bluuebunny/crossref_metadata_2025 huggingface dataset:
The influence of hydrothermal alteration on volcano stability: a case study of La Soufrière de Guadeloupe (France)
Authors: Heap Michael , Baumann Tobias , Rosas-Carbajal Marina , Komorowski Jean-Christophe , Gilg H. Albert , Villeneuve Marlène , Moretti Roberto , Baud Patrick , Carbillet Lucille , Harnett Claire , Reuschlé Thierry
Published: March 2021

Volcanoes are inherently unstable structures that spread and frequently experience mass wasting events (such as slope failure, rockfalls, and debris flows). Hydrothermal alteration, common to many volcanoes, is often invoked as a mechanism that contributes significantly to volcano instability. We present here a study that combines laboratory deformation experiments, geophysical data, and large-scale numerical modelling to better understand the influence of hydrothermal alteration on volcano stability. La Soufrière de Guadeloupe (France) is a hazardous andesitic volcano that hosts a large hydrothermal system and therefore represents an ideal natural laboratory for our study. Uniaxial and triaxial deformation experiments were performed on samples prepared from 17 variably-altered (alteration minerals include quartz, cristobalite, tridymite, hematite, pyrite, alunite, natro-alunite, gypsum, kaolinite, and talc) blocks collected from La Soufrière de Guadeloupe. Our uniaxial compressive strength experiments show that strength and Young’s modulus decrease as a function of increasing porosity and increasing alteration. Triaxial deformation experiments show that cohesion decreases as a function of increasing alteration, but that the angle of internal friction does not change systematically. We first combined recent muon tomography data with our laboratory data to create a 3D strength map of La Soufrière de Guadeloupe. The low-strength zone beneath the southern flank of the volcano exposed by our 3D strength map is coincident with the hydrothermal system. We then assigned laboratory-scale and upscaled mechanical properties (e.g., Young’s modulus, cohesion, and angle of internal friction) to zones identified by a recent electrical survey of the dome of La Soufrière de Guadeloupe. Numerical modelling (using the software LaMEM) was then performed on a cross-section of the volcano informed by the recent electrical data, and on a cross-section in which we artificially increased the size of the hydrothermally altered zone. Our modelling shows (1) the importance of using upscaled values in large-scale models and (2) that hydrothermal alteration significantly increases the surface velocity and strain rate of the volcanic slope. We therefore conclude, using models informed by experimental data, that hydrothermal alteration decreases volcano stability and thus expedites volcano spreading and increases the likelihood of mass wasting events and associated volcanic hazards. Hydrothermal alteration, and its evolution, should therefore be monitored at active volcanoes worldwide.
How weakened cold pools open for convective self-aggregation
Authors: Nissen Silas Boye , Haerter Jan O.
Published: March 2021

In radiative-convective equilibrium (RCE) simulations, convective self-aggregation (CSA) is the spontaneous organization into segregated cloudy and cloud-free regions. Evidence exists for how CSA is stabilized, but how it arises favorably on large domains is not settled. Using large-eddy simulations (LES), we link the spatial organization emerging from the interaction of cold pools (CPs) to CSA. We systematically weaken simulated rain evaporation to reduce maximal CP radii, Rmax, and find reducing Rmax causes CSA to occur earlier. We further identify a typical rain cell generation time and a minimum radius, Rmin, around a given rain cell, within which the formation of subsequent rain cells is suppressed. Incorporating Rmin and Rmax, we propose a toy model that captures how CSA arises earlier on large domains: when two CPs of radii ri,j ∈ [Rmin, Rmax] collide, they form a new convective event. These findings imply that CPs play a crucial role in RCE simulations by preventing the onset of CSA.
Spatio-temporal analysis of precipitation-based drought indices in Kucuk Menderes River Basin, Turkey
Authors: Cavus Yonca , Eris Ebru , Aksoy Hafzullah , Burgan Halil Ibrahim , Aksu Hakan , Boyacioglu Hulya
Published: March 2021

Drought is one of the extreme hydrological events which may seriously affect the majority of the population in many ways such as economically, socially and environmentally. Researches on the drought analysis may prevent these adverse consequences to a significant extent. Droughts are characterized by using various meteorological and hydrological indicators (i.e. precipitation, temperature, streamflow etc.). These indicators are used to derive drought indices. Spatio-temporal drought is analysed both in time and space by using drought indices based on site-specific precipitation and temperature data. In this study, Standardized Precipitation Index (SPI) using only precipitation data and Standardized Precipitation Evapotranspiration Index (SPEI) using precipitation and temperature data are considered at various time scales changing from 1 to 24 months for a more detailed drought characterization. On the other hand, so-called Dimensionless Precipitation Anomaly Index (DPAI) is introduced at annual scale in this study. The DPAI is used to determine dry periods from the recorded precipitation data. Cases are studied in Kucuk Menderes River Basin located in the Aegean region of Turkey. Precipitation and temperature data obtained from five meteorological stations over the river basin are used to determine drought index time series. Drought risk graphs and drought severity maps are obtained from time series of the drought indices. Drought risk is the likelihood of the drought occurrence that is quantified with the frequency calculated from the SPI and SPEI time series. As for the drought severity maps, they are created to understand its basin-scale variation by using the severities calculated from the dry periods of SPI and SPEI time series. Results show that the prolonged severe historical dry periods of the river basin are correctly identified by the drought indices. These indices used in this study based on easily available meteorological data are simple tools to explain temporal variability at a site or spatial variability over the basin. Also, the spatial distribution of drought severity over the river basin does not show a significant variability though more severe droughts are observed in the inner part of the river basin. Mild drought dominates at each time scale, this stems from the tendency of precipitation fluctuating around the average. Results in the study have considerable importance both in science and practice of drought. Although the methodology established from basic tools using meteorological data, the outcomes of the study are expected to become beneficial for drought management plans.
3D tomographic imaging of the Cayman Trough lithosphere: challenges, ongoing work and first results
Authors: Gómez de la Peña Laura , Grevemeyer Ingo , Dannowsky Anke , Meléndez Adrià , Peirce Christine , van Avendonk Harm
Published: March 2021

