Complexity‐reduction modelling for assessing the macro‐scale patterns of historical soil moisture in the Euro‐Mediterranean region

Complexity‐reduction modelling can be useful for increasing the understanding of how the climate affects basin soil moisture response upon historical times not covered by detailed hydrological data. For this purpose, here is presented and assessed an empirical regression‐based model, the European Soil Moisture Empirical Downscaling (ESMED), in which different climatic variables, easily available on the web, are addressed for simplifying the inherent complexity in the long‐time studies. To accommodate this simplification, the Palmer Drought Severity Index, the precipitation, the elevation and the geographical location were used as input data in the ESMED model for predicting annual soil moisture budget. The test area was a large region including central Europe and Mediterranean countries, and the spatial resolution was initially set at 50 km. ESMED model calibration was made according to the soil moisture values retrieved from the Terrestrial Water Budget Data archive by selecting randomly 285 grid points (out of 2606). Once parameterized, ESMED model was performed at validation stage both spatially and temporally. The spatial validation was made for the grid points not selected in the calibration stage while the comparison with the soil moisture outputs of the Global Land Data Assimilation System–NOAH10 simulations upon the period 1950–2010 was carried out for the temporal validation. Moreover, ESMED results were found to be in good agreement with a root‐zone soil moisture product obtained from active and passive microwave sensors from various satellite missions. ESMED model was thus found to be reliable for both the temporal and spatial validations and, hence, it might represent a useful tool to characterize the long‐term dynamics of soil moisture–weather interaction. Copyright © 2013 John Wiley & Sons, Ltd.     

Use of Remote Imagery to Analyse Changes in Morphology and Longitudinal Large Wood Distribution in the Blanco River After the 2008 Chaitén Volcanic Eruption,Southern Chile

The 2008 Chaitén volcanic eruption generated significant changes in the channel morphology and large wood (LW) abundance along the fluvial corridor of the Blanco River, southern Chile. Comparisons of remote sensing images from the pre‐eruption (year 2005) and post‐eruption (years 2009 and 2012) conditions showed that in a 10.2 km long study segment the Blanco River widened 3.5 times from 2005 to 2009, and that the maximum enlargement was nine times the original width. Changes in channel width were lower between the years 2012 and 2009. The sinuosity and braiding indexes also changed between 2005 and 2009. After the eruption the channel sinuosity was higher and specific river reaches developed a braided pattern, but by 2012 the channel was recovering pre‐eruption characteristics. Huge quantities of LW were introduced to the study segment; individual LW per km of channel length were 1.6 and 74.3 in 2005 and 2009, respectively, and more than 30 log jams km^?1 were observed in the year 2009. Between 2009 and 2012 the quantity of LW was very similar. Statistically significant relationships were found between the number of log jams and channel sinuosity and between the number of pieces of large wood with sinuosity and channel width. Wood was highly dynamic between 2009 and 2012: 78% of individual pieces and 48% of log jams identified in the 2009 image had moved by 2012. Finally the supervised classification of imagery associated with ArcMap tools was tested to identify large wood.     

Numerical solution of the discontinuous-bottom Shallow-water Equations with hydrostatic pressure distribution at the step

Free-surface flows are usually modelled by means of the Shallow-water Equations: this system of hyperbolic equations exhibits a source term which is proportional to the product of the water depth by the bed slope, and which takes into account the effect of gravity onto fluid mass. Recently, much attention has been paid to the case in which bottom discontinuities are present in the physical domain to be represented: in this case, it is difficult to define the non-conservative product in the distributional sense. Here, the discontinuous-bottom Shallow-water Equations with hydrostatic pressure distribution at the bed step (Bernetti et al., 2006) are discussed in the context of the theory of Dal Maso et al. (1995) [9]; finally, a first-order numerical scheme is presented, which is consistent for regular solutions, and which is able to capture contact discontinuities at bottom steps. Numerous tests are presented to show the feasibility of the scheme and its ability to converge to the exact solution in the cases of smooth as well as discontinuous bed profiles.     

