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"Molnar, Peter"
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Open-source, low-cost, in-situ turbidity sensor for river network monitoring
Fine sediment transport in rivers is important for catchment nutrient fluxes, global biogeochemical cycles, water quality and pollution in riverine, coastal and marine ecosystems. Monitoring of suspended sediment in rivers with current sensors is challenging and expensive and most monitoring setups are restricted to few single site measurements. To better understand the spatial heterogeneity of fine sediment sources and transport in river networks there is a need for new smart water turbidity sensing that is multi-site, accurate and affordable. In this work, we have created such a sensor, which detects scattered light from an LED source using two detectors in a control volume, and can be placed in a river. We compare several replicates of our sensor to different commercial turbidity probes in a mixing tank experiment using two sediment types over a wide range of typical concentrations observed in rivers. Our results show that we can achieve precise and reproducible turbidity measurements in the 0–4000 NTU or 0–16g/L range. Our sensor can also be used directly as a suspended sediment sensor and bypass an unnecessary calibration to Formazin. The developed turbidity sensor is much cheaper than existing options of comparable quality and is especially intended for distributed sensing across river networks.
Journal Article
Global warming accelerates soil heterotrophic respiration
Carbon efflux from soils is the largest terrestrial carbon source to the atmosphere, yet it is still one of the most uncertain fluxes in the Earth’s carbon budget. A dominant component of this flux is heterotrophic respiration, influenced by several environmental factors, most notably soil temperature and moisture. Here, we develop a mechanistic model from micro to global scale to explore how changes in soil water content and temperature affect soil heterotrophic respiration. Simulations, laboratory measurements, and field observations validate the new approach. Estimates from the model show that heterotrophic respiration has been increasing since the 1980s at a rate of about 2% per decade globally. Using future projections of surface temperature and soil moisture, the model predicts a global increase of about 40% in heterotrophic respiration by the end of the century under the worst-case emission scenario, where the Arctic region is expected to experience a more than two-fold increase, driven primarily by declining soil moisture rather than temperature increase.
Soil’s role in Earth’s carbon budget is uncertain. A new model links soil temperature and moisture to global soil respiration. Heterotrophic respiration has risen by 2% per decade since the 1980s, with a projected 40% increase by century end.
Journal Article
Comparisons of the kinematics and deep structures of the Zagros and Himalaya and of the Iranian and Tibetan plateaus and geodynamic implications
We compare the geologic histories, the deep structures, and the present‐day kinematics of deformation of the Himalaya and the adjacent Tibetan Plateau with those of the Zagros and Iranian Plateau to test geodynamic processes of continental collision. Shortly after India and Arabia collided with Eurasia, horizontal shortening manifested itself by folding and thrust faulting of sedimentary rock detached from India's and Arabia's underlying crystalline basement. Subsequently, slip on thrust faults stacked slices of India's basement to build the Himalaya on India's northern margin. Such faulting has not yet developed in the Zagros, where collision is more recent and Arabia penetrates into Eurasia more slowly than India does, so that postcollision convergence with Eurasia is less. The greater elevation, thicker crust, and more marked heterogeneity of the upper mantle beneath the Tibetan than beneath the Iranian Plateau also reflect a more advanced stage of development. Moreover, while thrust or reverse faulting and crustal shortening continue on the margins of both plateaus, normal faulting, suggesting horizontal extension and crustal thinning, occurs within Tibet but not in Iran. Hence, the balance of forces that built the high Tibetan Plateau must have changed, apparently some time since ∼15 Ma. Removal of Tibetan mantle lithosphere could have altered that balance. If mantle lithosphere beneath the Iranian Plateau has been removed, however, the change in force balance has been too small to initiate normal faulting. Low seismic wave speeds in the uppermost mantle just beneath the Moho of both plateaus suggest (to us) that lithosphere beneath both is thin, consistent with late Cenozoic removal of it, but alternative explanations might account for these low speeds. Despite its apparently thin, and hence presumably weak, mantle lithosphere, much of central Iran undergoes little deformation. It illustrates how a crustal block can behave rigidly not necessarily because it is strong but because deviatoric stresses can be small. Whereas differences between the two regions clearly depend on the amount that Arabia and India have penetrated into Eurasia, which scales with both the dates of collision and rates of convergence, we see no differences in the operative processes that depend on the present‐day rates of convergence.