About 25% of the Earth’s mid-ocean ridges spread at ultraslow rates of less than 20 mm/yr. However, most of these ultraslow spreading ridges are located in geographically remote areas, which hamper investigation. Consequently, how the crust forms and ages at such spreading centres, which traditional models predict to be magma-starved and cold, remains poorly understood.

CAYSEIS project was proposed to survey the Cayman Trough area in order to obtain new data that constraints the nature of the crust, tectonic structures, lithologies outcropping and hydrothermal processes taking place in this area, which includes the Mid Cayman ultra-slow spreading centre (MSCS) with spreading rates of ~15-17 mm/yr. Understanding the sub-seabed geophysical structure of the MCSC is key to understanding not only the lithologies and structures exposed at the seabed, but more fundamentally, how they are related at depth and what role hydrothermal fluid flow plays in the geodynamics of ultraslow spreading. CAYSEIS was a joint and multidisciplinary programme of German, British and US American top tier scientists designed for the obtaining of a new high-quality dataset, including 3D Wide-Angle Seismic (WAS), magnetic, gravimetric and seismological data.

We took leverage of the CAYSEIS dataset to invert a 3D velocity model of the Cayman Trough lithosphere using the Tomo3D code (Meléndez et al., 2015; 2019). This is one of the first times that the Tomo3D code is used for 3D inversion of real datasets. Thus, we are checking our results comparing them with travel time tomographic inversions of 2D lines and testing the different parameters to obtain the more accurate and higher resolution model as possible. The results of this experiment show not only the lithospheric structure along and across the MSCS, including the exhumed Ocean Core Complexes in the surrounding areas, but the 3D lithospheric configuration of the region which is important to understand the crustal formation processes and evolution of ultra-slow spreading settings.
The observation and modeling of air-land interaction over heterogeneous landscapes of the Third Pole
Authors: Ma Yaoming , Hu Zeyong , Wang Binbin , Zhong Lei , Ma Weiqiang , Han Cunbo , Chen Xuelong , Liu Lian , Subba Sunil , Xie Zhipeng , Wang Yuyang
Published: March 2021

The exchange of heat and water vapor between land surface and atmosphere over the Third Pole region (Tibetan Plateau and nearby surrounding region) plays an important role in Asian monsoon, westerlies and the northern hemisphere weather and climate systems. Supported by various agencies in the People’s Republic of China, a Third Pole Environment (TPE) observation and research Platform (TPEORP) is now implementing over the Third Pole region. The background of the establishment of the TPEORP, the establishing and monitoring plan of long-term scale (5-10 years) of it will be shown firstly. Then the preliminary observational analysis results, such as the characteristics of land surface energy fluxes partitioning and the turbulent characteristics will also been shown in this study. Then, the parameterization methodology based on satellite data and the atmospheric boundary layer (ABL) observations has been proposed and tested for deriving regional distribution of net radiation flux, soil heat flux, sensible heat flux and latent heat flux (evapotranspiration (ET)) and their variation trends over the heterogeneous landscape of the Tibetan Plateau (TP) area. To validate the proposed methodology, the ground measured net radiation flux, soil heat flux, sensible heat flux and latent heat flux of the TPEORP are compared to the derived values. The results showed that the derived land surface heat fluxes over the study areas are in good accordance with the land surface status. These parameters show a wide range due to the strong contrast of surface feature. And the estimated land surface heat fluxes are in good agreement with ground measurements, and all the absolute percent difference in less than 10% in the validation sites. The sensible heat flux has increased slightly and the latent heat flux has decreased from 2001 to 2018 over the TP. It is therefore conclude that the proposed methodology is successful for the retrieval of land surface heat fluxes and ET over heterogeneous landscape of the TP area. Further improvement of the methodology and its applying field over the whole Third Pole region and Pan-Third Pole region were also discussed.
Reservoir Computing as a Tool for Climate Predictability Studies
Authors: Nadiga Balasubramanya
Published: March 2021

  Reduced-order dynamical models play a central role in developing our
  understanding of predictability of climate irrespective of whether
  we are dealing with the actual climate system or surrogate climate
  models. In this context, the Linear Inverse Modeling (LIM) approach,
  by helping capture a few essential interactions between dynamical
  components of the full system, has proven valuable in being able to
  provide insights into the dynamical behavior of the full system.

