Changes in the firn structure of the western Greenland Ice Sheet caused by recent warming

Atmospheric warming over the Greenland Ice Sheet during the last 2 decades has increased the amount of surface meltwater production, resulting in the migration of melt and percolation regimes to higher altitudes and an increase in the amount of ice content from refrozen meltwater found in the firn above the superimposed ice zone. Here we present field and airborne radar observations of buried ice layers within the near-surface (0–20 m) firn in western Greenland, obtained from campaigns between 1998 and 2014. We find a sharp increase in firn-ice content in the form of thick widespread layers in the percolation zone, which decreases the capacity of the firn to store meltwater. The estimated total annual ice content retained in the near-surface firn in areas with positive surface mass balance west of the ice divide in Greenland reached a maximum of 74 ± 25 Gt in 2012, compared to the 1958–1999 average of 13 ± 2 Gt, while the percolation zone area more than doubled between 2003 and 2012. Increased melt and column densification resulted in surface lowering averaging −0.80 ± 0.39 m yr−1 between 1800 and 2800 m in the accumulation zone of western Greenland. Since 2007, modeled annual melt and refreezing rates in the percolation zone at elevations below 2100 m surpass the annual snowfall from the previous year, implying that mass gain in the region is retained after melt in the form of refrozen meltwater. If current melt trends over high elevation regions continue, subsequent changes in firn structure will have implications for the hydrology of the ice sheet and related abrupt seasonal densification could become increasingly significant for altimetry-derived ice sheet mass balance estimates

Analysis of river bed dynamic evolution following a landslide dam

Landslides and debris flows can strongly interact with the river network and its mass transport processes, determining modifications of the river pattern with consequent effects on the hydrodynamic phenomena, alterations of the existing morphologies and possible interferences with anthropic works. Modifications of the cross section geometry and channel slope may produce changes in the sediment budget, with consequent repercussions on the stream evolutionary dynamics and its equilibrium configuration, leading to a new river branch arrangement. In this paper, investigations were carried out on a gravel-bed reach in the middle valley of the Noce River in Basilicata (Italy), which in 2007 suffered a progressive morpho-hydrodynamic change caused by a landslide. Because of the phenomenon complexity, mainly due to the mutual interaction between the landslide and the river transport dynamics, an integrated approach that combines field observations and numerical modelling in a spatial scale and natural environment, rarely available in literature, is suggested. The results highlight a satisfying correspondence between the altimetric profiles obtained through the numerical models and those deriving from the field surveys.Peer ReviewedPostprint (published version

The evaluation of rating curve in bed rivers with sediment transport

The measure of the water discharge in rivers is important within the cognitive actions addressed to identify a management policy concerning the water resources. In particular, it is essential for a planning of the interventions in a middle and long term in relation to the control activity and environmental protection respectly to the forecasting and prevention of natural hazard. The measure methods in natural channels are generally based on the use of hydrometers combined with rating curves in steady flows. The relation between water level and discharge is determined by measures of velocities in conditions of low and mean flows, and more rarely during high flows. In the latter case, practical difficulties in measurement lead to extrapolate discharge values on statistical basis which could involve significant errors in rating curves at high levels. Furthermore the steady rating curve cannot to estimate in rigorous way the discharges in presence of sediment transport, which often happens with the high flows modifying the geometrical and morphological river characteristics. In this context, the present work describes a numerical-experimental approach to estimate the water discharges on the basis of numerical models at fixed and mobile bed, calibrated by simultaneous measure series of water level and velocities in gauged stations. In the first step, the application of fixed bed model allowed a more accurate extrapolation of rating curves for elevated discharges through the roughness coefficient correction. Successively the use of the mobile bed model, considering simplified hypothesis, allowed to analyze the sediment transport effects on rating curve shape. The reliability of such approach has been evaluated on a gauged section located upstream a single thread alluvial reach in the middle valley of the Noce River in Basilicata region (Italy). This reach is characterized by a narrow and confined bed, which was interested by a progressive morpho-hydrodynamic change caused by a landslide in the right side slope of the basin in July 2007

Assessment methodology for the prediction of landslide dam hazard

This paper represents a contribution to the study of hazard caused by the interaction between landslides and river courses. The effects of such interferences are often catastrophic and could include the formation of upstream lakes, potential dam failure, river bed dynamics and morphological alterations. These scenarios could be substantially reduced if it was possible to predict the eventuality that a moving landslide would block the river. This is a complex topic because it involves composite geomorphic phenomena concerning both hillslope and river systems and their interpretation, through model approaches, is still under development and testing. In this study, a methodology developed in the framework of European Research Project IMPRINTS (FP7) was adopted and integrated in order to identify the areas of triggering and propagation of landslides and to characterize the possible scenarios of the interaction with river networks. Different deterministic and probabilistic approaches, calibrated using a case test in the middle valley of the Noce River in Basilicata (Italy), were applied and compared at basin scale

Analysis of river bed dynamic evolution following a landslide dam

Landslides and debris flows can strongly interact with the river network and its mass transport processes, determining modifications of the river pattern with consequent effects on the hydrodynamic phenomena, alterations of the existing morphologies and possible interferences with anthropic works. Modifications of the cross section geometry and channel slope may produce changes in the sediment budget, with consequent repercussions on the stream evolutionary dynamics and its equilibrium configuration, leading to a new river branch arrangement. In this paper, investigations were carried out on a gravel-bed reach in the middle valley of the Noce River in Basilicata (Italy), which in 2007 suffered a progressive morpho-hydrodynamic change caused by a landslide. Because of the phenomenon complexity, mainly due to the mutual interaction between the landslide and the river transport dynamics, an integrated approach that combines field observations and numerical modelling in a spatial scale and natural environment, rarely available in literature, is suggested. The results highlight a satisfying correspondence between the altimetric profiles obtained through the numerical models and those deriving from the field surveys.Peer Reviewe