How did the suspended sediment load change in the North Caucasus during the Anthropocene?

Quantifying and understanding catchment sediment fluxes is crucial both from a scientific and environmental management perspective. To deepen the understanding of landuse impacts and climate change on sediment load, we explore factors controlling the suspended sediment load formation in the Northern Caucasus during the Anthropocene. We examine how sediment flux of various river basins with different land-use/landcover and glacier cover changes during the 1925–2018 period. Our analysis is based on observed mean annual suspended sediment discharges (SSD, kg s⁻¹) and annual fluxes (SSL, t year⁻¹) from 33 gauging stations of The Federal Service for Hydrometeorology and Environmental Monitoring (Russia). SSL series have been analysed to detect statistically significant changes during the 1925–2018 period. The occurrence of abrupt change points in SSD was investigated using cumulative sum (CUSUM) charts. We found that SSL has decreased by −1.17% per year on average at most gauges. However, the decline was not linear. Several transition years are expected in the region increasing trends from the 1950s and decreasing trends from 1988 to 1994. Correlation analyses showed that variation in SSL trend values is mainly explained by gauging station altitude, differences in landuse (i.e. the fraction of cropland), and catchment area. Nonetheless, more accurate quantifications of SSL trend values and more refined characterizations of the catchments regarding (historical) landuse, soil types/lithology, weather conditions, and topography may reveal other tendencies.     

How do hydrologic modeling decisions affect the portrayal of climate change impacts?

End users face a range of subjective decisions when evaluating climate change impacts on hydrology, but the importance of these decisions is rarely assessed. In this paper, we evaluate the implications of hydrologic modelling choices on projected changes in the annual water balance, monthly simulated processes, and signature measures (i.e. metrics that quantify characteristics of the hydrologic catchment response) under a future climate scenario. To this end, we compare hydrologic changes computed with four different model structures – whose parameters have been obtained using a common calibration strategy – with hydrologic changes computed with a single model structure and parameter sets from multiple options for different calibration decisions (objective function, local optima, and calibration forcing dataset). Results show that both model structure selection and the parameter estimation strategy affect the direction and magnitude of projected changes in the annual water balance, and that the relative effects of these decisions are basin dependent. The analysis of monthly changes illustrates that parameter estimation strategies can provide similar or larger uncertainties in simulations of some hydrologic processes when compared with uncertainties coming from model choice. We found that the relative effects of modelling decisions on projected changes in catchment behaviour depend on the signature measure analysed. Furthermore, parameter sets with similar performance, but located in different regions of the parameter space, provide very different projections for future catchment behaviour. More generally, the results obtained in this study prompt the need to incorporate parametric uncertainty in multi‐model frameworks to avoid an over‐confident portrayal of climate change impacts. Copyright © 2015 John Wiley & Sons, Ltd.     

How does afforestation affect the hydrology of a blanket peatland? A modelling study

Over the last century, afforestation in Ireland has increased from 1% of the land area to 10%, with most plantations on upland drained blanket peatlands. This land use change is considered to have altered the hydrological response and water balance of upland catchments with implications for water resources. Because of the difficulty of observing these long‐term changes in the field, the aim of this study was to utilize a hydrological model to simulate the rainfall runoff processes of an existing pristine blanket peatland and then to simulate the hydrology of the peatland if it were drained and afforested. The hydrological rainfall runoff model (GEOtop) was calibrated and validated for an existing small (76 ha) pristine blanket peatland in the southwest of Ireland for the 2‐year period, 2007–2008. The current hydrological response of the pristine blanket peatland catchment with regard to streamflow and water table (WT) levels was captured well in the simulations. Two land use change scenarios of afforestation were also examined, (A) a young 10‐year‐old and (B) a semi‐mature 15‐year‐old Sitka Spruce forest. Scenario A produced similar streamflow dynamics to the pristine peatland, whereas total annual streamflow from Scenario B was 20% lower. For Scenarios A and B, on an annual average basis, the WT was drawn down by 16 and 20 cm below that observed in the pristine peatland, respectively. The maximum WT draw down in Scenario B was 61 cm and occurred in the summer months, resulting in a significant decrease in summer streamflow. Occasionally in the winter (following rainfall), the WT for Scenario B was just 2 cm lower than the pristine peatland, which when coupled with the drainage networks associated with afforestation led to higher peak streamflows. Copyright © 2012 John Wiley & Sons, Ltd.     

How do streamflow generation mechanisms affect watershed hypsometry?