  We demonstrate that Reservoir Computing (RC), a form of machine
  learning suited for learning in the context of chaotic dynamics,
  provides an alternative nonlinear approach that improves on the LIM
  approach. We do this in the example setting of predicting sea
  surface temperature in the North Atlantic in the pre-industrial
  control simulation of a popular earth system model, the Community
  Earth System Model version 2 (CESM2) so that we can compare the
  performance of the new RC based approach with the traditional LIM
  approach both when learning data is plentiful and when such data is
  more limited. The useful predictive skill of the RC approach over a
  wider range of conditions---larger number of retained EOF
  coefficients, extending well into the limited data regime,
  etc.---suggests that this machine learning approach may have a use
  in climate predictability studies. While the possibility of
  developing a climate emulator---the ability to continue the
  evolution of the system on the attractor long after failing to be
  able to track the reference trajectory---is demonstrated in context
  of the Lorenz-63 system, it is suggested that further development of
  the RC approach may permit such uses of the new approach in settings
  of relevance to realistic predictability studies.
Ecological impacts caused by the alternance of wet/dry episodes occurred in the last 2,000 years in southern Tibetan Plateau: A paleoecological record from Lake Nam Co
Authors: Galindo Paula , Frenzel Peter , Anslan Sten , Rigterink Sonja , Massaferro Julieta , Kang Wengang , Wuennemann Bernd , Pérez Liseth , Hoelzmann Philipp , Börner Nicole , Schwarz Anja , Peng Ping , Zhu Liping , Schwalb Antje
Published: March 2021

High altitudinal aquatic ecosystems are subject to environmental change due to global warming and increasing solar radiation. The Nam Co catchment is part of the highest and largest alpine plateau on Earth, where the effects of climate change are expressed stronger than the global average. Thus, this area has experienced rapid changes in biodiversity. Fluctuations between wetter and drier periods during the last 2,000 calibrated (cal.) years were detected. These changes may alter the dynamics in ecosystems and therefore their resilience to climate change.

A ~65 cm sediment record from Nam Co spanning the late Holocene, was analyzed to evaluate the assemblage composition of three of the most abundant and diverse benthic taxa (Arcellinidae, Ostracoda and Chironomidae) and the diverse family of small bivalves (Sphaeriidae). In general, the presence of the bivalve Pisidium stewarti, together with a high abundance of black-coated ostracod shells, and high Ca/Ti and Zr/Rb ratios correspond to the driest period (~ 1,000 - 1,860 cal. years BP) detected in our sediment record. For the last 256 cal. years, higher lake levels were inferred from aquatic fauna composition and geochemical analysis (XRF and XRD) suggesting a more humid environment. This period was characterized by higher temperatures and a higher input of organic matter. Species not previously reported for Lake Nam Co such as Arcellinida species, the ostracod Ilyocypris angulata, several chironomid species, and the bivalve P. stewarti, were observed. These new records, as well as the detection of varieties in morphological structures (e.g. spines, aggregate material, valve ornamentations, etc.) highlight the probable existence of cryptic species in the ecosystem, which is an important factor to take into account for biodiversity evaluation and paleoenvironmental inferences, due to potential misleading ecological interpretation.

Therefore, emphasis should be placed on combining ecology, morphology and DNA analysis to corroborate the taxonomy of species already described, and determine the accurate richness and distribution of the species in an environment where endemism is expected. This is essential in order to evaluate possible losses or gains in terms of diversity that climate change may exert on aquatic ecosystems in the future.
A Bayesian mixing model framework for quantifying temporal and spatial variation in source of sediment to lakes across hydrological gradients of floodplains
Authors: Kay Mitchell , Swanson Heidi , Burbank Jacob , Owca Tanner , MacDonald Lauren , Savage Cory , Remmer Casey , Neary Laura , Wiklund Johan , Wolfe Brent , Hall Roland
Published: March 2021

