bluuebunny/crossref_metadata_2025 huggingface dataset:
Assessment of the WRF-Hydro uncoupled hydro-meteorological model on flashy watersheds of the tropical island of New Caledonia (South-West Pacific)
Authors: Cerbelaud Arnaud , Lefèvre Jérôme , Genthon Pierre , Menkes Christophe
Published: March 2021

Situated in the South-West Pacific, New Caledonia is a tropical island dominated by a central mountain range and is subject to cyclones, regular intense precipitation events and flash-flooding. Recent fine-scaled projections of climate change in New Caledonia show that the frequency and intensity of extreme precipitation events could be reduced by ~ 20% by 2080-2100 [Dutheil et al., 2020]. This paper investigates the ability of the WRF-Hydro/Noah-MP modelling framework to represent the hydrological regime of six watersheds in New Caledonia. A nearly 2-year long WRF ideal atmospheric forcing was completed with observed precipitations from 24 rain gauges using two rainfall spatial interpolation methods at 0.2 km-resolution. This study mainly seeks to calibrate the uncoupled WRF-Hydro/Noah-MP system as well as to evaluate its performance upon short and contrasted heavy rainfall events between 2012 and 2014. Particular attention was paid to (i) the sensitivity of calibration processes to rainfall spatial interpolation methods, (ii) the consistency in modelled soil moisture storage and (iii) the reliability of hydrograph separation provided by WRF-Hydro.

After automatic calibration relying upon the DDS algorithm [Tolson and Shoemaker, 2007], streamflow simulations show overall good performance with Nash–Sutcliffe efficiencies (NSE) greater than 0.6 on a 21-month period for all watersheds. Standard hydrological features of all studied watersheds are well reproduced. The quality of simulation is found to be decreasing with lower values of runoff coefficient. We show on three watersheds that spatial distribution of rainfall can highly condition the calibration process and thus greatly modify modelled soil moisture storage and in result the shape of simulated flash floods. WRF-Hydro’s hydrograph decomposition between surface and underground runoff is presented and compared with known characteristics of watersheds as well as with other quickflow/baseflow separation methods. To our knowledge, this work is the first attempt to use the uncoupled WRF-Hydro hydro-meteorological model for flash flood analysis in New Caledonia and opens a pathway to study multiple hydrological and climatic features in the region in the context of climate change.

Keywords: hydro-meteorological modelling, WRF-Hydro, Noah-MP, flash flood, rainfall spatial interpolation, hydrograph separation, baseflow, New-Caledonia
Analysis of paleosol-based proxies from the Turkana Basin through paleo-landscape and paleoclimate reconstruction
Authors: Manning Margaret , Beck Catherine , Beverly Emily
Published: March 2021

The Turkana Basin is world famous for its extensive outcrops that provide insights into the paleoclimate and paleolandscapes in which hominins evolved over the past ~4 Ma. The Nachukui Formation, part of the Omo Group, reflects basin-wide dynamic processes of interlaced sequences including floodplains, deltas, and river systems throughout the Plio-Pleistocene. Paleosols associated with floodplains of the fluvial systems provide a valuable window into better understanding key intervals within this record and are frequently associated with fossiliferous fluvial sequences. This study analyzed three paleosols taken from outcrops of the Kaitio and Natoo Members of the Nachukui Formation. In particular, the Kaitio Mmb was assumed to be simply a lacustrine environment deposited during the longest-lived part of Paleolake Lorenyang (~1.7-2 Ma). However, recent studies have worked to provide a more comprehensive understanding of this member, indicating it was a far more dynamic lacustrine margin than previously recognized. This research builds upon this stratigraphic framework to integrate paleosol-based geochemical proxies to better reconstruct the paleoclimate and paleoenvironment of West Turkana Kaitio (WTK). This includes 1) x-ray fluorescence (XRF) elemental analysis of bulk sediment, and 2) stable isotope analysis on both bulk sediment and pedogenic carbonates. These data allowed us to make estimates of mean annual precipitation (MAP), vegetation type, and paleotemperatures. Using the CalMag and CIA-K weathering indices, the MAP estimates range from 351-933 mm of rain/year, with the means for both proxies ranging from 351-917 mm with an average MAP of 761.75 mm. The CIA-K weathering index produced MAP values of 503-933 mm with an average 812.88 mm. Compared to modern average rainfall values in the basin (324.1-151.6 mm/yr), our MAP estimates indicate the basin experienced more precipitation in the Plio-Pleistocene than it does today. Pairing the geochemical data with our sedimentological assessment allowed us to better characterize these paleosols for a more in depth understanding of the depositional environment of the Kaitio Member. 
Developing a climate-driven root zone water stress function for different climates and ecosystems
Authors: Nóbrega Rodolfo , Prentice Iain Colin
Published: March 2021