Several studies have shown that the dominant streamflow generation mechanism in a river basin can leave distinct geomorphological signatures in basin topography. In particular, it has been suggested previously that basins generated by groundwater discharge tend to have a larger hypsometric integral than surface runoff basins because fluvial erosion is more focused in the valleys where groundwater discharge tends to occur. In this analysis, we aim to clarify this relationship by developing an alternative method to quantify the effects of streamflow generation mechanisms on basin hypsometry and by using a numerical model that can generate streamflow by different processes to evaluate the sensitivity of the results to the hydrological and geomorphological properties of the basin. The model results suggest that the hypsometric characteristics that are usually associated with groundwater discharge basins, such as a larger hypsometric integral, occur primarily when drainage networks are still advancing in the watershed. During later stages of development, an additional factor such as lithological controls or a distinct geomorphological process would be needed to preserve these features. The model results also show that the hypsometric effects are stronger when the parameters of the fluvial erosion process promote the influence of small discharge rates. Copyright © 2007 John Wiley & Sons, Ltd.     

Impacts of major volcanic eruptions over the past two millennia on both global and Chinese climates: A review

Major volcanic eruptions(MVEs) have attracted increasing attention from the scientific community. Previous studies have explored the climatic impact of MVEs over the past two millennia. However, proxy-based reconstructions and climate model simulations indicate divergent responses of global and China’s regional climates to MVEs. Here, we used multiple data from observations, reconstructions, simulations, and assimilations to summarize the historical facts of MVEs, the characteristics and mechani...     

New insights on the tsunami recording of the May, 21, 2003, Mw 6.9 Boumerdès earthquake from tidal data analysis

We analyzed sea level data from a set of tide gauge stations located in the central and western Mediterranean Sea, that recorded the tsunami generated by the Mw 6.8 Boumerdès earthquake striking the coast of Algeria on May 21, 2003. This earthquake caused more than 2200 victims and thousands of injured. The causative fault was located a few kilometers offshore and during the rupture a tsunami was triggered. Waves were felt along a large part of the western and northern Mediterranean coasts, and in the Balearic islands waves higher that 2 m were measured. In this paper we analyze a more complete tidal data set, with respect to previous studies, now consisting of 22 tidal stations located in Italy, France and Spain. To characterize the change of the tidal signal at each station we used the Empirical Mode Decomposition (EMD). By means of this technique, which is suitable to analyze and to characterize the dynamical behavior of non-stationary time series, we provide a precise measurement of the arrival times and amplitudes at the tidal stations and identify how this tsunami affected the principal and long term tidal components. Our findings improve previous results for this earthquake, since they allow the detection of significant amplitude fluctuations associated with the tsunami in the majority of stations, including the farthest ones.     

Research on the Characteristics of Large Earthquake Activity on the Active Tectonic Boundaries on the Chinese Mainland

INTRODUCTIONThe active blocks refer tothe geologic units that formedinlate Cenozoic (100 ~120 ka BP) andhave been highly active as fault zones since late Quaternary with relatively uniform motion styles(Zhang Guomin,et al .,2000 ;Zhang Peizhen,et al .,2003) .The active blocks are relativelyintactand have uniformmotion modalities ,their boundary zones (also called the active boundaries) are thelocalized or centralized zones of interactions and differential movement among the active block…     

How does DEM resolution affect microtopographic characteristics,hydrologic connectivity,and modelling of hydrologic processes?

The resolution of a digital elevation model (DEM) is a crucial factor in watershed hydrologic and environmental modelling. DEM resolution can cause significant variability in the representation of surface topography, which further affects quantification of hydrologic connectivity and simulation of hydrologic processes. The objective of this study is to examine the effects of DEM resolution on (1) surface microtopographic characteristics, (2) hydrologic connectivity, and (3) the spatial and temporal variations of hydrologic processes. A puddle‐to‐puddle modelling system was utilized for surface delineation and modelling of the puddle‐to‐puddle overland flow dynamics, surface runoff, infiltration, and unsaturated flow for nine DEM resolution scenarios of a field plot surface. Comparisons of the nine modelling scenarios demonstrated that coarser DEM resolutions tended to eliminate topographic features, reduce surface depression storage, and strengthen hydrologic connectivity and surface runoff. We found that reduction in maximum depression storage and maximum ponding area was as high as 97.56% and 76.36%, respectively, as the DEM grid size increased from 2 to 80 cm. The paired t‐test and fractal analysis demonstrated the existence of a threshold DEM resolution (10 cm for the field plot), within which the DEM‐based hydrologic modelling was effective and acceptable. The effects of DEM resolution were further evaluated for a larger surface in the Prairie Pothole Region subjected to observed rainfall events. It was found that simulations based on coarser resolution DEMs (>10 m) tended to overestimate ponded areas and underestimate runoff discharge peaks. The simulated peak discharge from the Prairie Pothole Region surface reduced by approximately 50% as the DEM resolution changed from 2 to 90 m. Fractal analysis results elucidated scale dependency of hydrologic and topographic processes. In particular, scale analysis highlighted a unique constant–threshold–power relationship between DEM scale and topographic and hydrologic parameters/variables. Not only does this finding allow one to identify threshold DEM but also further develop functional relationships for scaling to achieve valid topographic characterization as well as effective and efficient hydrologic modelling. Copyright © 2016 John Wiley & Sons, Ltd.     