Episodic flood events are critical for recharging water balance of floodplain lakes and maintaining their ecological integrity, yet are subject to alteration in frequency and magnitude by natural and anthropogenic processes that operate over a range of spatial and temporal scales. To evaluate roles of potential stressors, paleolimnological reconstructions are used to obtain insights into hydrological variability of dynamic floodplain lakes. However, spatial and temporal integration is often underdeveloped because different paleolimnological measurements must be applied across lakes due to the wide range of energy conditions that impart marked differences in sediment composition. Here, we use a linear discriminant analysis to identify 10 significant elemental concentrations in surveyed sediment from multiple sampling campaigns that distinguish the geochemical fingerprints of three end-member sources in lakes at the Peace-Athabasca Delta (PAD; Canada): the Athabasca River, the Peace River and local catchment runoff. Over 90% of the sediment samples were correctly classified into the original groups after cross-validation due to the distinctiveness of the three end members, which permits development of a robust Bayesian mixing model to discern the relative contributions of sediment from the three sources. We evaluate the mixing model at two adjacent lakes in the Athabasca sector of the PAD and demonstrate its effectiveness to discriminate three known hydrological phases during the past 300 years. Notably, the model infers ~60% of the sediment originated from the Peace River during the largest ice-jam flood event on record (1974), which was unrecognized by other methods. We then applied our model to sediment records from 18 lakes spanning the hydrological gradients across the 6000 km2 PAD to further probe the hydrological evolution during the past ~150 years. Results demonstrate decline in frequency of flooding from both the Athabasca and Peace rivers and lake-level drawdown since the early 20th century and align remarkably well with prior interpretation of conventional paleohydrological records of individual lakes. We advocate our approach provides a universal method that can be applied across the full range of sediment composition to quantify change in source, frequency and magnitude of river floodwaters to lakes and is transferable to other dynamic floodplain landscapes where variation of sediment composition challenges efficacy of other approaches.
Global warming decreases rainfall but increases short-duration rain-rates during heavy precipitation events in the eastern Mediterranean
Authors: Armon Moshe , Marra Francesco , Garfinkel Chaim , Rostkier-Edelstein Dorita , Adam Ori , Dayan Uri , Enzel Yehouda , Morin Efrat
Published: March 2021

Heavy precipitation events (HPEs) in the densely populated eastern Mediterranean trigger natural hazards, such as flash floods and urban flooding. However, they also supply critical amounts of fresh water to this desert-bounded region. The impact of global warming on such events is thus vital to the inhabitants of the region. HPEs are poorly represented in global climate models, leading to large uncertainty in their sensitivity to climate change. Is total rainfall in HPEs decreasing, as projected for the mean annual rainfall? Are short duration rain rates decreasing, or rather increasing as expected from the higher atmospheric moisture content? Where are the changes more pronounced, near the sea or farther inland towards the desert? To answer these questions, we have identified 41 historical HPEs from a long weather radar record (1990-2014) and simulated them in the same resolution (1 km2) using the convection-permitting weather research and forecasting (WRF) model. Results were validated versus the radar data, and served as a control group to simulations of the same events under ‘pseudo global warming’ (PGW) conditions. The PGW methodology we use imposes results from the ensemble mean of 29 Coupled Model Intercomparison Project Phase 5 (CMIP5) models for the end of the century on the initial and boundary conditions of each event simulated. The results indicate that HPEs in the future may become more temporally focused: they are 6% shorter and exhibit maximum local short-duration rain rates which are ~20% higher on average, with larger values over the sea and the wetter part of the region, and smaller over the desert. However, they are also much drier; total precipitation during the future-simulated HPEs decreases substantially (~-20%) throughout the eastern Mediterranean. The meteorological factors leading to this decrease include shallower cyclones and the projected differential land-sea warming, which causes reduced relative humidity over land. These changing rainfall patterns are expected to amplify water scarcity – a known nexus of conflict and strife in the region – highlighting the urgent need for deeper knowledge, and the implementation of adaptation and mitigation strategies.
Analysing the tidal state of a pre-plate tectonic Earth during the Archean Eon (3.9 Ga)
Authors: Davies Hannah , Green Mattias , Duarte João
Published: March 2021

Deep time investigations of the Earth have revealed a relationship between plate tectonic motion and the intensity of the tide. Tidal energetics change as continental plates disperse and aggregate in the supercontinent cycle, altering ocean basins around them. The question is, could enhanced tides occur on Earth before plate tectonics started e.g., during the Archean?  

Here we have coupled an established tidal model with an ensemble of potential topographies of the Archean Earth to establish a statistically significant approximation of Archean tidal energetics. Land area is restricted to 5 – 15% with the rest representing primordial ocean – containing no major plate tectonic features i.e., trenches and ridges. Ocean volume is preserved at close to present-day which means oceans are on average 1 km shallower than present-day oceans. Archean day length is set at 13.1 hours with the semi-diurnal tide occurring every 6.8 hours. Equilibrium tide is around 3.4x the present-day value due to the proximity of the Moon.

The aim of this study is to assess the relationship of the Earth Moon system during this primordial stage to better understand the potential role tides had in the origin of life, and to quantify the tidal state of a primordial rocky planet with a young, nearby moon. Understanding the tidal state of Earth at this early time is important for exoplanetary studies as it broadens our scope of planets which may be hospitable to life.

