected by the 2008 NW Peloponnese (Western Greece) in order to map the recently-recognized E-W striking Pineios River normal fault zone with a high degree of accuracy, and to better understand its contribution to the evolution of the ancient region of Elis during Holocene time.Quantitative constraints on deformation caused by the faulting were applied through the application of morphometric and morphotectonic indices including drainage network asymmetry, longitudinal river profiles and valley floor slope changes, the river sinuosity index (SI) of modern channels as well as mountain front indices including mountain front sinuosity (Smf) and percentage of faceting along mountain front (F%). All of the aforementioned indicated that the Pineios fault zone is a highly active structure.The study area consists mainly of a succession of Pliocene to Holocene sediments. Already published 230Th/238U dating of corals from the upper layers of the sequence indicates a Tyrrhenian age for samples spanning three complete sections from the footwall of the Pineios fault zone. The deposition ages were determined to be 103 ka for the Psari section (at an elevation of 40-45 m above a.s.l.), 118 ka for the Neapolis section (at an elevation of 60–65 m a.s.l.) and 209 ka for the Aletreika section (at an elevation of 140–145 m a.s.l.). The sampling sites that are located north of Pineios fault zone should be located on a single fault block because there is no sign of tectonic disruption between them. The ages of these dated samples correspond to oxygen isotope stages 5.3, 5.5 and 7.3. These stages represent high sea-level stands for the Mediterranean Sea and especially for the western coast of Peloponnese. In particular, at 103 ka sea-level was ~13 m below present sea-level, at 118 ka it was ~1 m below present sea-level and at 209 ka it was ~7 m below present sea-level. From the age of each sample and the sea-level change that has occurred since deposition, uplift rates for the footwall of the Pineios fault zone were calculated as ~0.26 mm/yr for the Psari area, ~0.50 mm/yr for the Neapoli area and ~0.64 mm/yr for the Aletreika area. The maximum uplift rate of 0.64 mm/yr occurs in close proximity to the fault zone. The areas with lower uplift rates are located much further to the north. Because all sample locations are inferred to be within the same fault block, this implies back tilting of the fault block toward north, in full agreement with the rotational block-faulting inferred from structural studies based on fieldwork in the surrounding area.
Antoniou V, Mavroulis S, Theocharis D, Skourtsos E, Vassilakis E, Lekkas E. Post-fire landslide susceptibility mapping in the 2016 fire-affected areas of Chios Island (Northeastern Aegean Sea, Greece). EGU2018-7452. 2018;19.Abstract
n July 25 and August 26 2016 wildfires broke out in the southwestern and central-western part of Chios Island(NE Aegean Sea, Greece), respectively. The first affected an area of approximately 47km2 and burned throughalmost 90% of olive groves and mastic trees, while the second broke out in a forested area and affected approximately6.6km2 of forest and farmland.A research aiming at the post-fire landslide susceptibility (LS) mapping of both areas was conducted. Morphologicaldata (slope, aspect, curvature, drainage network) derived from a 5m-DEM model of the areas was used.Lithological and geological data (lithology, tectonic structures) were digitized from previous field work maps.Land cover was derived from Worldview-2 satellite images before and after the fire events. Soil thickness was derivedfrom field survey observations within the fire-affected areas, road network from OpenStreetMap and rainfalldata resulted from related measurements derived from Chios meteorological station. Post-fire landslide inventorywas created after an extensive field survey of both areas before the beginning of the rainfall period (October 2016)and before the end of winter season (February 2017).Data classification of each factor according to their estimated LS followed, by using the reverse ranking method,where 1 is the least susceptible and 10 is the most one. Each category was normalized to 100% and the final rasterthematic maps of landslide controlling factors were produced. Finally, using numerical weight for each factor,which was assigned by the Analytic Hierarchy Process using Pairwise Comparison Method and according to theweighted linear combination, a map was generated where each cell has a certain post-fire LS index (LSI) value.The higher the LSI value, the higher the LS, whereas lower LSI value means lower LS.This procedure was repeated twice, first using pre-fire land cover and secondly using the severity of the fire events.The resulted maps, classified with natural breaks method, constitute the final pre- and post-fire LS maps of theaffected areas with five LS categories: very low, low, moderate, high and very high.Comparison of these two final maps showed, more or less, the same LS areas, but with LSI value enhanced. Thevalidated results showed good agreement between post-fire landslide occurrence and the produced post-fire LS maps.
Diakakis M, Nikolopoulos E, Mavroulis S, Vassilakis E, Korakaki E. The role of wildfires in inducing hydrogeomorphological disasters in the Mediterranean. A case from Greece. EGU2018-7452. 2018;19.Abstract
Although forest fires are an integral part of Mediterranean forest ecosystems, they constitute one of the most devastating natural hazards in the region. Apart from the direct consequences, fires induce well-documented longer term effects in the geomorphological and hydrological processes, influencing environmental factors that in turn can affect the occurrence of other natural hazards, such as floods and mass movement phenomena.This work focuses on the forest fire of 2007 in Peloponnese, Greece that burnt 1773 km2, causing 78 fatalities and very significant damages in property and infrastructure and went down as the largest fire in the country’s record. It examines the occurrence of flood and mass movement phenomena, before and after this mega-fire and studies different influencing factors to investigate the degree to which the 2007 fire and/or other parameters have affected their frequency.Observational evidence based on several data sources collected during the period 1989-2016 show that the 2007 fire has contributed to an increase of average flood and mass movement events frequency by approximately 3.3 and 5.6 times respectively.Fire affected areas record a substantial increase in the occurrence of both phenomena, presenting a noticeably stronger increase compared to neighbouring areas that have not been affected. Examination of the monthly occurrence of events showed an increase even in months of the year were rainfall intensity presented decreasing trends.Although no major land use changes has been identified and chlorophyll is shown to recover 2 years after the fire incident, differences on the type of vegetation as tall forest has been substituted with lower vegetation are considered significant drivers for the observed changes in hydrogeomorphic response of the fire affected basins.The findings of this work are strong indications that future climatic change, with more frequent and severe droughts and storms will be a disastrous combination for the Mediterranean region.
Chrysafis I, Christopoulou A, Kazanis D, Farangitakis G-P, Mallinis G, Mitsopoulos I, Arianoutsou M, Emm. V, Antoniou V, Theofanous N, et al.