6th April 2009 L��Aquila earthquake, Italy: reinforced concrete building performance

On 6th April 2009 an earthquake of magnitude M _w =  6.3 occurred in the Abruzzo region; the epicentre was very close to the city of L’Aquila (about 6 km away). The event produced casualties and damage to buildings, lifelines and other infrastructures. An analysis of the main damage that reinforced concrete (RC) structures showed after the event is presented in this study. In order to isolate the main causes of structural and non-structural damage, the seismological characteristics of the event are examined, followed by an analysis of the existing RC building stock in the area. The latter issue came under scrutiny after the release of official data about structural types and times of construction, combined with a detailed review of the most important seismic codes in force in the last 100 years in Italy. Comparison of the current design provisions of the Italian and European codes with previous standards allows the main weaknesses of the existing building stock to be determined. Damage to structural and non-structural elements is finally analyzed thanks to photographic material collected in the first week after the event; the main causes of damage are then inferred.     

Preliminary analysis of a soft‐storey mechanism after the 2009 L'Aquila earthquake

Observation of damage caused by the recent Abruzzo earthquake on April 6th 2009 showed how local interaction between infills and RC structures can lead to soft‐storey mechanisms and brittle collapses. Results of the present case study are based on observed damage caused by the earthquake in the zone of Pettino. Analytical model based on simulated design procedure was built up and time history analyses were employed to verify the causes of the structural collapse, as highlighted by observed damage. This failure mechanism was investigated taking into consideration all components of the ground motion. Nonlinear behavior of brick masonry infills was taken into account and two parametric hypotheses for infill mechanical properties were considered, given the uncertainties that typically characterize these nonstructural elements. Nonlinear modeling of infills was made by a three‐strut macro‐model aimed at considering both local and global interaction between RC frame and infills. Seismic input was characterized by the real signal registered during the mainshock near the case‐study structure. Different shear capacity models were considered in the assessment. Analytical results seem to confirm with good approximation the likely collapse scenario that damage observation highlighted; the lack of proper detailing in the columns made the local interaction between infills and RC columns and the strong vertical component of the ground motion to be the main causes of the brittle failure. Copyright © 2010 John Wiley & Sons, Ltd.     

Grain size and topographical differences between static and mobile armour layers

A series of laboratory flume experiments under conditions of sediment starvation (zero sediment feeding) and recirculation were conducted in order to identify the temporal evolution and surface properties of static and mobile armour layers. The experiments were carried out in an 8 m long flume using a bimodal grain‐size mixture (D₅₀ = 6·2 mm) and a range of shear stresses ranging from 4·0 to 8·6 N m^–2. The results confirm that a static armour layer is coarser than a mobile one, and that the grain size of a mobile armour layer is rather insensitive to changes in the imposed flow strength. An analysis of laser scan bed surveys revealed the highly structured and imbricated nature of the static armour layer. Under these conditions the vertical roughness length scale of the bed diminished and it became topographically less complex at higher forming discharges. The topography of mobile armour layers created by rising discharges differed. They exhibited a greater roughness length scale and were less organized, despite the fact that the grain size of the surface material maintained an approximately constant value during recirculation. Also, the mobile armour tended to create larger cluster structures than static armour layers when formed by higher discharges. These differences were mainly due to the transport of the coarser fraction of bed sediments, which diminished to zero over the static armour because of being hidden within the bed, whereas in the mobile armour the coarser particles protruded into the flow and were actively transported, increasing the vertical roughness length scale. Overall, the results show that an examination of the grain size characteristics of armour layers cannot be used to infer sediment mobility and bed roughness. Detailed elevation models of exposed surfaces of gravel‐bed rivers are required to provide critical insight on the sediment availability and sedimentation processes. Copyright © 2011 John Wiley & Sons, Ltd.