We found coastal and open ocean resonance in many of the ensemble topographies. Total global dissipation in the ensembles varies from 75 – 150% of present-day dissipation rates due to elevated equilibrium tide and greater area where the tide can dissipate. When regional and open ocean resonance does occur, it can raise total global dissipation to >150% of present-day values and can cause regional macrotidal amplitudes (>2m).
Mapping trends in woody cover throughout Namibian savannah with MODIS seasonal phenological metrics and field inventory data
Authors: Wingate Vladimir
Published: March 2021

Woody vegetation is an integral component of Namibian savannahs and essential to people’s livelihoods. Savannah vegetation varies in response to climatic, environmental and anthropogenic factors, moreover, its constituent plant functional types (woody and herbaceous vegetation) exhibit divergent phenological characteristics. Together, these make accurate estimates of changes in tree and shrub cover densities over time difficult to achieve. Two contrasting land degradation processes affecting woody vegetation cover are widespread: (i) the replacement of the herbaceous layer with hardy shrubs (shrub encroachment) and (ii) the loss of forest cover (deforestation). Both processes impact a range of ecosystem services, from local (i.e. local forage and timber resources) to global scales (i.e. biome carbon sequestration). To map trends in woody cover, field observations from 484 sample plots were used to model percentage woody cover as a function of seasonal phenological metrics derived from the MODIS NDVI time-series. An independent validation dataset found a RMSE of 19.73% and an R2 of 0.93%. Trends in modelled woody cover were assessed in relation to land-use, population density and mean annual precipitation. An overall declining trend was identified, with certain land-uses, including protected areas, revealing a declining trend. Significant negative trends covered 11.80% of the study area, while 9.20% underwent positive trends. Trends in woody vegetation cover are mostly unrelated to those of precipitation, except for certain areas which show high coefficients of determination, and imply the presence of predominantly herbaceous vegetation. As such, this study presents a novel method for the identification of grasslands in Namibia.
The heat balance shapes deep convection in the Irminger Sea
Authors: Iakovleva Diana , Bashmachnikov Igor
Published: March 2021

The Irminger Sea is one of the key region in the North Atlantic where deep winter convection develops.

We use ARMOR-3D dataset (0.25×0.25˚, from 1993) for calculating of heat (and freshwater) content, oceanic heat fluxes in the upper 500-m layer and the vertical heat exchange with the lower layers through the 500 m level. The air-sea heat exchange was derived from the OAFlux dataset (1×1˚), the radiation balance was obtained from the ERA-Interim reanalysis (0.25×0.25˚).

Computation of the heat balance was done over a closed region covering the central and western Irminger Sea (58-62˚ N and 36-44˚ W). The computations were repeated for several similar rectangular areas to analyze sensitivity of the analysis to the choice of boundaries of the region. However, the results of the analysis were largely independent from these variations.

The upper ocean heat advection in the study region was 37 TW (integrated along all boundaries of the region, sign «+» means that flux is directed to the study region), and was the dominant term in the annual mean heat balance. The annual mean latent heat flux (-21 TW) and sensible heat flux (-5 TW) were directed from the ocean. The annual mean radiation balance was 8 TW (to the ocean), while vertical heat exchange with the lower layers was low (-0.1 TW). On average, heat balance of upper 500-m layer was positive, and not all heat fluxes might be considered. For example, the contribution of horizontal mesoscale eddy exchange could be important. However, the amplitude of the interannual variability of the heat balance of about 15 TW was close to that of the heat content (about 20 TW), while the correlation between the parameters was significant and high (0.79) (after removal of the quadratic trend 0.80). This suggests that the main heat fluxes, which affect the interannual variability of the heat content in the upper 500-m layer were taken into account.

Interannual variability of maximum convection depth in the central Irminger Sea was found to significantly correlate with the upper ocean heat content mean over September-November (-0.73); both parameters showed a similar long-term tendency. The correlation of the convection depth with the freshwater content (September-November) was significantly less and positive (0.49). The latter is counterintuitive, as we expect a decrease of the convective depth with an increase of the upper ocean freshwater contents. It can be assumed this correlation was induced by a high negative correlation between the upper ocean heat and freshwater contents in the region (-0.64). The analysis, thus, suggests that the long-term variability of deep convection in the Irminger Sea was shaped by variability of the main heat fluxes, entering the region.
Selection of an optimal algorithm for outlier detection in GNSS time series
Authors: Le Thi Nhung , Männel Benjamin , Jarema Mihaela , Krishna Seemala Gopi , Heki Kosuke , Schuh Harald
Published: March 2021

In data mining, outliers can lead to misleading interpretations of statistical results, particularly in deformation monitoring based on fluctuations and disturbances simulated by numerical models for the analysis of deformations. Therefore, outlier filtering cannot be ignored in data standardization. However, it is not likely that a filtering algorithm is efficient for every data pattern. We investigate five outlier filtering algorithms using MATLAB® (Release 2020a): moving average, moving median, quartiles, Grubbs, and generalized extreme Studentized deviation (GESD) to select the optimal algorithms applied for GNSS time series data. This study is conducted on two types of data used for ionosphere disturbance analysis in the region of the Ring of Fire and crustal deformation monitoring in Germany, one showing seasonal time series patterns and the other presenting the trend models. We apply the simple random sampling method that ensures the principles of unbiased surveying techniques. The optimal algorithm selection is based on the sensitivity of outlier detection and the capability of the central tendency measures. The algorithm robustness is also tested by altering random outliers but maintaining the standard distribution of each dataset. Our results show that the moving median algorithm is most sensitive for outlier detection because it is robust statistics and is not affected by anomalies; followed in turn by quartiles, GESD, and Grubbs. The outlier filtering capability of the moving average algorithm is least efficient, with a percentage of outlier detection below 20% compared to the moving median (corresponding 95% probability). In deformation analysis, disturbances on numerical models are often the basis for motion assessment, while these anomalies are smoothed by moving median filtering. Hence, the quartiles algorithm can be considered in this case. Overall, the moving median is best suited to filter outliers for seasonal and trend time series data; in particular, for deformation analysis, the optimal solution is applying the quartiles or extending the threshold factor and the sliding window of the moving median.

