Seasonal low-degree changes in terrestrial water mass load from global GNSS measurements

Large-scale mass redistribution in the terrestrial water storage (TWS) leads to changes in the low-degree spherical harmonic coefficients of the Earth’s surface mass density field. Studying these low-degree fluctuations is an important task that contributes to our understanding of continental hydrology. In this study, we use global GNSS measurements of vertical and horizontal crustal displacements that we correct for atmospheric and oceanic effects, and use a set of modified basis functions similar to Clarke et al. (Geophys J Int 171:1–10, 2007) to perform an inversion of the corrected measurements in order to recover changes in the coefficients of degree-0 (hydrological mass change), degree-1 (centre of mass shift) and degree-2 (flattening of the Earth) caused by variations in the TWS over the period January 2003–January 2015. We infer from the GNSS-derived degree-0 estimate an annual variation in total continental water mass with an amplitude of \((3.49 \pm 0.19) \times 10^{3}\) Gt and a phase of \(70^{\circ } \pm 3^{\circ }\) (implying a peak in early March), in excellent agreement with corresponding values derived from the Global Land Data Assimilation System (GLDAS) water storage model that amount to \((3.39 \pm 0.10) \times 10^{3}\) Gt and \(71^{\circ } \pm 2^{\circ }\), respectively. The degree-1 coefficients we recover from GNSS predict annual geocentre motion (i.e. the offset change between the centre of common mass and the centre of figure) caused by changes in TWS with amplitudes of \(0.69 \pm 0.07\) mm for GX, \(1.31 \pm 0.08\) mm for GY and \(2.60 \pm 0.13\) mm for GZ. These values agree with GLDAS and estimates obtained from the combination of GRACE and the output of an ocean model using the approach of Swenson et al. (J Geophys Res 113(B8), 2008) at the level of about 0.5, 0.3 and 0.9 mm for GX, GY and GZ, respectively. Corresponding degree-1 coefficients from SLR, however, generally show higher variability and predict larger amplitudes for GX and GZ. The results we obtain for the degree-2 coefficients from GNSS are slightly mixed, and the level of agreement with the other sources heavily depends on the individual coefficient being investigated. The best agreement is observed for \(T_{20}^C\) and \(T_{22}^S\), which contain the most prominent annual signals among the degree-2 coefficients, with amplitudes amounting to \((5.47 \pm 0.44) \times 10^{-3}\) and \((4.52 \pm 0.31) \times 10^{-3}\) m of equivalent water height (EWH), respectively, as inferred from GNSS. Corresponding agreement with values from SLR and GRACE is at the level of or better than \(0.4 \times 10^{-3}\) and \(0.9 \times 10^{-3}\) m of EWH for \(T_{20}^C\) and \(T_{22}^S\), respectively, while for both coefficients, GLDAS predicts smaller amplitudes. Somewhat lower agreement is obtained for the order-1 coefficients, \(T_{21}^C\) and \(T_{21}^S\), while our GNSS inversion seems unable to reliably recover \(T_{22}^C\). For all the coefficients we consider, the GNSS-derived estimates from the modified inversion approach are more consistent with the solutions from the other sources than corresponding estimates obtained from an unconstrained standard inversion.     

MHYDAS‐Erosion: a distributed single‐storm water erosion model for agricultural catchments

In this paper, we present MHYDAS‐Erosion, a dynamic and distributed single‐storm water erosion model developed as a module of the existing hydrological MHYDAS model. As with many catchment erosion models, MHYDAS‐Erosion is able to simulate sediment transport, erosion and deposition by rill and interrill processes. Its originality stems from its capacity to integrate the impact of land management practices (LMP) as key elements controlling the sedimentological connectivity in agricultural catchments. To this end, the water‐sediment pathways are first determined by a specific process‐oriented procedure defined and controlled by the user, which makes the integration of LMP easier. The LMP dynamic behaviours are then integrated into the model as a time‐dependent function of hydrological variables and LMP characteristics. The first version of the model was implemented for vegetative filters and tested using water and sediment discharge measurements at three nested scales of a densely instrumented catchment (Roujan, OMERE Observatory, southern France). The results of discharge and soil loss for simulated rainfall events have been found to acceptably compare with available data. The average R² values for water and sediment discharge are 0·82 and 0·83, respectively. The sensitivity of the model to changes in the proportion of LMP was assessed for a single rain event by considering three scenarios of the Roujan catchment management with vegetative filters: 0% (Scenario 1), 18% (Scenario 2, real case) and 100% (Scenario 3). Compared to Scenario 2 (real case), soil losses decreased for Scenario 3 by 65% on the agricultural plot scale, 62% on the sub‐catchment scale and 45% at the outlet of the catchment and increased for Scenario 1 by 0% on the plot scale, 26% on the sub‐catchment scale and 18% at the outlet of the catchment. Copyright © 2010 John Wiley & Sons, Ltd.     

The social–ecological system framework as a knowledge classificatory system for benthic small-scale fisheries

Ostrom proposed the underpinnings of a framework for the systematic study of the governance of complex social–ecological systems. Here we hypothesize that Ostrom's social–ecological system framework can be useful to build a classification system for small-scale benthic fisheries, regarding their governance processes and outcomes. The purpose of this paper is to contribute to knowledge accumulation of benthic fisheries. To tailor the framework, we relied on discussions among experts and a systematic literature review of benthic fisheries from 1980 to 2010. This literature review helped us refine variable definitions and provide readers with illustrative reference papers. We then illustrate the approach and its potential contributions through two studies of the emergence of self-organization in Mexico and Chile. We highlight synthetic lessons from the cases and the overall approach as well as reflect on remaining challenges to the development of a social–ecological system framework as a diagnostic tool for knowledge accumulation and synthesis.     

