The possibility to exploit the muon scattering for the elemental discrimination of materials in a given volume is well known. When more than one material is present along the muon path, it is often important to discern the order in which they are stacked. The scattering angle due to the target volume can be split into two interior angles in the tomographic setups based on the muon scattering, and we call this property as the triangular correlation where the sum of these two interior angles is equal to the scattering angle. In this study, we apply this triangular correlation for a multi-block material configuration that consist of concrete, stainless steel, and uranium. By changing the order of this material set, we employ the GEANT4 simulations and we show that the triangular correlation is valid in the multi-block material setups, thereby providing the possibility of supportive information for the coarse prediction of the material order in such configurations.
Albeit slow and not without its challenges, lead (Pb) emissions and sources in the United States (U.S.) have decreased immensely over the past several decades. Despite the prevalence of childhood Pb poisoning throughout the 20th century, most U.S. children born in the last two decades are significantly better off than their predecessors in regards to Pb exposure. However, this is not equal across demographic groups and challenges remain. Modern atmospheric emissions of Pb in the U.S. are nearly negligible since the banning of leaded gasoline in vehicles and regulatory controls on Pb smelting plants and refineries. This is evident in the rapid decrease of atmospheric Pb concentrations across the U.S over the last four decades. One of the most significant remaining contributors to air Pb is aviation gasoline (avgas), which is minor compared to former Pb emissions. However, continual exposure risks to Pb exist in older homes and urban centers, where leaded paint and/or historically contaminated soils+dusts can still harm children. Thus, while effective in eliminating nearly all primary sources of Pb in the environment, the slow rate of U.S. Pb regulation has led to legacy, secondary sources of Pb in the environment. More proactive planning, communication, and research of commonly used emerging contaminants of concern that can persist in the environment long after their initial use (i.e., PFAS) should be prioritized so that the same mistakes are not made again.
1. This study combines two approaches to explore the utility of Monod growth kinetics to predict competition outcomes between freshwater cyanobacteria and chlorophytes at low iron Fe. Fe threshold concentrations (FeT) below which growth ceases, and growth affinities (slope of Fe concentration vs growth rate near FeT) were estimated for three large-bodied cyanobacteria (two N-fixers and Microcystis) and two chlorophytes in batch cultures. 2. Mean FeT for N-replete cyanobacteria, N-deplete (when N-fixing) cyanobacteria and chlorophytes were 0.076, 0.736 and 0.245 nmol L-1 , respectively. Mean affinities were 0.937, 0.597 and 0.412 L nmol-1 d-1 , respectively. Assuming that the mean affinities are representative of their groups, affinities predict that N-replete cyanobacteria are more efficient at acquiring Fe than chlorophytes and should dominate when Fe is low but greater than their FeT. 3. A second study evaluated the competitive abilities of a pico-cyanobacterium and a third chlorophyte in dual species, serial dilution culture. The pico-cyanobacterium was dominant at 50 nmol L-1 total Fe (which limited both taxa) and 500 nmol L-1 total Fe. At 0.5 nmol L-1 total Fe, a stressful concentration below FeT during most of the incubation, growth rates and cell densities were extremely low but neither had washed out after several months. 4. These results show that Monod kinetics can successfully predict competition outcomes in laboratory settings at low Fe. While important, Monod kinetics are only one mechanism governing competition between cyanobacteria and eukaryotes in natural systems. Observed deviations from Monod predictions can be partially explained with known mechanisms.
To increase drought preparedness in semi-arid regions many small and medium reservoirs have been built in recent decades. Together these reservoirs form a Dense Reservoir Network (DRN) and its presence generates numerous challenges for water management. Most of the reservoirs that constitute the network are unmonitored and unregistered, posing questions on their cumulative effects on strategic reservoirs and water distribution at watershed scale. Their influence on hydrological drought propagation is thus largely unexplored. The objective of this study is then to assess the DRN effects on droughts both in time and space. This study utilized a mesoscale semi-distributed hydrological model to reproduce the DRN in a large-scale tropical semiarid watershed (19,530 km2), which presents both a network of large strategic reservoirs and a DRN. To investigate the effects in time and space generated by the network’s presence, the differences between multiple network scenarios were analyzed. Results show that the presence of the DRN accelerates the transition from meteorological to hydrological drought phases by 20% on average and slows down the recharge in strategic reservoirs by 25%, leading to a 12% increase of periods in hydrological drought conditions in a highly strategic basin and 26% without strategic reservoirs. In space, the DRN shifts upstream the basin’s water storage capacity by 8%, but when both large and small reservoirs are present the stored volume distribution behavior is not straightforward. The findings confirm the need to consider small reservoirs when addressing drought management policies at regional scale.