Plant roots have less water available when soils have low moisture content and, consequently, limit their root-to-leaf water potential gradient to protect their xylem, which reduces H2O and CO2 exchanges with the atmosphere. In vegetation, hydrological and land-surface models, plant responses to reduced available water in the soil have been implemented in various ways depending on data availability, type of ecosystem, and modelling assumptions. Most models use soil water stress functions – commonly known as beta functions – to reduce transpiration and carbon assimilation, by applying a factor that reflects the soil water availability for plants. These functions usually produce reasonably satisfactory results, but rely on the information on soil properties (e.g. wilting point and field capacity) that are not widely available. On a global level, soil information is mediocre, and data uncertainty is compensated by tuning parameters that rarely represent a physiological process. We propose instead the use of a beta function derived from a mass-balance approach focused on the root zone water capacity. This method quantifies the root zone water storage by calculating the accumulated water deficit based on the balance between water influxes and effluxes, and it does not require land-cover or soil information. We assessed how our approach performs compared to those other soil water stress functions. We used global datasets, including WDFE5 and PMLv2, to extract precipitation and evapotranspiration and compute water deficit. For most vegetation types and climates our approach yielded promising results. Worst results were found for some (semi-)arid sites due to the overestimation of the water deficit. We aim to deliver an approach that can be easily applied on global scales.
Assimilating sparse data in glaciological inverse problems
Authors: Shapero Daniel , Nixon-Hill Reuben
Published: March 2021

Most of the existing work on solving inverse problems in glaciology has assumed that the observational data used to constrain the model are spatially dense. This assumption is very convenient because it means that the model-data misfit term in the objective functional can be written as an integral. In many scenarios, however, the computational mesh can locally be much finer than the observational grid, or the observations can have large patches of missing data. Moreover, pretending as if the observations are a globally-defined continuous field obscures valuable information about the number of independent measurements we have. It is then impossible to apply a posteriori sanity checks on the expected model-data misfit from regression theory. Here we'll describe some recent work we've done on assimilating sparse point data into ice flow models and how this allows us to be more rigorous about the statistical interpretation of our results. For now we are focusing on the kinds of inverse problems that have been solved in the glaciology literature for a long time -- inferring rheology and basal friction from surface velocities. But these developments open up the possibility of assimilating new sources of data, such as measurements from strain gauges or ice cores.
The effect of different contributing sensors in IMERG-Final precipitation estimates
Authors: Ayat Hooman , Evans Jason , Behrangi Ali
Published: March 2021

Ground observation absence in many parts of the world highlights the importance of merged satellite precipitation products. In this study, we aim to evaluate the effect of different sources of data in the uncertainties of a merged satellite product, by comparing the Integrated Multi-satellitE Retrievals for GPM (IMERG) final-product V06B with a ground-radar product, Multi-Radar Multi-Sensor (MRMS), over eastern United-States during the hurricane days that occurred in 2016-2018 using both pixel-based and object-based approaches. The results showed that IMERG had better agreement in terms of the average precipitation intensity and area when the passive microwave (PMW) sensor overpass is matched instantaneously with MRMS in comparison with the temporally averaged MRMS data (MRMS-Averaged) with a bias reduction of 75% and 65%, respectively. PMW observations tend to show storms with smaller areas in the IMERG final product in comparison with MRMS, possibly due to the effect of light precipitation not detected properly by PMW sensors. However, by removing the light precipitation (less than 1mm/hr) in the object-based approach, hurricane objects in the IMERG final product tend to be larger during the PMW observations, which might be related to different viewing angles of sensors contributing to MRMS and IMERG products. Precipitation estimates in the IMERG final product have smaller areas with higher average intensity during the PMW observations compared to data estimated by Morph or IR (morph/IR) observations. It is probably related to the effect of morphing technique, leading to homogenization of the varying rainstorm characteristics. The quality of IMERG data changes with the longer absence of the PMW observations. IMERG data estimated by morph/IR observations, with a 30-minute time-distance to the nearest PMW observation, showed the best agreement with MRMS-Averaged even in comparison with PMW estimates, possibly due to the time-lag in recording the precipitation between satellites and ground-radars. It is also possible to be related to the homogenizing nature of morphing technique in IMERG and averaging MRMS data in time in MRMS-Averaged, relaxing the differences between PMW observations and MRMS. However, the morph/IR data quality deteriorates with the longer absence of PMW sensors. The inter-comparison of PMW sensors showed the priority of imagers over sounders with GMI as the best among imagers and MHS as the best among sounders in terms of correlation and average intensity compared to MRMS; however, SSMIS was the best in capturing the precipitation area.
Development and calibration of instrumented rock for monitoring rockfalls
Authors: Gu Peng , Valyrakis Manousos
Published: March 2021

Rockfalls can be detrimental to the safety of people and exposed infrastructure or property. Especially in the mountainous areas, rockfall disasters are common and unpredictable. In many countries and regions around the world, rockfalls have directly and indirectly caused great economic losses and even loss of life. In Scotland, an average of 1.4 million pounds a year is lost due to rockfalls. In China, a direct economic loss of 170 million pounds was caused and 858 people were killed by rockfalls In 2018. Most of the current prevention methods are costly and time-consuming. The objective of this study is to develop a new sensor that could monitor the dynamics of rockfall process. This paper discusses the development and calibration of a spherical instrumented rock with low-cost sensors, simulating spherical rocks and stones, which can be used to record the triaxial accelerations and angular velocities. The instrumented rock is tested on an appropriately designed dry flume for a range of slopes and fixed bed roughness. The preliminary experimental setup and results will be presented and discussed. By utilizing the impact forces obtained from the instrumented rock for the assessment for rock-fall dynamics with the designed dry flume physical experiments, we demonstrate how rockfall hazards can be monitored directly or indirectly using a low-cost tool.