Keywords: Outlier filtering, Time series, Deformation analysis, Moving median, Quartiles, MATLAB.
The continent-ocean transition architecture and breakup mechanism at the mid-northern South China Sea
Authors: Zhang Cuimei , Sun Zhen , Manatschal Gianreto , Pang Xiong , Li Sanzhong , Sauter Daniel , Peron-Pinvidic Gwenn
Published: March 2021

Ocean Continent Transition (OCT) located between the edge of the continental and unequivocal oceanic crust is an ideal laboratory to understand one of the most fundamental processes of Plate Tectonics, namely the mechanism of formation of a new plate boundary, also referred to as lithospheric breakup. However, the location and architecture of the OCT and the processes governing the rupture of continental lithosphere and creation of new oceanic crust remain debated. In this paper, we present newly released high-resolution seismic reflection profiles that image the complete transition from unambiguous continental to oceanic crust in the mid-northern South China Sea (SCS), accompanied with IODP drill hole and gravity data, with the aim to map the OCT and explore where, when and how lithospheric breakup occur.

Based on observations and interpretations we define the limits of OCT. The results show that OCT corresponds to hybrid crust resulting from the complex interaction between crustal thinning along detachment systems and accretion of new syn-tectonic igneous materials. The observations suggest a sharp along strike transition in the OCT from a lower to an upper plate setting over a lateral distance of 25 km. The breakup in the northern SCS and the conjugate margin occurred asymmetrically and was accomplished by core-complex type structures related to a successive oceanward transition from tectonic to magma-controlled processes during plate separation. The along-strike variability in the basement architecture and the abrupt flip in detachment polarity in the OCT imply a sharp transfer fault to explain the segmentation of the margin. Such segmentation results from inherited pre-rift crustal and/or lithospheric heterogeneities. It is important to note that the segmentation did not control breakup and subsequent oceanic accretion.
Stable isotope composition of precipitation as signal of possible climate change: the case of the mountain Učka (Northern Adriatic, Croatia)
Authors: Mance Diana , Topolnjak Ema , Crnov Anita , Mance Davor , Radišić Maja , Rubinić Josip
Published: March 2021

The highest average annual rainfall in Croatia is in the Northern Adriatic, with some parts of the region receiving more than 2000 mm per year. Characteristics of the region’s weather are periods of intense rain alternating with dry periods in which the amount of precipitation can be negligible for more than a month. The area's water supply relies on karst groundwater sources that are primarily fed by Mediterranean precipitation. The aforementioned precipitation regime results in high groundwater yields in the cold part of the hydrological year and substantially decreased water quantities in the summer months. Under such specific conditions, it is of considerable importance to find out about the potential for climate change in order to ensure timely adjustment of the management and use of natural sources of water.

We present a comparison of the isotopic composition of precipitation collected on the mountain Učka in periods 2008-2011 and 2019-2020. Rain gauges were located on a vertical gradient from sea level up to nearly 1400 m. Unlike the isotopic altitude effect that did not change significantly compared to the one reported for the first period (Roller-Lutz et al, 2013), the weighted means of isotopic values were more positive in the second period.  For the cold part of the hydrological year, local meteoric water line has recently moved to higher values, indicating the sources of precipitation from drier Mediterranean regions. Local meteoric water line for the warm part of the last hydrological year, indicates presence of increased evaporation and thus confirms lower precipitation amounts.

 

Roller-Lutz Zvjezdana, Mance Diana, Hunjak Tamara, Lutz Hans O. (2013) On the isotopic altitude effect of precipitation in the Northern Adriatic (Croatia), Isotopes in Hydrology, Marine Ecosystems and Climate Change Studies. Vol. I. Proceedings of an International Symposium

 

This work was supported by the University of Rijeka as part of the research project uniri-pr-prirod-19-24.
Real Driving NOx Emission Measurements of Vehicles with ICAD instruments for Plume Chasing
Authors: Schmidt Christina , Pöhler Denis , Engel Tobias , Horbanski Martin , Lampel Johannes , Schmitt Stefan , Platt Ulrich
Published: March 2021

Nitrogen Oxide (NOx) emissions from vehicles are a major cause of poor air quality in urban areas. The emissions per vehicle are regulated by the EURO Norm (EURO V: 2000mg/kWh, EURO VI: 460mg/kWh). Existing possibilities to measure whether the vehicles comply with the regulations (e.g. PEMS: Portable Emission Measurement System) are rare and costly. Within the framework of the EU project CARES (City Air Remote Emission Sensing) different remote emission sensing techniques and instruments are further developed. ‘Plume Chasing’ is one of them. With the Plume Chasing method, the emissions of a vehicle are measured in the wake of the investigated vehicle, i.e. in the diluted emission plume. This is done with a for this purpose optimized ICAD NOx-CO2 instrument (Airyx GmbH), that allows fast (1s time resolution) and simple measurements with high accuracy (sub ppb for NOx) with a high measurement range (0-5000ppb). With these characteristics, it is perfectly suitable to detect malfunctioning or illegally manipulated emission control systems like SCR (selective catalytic reduction).

