Current European flood-rich period exceptional compared with past 500 years.

There are concerns that recent climate change is altering the frequency and magnitude of river floods in an unprecedented way1. Historical studies have identified flood-rich periods in the past half millennium in various regions of Europe2. However, because of the low temporal resolution of existing datasets and the relatively low number of series, it has remained unclear whether Europe is currently in a flood-rich period from a long-term perspective. Here we analyse how recent decades compare with the flood history of Europe, using a new database composed of more than 100 high-resolution (sub-annual) historical flood series based on documentary evidence covering all major regions of Europe. We show that the past three decades were among the most flood-rich periods in Europe in the past 500 years, and that this period differs from other flood-rich periods in terms of its extent, air temperatures and flood seasonality. We identified nine flood-rich periods and associated regions. Among the periods richest in floods are 1560-1580 (western and central Europe), 1760-1800 (most of Europe), 1840-1870 (western and southern Europe) and 1990-2016 (western and central Europe). In most parts of Europe, previous flood-rich periods occurred during cooler-than-usual phases, but the current flood-rich period has been much warmer. Flood seasonality is also more pronounced in the recent period. For example, during previous flood and interflood periods, 41 per cent and 42 per cent of central European floods occurred in summer, respectively, compared with 55 per cent of floods in the recent period. The exceptional nature of the present-day flood-rich period calls for process-based tools for flood-risk assessment that capture the physical mechanisms involved, and management strategies that can incorporate the recent changes in risk.

Real-Time Gamma Radioactive Source Localization by Data Fusion of 3D-LiDAR Terrain Scan and Radiation Data from Semi-Autonomous UAV Flights.

Rapid and accurate reconnaissance in the event of radiological and nuclear (RN) incidents or attacks is vital to launch an appropriate response. This need is made stronger by the increasing threat of RN attacks on soft targets and critical infrastructure in densely populated areas. In such an event, even small radioactive sources can cause major disruption to the general population. In this work, we present a real-time radiological source localization method based on an optimization problem considering a background and radiation model. Supported by extensive real-world experiments, we show that an airborne system using this method is capable for reliably locating category 3-4 radioactive sources according to IAEA safety standards in real time from altitudes up to 150 m. A sensor bundle including a LiDAR sensor, a Gamma probe as well as a communication module was mounted on a UAV that served as a carrier platform. The method was evaluated on a comprehensive set of test flights, including 28 flight scenarios over 316 min using three different radiation sources. All additional gamma sources were correctly detected, multiple sources were detected if they were sufficiently separated from each other, with the distance between the true source position and the estimated source averaging 17.1 m. We also discuss the limitations of the system in terms of detection limit and source separation.

Nonlinear Lock-In Infrared Microscopy: A Complementary Investigation Technique for the Analysis of Functional Electroceramic Components.

Using lock-in infrared microscopy as a tool for current detection on the micrometer scale in AC-driven specimens in combination with iterative grinding procedure allows preparation of current dominating microstructure regions on well-polished surfaces. This technique is applied successfully on varistor components based on specially doped ZnO-based varistor ceramics. This peculiar electroceramic material exhibits exceptional high nonlinear current-voltage (I-V) characteristics, described by a power law according I~V(α), caused by double Schottky barriers at the grain boundaries. As a novelty the thermographic response is used to evaluate local electrical properties, namely the nonlinearity coefficient α, on basis of higher order harmonics with respect to the basic electrical driving AC-frequency. To correlate the observed electrical properties to the microstructure, the polar crystal orientation of the relevant ZnO grains is determined by combining electron backscatter diffraction and orientation-dependent patterns as a result of a chemical etching procedure. These findings support a modified new model for describing the grain boundary controlled current flow in a varistor microstructure including orientation-dependent barrier properties. Hence, the experimentally observed current direction-dependent behavior can be described consistently.

Changing summer precipitation variability in the Alpine region: on the role of scale dependent atmospheric drivers.

Summer precipitation totals in the Alpine Region do not exhibit a systematic trend over the last 120 years. However, we find significant low frequency periodicity of interannual variability which occurs in synchronization with a dominant two-phase state of the atmospheric circulation over the Alps. Enhanced meridional flow increases precipitation variability through positive soil moisture precipitation feedbacks on the regional scale, whereas enhanced zonal flow results in less variability through constant moisture flow from the Atlantic and suppressed feedbacks with the land surface. The dominant state of the atmospheric circulation over the Alps in these periods appears to be steered by zonal sea surface temperature gradients in the mid-latitude North Atlantic. The strength and the location of the westerlies in the mid-latitude Atlantic play an important role in the physical mechanisms linking atmosphere and oceanic temperature gradients and the meridional/zonal circulation characteristics.

Large-scale heavy precipitation over central Europe and the role of atmospheric cyclone track types.

Precipitation patterns over Europe are largely controlled by atmospheric cyclones embedded in the general circulation of the mid-latitudes. This study evaluates the climatologic features of precipitation for selected regions in central Europe with respect to cyclone track types for 1959-2015, focusing on large-scale heavy precipitation. The analysis suggests that each of the cyclone track types is connected to a specific pattern of the upper level atmospheric flow, usually characterized by a major trough located over Europe. A dominant upper level cut-off low (COL) is found over Europe for strong continental (CON) and van Bebber's type (Vb) cyclones which move from the east and southeast into central Europe. Strong Vb cyclones revealed the longest residence times, mainly due to circular propagation paths. The central European cyclone precipitation climate can largely be explained by seasonal track-type frequency and cyclone intensity; however, additional factors are needed to explain a secondary precipitation maximum in early autumn. The occurrence of large precipitation totals for track events is strongly related to the track type and the region, with the highest value of 45% of all Vb cyclones connected to heavy precipitation in summer over the Czech Republic and eastern Austria. In western Germany, Atlantic winter cyclones are most relevant for heavy precipitation. The analysis of the top 50 precipitation events revealed an outstanding heavy precipitation period from 2006 to 2011 in the Czech Republic, but no gradual long-term change. The findings help better understand spatio-temporal variability of heavy precipitation in the context of floods and may be used for evaluating climate models.

Piezotronically modified double Schottky barriers in ZnO varistors.

Double Schottky barriers in ZnO are modified piezotronically by the application of mechanical stresses. New effects such as the enhancement of the potential barrier height and the increase or decrease of the natural barrier asymmetry are presented. Also, an extended model for the piezotronic modification of double Schottky barriers is given.