Key words: rockfalls, instrumented rock, sensors, dynamics of process, earth surface hazards
Non-stationary Modeling of Extreme Precipitation over Monsoon Asia – Role of Teleconnection Time Lags 
Authors: Nagaraj Meghana , Kasturirengan Srinivasan , Maria Sojan Jency , Srivastav Roshan
Published: March 2021

Extreme precipitation events are increasing due to climate change and leading to frequent flooding and severe droughts. These events vary in both space and time and are positively correlated with the climate teleconnections representing the oscillations of the ocean-atmospheric system. However, large numbers of climate signals and the precipitation response may vary at certain time lags with each climate indices. This study identifies time lags for climate indices using cross-correlation analysis between extreme precipitation and climate indices. These time-lagged climate indices are used as a covariate to fit a non-stationary generalized extreme value (NS-GEV) model over Monsoon Asia. The best NS-GEV model among non-stationary models is selected based on Akaike information criteria (AICc). Results show that the correlation between precipitation and different climate indices is spatially non-uniform. Incorporating time lag climate indices as covariate improves the performance of the non-stationary models. This study helps in understanding the teleconnections influencing the variation of extreme precipitation in a non-stationary framework and to revise the infrastructure designs and flood risk assessment.
Monitoring on land subsidence in reclaimed land with space-based synthetic aperture radar observations.
Authors: Park Seo-Woo , Hong Sang-Hoon
Published: March 2021

Land subsidence is often occurred by compaction of alluvial sediments due to groundwater extraction and threatens invaluable lives and properties. Space-based interferometric Synthetic Aperture Radar (SAR) observation has been widely used to estimate surface displacement precisely. Especially, Small BAseline Subset (SBAS) technique with SAR Interferometry (InSAR) could serve to monitor a time-series of the land subsidence. In this study, the SBAS with L-band ALOS PALSAR and C-band Sentinel-1 observations have been applied to investigate the land subsidence in Noksan reclaimed land, Busan, South Korea. The average velocity showing the largest displacement is -3.40 cm/year from ALOS PALSAR and -2.17 cm/year with Sentinel-1 dataset at the line of sight (LOS) direction. An annual subsidence rate of -2.77 cm/year was estimated assuming that the surface has been deformed linearly for the data acquisition period.
Multichannel Heterodyne Spectroradiometer for Atmospheric Greenhouse Gas Measurements
Authors: Zenevich Sergei , Gazizov Iskander , Churbanov Dmitry , Spiridonov Maxim , Rodin Alexander
Published: March 2021

We present a portable, multichannel laser heterodyne spectroradiometer (MLHS) with a spectral resolution of 0.0013 cm-1 for precision column measurements and vertical profiling of atmospheric greenhouse gases (GHG). Sample spectra of CO2 and CH4 absorption lines obtained by direct Sun observations have allowed us to measure GHG column abundance with a precision of 0.5% for CO2 and 10% for CH4, as well as to retrieve their vertical profiles and to get a vertical profile of the stratospheric wind Rodin et al. (2020). The fundamentals and specifics of the multichannel configuration implementation of heterodyne receivers are presented in Zenevich et al. (2020). This work presents the first data of atmospheric CO2 and CH4 measurements, which were taken in a 4-channel configuration of the heterodyne receiver. Such configuration has allowed us to get atmospheric spectra with the SNR 300-500 within 2 minutes period of signal integration and keep the high spectral resolution. The results of retrieving CO2 and CH4 vertical concentration profiles and vertical profiles of the stratospheric wind are also presented.

 

Acknowledgments

This work has been supported by the Russian Foundation for Basic Research grants # 19-29-06104  (A.V. Rodin, M. V. Spiridonov, I.Sh. Gazizov) and # 19-32-90276 (S. G. Zenevich).

 

References:

Zenevich S. et al.: The improvement of dark signal evaluation and signal-to-noise ratio of multichannel receivers in NIR heterodyne spectroscopy application for simultaneous CO2 and CH4 atmospheric measurements, OSA Continuum, 3, 7, 1801-1810, doi:10.1364/OSAC.395094, 2020.