Several validation studies of Plume Chasing against the established PEMS have shown very good correlations. During a 3-day study in Sweden in November 2019, Plume Chasing measurements of a EURO V and a EURO VI truck were performed with activated as well as deactivated emission control system for several hours in different driving conditions. The derived Plume Chasing NOx emission values even for short measurement times of one and two minutes showed excellent correlation with the averaged PEMS NOx data of the trucks with R2~0.9. The study demonstrated the robustness of the Plume Chasing method in detecting high emitter trucks. To further test and optimise different measurement configurations and data analysis algorithms, within the CARES project several ICAD NOx-CO2 instruments are installed together with e.g. LICOR CO2-sensors or Condensation Particle Counters in a measurement vehicle from TNO, Netherlands.

Studies on German and Austrian highways in 2018 and 2019 showed that among several hundreds of trucks up to 35% of the EURO V trucks and up to 25% of the EURO VI trucks showed consistently high emissions exceeding the EURO norm limit, which provides strong evidence for a high number of defect or manipulated emission control systems. A recent study in Denmark showed 9,7% of the vehicles exceeding the standards. The vehicles were afterwards inspected by the police and defects or manipulations of the emission control system could be confirmed.
Water sustainability of South African crop production under current and future climatic conditions
Authors: Bonetti Sara , Mabhaudhi Tafadzwanashe , Slotow Rob , Dalin Carole
Published: March 2021

South Africa is a water scarce country, with 98% of available water resources already allocated. In addition, only 12% of the land is considered suitable for growing rainfed crops, making commercial agriculture production heavily dependent on irrigation. Current climate projections suggest that South Africa will experience increased frequency of drought events over the next century. This will have notable implications for food security, especially in rural communities that still depend on rainfed production for their livelihoods. In this work, we evaluate water sustainability for seventeen major crops produced in South Africa under current climatic and management conditions as well as under future climate scenarios. We map the spatial distribution of source- and crop-specific water use, and asses their sustainability in terms of water debt repayment time (i.e., the time needed to renew water resources used for annual crop production). We find high water debts in the Western and Eastern Cape regions, revealing unsustainable production due to irrigation in arid areas. Results from climate change scenarios suggest an intensification of such pressure on water resources and allow us to identify crop types and locations where production is likely to be more (or less) sustainable under future climatic conditions, a key step to informing land use planning decisions.
Runoff generation processes in permafrost-influenced area of the Heihe River Headwater
Authors: Zhang Fan , Xiao Xiong , Wang Guanxing
Published: March 2021

Permafrost degradation under global warming may change the hydrological regime of the headwater catchments in alpine area such as the Tibetan Plateau (TP). In this study, he runoff generation processes in permafrost-influenced area of the Heihe River Headwater were investigated with the following results: 1) The observed stable isotope values of various water types on average was roughly in the order of snowfall and snowmelt < bulk soil water (BSW) < rainfall , stream water, mobile soil water (MSW) , and lateral subsurface flow. The depleted spring snowmelt and enriched summer rainfall formed tightly bound soil water and MSW, respectively. The dynamic mixing between tightly bound soil water and MSW resuted in BSW with more depleted and variable stable isotopic feature than MSW. 2) Along with the thawing of the frozen soil, surface runoff and shallowsubsurface flow (SSF) at 30−60 cm was the major flow pathway in the permafrost influenced alpine meadow hillslope during spring snowmelt and summer rainfall period, reapectively, with the frozen soil maintaining supra-permafrost water level. 3) Comparison between two neighouring catchments under similar precipitation conditions indicated that streamflow of the lower catchment with less permafrost proportion and earlier thawing time has larger SSF and higher based flow component, indicating the potential changes of hydrological regims subject to future warming.
Biases of aerosol simulation in the AerChemMIP models over China and impact of emission uncertainties
Authors: Fan Tianyi , Liu Xiaohong , Wu Chenglai , Gao Yi , Zhang Qiang , Zhao Chuanfeng , Yang Xin , Li Yanglian
Published: March 2021