Journal Article
Changes in Plate Motions Caused by Increases in Gravitational Potential Energy of Mountain Belts
Reconstructions of motions of the Nazca, South American, and Indian plates record short‐duration (≲10 Myr) variations in angular velocity, which enable a vector‐based test of the hypothesis that mountain uplift can cause changes in plate motion. Reductions in velocity of Nazca and South America between ∼12 and 6 Ma coincide with a phase of rapid surface uplift in the Central Andes. Decrease in the rate of India's convergence with Eurasia between ∼20 and 10 Ma corresponds to an increase in gravitational potential energy per unit area (GPE) within Tibet, marked by a transition from crustal thickening to thinning. The vectorial test shows that, in each case, the only change in driving force capable of balancing the change in basal drag is an increased resistance along the convergent boundary to the plate. Changes in GPE associated with mountain uplift provide a calibration for basal drags on plates. Basal tractions of ∼0.1–1 MPa provide resisting forces comparable in magnitude to driving forces from GPE variation in ocean lithosphere. The rapid change in motion of the Indian plate between about 48 and 41 Ma is explained by the juxtaposition of the Indian continent against the Andean‐type margin of the Transhimalaya and reduction in driving force due to loss of the slab. The net slab driving force lost was ∼2–4 TN m−1, in agreement with previous studies suggesting that forces resisting slabs' penetration into the mantle largely offset their negative buoyancy. Key Points Calculation of forces required to cause rapid changes in plate motion test the hypothesis that some stem from increase in gravitational potential energy (GPE) of mountains Rapid decreases in velocity of Nazca, South American, and Indian plates require increases in resistance at their convergent boundaries Geological evidence shows that the Miocene decreases in velocity were contemporaneous with increases in GPE of the Andes and Tibet
Journal Article
Source apportionment of fine atmospheric particles using positive matrix factorization in Pretoria, South Africa
In Pretoria South Africa, we looked into the origins of fine particulate matter (PM
2.5
), based on 1-year sampling campaign carried out between April 18, 2017, and April 17, 2018. The average PM
2.5
concentration was 21.1 ± 15.0 µg/m
3
(range 0.7–66.8 µg/m
3
), with winter being the highest and summer being the lowest. The XEPOS 5 energy dispersive X-ray fluorescence (EDXRF) spectroscopy was used for elemental analysis, and the US EPA PMF 5.0 program was used for source apportionment. The sources identified include fossil fuel combustion, soil dust, secondary sulphur, vehicle exhaust, road traffic, base metal/pyrometallurgical, and coal burning. Coal burning and secondary sulphur were significantly higher in winter and contributed more than 50% of PM
2.5
sources. The HYSPLIT model was used to calculate the air mass trajectories (version 4.9). During the 1-year research cycle, five transportation clusters were established: North Limpopo (NLP), Eastern Inland (EI), Short-Indian Ocean (SIO), Long-Indian Ocean (LIO), and South Westerly-Atlantic Ocean (SWA). Local and transboundary origin accounted for 85%, while 15% were long-range transport. Due to various anthropogenic activities such as biomass burning and coal mining, NLP clusters were the key source of emissions adding to the city’s PM rate. In Pretoria, the main possible source regions of PM
2.5
were discovered to be NLP and EI. Effective control strategies designed at reducing secondary sulphur, coal burning, and fossil fuel combustion emissions at Southern African level and local combustion sources would be an important measure to combat the reduction of ambient PM
2.5
pollution in Pretoria.
Journal Article
LATE CENOZOIC INCREASE IN ACCUMULATION RATES OF TERRESTRIAL SEDIMENT: How Might Climate Change Have Affected Erosion Rates?
▪ Abstract Accumulation rates of terrestrial sediment have increased in the past few million years both on and adjacent to continents, although not everywhere. Apparently, erosion has increased in elevated terrain regardless of when last tectonically active or what the present-day climate. In many regions, sediment coarsened abruptly in late Pliocene time. Sparser data suggest increased sedimentation rates at ∼15 Ma, approximately when oxygen isotopes in benthic foraminifera imply high-latitude cooling. If climate change effected accelerated erosion, understanding how it did so remains the challenge. Some obvious candidates, such as lowered sea level leading to erosion of continental shelves or increased glaciation, account for increased sedimentation in some, but not all, areas. Perhaps stable climates that varied slowly allowed geomorphic processes to maintain a state of equilibrium with little erosion until ∼3–4 Ma, when large oscillations in climate with periods of 20,000–40,000 years developed and denied the landscape the chance to reach equilibrium.
