On the role of spatial resolution on snow estimates using a process‐based snow model across a range of climatology and elevation

Hydrological processes in mountainous settings depend on snow distribution, whose prediction accuracy is a function of model spatial scale. Although model accuracy is expected to improve with finer spatial resolution, an increase in resolution comes with modelling costs related to increased computational time and greater input data and parameter information. This computational and data collection expense is still a limiting factor for many large watersheds. Thus, this work's main objective is to question which physical processes lead to loss in model accuracy with regard to input spatial resolution under different climatic conditions and elevation ranges. To address this objective, a spatially distributed snow model, iSnobal, was run with inputs distributed at 50‐m—our benchmark for comparison—and 100‐m resolutions and with aggregated (averaged from the fine to the large resolution) inputs from the 50‐m model to 100‐, 250‐, 500‐, and 750‐m resolution for wet, average, and dry years over the Upper Boise River Basin (6,963 km²), which spans four elevation bands: rain dominated, rain–snow transition, and snow dominated below treeline and above treeline. Residuals, defined as differences between values quantified with high resolution (>50 m) models minus the benchmark model (50 m), of simulated snow‐covered area (SCA) and snow water equivalent (SWE) were generally slight in the aggregated scenarios. This was due to transferring the effects of topography on meteorological variables from the 50‐m model to the coarser scales through aggregation. Residuals in SCA and SWE in the distributed 100‐m simulation were greater than those of the aggregated 750 m. Topographic features such as slope and aspect were simplified, and their gradient was reduced due to coarsening the topography from the 50‐ to 100‐m resolution. Therefore, solar radiation was overestimated, and snow drifting was modified and caused substantial SCA and SWE underestimation in the distributed 100‐m model relative to the 50‐m model. Large residuals were observed in the wet year and at the highest elevation band when and where snow mass was large. These results support that model accuracy is substantially reduced with model scales coarser than 50 m.     

Damage mechanics applied to performance‐based design of reinforced concrete columns

Performance‐based design methodology is based on reaching performance objectives that are associated to certain damage conditions. These performance objectives are related to the seismic hazard and to the performance levels. In actual application, reliable tools are required for capturing the evolution of the damage condition as well as for measuring and locating it. Moreover, it is essential to accurately establish the relationship between the damage and the performance levels. This paper shows the application of damage mechanics to performance‐based design. A layered damage mechanics‐based finite element program is presented with a discussion on modeling for prediction of the response of normal‐strength and high‐strength concrete columns subjected to cyclic flexural loading and various axial load levels. The damage indices derived from these analyses were used to elaborate several damage charts expressed as a function of drift and displacement ductility. This makes it possible to establish a relationship between the damage state and the performance levels. Results have demonstrated the ability of the damage mechanics modeling to accurately predict the behavior of the specimens tested. Copyright © 2017 John Wiley & Sons, Ltd.     

Evaluation of a Finite-Element Sea-Ice Ocean Model (FESOM) set-up to study the interannual to decadal variability in the deep-water formation rates

The characteristics of a global set-up of the Finite-Element Sea-Ice Ocean Model under forcing of the period 1958–2004 are presented. The model set-up is designed to study the variability in the deep-water mass formation areas and was therefore regionally better resolved in the deep-water formation areas in the Labrador Sea, Greenland Sea, Weddell Sea and Ross Sea. The sea-ice model reproduces realistic sea-ice distributions and variabilities in the sea-ice extent of both hemispheres as well as sea-ice transport that compares well with observational data. Based on a comparison between model and ocean weather ship data in the North Atlantic, we observe that the vertical structure is well captured in areas with a high resolution. In our model set-up, we are able to simulate decadal ocean variability including several salinity anomaly events and corresponding fingerprint in the vertical hydrography. The ocean state of the model set-up features pronounced variability in the Atlantic Meridional Overturning Circulation as well as the associated mixed layer depth pattern in the North Atlantic deep-water formation areas.     

