Uncertainties in projected runoff over the conterminous United States

Projections of runoff from global multi-model ensembles provide a valuable basis for the estimation of future hydrological extremes. However, projections suffer from uncertainty that originates from different error sources along the modeling chain. Hydrological impact studies have generally partitioned these error sources into global impact and global climate model (GIM and GCM, respectively) uncertainties, neglecting other sources, including scenarios and internal variability. Using a set of GIMs driven by GCMs under different representative concentration pathways (RCPs), this study aims to partition the uncertainty of future flows coming from GIMs, GCMs, RCPs, and internal variability over the CONterminous United States (CONUS). We focus on annual maximum, median, and minimum runoff, analyzed decadally over the twenty-first century. Results indicate that GCMs and GIMs are responsible for the largest fraction of uncertainty over most of the study area, followed by internal variability and to a smaller extent RCPs. To investigate the influence of the ensemble setup on uncertainty, in addition to the full ensemble, three ensemble configurations are studied using fewer GIMs (excluding least credible GIMs in runoff representation and GIMs accounting for vegetation and CO₂ dynamics), and excluding intermediate RCPs. Overall, the use of fewer GIMs has a minor impact on uncertainty for low and medium flows, but a substantial impact for high flows. Regardless of the number of pathways considered, RCPs always play a very small role, suggesting that improvement of GCMs and GIMs and more informed ensemble selections can yield a reduction of projected uncertainties.     

Analysis of changes in the magnitude,frequency, and seasonality of heavy precipitation over the contiguous USA

Theoretical and Applied Climatology - Gridded daily precipitation observations over the contiguous USA are used to investigate the past observed changes in the frequency and magnitude of heavy...     

An Analysis of the Coastal Fish Assemblage of the Ustica Island Marine Reserve (Mediterranean Sea)

A study of the coastal fish assemblages in the marine park of Ustica Island (Southern Tyrrhenian Sea, Mediterranean) was conducted from June 1994 to September 1995 and from June 1996 to September 1997. The principal aims of the research were to: (1) define the faunistic features of local fish communities; (2) assess the effectiveness of the protection regime of the marine park on the fish assemblages ('reserve effect'); (3) provide information on the distribution of some Epinephelus and Diplodus species in the shallowest depth zone of the island. During seasonal surveys, underwater visual censuses were carried out at several sites located in three zones of the island, each with a different level of protection. Observations were made along 250 m² transects at 3–5, 10–15 and 25–30 m depth ranges. Additional surveys were made by SCUBA diving and snorkelling. A statistically significant effect of depth on the fish community parameters was observed, whereas differences linked to protection level, zones, sites and seasons were not significant. The abundance and frequency of occurrence of some species, particularly dusky grouper Epinephelus marginatus , were positively correlated with the degree of protection of the different zones of the marine park. Certain sites of the island are important as nursery areas for three species of the genus Diplodus ( i.e., D. puntazzo, D. sargus and D. vulgaris ).     

Probabilistic seismic hazard assessment for South-Eastern France

The accurate evaluation and appropriate treatment of uncertainties is of primary importance in modern probabilistic seismic hazard assessment (PSHA). One of the objectives of the SIGMA project was to establish a framework to improve knowledge and data on two target regions characterized by low-to-moderate seismic activity. In this paper, for South-Eastern France, we present the final PSHA performed within the SIGMA project. A new earthquake catalogue for France covering instrumental and historical periods was used for the calculation of the magnitude-frequency distributions. The hazard model incorporates area sources, smoothed seismicity and a 3D faults model. A set of recently developed ground motion prediction equations (GMPEs) from global and regional data, evaluated as adequately representing the ground motion characteristics in the region, was used to calculate the hazard. The magnitude-frequency distributions, maximum magnitude, faults slip rate and style-of-faulting are considered as additional source of epistemic uncertainties. The hazard results for generic rock condition (Vs30 = 800 m/s) are displayed for 20 sites in terms of uniform hazard spectra at two return periods (475 years and 10,000 years). The contributions of the epistemic uncertainties in the ground motion characterizations and in the seismic source characterization to the total hazard uncertainties are analyzed. Finally, we compare the results with existing models developed at national scale in the framework of the first generation of models supporting the Eurocode 8 enforcement, (MEDD 2002 and AFPS06) and at the European scale (within the SHARE project), highlighting significant discrepancies at short return periods.     

Assessment of a monumental masonry bell-tower after 2016 Central Italy seismic sequence by long-term SHM

The response of the San Pietro monumental bell-tower located in Perugia, Italy, to the 2016 Central Italy seismic sequence is investigated, taking advantage of the availability of field data recorded by a vibration-based SHM system installed in December 2014 to detect earthquake-induced damages. The tower is located about 85 km in the NW direction from the epicenter of the first major shock of the sequence, the Accumoli Mw6.0 earthquake of August 24th, resulting in a small local PGA of about 30 cm/s², whereby near-field PGA was measured as 915.97 cm/s² (E–W component) and 445.59 cm/s² (N–S component). Similar PGA values also characterized the two other major shocks of the sequence (Ussita Mw5.9 and Norcia Mw6.5 earthquakes of October 26th and 30th, respectively). Despite the relatively low intensity of such earthquakes in Perugia, the analysis of long-term monitoring data clearly highlights that small permanent changes in the structural behavior of the bell-tower have occurred after the earthquakes, with decreases in all identified natural frequencies. Such natural frequency decays are fully consistent with what predicted by non-linear finite element simulations and, in particular, with the development of microcracks at the base of the columns of the belfry. Microcracks in these regions, and in the rest of tower, are however hardly distinguishable from pre-existing ones and from the physiological cracking of a masonry structure, what validates the effectiveness of the SHM system in detecting earthquake-induced damage at a stage where this is not yet detectable by visual inspections.     

