Impact of drought on wildland fires in Greece: implications of climatic change?

An increasing trend and a statistically significant positive correlation between wildfire occurrence, area burned and drought (as expressed by the Standardized Precipitation Index, SPI) have been observed all over Greece, during the period 1961?C1997. In the more humid and colder regions (Northern and Western Greece) the number of fires and area burned were positively correlated to both summer (SPI6_October) and annual drought (SPI12_September), whereas in the relatively more dry and hot regions (Southern and Central Greece) the number of fires and area burned were correlated only to summer drought. In 1978, Greece entered a period of prolonged drought, possibly as a result of the global climatic change. Data analysis of the period 1978?C1997 revealed a statistically significant increase in the mean annual number of fires, the area burned and the summer and annual drought episodes in the relatively more humid and colder regions (Northern and Western) of Greece (which in the past were characterized by less fires and area burned) compared to the more dry and hot regions (Southern and Eastern Greece), which always presented high fire activity. Additionally, analyzing the two sub-periods (1961?C1977, 1978?C1997) separately, drought was significantly correlated only to fire occurrence during the years 1961?C1977, whereas during 1978?C1997 drought was significantly correlated mainly to area burned. It became obvious that drought episodes, although they are not solely responsible for fire occurrence and area burned, they exert an increasingly significant impact on wildfire activity in Greece.     

Parametric investigation of lateral spreading of gently sloping liquefied ground

This paper investigates the main parameters affecting the anticipated maximum surface displacements due to earthquake-induced lateral spreading of mildly sloping ground. The main tool used for this purpose is a numerical methodology employing a bounding surface plasticity model implemented in a finite difference code, which has been thoroughly validated against 16 published centrifuge lateral spreading experiments. This study shows that important problem parameters are the mean ground (surface) acceleration, the duration of strong shaking following the onset of liquefaction, the corrected SPT blowcount, the depth to the sliding plane, the inclination of the ground surface and the fines content of the liquefied soil layers. A new approximate multi-variable relation is proposed for the estimation of ground surface displacements due to lateral spreading in gently sloping ground, which includes the foregoing parameters. The form of the relation builds upon sliding block theory, but its final formulation is based on statistical analysis of the input data and the results from 120 parametric analyses performed with the validated numerical methodology. Comparison of the predictions of the proposed relation for ground surface displacement against pertinent field data (from 256 case histories) and centrifuge test measurements shows satisfactory accuracy. Furthermore, the variation of lateral displacements with depth is explored and distinct displacement patterns are proposed for uniform, 2-layer and 4-layer ground profiles.     

Multi‐objective risk‐informed design of floor isolation systems

The design of floor isolation systems (FISs) for the protection of acceleration sensitive contents is examined considering multiple objectives, all quantified in terms of the probabilistic system performance. The competing objectives considered correspond to (i) maximization of the level of protection offered to the sensitive content (acceleration reduction) and (ii) minimization of the demand for the isolator displacement capacity and, more importantly, for the appropriate clearance to avoid collisions with surrounding objects (floor displacement reduction). Both of these objectives are probabilistically characterized utilizing a versatile, simulation‐based framework for quantifying seismic risk, addressing all important uncertainties related to the seismic hazard and the structural model. FIS performance is assessed through time‐history analysis, allowing for all important sources of nonlinearity to be directly addressed in the design framework. The seismic hazard is described through a stochastic ground motion model. For efficiently performing the multi‐objective optimization, an augmented surrogate modeling methodology is established, considering development of a single metamodel with respect to both the uncertain model parameters and the design variables for the FIS system. This surrogate model is then utilized to simultaneously support the probabilistic risk assessment and the design optimization to provide the Pareto front of dominant designs. Each of these designs establishes a different compromise between the considered risk‐related objectives offering a variety of potential options to the designer. Within the illustrative example, the efficiency of the established framework is exploited to compare three different FIS implementations, whereas the impact of structural uncertainties on the optimal design is also evaluated. Copyright © 2016 John Wiley & Sons, Ltd.     