A field demonstration of the simulation optimization approach for remediation system design

While significant progress has been made in the theoretical development of the simulation/optimization (S/O) approach for ground water remediation design, its application to large, field-scale problems has remained limited. To demonstrate the applicability and usefulness of the S/O approach under real field conditions, an optimization demonstration project was conducted at the Massachusetts Military Reservation in Cape Cod, Massachusetts, involving the design of a pump-and-treat system for the containment and cleanup of a large trichloroethylene (TCE) plume. The optimization techniques used in this study are based on evolutionary algorithms coupled with a response function approach for greater computational efficiency. The S/O analysis was performed parallel to a conventional trial-and-error analysis based on simulation alone. The results of this study demonstrate that not only would it be possible to remove more TCE mass under the same amount of pumping assumed in the trial-and-error design, but also substantial cost savings could be achieved by reducing the number of wells needed and adapting dynamic pumping. In spite of the large model size of more than 500,000 nodes and a long planning horizon of 30 years, the optimization modeling was carried out successfully on desktop PCs. This field demonstration project clearly illustrates the potential benefits of applying optimization techniques in remediation system design.     

Influence of rainfall spatial variability on flood prediction

This paper deals with the sensitivity of distributed hydrological models to different patterns that account for the spatial distribution of rainfall: spatially averaged rainfall or rainfall field. The rainfall data come from a dense network of recording rain gauges that cover approximately 2000 km² around Mexico City. The reference rain sample accounts for the 50 most significant events, whose mean duration is about 10 h and maximal point depth 170 mm. Three models were tested using different runoff production models: storm-runoff coefficient, complete or partial interception. These models were then applied to four fictitious homogeneous basins, whose sizes range from 20 to 1500 km². For each test, the sensitivity of the model is expressed as the relative differences between the empirical distribution of the peak flows (and runoff volumes), calculated according to the two patterns of rainfall input: uniform or non-uniform. Differences in flows range from 10 to 80%, depending on the type of runoff production model used, the size of the basin and the return period of the event. The differences are generally moderate for extreme events. In the local context, this means that uniform design rainfall combining point rainfall distribution and the probabilistic concept of the areal reduction factor could be sufficient to estimate major flood probability. Differences are more significant for more frequent events. This can generate problems in calibrating the hydrological model when spatial rainfall localization is not taken into account: a bias in the estimation of parameters makes their physical interpretation difficult and leads to overestimation of extreme flows.     

Erosion rather than plant dieback as the mechanism of marsh loss in an estuarine marsh

Coastal marsh loss in Louisiana is attributed to plane dieback caused by processes that stress vegetation, and a common landscape pattern is broken marsh that expands at the expense of surrounding unbroken marsh. We tested the hypothesis that vegetation is more stressed in broken marsh than in adjacent unbroken marsh, as indicated by vegetation aboveground biomass, species diversity and soil Eh, on transects that extended from broken marsh to unbroken marsh at Marsh Island, Louisiana. Soil Eh, vegetation above-ground biomass and species diversity did not differ between broken marsh and unbroken marsh, and above-ground biomass was similar to that reported from other marshes. Thus, we rejected the hypothesis that marsh loss is related to vegetation stress. Two factors were related to vegetation vigour: soil drainage and soil bulk density. Surprisingly, significant soil drainage occurred in broken marsh but not in unbroken marsh. Above-ground biomass of the dominant plant, Spartina patens (Aiton) Muhl., was lowest where soil bulk density was less than 0-08 gcm⁻³, which illustrated the importance of mineral matter accumulation in submerging coastal marshes. The mechanism of marsh loss appeared to be erosion below the living root zone, as indicated by the vertical and often undercut marsh-water interface, and by the separation of sod clasts. This is different from more rapid marsh loss associated with plant stress which we observed in other Louisiana marshes only 135 km away, indicating that marsh loss mechanisms can vary spatially even within a relatively small region.     

Timescale dependence in river channel migration measurements

Accurately measuring river meander migration over time is critical for sediment budgets and understanding how rivers respond to changes in hydrology or sediment supply. However, estimates of meander migration rates or streambank contributions to sediment budgets using repeat aerial imagery, maps, or topographic data will be underestimated without proper accounting for channel reversal. Furthermore, comparing channel planform adjustment measured over dissimilar timescales are biased because short- and long-term measurements are disproportionately affected by temporary rate variability, long-term hiatuses, and channel reversals. We evaluate the role of timescale dependence for the Root River, a single threaded meandering sand- and gravel-bedded river in southeastern Minnesota, USA, with 76 years of aerial photographs spanning an era of landscape changes that have drastically altered flows. Empirical data and results from a statistical river migration model both confirm a temporal measurement-scale dependence, illustrated by systematic underestimations (2–15% at 50 years) and convergence of migration rates measured over sufficiently long timescales (> 40 years). Frequency of channel reversals exerts primary control on measurement bias for longer time intervals by erasing the record of observable migration. We conclude that using long-term measurements of channel migration for sediment remobilization projections, streambank contributions to sediment budgets, sediment flux estimates, and perceptions of fluvial change will necessarily underestimate such calculations. © 2019 John Wiley & Sons, Ltd.     