Rodin, A. et al.: Vertical wind profiling from the troposphere to the lower mesosphere based on high-resolution heterodyne near-infrared spectroradiometry, Atmos. Meas. Tech., 13, 2299–2308, doi:10.5194/amt-13-2299-2020, 2020.
Paleomagnetism of the Upper Cretaceous oceanic red beds in southern Tibet, China: Implications for the extent of Greater India at ~75 Ma
Authors: Yuan Jie , Yang Zhenyu , Deng Chenglong
Published: March 2021

The extent of Greater India with precise and accurate chronological control is a key issue that concerns the spatio-temporal pattern and tectonic models of the India-Asia collision. Here we carried out a detailed magnetostratigraphic and paleomagnetic study on the Upper Cretaceous oceanic red beds (CORBs) (Chuangde Formation) exposed in the Tethyan Himalaya terrane. The high temperature (650‒690°C) magnetic components are isolated from two separated sections at Cailangba and display both normal and reverse polarities, which were used to construct magnetic polarity sequences of the sections that can be subsequently correlated to the geomagnetic polarity time scale (GPTS) to better estimate the age of the rocks. With the aid of previously published biostratigraphy by Chen et al. (2011, Sedimentary Geology), the polarity magnetozones of the Cailangba B section are correlated to chron C32r.2r (74.3–74.0 Ma) and the upper part of chron C33n (79.9–74.3 Ma), and the single normal polarity magnetozone of the Cailangba A section is correlated to the upper part of chron C33n (79.9–74.3 Ma). As a result, the CORBs in the Cailangba A and B sections represent the time interval of 76.2–74.0 Ma by magnetobiostratigraphy. Two independent methods of inclination shallowing correction were tested, which all indicate a bias inclination of ~70%. After inclination shallowing correction, the mean inclination increased to ‒35.0°, giving what we propose to be a high-quality Late Cretaceous paleopole of 40.8°N/256.3°E, A95 =1.8°. Our findings indicate that the Indian passive continental margin was situated at a paleolatitude of 19.4° ± 1.8°S at ~75 Ma. These data suggest that Greater India extended about 715 ± 374 km farther north from the present northern margin of India in the Late Cretaceous, implying a latitudinal width of 3641 ± 308 km for the Neo-Tethys Ocean that still separated the Lhasa terrane of southern part of the Asian plate and the Greater India.
Exploring environmental factors driving wildfire occurrences in Alaskan tundra
Authors: He Jiaying , Loboda Tatiana , French Nancy , Chen Dong
Published: March 2021

Tundra fires are common across the pan-Arctic region, particularly in Alaska. Fires lead to significant impacts on terrestrial carbon balance and ecosystem functioning in the tundra. They can even affect the forage availability of herbivorous wildlife and living resources of local human communities. Also, interactions between fire and climate change can enhance the fire impacts on the Arctic ecosystems. However, the drivers and mechanisms of wildland fire occurrences in Alaskan tundra are still poorly understood. Research on modeling contemporary fire probability in the tundra is also lacking. This study focuses on exploring the critical environmental factors controlling wildfire occurrences in Alaskan tundra and modeled the fire ignition probability, accounting for ignition source, fuel types, fire weather conditions, and topography. The fractional cover maps of fuel type components developed Chapter 2 serve as input data for fuel type distribution. The probability of cloud-to-ground (CG) lightning and fire weather conditions are simulated using WRF. Topographic features are also calculated from the Digital Elevation Model (DEM) data. Additionally, fire ignition locations are extracted from Moderate Resolution Imaging Spectroradiometer (MODIS) active fire product for Alaskan tundra from 2001 to 2019. Empirical modeling methods, including RF and logistic regression, are then utilized to model the relationships between environmental factors and wildfire occurrences in the tundra and to evaluate the roles of these factors. Our results suggested that CG lightning is the primary driver controlling fire ignitions in the tundra, while warmer and drier weather conditions also support fires. We also projected future potential of wildland fires in this tundra region with Coupled Model Intercomparison Projects Phase 6 (CMIP6) data. The results of this study highlight the important role of CG lightning in driving tundra fires and that incorporating CG lightning modeling is necessary and essential for fire monitoring and management efforts in the High Northern Latitudes (HNL).
Spatial extent of hydrological drought in the United States: changes and hydro-meteorological drivers
Authors: Brunner Manuela Irene , Swain Daniel L. , Gilleland Eric , Wood Andrew W.
Published: March 2021

Droughts can seriously challenge water management if they have large spatial extents. These extents may change in a warming climate along with changes in underlying hydro-meteorological drivers. Therefore, we ask (1) how streamflow drought spatial extent has changed over the period 1981-2018 in the United States, (2) which physical drivers govern drought spatial extent, and (3) whether/how the importance of these drivers has changed over time. We analyze temporal changes in streamflow drought extents and their drivers using drought events extracted for 671 catchments in the conterminous United States using a variable threshold-level approach. Drought spatial extents are determined as the percentage of catchments affected by drought during a certain month. Then, important drivers are identified by determining the spatial percentage overlap of the area under streamflow drought with precipitation droughts, temperature anomalies, snow-water-equivalent deficits, and soil moisture deficits. Finally, the spatial extent and overlap time series are used in a trend analysis to determine changes in drought spatial extent and to identify changes in the importance of different variables as drivers of drought spatial extent. Our analyses show that (1) drought spatial extents have increased, mainly because of increases in the extent of small droughts; (2) drought extents overall substantially overlap with soil moisture deficits and the relationship of drought to precipitation and temperature varies seasonally; (3) the importance of temperature as a driver of drought extent has increased over time. We therefore conclude that continued global warming may further increase the probability of spatially compounding drought events, which requires adaptation of regional drought management strategies.