As an important anthropogenic interference on the water cycle, reservoir operation behavior remains challenging to be properly represented in hydrologic models, thus limiting the capability of predicting streamflow under the interactions between hydrologic variability and operational preferences. Data-driven models provide a promising approach to represent reservoir operation rules by capturing relationships embedded in historical records. Similar to hydrologic processes vary across temporal scales, reservoir operations manifest themselves at different timescales, prioritizing different targets to mitigate streamflow variability at a given time scale. To capture interactions of reservoir operations across time scales, we proposed a hierarchical temporal scale framework to investigate the behaviors of over 300 major reservoirs across the Contiguous United States with a wide range of streamflow conditions. Machine learning models were constructed to simulate reservoir operation at daily, weekly, and monthly scales, where decisions at short-term scales interact with long-term decisions. We found that the hierarchical temporal scale configuration better captures reservoir releases than models constructed at a single time scale, especially for reservoirs with multiple operation targets. Model-based sensitivity analysis shows that for more than one third of the studied reservoirs, the release schemes, as a function of decision variables, vary at different time scales, suggesting that operators are commonly faced with complicated trade-offs to serve multiple purposes. The proposed hierarchical temporal scale approach is flexible to incorporate various data-driven models and decision variables to derive reservoir operation rule, providing a robust framework to understand the feedbacks between natural streamflow variability and human interferences across time scales.
The thermal balance of forests regulates land-atmosphere feedbacks. Forests dominated by different plant functional types have contrasting energy balances, but little is known about the influence of forest structure and functional traits. By combining spaceborne measurements of land surface temperature from ECOSTRESS with ground-based meteorological data, we estimate the thermal balance at the surface (∆Tcan-air) during four summers in a region located at the Mediterranean-temperate ecotone in the NE Iberian Peninsula. We then analyze the spatiotemporal drivers of ∆Tcan-air by quantifying the effects of meteorology, forest structure (e.g. basal area, tree height) and ecophysiology (hydraulic traits, water use efficiency), during normal days and hot spells. Canopy temperatures fluctuate according to changes in air temperature but are on average 3.2˚K warmer than the near-surface air. During hot spells, ∆Tcan-air is smaller than normal periods because the advection of hot and dry air masses from the Sahara region results in a sudden increase in air temperature relative to the canopy temperature. Vapor pressure deficit (VPD) is negatively correlated to ∆Tcan-air, since the highest VPD values coincide with peaks in heat advection. Still canopy temperatures increase with VPD due to decreased transpiration and stomatal conductance and transpiration. Meanwhile, soil water availability is shown to enhance evaporative cooling. Importantly, we demonstrate that plot-scale forest structural and hydraulic traits are key determinants for the forest thermal balance. The integration of functional traits and forest structure over relevant spatial scales could improve our ability to understand and model land-atmosphere feedbacks in forested regions.
Transpiration is a key process driving energy, water and thus carbon dynamics. Global T products are fundamental for understanding and predicting vegetation processes. However, validation of these transpiration products is limited, mainly due to lack of suitable datasets. We propose a method to use SAPFLUXNET, the first quality-controlled global tree sap flow database, for evaluating transpiration products at global scale. Our method is based on evaluating temporal mismatches, rather than absolute values, by standardizing both transpiration and sap flow products. We evaluate how transpiration responses to hydro-meteorological variation from the Global Land Evaporation Amsterdam Model (GLEAM), a widely used global transpiration product, compare to in-situ responses from SAPFLUXNET field data. Our results show GLEAM and SAPFLUXNET temporal trends are in good agreement, but diverge under extreme conditions. Their temporal mismatches differ depending on the magnitude of transpiration and are not random, but linked to energy and water availability. Despite limitations, we show that the new global SAPFLUXNET dataset is a valuable tool to evaluate T products and identify problematic assumptions and processes embedded in models. The approach we propose can, therefore, be the foundation for a wider use of SAPFLUXNET, a new, independent, source of information, to understand the mechanisms controlling global transpiration fluxes.
Impact evaluation (IE) of large infrastructure presents numerous challenges, and investments in urban piped water and sanitation are no exception. Here we present methods for more systematic assessment of the implications of such interventions, discussing tradeoffs between validity, relevance and practicality that arise from alternative approaches. Then, to more clearly illustrate the many issues that typically arise in such IEs, we draw on an example application in Zarqa, Jordan, where the Millennium Challenge Corporation invested about US$275 million to upgrade and extend piped water and sewer networks, as well as increase the capacity of the country’s largest wastewater treatment plant. The theory of change for the intervention took a systems view of impacts: the project aimed to improve water supply to urban areas while maintaining flows to irrigators through enhanced wastewater reuse. The case adds valuable evidence on the impacts of large infrastructure investments and illustrates well the challenges of capturing spillovers, mitigating study contamination, maintaining statistical power, and determining overall welfare effects, in situations involving diverse market and nonmarket impacts. These limitations notwithstanding, the case highlights the high value of conducting IEs, and why applied researchers should not give up on pragmatic and interdisciplinary collaborations to evaluation in the face of complex interventions.