Observations of the Hα hydrogen emission on Spitsbergen during the proton event of January 22, 2012

The behavior of the Hα hydrogen emission at Barentsburg observatory during precipitation of high-energy solar protons and sudden impulse (SI) on January 22, 2012, was studied. The emission intensity was determined with a spectrometer, which gives the meridian arc spectrum image. It has been shown that the Hα emission luminosity onset coincides with SI and is caused by precipitation of solar wind protons through the cusp.     

Influence of volcanic glass on the magnetic signal of different paleosols in Córdoba,Argentina

This contribution comprises geological and magnetic results obtained in loess and paleosols profiles outcropped in the Pampean plain (Argentina). The sedimentary sequence exposed in Córdoba province is represented by four profiles Corralito I, Corralito II, Monte Ral815o and Lozada, 32°S 64°14'W (Argentina). These profiles were mineralogically described and magnetically analyzed. The sediments that compound the profiles contain volcanic glass between 20 and 90%. The results of two paleosols with different percentage of volcanic glass in the parent material (correlated to Marine Isotope Stage 5, MIS 5) exposed at Corralito I and Lozada, were compared; an important relationship between environmental magnetism signal and volcanic glass content was observed. All the results suggest that there are variations between different paleosols of the same area and age; such variations are attributed to content of volcanic glass in parent material; time of exposure of the parent material to pedogenic processes; and geomorphological place of each profile. At present, it is not possible to quantify certainly the paleo-precipitation index. Only qualitative interpretation can be done taking into account many variables of the geological system.     

Did the 1999 earthquake swarm on Gakkel Ridge open a volcanic conduit? A detailed teleseismic data analysis

In 1999, a seismic swarm of 237 teleseismically recorded events marked a submarine eruption along the Arctic Gakkel Ridge, later on also analyzed by sonar, bathymetric, hydrothermal, and local seismic studies. We relocated the swarm with the global location algorithm HYPOSAT and analyzed the waveforms of the stations closest to the events by cross-correlation. We find event locations scattered around 85°35^′ N and 85° E at the southern rift wall and inside the rift valley of the Gakkel Ridge. Waveforms of three highly correlating events indicate a volumetric moment tensor component and highly precise referenced double-difference arrival times lead us to believe that they occur at the same geographical position and mark the conduit located further southeast close to a chain of recently imaged volcanic cones. This result is supported by station residual anomalies in the direction of the potential conduit. Seismicity is focused at the crust–mantle boundary at 16–20 km depth, but ascending toward the potential conduit during the beginning of April 1999, indicating an opening of the vent.     

Palaeoenvironment reconstruction,volcanic evolution and geochronology of the Cerro Blanco subcomplex,Nevados de Chillán volcanic complex,central Chile

Nevados de Chillán Volcanic Complex, central Chile, has been active for at least 640 ka—a period spanning a number of glacial and interglacial periods. Geologic mapping, radiometric dating and geochemical analysis have identified six new volcanic units and produced four new ⁴⁰Ar/³⁹Ar ages for Cerro Blanco, the northern subcomplex of Nevados de Chillán volcano. Compositions range from dacite to basaltic-andesite and a new geologic map is presented. Examination of lava fracture structures on both newly mapped lavas and those mapped during previous studies has enabled interpretations of former eruptive environments. Palaeoenvironment reconstructions, combined with ⁴⁰Ar/³⁹Ar ages and comparison with the marine oxygen isotope record, show that at least three phases of volcanic activity have occurred during the evolution of Cerro Blanco: (1) a constructive, pre-caldera collapse period; (2) a period of caldera formation and collapse; and (3) a constructive period of dome growth forming the modern day volcanic centre. This style of volcanic evolution, whereby large-scale caldera collapse is followed by growth of a new stratocone is common at Andean volcanoes.     