 
Quartz-in-garnet elastic barometry vs. conventional thermobarometers: a comparison across diverse tectonic settings
Authors: Cisneros Miguel , Behr Whitney
Published: March 2021

In recent years, elastic thermobarometry has gained wider acceptance and utility within the petrologic community and beyond. In particular, quartz-in-garnet (qtz-in-grt) elastic barometry is widely used because of the ubiquity of garnet in metamorphic rocks. The technique is based on using Raman spectroscopy to quantify strains recorded by inclusions, and modeling the elastic evolution of the inclusion-host pair to constrain the initial conditions of inclusion entrapment. Recent studies have validated the technique experimentally by comparing pressures from the qtz-in-grt barometer with experimental conditions of garnet growth and entrapment of quartz, and have shown that the barometer can provide reliable pressure conditions of garnet growth. However, current experimental studies fail to capture the reliability of the technique under disparate pressure (P), temperature (T) and deformation conditions, and studies that systematically compare qtz-in-grt barometry and conventional thermobarometry are lacking. 

In this work, we compare P conditions from qtz-in-grt barometry and conventional thermobarometry from the following locations: spatially and temporally variant high P/T subduction zone eclogite blocks from the Franciscan Complex in California, high P/T subduction zone rocks of varying compositions from Syros, Greece, high P/T and low P/T rocks of varying compositions from the Betics system in Spain, low P/T schists from the Jajarkot and Karnali klippen in the Himalaya, high-P rocks from the Alps, and low P/T metapelites from northeast Nevada. Qtz-in-grt barometry constraints from the Franciscan and Syros show good agreement with some reference P-T conditions, but disagree with some thermodynamic equilibria constraints and subsets of multi-mineral thermobarometry calibrations. Qtz-in-grt barometry constraints from the Himalaya are in excellent agreement with reference P constraints. Measurements of samples from other localities are currently in progress. This set of quartz inclusion analyses further allows us to evaluate the effects of inclusion geometry, anisotropy, P and T conditions of garnet growth, and P and T paths on the ultimate P conditions recorded by the qtz-in-grt barometer. The data-set also provides insights into the possible limitations of other techniques (e.g., conventional thermobarometry).
An investigation of the bias in the median track of Monsoon Low Pressure Systems over the Indian subcontinent in CESM1.2.2 simulations
Authors: Thomas Tresa Mary , Bala Govindasamy , Srinivas Venkata Vemavarapu
Published: March 2021

Monsoon low pressure systems (LPS) are synoptic scale tropical disturbances that form in the Indian subcontinent over the quasi-stationary monsoon trough axis during the monsoon period (June to September). In a recent study, we showed that 60-70% of monsoon rainfall and 78% of extreme precipitation events in India are associated with LPS. Global circulation models (GCMs) have been used to understand the behavior of tropical disturbances in the past. It has been found that model resolution plays a key role in simulating the climatology of tropical storms, with finer resolution (of the order of 20-100km) required to better represent the genesis and propagation of these storms. As GCMs can be run at these finer resolutions today, various characteristics of LPS in the Indian subcontinent can be studied. It has been found that most CMIP5 GCMs show a southward latitudinal shift in the monsoon trough location and hence in the LPS tracks and associated characteristics. This shift has been attributed to a weaker simulated meridional tropospheric temperature gradient (MTG) in the models. However, the cause of weaker MTG in models is not known. In this study, we investigate the reason for the weaker MTG and hence the southward latitudinal shift of LPS tracks in the Climate Earth System Model (CESM1.2.2). A present-day control simulation is performed at 0.9°×1.25° horizontal resolution, and output is saved at 6-hourly intervals for LPS track analysis. We find that CESM is capable of simulating the general behavior of monsoon over the Indian subcontinent in terms of seasonality, propagation of monsoon rainfall, and mean monsoon winds. LPS are tracked in the CESM outputs by our recently proposed Automated Tracking Algorithm using Geopotential Criteria (ATAGC). A southward latitudinal shift is observed in the median track of LPS in CESM present-day simulations. The value of MTG is also significantly smaller compared to the observed MTG. The results from investigations on the likely causes for the weaker MTG in CESM will be presented at the meeting.
PythOm: A python toolbox implementing recent advances in rainfall intensity (ombrian) curves
Authors: Iliopoulou Theano , Koutsoyiannis Demetris
Published: March 2021

Curves of rainfall intensity at various scales and for various return periods, else known as ombrian (or IDF) curves, are central design tools in hydrology and engineering. Construction of such curves often relies heavily on empirical or semi-empirical approaches, which hinder their applicability over large scales, and preclude simulation. Recent work by Koutsoyiannis (2020) has advanced these curves to theoretically-consistent stochastic models of rainfall intensity (ombrian models) extending their applicability to the full range of available scales, e.g. from minutes to decades. We present an open-source python toolbox implementing these advances in a straightforward and user-friendly manner and prove its applicability. The toolbox also employs advanced statistical fitting methods for extremes (K-moments), accounts for bias induced by temporal dependence, and allows optional blending of daily-scale data to reduce uncertainty of sub-daily records. The end result is the parameterization of the ombrian model and the graphical representation of rainfall intensity for any range of scales (supported by the data) and return periods.