Evaluating historical simulations from global climate models (GCMs) remains an important exercise for better understanding future projections of climate change and variability in rapidly warming regions, such as the Arctic. As an alternative approach for comparing climate models and observations, we set up a machine learning classification task using a shallow artificial neural network (ANN). Specifically, we train an ANN on maps of annual mean near-surface temperature in the Arctic from a multi-model large ensemble archive in order to classify which GCM produced each temperature map. After training our ANN on data from the large ensembles, we input annual mean maps of Arctic temperature from observational reanalysis and sort the prediction output according to increasing values of the ANN’s confidence for each GCM class. To attempt to understand how the ANN is classifying each temperature map with a GCM, we leverage a feature attribution method from explainable artificial intelligence. By comparing composites from the attribution method for every GCM classification, we find that the ANN is learning regional temperature patterns in the Arctic that are unique to each GCM relative to the multi-model mean ensemble. In agreement with recent studies, we show that ANNs can be useful tools for extracting regional climate signals in GCMs and observations.
We develop a regional hydrological model that applies to arid and semi-arid regions, by explicitly considering the effect of irrigation on the hydrological processes. A new irrigation module is here integrated into the recently introduced Atmospheric and Hydrological Modelling System (AHMS) for the quantitative assessment of basin-scale hydrological response to climate change and the impact of anthropogenic activities on water resources. The land surface, channel routing and groundwater modules of the AHMS are extended here to incorporate the new module. We then apply the model to simulating the hydrological processes in the Yellow River Basin, an arid and semi-arid region where irrigation constitutes the most important source of water use. The model is calibrated and validated using in-situ and remote sensing observations. This study demonstrates the capability of the AHMS for regional hydrological modelling in arid and semi-arid basins where irrigation profoundly influences the water balance.
Evidence based on sparse tree-ring data suggests a severe sustained drought occurred in the 2nd century CE that could have rivaled medieval period droughts in the Colorado River basin (Gangopadhyay et al. 2022). Most of these tree-ring data have been used in gridded drought reconstructions (Cook et al., 2010) which extend back to 1 CE over an area that includes the intermountain western US. However, the 2nd century drought has not been highlighted in prior studies given the sparseness of the data available for this time period. A new reconstruction of Colorado River flow based on these data documents a notably severe and sustained drought over much of the 2nd century (Gangopadhyay et al. 2022). While this reconstruction suggests that the drought exceeds the severity and duration of any drought in the past 2000 years, a complete assessment of the 2nd century drought is challenging due to the sparseness of data. In this poster presentation, we describe the tree-ring data available, along with other proxy data that provide evidence for the 2nd century drought and support its severity. In our conclusions, we discuss outstanding questions and thoughts for further work.
Models and observations suggest that particle flux attenuation is lower across the mesopelagic zone of anoxic environments compared to oxic environments. Flux attenuation is controlled by microbial metabolism as well as aggregation and disaggregation by zooplankton, all of which also shape the relative abundance of differently sized particles. Observing and modeling particle spectra can provide information about the contributions of these processes. We measured particle size spectrum profiles at one station in the oligotrophic Eastern Tropical North Pacific Oxygen Deficient Zone (ETNP ODZ) using an underwater vision profiler (UVP), a high-resolution camera that counts and sizes particles. Measurements were taken at different times of day, over the course of a week. Comparing these data to particle flux measurements from sediment traps collected over the same time-period allowed us to constrain the particle size to flux relationship, and to generate highly resolved depth and time estimates of particle flux rates. We found that particle flux attenuated very little throughout the anoxic water column, and at some time-points appeared to increase. Comparing our observations to model predictions suggested that particles of all sizes remineralize more slowly in the ODZ than in oxic waters, and that large particles disaggregate into smaller particles, primarily between the base of the photic zone and 500 m. Acoustic measurements of multiple size classes of organisms suggested that many organisms migrated, during the day, to the region with high particle disaggregation. Our data suggest that diel-migrating organisms both actively transport biomass and disaggregate particles in the ODZ core.