A focusing approach to ground water detection by means of electrical and EM methods: the case of Paliouri, Northern Greece

In this paper the main results from the implementation and interpretation of a geophysical survey carried out in Chalkidiki (Northern Greece) are presented. The objective of the geophysical survey was to study the general geological conditions of the area (stratigraphy and tectonism) and to focus on the hydrogeological behaviour of the geological formations in the area. The ultimate target was to point out the most promising locations for the successful construction of hydro wells. Since direct hydrogeological information was not available, three different geophysical techniques were applied in order to follow a step by step approach to the exploration of the study area. Firstly, the Very Low Frequency (VLF) electromagnetic method was applied since the majority of the area was dominated by the formation of ophiolites and water flow was possibly expected only in fractured zones at a relatively small depth. Secondly, at the locations of the conductive zones detected by the VLF survey additional Electrical Resistivity Tomography (ERT) sections at different scales were measured to provide more detailed information about the geometrical characteristics of them. Finally, Self-Potential (SP) measurements along the same profiles were conducted in order to provide supplementary information concerning the nature of the conductive zones such as the possible relation with electrokinetic sources. The combined interpretation of the geophysical data proved very efficient for deciding the most promising locations for the construction of hydro wells.     

Progressive Failure of Slopes: Stochastic Simulation Based on Transition Probabilities and Markov Chains

Geotechnical and Geological Engineering - A reliability analysis framework for the stochastic simulation of slope progressive failure is proposed in the current work. Progressive failure is...     

Advances in surrogate modeling for storm surge prediction: storm selection and addressing characteristics related to climate change

This paper establishes various advancements for the application of surrogate modeling techniques for storm surge prediction utilizing an existing database of high-fidelity, synthetic storms (tropical cyclones). Kriging, also known as Gaussian process regression, is specifically chosen as the surrogate model in this study. Emphasis is first placed on the storm selection for developing the database of synthetic storms. An adaptive, sequential selection is examined here that iteratively identifies the storm (or multiple storms) that is expected to provide the greatest enhancement of the prediction accuracy when that storm is added into the already available database. Appropriate error statistics are discussed for assessing convergence of this iterative selection, and its performance is compared to the joint probability method with optimal sampling, utilizing the required number of synthetic storms to achieve the same level of accuracy as comparison metric. The impact on risk estimation is also examined. The discussion then moves to adjustments of the surrogate modeling framework to support two implementation issues that might become more relevant due to climate change considerations: future storm intensification and sea level rise (SLR). For storm intensification, the use of the surrogate model for prediction extrapolation is examined. Tuning of the surrogate model characteristics using cross-validation techniques and modification of the tuning to prioritize storms with specific characteristics are proposed, whereas an augmentation of the database with new/additional storms is also considered. With respect to SLR, the recently developed database for the US Army Corps of Engineers’ North Atlantic Comprehensive Coastal Study is exploited to demonstrate how surrogate modeling can support predictions that include SLR considerations.     

How a sharp rostral dimorphism affects the life history,population structure and adaptability of a small shrimp: the case study of Hippolyte sapphica

The rostrum shows a large variation across caridean shrimps; however, our knowledge about the biological significance of this morphological structure is very limited, and information on its genetic control is completely absent. The present study concentrates on an unusual rostral dimorphism in a population of small Mediterranean caridean shrimp and combines laboratory and field observations. Analysis of lab‐reared offspring supports the hypothesis that the post‐larval elongation of the rostrum is controlled by a single genetic locus, with the long dentate rostrum representing the recessive state and the short larval‐like rostrum representing the completely dominant state. The short rostrum is a sparsely distributed character; our results obtained from field studies suggest that it reduces the viability and probability of egg‐bearing among large females but, unexpectedly, the specimens with a short rostrum show consistently more rapid sex differentiation and a significantly higher propensity to become males. Therefore, it has to be concluded that, under certain conditions, a single emergent character could influence the species evolution in a rather complex manner, thus affecting the life history, population structure and dynamics and mortality in certain subgroups. In turn, the genetic factors responsible for the different phenotypes would tend to be segregated through different subpopulations and size classes, thus partially escaping the negative selective pressure.     

Correlation of fabric tensors for granular materials using 2D DEM

Acta Geotechnica - Soil fabric anisotropy can be quantitatively assessed by means of fabric tensors introduced as internal variables in constitutive models and defined by unit vectors along the...     

Language‐Independent Access to History Textbooks: Utilizing GIS Functionality with Spatiotemporal and Thematic Metadata

Integrating and accessing structured textual content obtained from different sources is a challenging task and becomes even more so when dealing with multiple languages. The objective of this article is to showcase the technological efforts towards the creation of a digital European history textbook repository that integrates respective textbooks from various countries and publishers. The content integration is achieved by introducing language independent metadata based on space (locations), time (dates), and thematic categories (history gazetteer). Providing adequate interfaces such metadata can be used to offer language‐independent access to Multilanguage history textbook content. The specific focus in this article will be on (1) presenting the metadata, (2) the data management approach including indexing the history textbook content and (3) the resulting textbook repository including its GIS‐based interface, allowing for a combination of map, timeline and keyword based search of the history content.