Reference: Koutsoyiannis, D. 2020. ‘Rainfall extremes and Ombrian modelling’ in Stochastics of Hydroclimatic Extremes - A Cool Look at Risk (ed 0), National Technical University of Athens, Athens, pp 243-273, http://www.itia.ntua.gr/en/docinfo/2000/.
Land use types influence soil microbial community through effects on soil properties in the dry-hot valley region in southwestern China
Authors: Liu Taicong , Rong Li , Duan Xingwu , Chen Zhe
Published: March 2021

Abstract: Land use is one of the most important forms in agricultural production. Non-appropriate land use can cause deterioration of physical, chemical and biological properties of soil, thus affecting sustainable agriculture. Earlier reports showed that land use drastically altered microbial community composition. However, the mechanism of land use on microbial communities is still not fully understood. In the present study, we focus on the dry hot valley, characterized by high temperature and low humility, to test whether soil properties from four primary land uses including the land conversion from farmland (SLC), sugarcane land (SL), maize land with conventional tillage (CT) and bare land (BL) have different influences on soil microbial communities. The results showed that land uses altered bacterial and fungal community composition. In SL and BL, we found the respective absence of a kind of fungi at phylum the level. The abundances of several bacterial phyla in SL such as Gemmatimonadets and Acidobacteria associated with promoting mineralization were higher than that in other land uses. RDA indicated that bacterial communities were influenced by soil total nitrogen, total organic carbon and available potassium contents, and fungal communities were dominated by available potassium contents. SEM (structural equation model) showed that land use has direct and indirect effects on bacterial composition, while only indirect effects on fungal by land use. Land use indirectly affected bacterial composition through effects on soil moisture, clay and available potassium contents, whereas through effects on clay and available potassium for fungal composition. Land use exhibited greater impacts on bacterial composition than fungal composition, implying bacteria was more sensitive to land use changes compared to fungi in the dry-hot valley. Considering the low level of total potassium in soil under SL and CT, elevated potassium fertilizer would be a beneficial pathway to improve soil microbial composition and soil nutrients in the dry hot valley.

Key word: Land use, Soil microbial community, Dry-hot valley, Soil properties, Structural equation model.
Extracting the cumulative distribution location of highly intermittent river from Sentinel-1 time series in an alpine catchment on the Tibetan Plateau
Authors: Fei Junyuan , Liu Jintao
Published: March 2021

Highly intermittent rivers are widespread on the Tibetan Plateau and deeply impact the ecological stability and social development downstream. Due to the highly intermittent rivers are small, seasonal variated and heavy cloud covered on the Tibetan Plateau, their distribution location is still unknown at catchment scale currently. To address these challenges, a new method is proposed for extracting the cumulative distribution location of highly intermittent river from Sentinel-1 time series in an alpine catchment on the Tibetan Plateau. The proposed method first determines the proper time scale of extracting highly intermittent river, based on which the statistical features are calculated to amplify the difference between land covers. Subsequently, the synoptic cumulative distribution location is extracted through Random Forest model using the statistical features above as explanatory variables. And the precise result is generated by combining the synoptic result with critical flow accumulation area.  The highly intermittent river segments are derived and assessed in an alpine catchment of Lhasa River Basin. The results show that the the intra-annual time scale is sufficient for highly intermittent river extraction. And the proposed method can extract highly intermittent river cumulative distribution locations with total precision of 0.62, distance error median of 64.03 m, outperforming other existing river extraction method.
Influence of Aperture Distribution on Flow in Fractal-Fracture Networks
Authors: Sahu Ajay Kumar , Roy Ankur
Published: March 2021

While fractal models are often employed for describing the geometry of fracture networks, a constant aperture is mostly assigned to all the fractures when such models are flow simulated. While network geometry controls connectivity, it is fracture aperture that controls the conductivity of individual fractures as described by the well-known cubic-law. It would therefore be of practical interest to investigate flow patterns in a fractal-fracture network where the apertures also scale as a power-law in accordance to their position in the hierarchy of the fractal. A set of synthetic fractal-fracture networks and two well-connected natural fracture maps that belong to the same fractal system are used for this purpose. The former, with connectivity above the percolation threshold, are generated by spatially locating the fractured and un-fractured blocks in a deterministic and random manner. A set of sub-networks are generated from a given fractal-fracture map by systematically removing the smaller fracture segments. A streamline simulator based on Darcy's law is used for flow simulating the fracture networks, which are conceptualized as two-dimensional fracture continuum models. Porosity and permeability are assigned to a fracture within the continuum model based on its aperture value and there is nearly no matrix porosity or permeability. The recovery profiles and time-of-flight values for each network and its dominant sub-networks at different time steps are compared.