Numerical homogenization-based seismic assessment of an English-bond masonry prototype: Structural level application

A multiscale strategy is evaluated at a structural level for the analysis of unreinforced masonry structures. The mechanical characterization of the masonry is deduced from homogenization-based micro-scale finite element (FE) models. The derived data are here employed at a structural level via a discrete FE model. The discrete FE model is composed of quadrilateral rigid plates interconnected through vertical and horizontal interfaces. On the interfaces, between adjoining discrete elements, a model that accounts for the in- and out-of-plane behavior of masonry, with damage and plasticity, is adopted. Such interfaces represent the material pre- and post-peak regimes, its orthotropy, and, depending on the micro-model assumed, account by three-dimensional shear effects that are especially important for multi-leaf walls and complex regular textures. The discrete model has been implemented in an advanced structural analysis software where powerful built-in features as the arc-length method, line-search algorithm, and implicit or explicit solver schemes are available. The multi-scale model is applied for the dynamic study of a small English-bond masonry house prototype subjected to a series of consecutive earthquake records. Detailed comparisons between the experimental and numerical data are presented, including the results obtained through a continuous total strain rotating crack model. Quasi-static and dynamic analyses are conducted. Results demonstrate that when enough experimental information is available on the masonry components under tension, shear, and compression regimes, the approach predicts well the seismic structural response in terms of time-history displacements, seismic capacity, and damage patterns. The required computational cost (CPU time) is very attractive.     

Changes in monthly baseflow across the U.S. Midwest

Characterizing streamflow changes in the agricultural U.S. Midwest is critical for effective planning and management of water resources throughout the region. The objective of this study is to determine if and how baseflow has responded to land alteration and climate changes across the study area during the 50‐year study period by exploring hydrologic variations based on long‐term stream gage data. This study evaluates monthly contributions to annual baseflow along with possible trends over the 1966–2016 period for 458 U.S. Geological Survey streamflow gages within 12 different Midwestern states. It also examines the influence of climate and land use factors on the observed baseflow trends. Monthly contribution breakdowns demonstrate how the majority of baseflow is discharged into streams during the spring months (March, April, and May) and is overall more substantial throughout the spring (especially in April) and summer (June, July, and August). Baseflow has not remained constant over the study period, and the results of the trend detection from the Mann–Kendall test reveal that baseflows have increased and are the strongest from May to September. This analysis is confirmed by quantile regression, which suggests that for most of the year, the largest changes are detected in the central part of the distribution. Although increasing baseflow trends are widespread throughout the region, decreasing trends are few and limited to Kansas and Nebraska. Further analysis reveals that baseflow changes are being driven by both climate and land use change across the region. Increasing trends in baseflow are linked to increases in precipitation throughout the year and are most prominent during May and June. Changes in agricultural intensity (in terms of harvested corn and soybean acreage) are linked to increasing trends in the central and western Midwest, whereas increasing temperatures may lead to decreasing baseflow trends in spring and summer in northern Wisconsin, Kansas, and Nebraska.     

Roles of methane and carbon dioxide in geological processes on Mars

We discuss in this paper possible roles of methane and carbon dioxide in geological processes on Mars. These volatiles in the martian crust may migrate upward from their sources either directly or via various traps (structural, sedimentary, ground ice, gas hydrates). They are then likely emitted to the atmosphere by seepage or through diverse vent structures. Though gas hydrates have never been directly detected on Mars, theoretical studies favor their presence in the crust and polar caps; they could have played an important role as significant gas reservoirs in the subsurface. The martian gas hydrates would possibly be a binary system of methane and carbon dioxide occupying clathrate cavities. Landforms such as mud volcanoes with well-known linkage to gas venting are extensively distributed on Earth, and methane is the primary gas involved. Thus, identification of these landforms on Mars could suggest that methane and possibly carbon dioxide have contributed to geological processes of the planet. For example, we present a newly identified field in Chryse Planitia where features closely resembling terrestrial mud volcanoes occur widely, though with no observable activity. We also present results of a preliminary search for possible recent or present-day, methane-emission zones in the regions over which enrichments of atmospheric methane have been reported.     

Nonlinear sediment thickness increase on the western East Pacific Rise flank, 45°S

Sediment thickness was evaluated on the western flank of the East Pacific Rise (EPR) at 45°S, based on high-resolution seismic data gathered during cruise 213/2 of R/V Sonne in 2011. Two zones with distinctly different sediment thickness were identified, separated by a transitional zone bordering a pseudo-fault. Sediment in the more distal zone 2 is almost twice as thick (~120 m) as in zone 1 close to the EPR. This is in contrast to the expected progressive sedimentary column thickening with seafloor age and distance from the spreading axis. The younger of two seismic units detected within the sedimentary column (EPR-2) occurs mainly in the distal zone on crust older than 9 Ma, whereas on younger crust it is present only in small isolated bodies. Both sedimentary units drape the basement. The drape is interpreted to represent particle settling from suspension and a generally low regional primary productivity. The spatial variation in sediment thickness cannot be explained by existing models, and other processes considered in the present case are (1) higher productivity in the western sector of the survey area, where thicker sediments were observed (zone 2), (2) the formation of sediment drifts near basement highs (‘seamount effect’), due to flow of Lower Circumpolar Deep Water affecting sediment deposition, and (3) erosion and/or non-deposition of the younger EPR-2 unit, due to elevated bed shear stresses associated with eddies transferring kinetic energy to the seafloor