Journal Article
Evaluating methods for debris-flow prediction based on rainfall in an Alpine catchment
The prediction of debris flows is relevant because this type of natural hazard can pose a threat to humans and infrastructure. Debris-flow (and landslide) early warning systems often rely on rainfall intensity–duration (ID) thresholds. Multiple competing methods exist for the determination of such ID thresholds but have not been objectively and thoroughly compared at multiple scales, and a validation and uncertainty assessment is often missing in their formulation. As a consequence, updating, interpreting, generalizing and comparing rainfall thresholds is challenging. Using a 17-year record of rainfall and 67 debris flows in a Swiss Alpine catchment (Illgraben), we determined ID thresholds and associated uncertainties as a function of record duration. Furthermore, we compared two methods for rainfall definition based on linear regression and/or true-skill-statistic maximization. The main difference between these approaches and the well-known frequentist method is that non-triggering rainfall events were also considered for obtaining ID-threshold parameters. Depending on the method applied, the ID-threshold parameters and their uncertainties differed significantly. We found that 25 debris flows are sufficient to constrain uncertainties in ID-threshold parameters to ±30 % for our study site. We further demonstrated the change in predictive performance of the two methods if a regional landslide data set with a regional rainfall product was used instead of a local one with local rainfall measurements. Hence, an important finding is that the ideal method for ID-threshold determination depends on the available landslide and rainfall data sets. Furthermore, for the local data set we tested if the ID-threshold performance can be increased by considering other rainfall properties (e.g. antecedent rainfall, maximum intensity) in a multivariate statistical learning algorithm based on decision trees (random forest). The highest predictive power was reached when the peak 30 min rainfall intensity was added to the ID variables, while no improvement was achieved by considering antecedent rainfall for debris-flow predictions in Illgraben. Although the increase in predictive performance with the random forest model over the classical ID threshold was small, such a framework could be valuable for future studies if more predictors are available from measured or modelled data.
Journal Article
An advanced stochastic weather generator for simulating 2‐D high‐resolution climate variables
A new stochastic weather generator, Advanced WEather GENerator for a two‐dimensional grid (AWE‐GEN‐2d) is presented. The model combines physical and stochastic approaches to simulate key meteorological variables at high spatial and temporal resolution: 2 km × 2 km and 5 min for precipitation and cloud cover and 100 m × 100 m and 1 h for near‐surface air temperature, solar radiation, vapor pressure, atmospheric pressure, and near‐surface wind. The model requires spatially distributed data for the calibration process, which can nowadays be obtained by remote sensing devices (weather radar and satellites), reanalysis data sets and ground stations. AWE‐GEN‐2d is parsimonious in terms of computational demand and therefore is particularly suitable for studies where exploring internal climatic variability at multiple spatial and temporal scales is fundamental. Applications of the model include models of environmental systems, such as hydrological and geomorphological models, where high‐resolution spatial and temporal meteorological forcing is crucial. The weather generator was calibrated and validated for the Engelberg region, an area with complex topography in the Swiss Alps. Model test shows that the climate variables are generated by AWE‐GEN‐2d with a level of accuracy that is sufficient for many practical applications. Key Points A new advanced subdaily stochastic weather generator (AWE‐GEN‐2d) is presented The model combines physical and stochastic approaches to simulate key climate variables at high spatial and temporal resolution It is relatively computationally efficient and allows the generation of multiple realizations accounting for natural climate variability
Journal Article
Intensification of Convective Rain Cells at Warmer Temperatures Observed from High-Resolution Weather Radar Data
This study contributes to the understanding of the relationship between air temperature and convection by analyzing the characteristics of rainfall at the storm and convective rain cell scales. High spatial–temporal resolution (1 km, 5 min) estimates from a uniquely long weather radar record (24 years) were coupled with near-surface air temperature over Mediterranean and semiarid regions in the eastern Mediterranean. In the examined temperature range (5°–25°C), the peak intensity of individual convective rain cells was found to increase with temperature, but at a lower rate than the 7%°C−1 scaling expected from the Clausius–Clapeyron relation, while the area of the individual convective rain cells slightly decreases or, at most, remains unchanged. At the storm scale, the areal convective rainfall was found to increase with warmer temperatures, whereas the areal nonconvective rainfall and the stormwide area decrease. This suggests an enhanced moisture convergence from the stormwide extent toward the convective rain cells. Results indicate a reduction in the total rainfall amounts and an increased heterogeneity of the spatial structure of the storm rainfall for temperatures increasing up to 25°C. Thermodynamic conditions, analyzed using convective available potential energy, were determined to be similar between Mediterranean and semiarid regions. Limitations in the atmospheric moisture availability when shifting from Mediterranean to semiarid climates were detected and explain the suppression of the intensity of the convective rain cells when moving toward drier regions. The relationships obtained in this study are relevant for nearby regions characterized by Mediterranean and semiarid climates.
Journal Article