The results from both the synthetic networks and the natural maps show that there is no significant decrease in recovery in the dominant sub-networks of a given fractal-fracture network. It may therefore be concluded that in the case of such hierarchical fractal-fracture systems with scaled aperture, the smaller fractures do not significantly contribute to the fluid flow.

Key-words: Fractal-fracture; Connectivity; Aperture; Dominant Sub-networks; Streamline Simulator; Recovery
Contemporary deformation and earthquake hazard of the Capital Circle of China inferred from GPS Measurements
Authors: Wei Shaogang , Xu Xiwei , Shen Tuo , Lei Xiaoqiong
Published: March 2021

The Capital Circle (CC) is a region with high risk of great damaging earthquake hazards. In our present study, by using a subset of rigorously GPS data around the North China Plain (NCP), med-small recent earthquakes data and focal mechanism of high earthquakes data covering its surrounding regions, the following major conclusions have been reached: (a) Driven by the deformation force associated with both eastward and westward motion, with respect to the NCP, of the rigid South China and the rigid Amurian block, widespread sinistral shear appear over the NCP, which results in clusters of parallel NNE-trending faults with predominant right-lateral strike-slips via bookshelf faulting within the interior of the NCP. (b) Fault plane solutions of recent earthquakes show that tectonic stress field in the NCP demonstrate overwhelming NE-ENE direction of the maximum horizontal principal stress, and that almost all great historical earthquakes in the NCP occurred along the NWW-trending Zhangjiakou-Bohai seismic belt and the NNE-trending Tangshan-Hejian-Cixian seismic belt. Additionally, We propose a simple conceptual model for inter-seismic deformation associated with the Capital Circle, which might suggest that two seismic gaps are located on the middle part of Tangshan-Hejian-Cixian fault seismic belt (Tianjin-Hejian segment) and the northeast part of Tanlu seismic belt (Anqiu segment), and constitute as, in our opinion, high risk areas prone to great earthquakes.
Seismic surface wave focal spot imaging: resolution tests using time-reversal simulations 
Authors: Giammarinaro Bruno , Hillers Gregor , Seydoux Leonard , Tsarsitalidou Christina , Catheline Stefan , Campillo Michel , Roux Philippe , de Rosny Julien
Published: March 2021

Converging surface wave fields create a large-amplitude feature at the origin referred to as focal spot. Its properties are governed by local medium properties and have long been used in medical imaging approaches such as passive elastography. Modern dense seismic arrays consisting of many hundreds of sensors allow now the application of noise correlation-based focal spot imaging in seismology. Here we use numerical experiments to study the resolution properties of focal spots to explore the limits of seismological data applications. Focal spot imaging is based on the correlation of diffuse isotropic wavefields. Here, however, we perform numerical experiments using an equivalent time-reversal approach to synthesize Rayleigh wave focal spots in an elastic half-space from Green’s functions computed with the AXITRA solver. Simulations are performed using an 85 x 85 receiver grid separated by 8 m and 72 time-reversal mirrors in the far field. The Rayleigh wave speed is 2 km/s near the surface and increases with depth for multi-layered media. The mirrors are located at the surface, on a circle at 12 km distance from the origin to simulate refocusing surface waves. Mirrors located inside the medium are used to simulate the contribution of biasing body waves. The 2D focal spot amplitude fields obtained under these conditions are compared, for frequencies between 2 and 15 Hz, to a theoretical near-field surface wave Green’s tensor parametrization using non-linear least square fitting techniques to demonstrate the feasibility of estimating the dispersion curve in multi-layered media. The set-up is further used to study effects of azimuthally variable energy fluxes on the dispersion estimates. Data from different distance ranges from the origin in the regression process to estimate dispersion mimics the effect of variable wavelength-to-aperture ratios. We find that the vertical-radial component is more sensitive to non-isotropic wavefields compared to the vertical-vertical component. However, the results for impinging P-waves energy shows that the vertical-radial component-based estimates are more stable and accurate. The tool can thus be used to test different filtering methods to account for anisotropic fluxes and P-wave energy to efficiently use each component. These results inform the focal spot imaging study using USArray data discussed in an accompanying abstract. 
Eccentric dipole of the geomagnetic field during the last reversal, last excursions, and the most significant Holocene anomalies
Authors: González-López Alicia , A. Campuzano Saioa , Rivera Pablo , Molina-Cardín Alberto , Pavón-Carrasco F. Javier , Osete M. Luisa
Published: March 2021