          Biases of aerosol simulation by models participating the Aerosol and Chemistry Model Intercomparison Project (AerChemMIP) were identified over China. Although the yearly trend of simulated aerosol optical depth (AOD) agrees with the MODIS satellite retrievals for the country-wide averages, this agreement is an offset between the underestimation of AOD over eastern China and the overestimation of AOD over western China. The AODs were underestimated over the Northeastern China Plain and the North China Plain all year along and overestimated over Sichuan Basin in the winter. These model biases were persistent over multiple years from 2002 to 2015. We attempt to evaluate the impact of emission uncertainties on model simulated aerosol properties and aerosol radiative forcing by comparing the simulations by the Community Earth System Model version 2 (CESM2) with the default inventory developed by the Community Emission Data System (CEDS) and with a country-level inventory (Multi-resolution Emission Inventory for China, MEIC). It turns out that the differences between simulations with the two emission inventories are much smaller than the differences between simulations and observations. Low-bias of precursor gases (e.g., SO2), too strong convergence of wind field, too strong dilution and transport by summer monsoon circulation, too much wet scavenging by precipitation, and too weak aerosol swelling due to low-biased relative humidity are suggested to be responsible for the biased AOD in eastern China. This indicates that the influence of emission inventory uncertainties on aerosol radiative forcing can be overwhelmed by influences of biased meteorology and aerosol processes. Therefore, it is necessary for climate models to perform reasonably well in the dynamical, physical and chemical processes in order to estimate the aerosol radiative forcing.   
Detecting stemflow-induced preferential flow pathways through time-lapse ground-penetrating radar surveys
Authors: Roder Ludmila , Di Prima Simone , Campus Sergio , Giadrossich Filippo , Stewart Ryan D. , Abou Najm Majdi R. , Winiarski Thierry , Angulo-Jaramillo Rafael , del Campo Antonio D. , Lassabatere Laurent , Roggero Pier Paolo
Published: March 2021

Research over the past several decades has shown that preferential flow is more the rule than the exception. However, our collective understanding of preferential flow processes has been limited by a lack of suitable methods to detect and visualize the initiation and evolution of non-uniform wetting at high spatial and temporal resolutions, particularly in real-world settings. In this study, we investigate water infiltration initiation by tree trunk and root systems. We carried out time-lapse ground penetrating radar (GPR) surveys in conjunction with a simulated stemflow event to provide evidence of root-induced preferential flow and generate a three-dimensional representation of the wetted zone.

We established a survey grid (3.5 m × 5 m, with a local slope of 10.3°), consisting of ten horizontal and thirteen vertical parallel survey lines with 0.5 m intervals between them. The horizontal lines were downslope-oriented. The grid was placed around a Quercus suber L. We collected a total of 46 (2 GPR surveys × 23 survey lines) radargrams using an IDS (Ingegneria Dei Sistemi S.p.A.) Ris Hi Mod v. 1.0 system with a 900-MHz antenna mounted on a GPR cart. Two grid GPR surveys were carried out before and after the artificial stemflow experiment. In the experiment, we applied 100 L of brilliant blue dye (E133) solution on the tree trunk. The stemflow volume of 100 L corresponded to 63.2 mm of incident precipitation, considering a crown projected area of 201 m2 and a 1.3% conversion rate of rainfall to stemflow. Trench profiles were carefully excavated with hand tools to remove soil and detect both root location and size and areas of infiltration and preferential pathways on the soil profile.

The majority (84.4%) of artificially applied stemflow infiltrated into the soil, while the remaining 15.6% generated overland flow, which was collected by a small v-shaped plastic channel placed into a groove previously scraped on the downhill side of the tree. The 3D diagram clearly demarcated the dimension and shape of the wetted zone, thus providing evidence of root-induced preferential flow along coarse roots. The wetted zone extended downslope up to a horizontal distance of 3 m from the trunk and down to a depth of approximately 0.7 m. Put all together, this study shows the importance of accounting for plant and trees trunk and root systems when quantifying infiltration.
Automatic tree species classification by using field data, image analysis and deep learning techniques in riparian forests
Authors: Kentsch Sarah , Lopez Caceres Maximo Larry , Diez Yago
Published: March 2021

Mixed forests are still little understood ecosystems. Their structure and composition are not well known and not clearly classified. In times of climate change, monitoring of forests is becoming increasingly important. Forest stands were usually researched by field work, which requires high costs and man-power. Field surveys are further only conducted in small patches of the forests, which does often not represent the whole forest. For mixed forests, usually only a dominate species is mentioned but the forests are not classified further. The greater need of better methods with high accuracies to detect and classify tree species in the forest encouraged this study.

UAVs have been proven to be an efficient tool to conduct automatic field surveys in forestry applications. These easy-to-use and cheap tools are able to gather images with a high resolution. Image processing with image analysis and deep learning techniques is an emerging part in forestry investigations. Therefore, we combined manual field surveys, image analysis and automatic classifications in our study.

The forests, we were investigating, are riparian forests in Shonai area, Japan, which are classified as mixed forests. 7 sites were chosen and field surveys were conducted. Most of the sites are located in flat areas, but 3 sites are located on slopes, where the access is difficult and field work barely possible. We imaged all sites in different seasons with UAVs and performed image analysis with computer vision and ArcGIS methods. Trees were detected and classified manually and automatically. A comparison of all applied methods was drawn, evaluated and will be provided.

Our first results are promising to characterize forests in a new dimension. We will provide detailed information about tree species composition, tree locations and forest structures. Mixed forests can be deeper analysed by maps of dominate and subdominant tree species. Area calculations for tree canopies will be highlighted for the main tree species. We will provide winter images for tree counting in heavy snowfall regions and classification accuracies of deep learning techniques.  