Analytical evaluation of structural component limit state probabilities

Probabilistic seismic assessment requires extensive computational effort resulting from variability both in input ground motions and mechanical properties. Nonetheless, such methodologies are of considerable importance, namely for pre-earthquake disaster planning or development of retrofitting programs. A framework for the analytical definition of closed form expressions for exceedance probabilities of structural component limit states, defined by limit values of structural response parameters, is proposed herein. The definition of these expressions is based on the probabilistic representation of the ground motion intensity and on the establishment of suitable expressions characterizing the evolution of structural demand with increasing earthquake intensity. Distinction is made between deformation-based and force-based structural parameters in the definition of such relations. Within the proposed framework, the limit states are defined by single deterministic thresholds of structural response quantities at the component level, as defined in structural codes. Different approaches are also discussed to account for the randomness of the mechanical properties and ground motion input within the proposed methodology. An application of the assessment of different limit state probabilities of members from a reinforced concrete building is presented, for which limit states and limit state capacities are defined according to the upcoming Part 3 of the Eurocode 8. Although the presented application only deals with member chord rotation and shear force limit state probabilities, the proposed methodology can be generalized to other deformation-based and force-based structural parameters.     

Wave disturbance behind low-crested structures: Diffraction and overtopping effects

In recent years the hydraulic performance of low-crested structures has been widely studied both theoretically and through experimental analyses, but only a few studies have been focused on the combined diffraction-overtopping effects on wave transmission and induced wave currents.In this paper hydraulic model tests conducted at the 3D wave basin of Delft University of Technology (Cáceres et al., 2008) were used to obtain and discuss two simple methods for predicting the wave height at the lee of a single detached breakwater of finite length and the related current regime. For the first time diffraction effects are expressly accounted for. The agreement with experimental data is encouraging.The main objective of the paper is to aid engineers in the first stage of the design process, when using a mathematical model could be unnecessarily excessive.     

Construction of an evolutionary deglaciation model for the Irish midlands based on the integration of morphostratigraphic and geophysical data analyses

Alternative, established models for the deglaciation of the midlands of Ireland are tested against an interpretation of a suite of deglacial sediments covering an area of 600 km² in the east central midland area. Interpretation of the sediments is based on geomorphological mapping, lithostratigraphic characterization of exposures and geotechnical data supported by electrical resistivity tomography (ERT) and ground penetrating radar (GPR). GPR depicted small‐scale sedimentological and deformational structures within low‐conductivity soft sediments, such as cross‐bedding, planar bedding, channel‐like features and faulting planes, and revealed the internal architecture of eskers, glaciodeltas, subaqueous fans and raised bogs. ERT data permitted the detection of depth to bedrock and the lithological characterization of unconsolidated sediments. The ten sites presented were surveyed by traditional mapping methods and/or geophysical techniques. This allowed the construction of a local model of the deglaciation of the area which recognized five main stages. An ice sheet covering most of Ireland withdrew as a single body as far as the midlands. At this stage, two main directions of ice retreat are identified from the spatial distribution of meltwater/overflow channels, esker and morainic ridges, and ice‐marginal glaciolacustrine deposits. A pattern of deglacial sedimentation into an expanding ice‐marginal glacial lake is depicted. The glacial lake was dammed to the west by two ice dome fronts, one decaying to the north‐west and another to the south‐west, and by the Shannon Basin watershed to the east. Glacial lake outlets identified along the watershed and the altitude of the topset/foreset interface zone depicted in glaciodeltaic deposits allowed the identification of three lake water levels. The highest level is at 87–89 m Ordnance Datum (OD), the second lake level at 84 m OD and the third at 78 m OD. Copyright © 2012 John Wiley & Sons, Ltd.     

New cranial remains of titanosaurian sauropod dinosaurs from the Late Cretaceous of Fox-Amphoux-Métisson (Var,SE France)

The Fox-Amphoux Syncline of the Aix Basin (SE France) has yielded a diverse Late Cretaceous vertebrate assemblage, including several taxa of dinosaurs. Here, we report on cranial material of titanosaurian sauropods, which consist of a partial braincase, two fragmentary skull roofs, and nine teeth, from the Métisson locality (Var Department). The braincase differs from those found previously in Europe (i.e., Ampelosaurus atacis, Lirainosaurus astibiae, and an unnamed juvenile skull from Romania) as well as from other titanosaurian braincases in having a groove that extends along the ventral surface of the occipital condyle neck (this feature may be autapomorphic). One of the fragmentary skull roofs may belong to the same taxon, whereas the other suggests the presence of a second titanosaur at Métisson very close to Ampelosaurus. Two dental morphologies are present in the sample; one of them includes teeth of different sizes. We suggest that this could be accounted for by age differences within a single taxon, or be due to different positions in the tooth row. The presence of a new, still unnamed titanosaurian taxon in the Ibero-Armorican Island supports previous works indicating a high titanosaurian diversity during the Campanian-Maastrichtian in southern Europe.