The geomagnetic field is commonly approximated to a geocentric tilted dipole. However, a next step in the approach of the geomagnetic field is the eccentric dipole which takes the first and second terms of the spherical harmonic representation of the geomagnetic field. In this work, we analyze the behavior of the eccentric dipole during the last reversal (Matuyama – Brunhes, 780 ka), the last excursions (Laschamp, 41 ka, and Mono Lake, 34 ka), and during two interesting features of the geomagnetic field observed during the Holocene (the South Atlantic Anomaly, from 1840 AD or older, and the Levantine Iron Age Anomaly, around 1000 BC). The last reversal and excursions are studied by using the IMMAB4 and LSMOD2 paleoreconstructions, respectively. We found that for these events the center of the eccentric dipole follows a common longitude path. The Holocene anomalies have been analyzed by using two of the most up-to-date paleoreconstructions for the last 3 millennia: the SHAWQ2k and the SHAWQ Iron Age paleoreconstructions. A common longitude path has not been observed between these anomalies.
Vertical movement of A. brasilense Sp7 and strain Cd in soil under different inoculation regimes
Authors: Chen Fengxian , Ronen Zeev , Arye Gilboa
Published: March 2021

Azospirillum brasilense Sp7 and Azospirillum brasilense Cd are two plant growth-promoting bacteria (PGPB). Traditional inoculation methods with PGPB are seed inoculation, seedling root inoculation and soil inoculation. Although these methods are simple to use, they are limited to apply at a specific plant growth stage. Therefore, PGPB inoculation by drip irrigation has been suggested as a means to deliver PGPB directly to the root zone during the plant growth stages. To quantify the intrinsic transport characteristics of two A. brasilense strains following point source inoculation, the properties of A. brasilense Sp7 and A. brasilense Cd (e.g., cell size, hydrophobicity, and zeta potential) and the adsorption characteristics on fine sand were measured. The transport and fate of the two strains were examined under transient water flow conditions with three soil inoculation regimes: (i) surface irrigation (ii) subsurface irrigation and (iii) soil premixing. The water content, bromide, and bacteria distribution in the soil profile were measured after 2 and 48 hours. The measured data were described using the attachment/detachment model using the Hydrus 2/3D code. The result showed that even though A. brasilense Sp7 and Cd exhibit similar hydrophilicity and zeta potential their adsorption and/or straining in the soil profile were differed. A. brasilense Cd has a smaller cell size, less adsorption and less straining than A. brasilense Sp7, thus its vertical movement is deeper. However, both strains accumulated at the vicinity of the water source. The results of this study will be presented and the pros and cons of three inoculation regimes will be discussed.
Mismatch between the optimal ages for ecosystem productivity and net CO2 sequestration in Norway spruce forests
Authors: Zhao Junbin , Lange Holger , Meissner Helge
Published: March 2021

Forests have climate change mitigation potential since they sequester carbon. However, their carbon sink strength might depend on management. As a result of the balance between CO2 uptake and emission, forest net ecosystem exchange (NEE) reaches optimal values (maximum sink strength) at young stand ages, followed by a gradual NEE decline over many years. Traditionally, this peak of NEE is believed to be concurrent with the peak of primary production (e.g., gross primary production, GPP); however, in theory, this concurrence may potentially vary depending on tree species, site conditions and the patterns of ecosystem respiration (Reco). In this study, we used eddy-covariance (EC)-based CO2 flux measurements from 8 forest sites that are dominated by Norway spruce (Picea abies L.) and built machine learning models to find the optimal age of ecosystem productivity and that of CO2 sequestration. We found that the net CO2 uptake of Norway spruce forests peaked at ages of 30-40 yrs. Surprisingly, this NEE peak did not overlap with the peak of GPP, which appeared later at ages of 60-90 yrs. The mismatch between NEE and GPP was a result of the Reco increase that lagged behind the GPP increase associated with the tree growth at early age. Moreover, we also found that newly planted Norway spruce stands had a high probability (up to 90%) of being a C source in the first year, while, at an age as young as 5 yrs, they were likely to be a sink already. Further, using common climate change scenarios, our model results suggest that net CO2 uptake of Norway spruce forests will increase under the future climate with young stands in the high latitude areas being more beneficial. Overall, the results suggest that forest management practices should consider NEE and forest productivity separately and harvests should be performed only after the optimal ages of both the CO2 sequestration and productivity to gain full ecological and economic benefits.
A (not so) random walk through hydrological space and time
Authors: Berkowitz Brian
Published: March 2021

A key philosophical perspective in science is that nature obeys general laws. Identification of these laws involves integration of system conceptualization, observation, experimentation and quantification. This perspective was a guiding principle of John Dalton’s research as he searched for patterns and common behaviors; he performed a broad range of experiments in chemistry and physics, and he entered over 200,000 observations in his meteorological diary during a period of 57 years. In this spirit, we examine general concepts based largely on statistical physics – universality, criticality, self-organization, and the relationship between spatial and temporal measures – and demonstrate how they meaningfully describe patterns and processes of fluid flow and chemical transport in hydrological systems. We discuss examples that incorporate random walks, percolation theory, fractals, and thermodynamics in analyses of hydrological systems – aquifers, soil environments and catchments – to quantify what appear to be universal dynamic behaviors and characterizations.