Lava effusion rates from hand-held thermal infrared imagery: an example from the June 2003 effusive activity at Stromboli

A safe, easy and rapid method to calculate lava effusion rates using hand-held thermal image data was developed during June 2003 at Stromboli Volcano (Italy). We used a Forward Looking Infrared Radiometer (FLIR) to obtain images of the active lava flow field on a daily basis between May 31 and June 16, 2003. During this time the flow field geometry and size (where flows typically a few hundred meters long were emplaced on a steep slope) meant that near-vertical images of the whole flow field could be captured in a single image obtained from a helicopter hovering, at an altitude of 750 m and ∼1 km off shore. We used these images to adapt a thermally based effusion rate method, previously applied to low and high spatial resolution satellite data, to allow automated extraction of effusion rates from the hand-held thermal infrared imagery. A comparison between a thermally-derived (0.23–0.87 m³ s⁻¹) and dimensionally-derived effusion rate (0.56 m³ s⁻¹) showed that the thermally-derived range was centered on the expected value. Over the measurement period, the mean effusion rate was 0.38±0.25 m³ s⁻¹, which is similar to that obtained during the 1985–86 effusive eruption and the time-averaged supply rate calculated for normal (non-effusive) Strombolian activity. A short effusive pulse, reaching a peak of ∼1.2 m³ s⁻¹, was recorded on June 3, 2003. One explanation of such a peak would be an increase in driving pressure due to an increase in the height of the magma contained in the central column. We estimate that this pulse would require the magma column to attain a height of ∼190 m above the effusive vent, which is approximately the elevation difference between the vent and the floor of the NE crater. Our approach gives an easy-to-apply method that has the potential to provide effusion rate time series with a high temporal resolution.Editorial responsibility: M. Carroll     

Ingested plastic in a diving seabird, the thick-billed murre (Uria lomvia), in the eastern Canadian Arctic

Plastic debris has become ubiquitous in the marine environment and seabirds may ingest debris which can have deleterious effects on their health. In the North Atlantic Ocean, surface feeding seabirds typically ingest high levels of plastic, while the diving auks which feed in the water column typically have much lower levels. We examined 186 thick-billed murres from five colonies in the eastern Canadian Arctic for ingested plastic debris. Approximately 11% of the birds had at least one piece of plastic debris in their gastrointestinal tracts, with debris dominated by user plastics. This is the first report of ingested plastics in an auk species in Canada’s Arctic, and the highest incidence of plastic ingestion to date for thick-billed murres (Uria lomvia).     

Post-depositional fracturing and subsidence of pumice flow deposits: Lascar Volcano,Chile

Unconsolidated pyroclastic flow deposits of the 1993 eruption of Lascar Volcano, Chile, have, with time, become increasingly dissected by a network of deeply penetrating fractures. The fracture network comprises orthogonal sets of decimeter-wide linear voids that form a pseudo-polygonal grid visible on the deposit surface. In this work, we combine shallow surface geophysical imaging tools with remote sensing observations and direct field measurements of the deposit to investigate these fractures and their underlying causal mechanisms. Based on ground penetrating radar images, the fractures are observed to have propagated to depths of up to 10 m. In addition, orbiting radar interferometry shows that deposit subsidence of up to 1 cm/year⁻¹ occurred between 1993 and 1996 with continued subsidence occurring at a slower rate thereafter. In situ measurements show that 1 m below the surface, the 1993 deposits remain 5°C to 15°C hotter, 18 years after emplacement, than adjacent deposits. Based on the observed subsidence as well as estimated cooling rates, the fractures are inferred to be the combined result of deaeration, thermal contraction, and sedimentary compaction in the months to years following deposition. Significant environmental factors, including regional earthquakes in 1995 and 2007, accelerated settling at punctuated moments in time. The spatially variable fracture pattern relates to surface slope and lithofacies variations as well as substrate lithology. Similar fractures have been reported in other ignimbrites but are generally exposed only in cross section and are often attributed to formation by external forces. Here we suggest that such interpretations should be invoked with caution, and deformation including post-emplacement subsidence and fracturing of loosely packed ash-rich deposits in the months to years post-emplacement is a process inherent in the settling of pyroclastic material.