Post-fire vegetation recovery mapping using multi-temporal Sentinel-2A imagery in Chios island, Greece

. EGU 2018-7452. 2018.Abstract
Remote sensing techniques offer the opportunity to study fire effects and vegetation recovery dynamics across large areas, providing essential information for effective management strategies development over fire-prone landscapes. Chios, the fifth largest of the Greek islands, has experienced recurring forest fires during the recent years, resulting to significant risk of environmental degradation. During the summer of 2016, the island experienced two severe wildfires, with the biggest one recorded in the southern part of the island. The affected area was mostly covered by maquis and phrygana (formations of low shrubs) (40.9%), while pine forests (Pinus brutia) represented 15.5% of the burned area. The aim of this study was to estimate and analyze the state of post-fire vegetation recovery in the island of Chios following major fire events occurred during the summer of 2016. A post-fire 8-band WorldView-2 image was used for burned area mapping by employing a geographic object-based classification approach, followed by field campaign for assessing post fire vegetation recovery, which was conducted during summer 2017 by establishing reference plots in the main pre-fire vegetation types (maquis, shrublands and pine forest areas) within the fire-affected area. A series of single and multi-temporal spectral indices including Normalized Burn Ratio, Normalized Difference Vegetation Index, Enhanced Vegetation Index and Soil Adjusted Vegetation Index, were derived from multi-temporal Sentinel-2 images. A random forest modelling procedure was performed for estimating post fire vegetation recovery within the burned area, as well as the areas of high risk erosion. We identified dNDVI, EVI and the second red edge band of Sentinel-2 as the most important spectral variables for predicting vegetation recovery within pre-fire areas. In the case of pre-fire areas with maquis, post-fire NBR, EVI and NDVI were selected as best predictors. Finally, the results revealed that vegetation recovery is more pronounced within the pre-fire pine forest areas, while topographic and geological sub-strata factors were also found significant in defining post-fire vegetation recovery.
Tsokos Α, Kotsi Ε, Petrakis S, Vassilakis E.

Combining series of multi-source high spatial resolution remote sensing datasets for the detection of shoreline displacement rates and the effectiveness of coastal zone protection measures

. Journal of Coastal Conservation [Internet]. 2018. pdfAbstract
The long-term change of the shoreline location is a phenomenon, which is highly factored in the design of construction projects along the coastal zone. Especially, beach erosion is characterized as one of the major problems at coastal areas and it is of high importance as a quite significant percentage of social development is concentrated in a relatively narrow zone not far from the waterfront. This study presents a methodology that aims to quantify the shoreline displacement rate by involving the processing of different types of remote sensing datasets such as aerial photographs, satellite images and unmanned aerial system data coupled with in-situ observations and measurements. Several photogrammetric techniques were used in order to orthorectify and homogenize a time series of remotely sensed data acquired from 1945 to 2017, representing a rapidly relocating coastal zone at the southern part of Corinth Gulf (Greece), as a case study. All images were digitally processed and optically optimized in order to produce a highly accurate representation of the shoreline at the time period of each acquisition. The data were imported in a Geographic Information System platform, where they were subjected to comparison and geostatistical analysis. High erosion rates were calculated, reaching the order of 0.18 m/year on average whilst extreme rates of 0.70 m/year were also observed in specific locations leading to the segmentation of the coastal zone according to its vulnerability and consequently the risk for further development as well as the effectiveness of measures already taken by the authorities.