The December 26, 2004, tsunami on Sumatra Island as a source of internal gravity waves in the earth’s atmosphere

Records of the coastal mareographs during the December 26, 2004, tsunami are used to study the fine structure of the tsunami wave power spectra. It is shown that a series of maxima is observed in their spectra near the source in a range of internal gravity wave frequencies of 0.2–1.2 mHz, which coincides with the frequencies of the natural oscillations of the Earth. This experimental finding enables us to propose a possible physical mechanism for the formation of tsunami waves as a result of oscillations in the sea bottom at these frequencies. Internal gravity waves in the Earth’s atmosphere excited in this way are found in the variations of the total electron content that resulted from this powerful earthquake.     

A field,laboratory, and literature review evaluation of the water retention curve of volcanic ash soils: How well do standard laboratory methods reflect field conditions?

Accurate determination of the water retention curve (WRC) of a soil is essential for the understanding and modelling of the subsurface hydrological, ecological, and biogeochemical processes. Volcanic ash soils with andic properties (Andosols) are recognized as important providers of ecological and hydrological services in mountainous regions worldwide due to their large fraction of small size particles (clay, silt, and organic matter) that gives them an outstanding water holding capacity. Previous comparative analyses of in situ (field) and standard laboratory methods for the determination of the WRC of Andosols showed contrasting results. Based on an extensive analysis of laboratory, experimental, and field measured WRCs of Andosols in combination with data extracted from the published literature we show that standard laboratory methods using small soil sample volumes (≤300 cm³) mimic the WRC of these soils only partially. The results obtained by the latter resemble only a small portion of the wet range of the Andosols' WRC (from saturation up to −5 kPa, or pF 1.7), but overestimate substantially their water content for higher matric potentials. This discrepancy occurs irrespective of site-specific land use and cover, soil properties, and applied method. The disagreement limits our capacity to infer correctly subsurface hydrological behaviour, as illustrated through the analysis of long-term soil moisture and matric potential data from an experimental site in the tropical Andes. These findings imply that results reported in past research should be used with caution and that future research should focus on determining laboratory methods that allow obtaining a correct characterization of the WRC of Andosols. For the latter, a set of recommendations and future directions to solve the identified methodological issues is proposed.     

Long-term Spatially Distributed Solutional Erosion: How Do We Put Solutes on the Map?

Much of the short-term solute process research in the last 20 years has focused on hydrochemical behaviour. This can help with the identification of solute source area type, but not the actual location of the solutional loss. The location and the spatial distribution of erosion are crucial to the identification of long-term landscale evolution. The way ahead lies in the fact that catchment budgeting and geochemical studies have been able to provide solute uptake rates. If these can be related to soil type, through a knowledge of soil mineralogy, reactive surface area and water flow rate, it may be possible to characterize the location and spatial distribution of solutional erosion through terrain analysis and soil maps in a geographical information system. © 1997 by John Wiley & Sons, Ltd.     

How can stream bank erosion be predicted on small water courses?Veri?cation of BANCS model on the Kubrica watershed

The current paper deals with the evaluation of the BANCS erosion prediction model and its two componentsethe Bank Erosion Hazard Index(BEHI) and Near-Bank Stress(NBS) indices. To construct the erosion prediction curves, 18 experimental sections were established on the Kubrica Stream, district of Trencín, Slovakia. Each section was assessed through the NBS index and BEHI index and real annual bank erosion was measured using erosion toe pins. Subsequently, the relations between the BEHI and real annual bank erosion was assessed through regression and correlation analyses. The relation proved to be moderately strong, with the correlation coefficient(R) reaching 0.47. Further, the relation between the NBS index and real annual bank erosion was evaluated, which was also moderately strong, with R= 0.65.Based on the measured data, two erosion prediction curves were constructed, the first for moderate BEHI, with R= 0.69 and coefficient of determination(R~2) of 0.47 and the second for high BEHI with R=0.74 and R~2= 0.55. The prediction curves were based on data from one year of measurements and can, therefore, be used only for discharges that occurred within that year and in the region where the model was developed. In the current case, according to runoff Curve Numbers(CN), the real culmination discharge was Q ? 1.88 m~3/s, which is roughly equivalent to 1.5-year recurrence interval flow(Q_1.5).     

A note on katabatic winds at the coasts of Adélieland and King George V land

Summary The persistence and strength of the katabatic winds of Adélie Land and King George V Land of the Antarctic are caused by the big temperature difference between the air over the ice cap and the neighbouring open sea. On days with strong insolation over the ice cap the temperature difference becomes during the afternoon hours small. The marked lulls in the gales from the ice cap occur generally at these times, particularly in December when insolation and heating of the surface air over the ice cap are at a maximum.