An analysis of concurrent extreme events of continental precipitation and Integrated Water Vapour Transport (IVT) is crucial to our understanding of the role of the major global mechanisms of atmospheric moisture transport, including that of the landfalling Atmospheric Rivers (ARs) in extratropical regions. For this purpose, gridded data on CPC precipitation and ERA-5 IVT at a spatial resolution of 0.5º were used to analyze these concurrent events, covering the period from Winter 1980/1981 to Autumn 2017. For each season, and for each point with more than 400 non-dry days, several copula models were fitted to model the joint distribution function of the two variables. At each of the analysed points, the best copula model was used to estimate the probability of a concurrent extreme. At the same time, within the sample of observed concurrent extremes, the proportion of days with landfalling ARs was calculated for the whole period and for two 15-year sub-periods, one earlier period and one more recent (warmer) period. Three metrics based on copulas were used to analyse carefully the influence of IVT on extreme precipitation in the main regions of occurrence of AR landfall. The results show that the probability of occurrence of concurrent extremes is strongly conditioned by the dynamic component of the IVT, the wind. The occurrence of landfalling ARs accounts for most of the concurrent extreme days of IVT and continental precipitation, with percentages of concurrent extreme days close to 90% in some seasons in almost all the known regions of maximum occurrence of landfalling ARs, and with percentages greater than 75% downwind of AR landfall regions. This coincidence was lower in tropical regions, and in monsoonal areas in particular, with percentages of less than 50%. With a few exceptions, the role of landfalling ARs as drivers of concurrent extremes of IVT and continental precipitation tends to show a decrease in recent (warmer) periods. For almost all the landfalling AR regions with high or very high probabilities of achieving a concurrent extreme, there is a general trend towards a lower influence of IVT on extreme continental precipitation in recent (warmer) periods.
Subsurface sequestration of carbon dioxide (CO2) requires long-term monitoring of the injected CO2 plume to prevent CO2 leakage along the wellbore or across the caprock. Accurate knowledge of the location and movement of the injected CO2 is crucial for risk management at a geological CO2-storage complex. Conventional methods for locating/assessing the injected CO2 plume in the subsurface assume a geophysical model, which is specific and may not be applicable to all types of CO2-injection reservoirs and scenarios. We developed an unsupervised-learning-based visualization of the subsurface CO2 plume that adapts and scales based on the data without requiring an assumption of the geophysical model. The data-processing workflow was applied to the cross-well tomography data from the SECARB Cranfield carbon geo-sequestration project. A multi-level clustering approach was developed to account for data imbalance due to the absence of CO2 in the large portion of the imaged reservoir. The first level of clustering differentiated CO2-bearing regions from the non-CO2 bearing regions and achieved a silhouette score of 0.85, a Calinski-Harabasz index of 160666, and a Davies-Bouldin index of 0.43, which are indicative of high quality, reliable clustering. The second level of clustering further differentiated the CO2-bearing regions into regions containing low, medium, and high CO2 content. Overall, the multi-level clustering achieved a silhouette score, Calinski-Harabasz index, and Davies-Bouldin index of 0.74, 59656, and 0.32, which confirm the high quality and reliability of the newly proposed unsupervised-learning-based visualization. Three distinct clustering techniques, namely k-means, mean-shift, and agglomerative, generated similar visualizations. In terms of the adjusted Rand index, the similarity of clusters identified by the three distinct clustering techniques is around 0.98, which indicates the robustness of the cluster labels assigned to various regions of the CO2-injection reservoir. Further, we find certain geophysical signatures, such as Fourier transform and wavelet transform, to be highly relevant and informative indicators of the spatial distribution of CO2 content.
For decades, the Arctic has been warming at least twice as fast as the rest of the globe. As a first step towards quantifying parametric uncertainty in Arctic feedbacks, we perform a variance-based global sensitivity analysis (GSA) using a fully-coupled, ultra-low resolution (ULR) configuration of version 1 of the Department of Energy’s Energy Exascale Earth System Model (E3SMv1). The study randomly draws 139 realizations of ten model parameters spanning three E3SMv1 components (sea ice, atmosphere and ocean), which are used to generate 75 year long projections of future climate using a fixed pre-industrial forcing. We quantify the sensitivity of six Arctic-focused quantities of interest (QOIs) to these parameters using main effect, total effect and Sobol sensitivity indices computed with a Gaussian process emulator. A sensitivity index-based ranking of model parameters shows that the atmospheric parameters in the CLUBB (Cloud Layers Unified by Binormals) scheme have significant impact on sea ice status and the larger Arctic climate. We also use the Gaussian process emulator to predict the response of varying each variable when the impact of other parameters are averaged out. These results allow one to assess the non-linearity of a parameter’s impact on a QOI and investigate the presence of local minima encountered during the spin-up tuning process. Our study confirms the necessity of performing global analyses involving fully-coupled climate models, and motivates follow-on investigations in which the ULR model is compared rigorously to higher resolution configurations to confirm its viability as a lower-cost surrogate in fully-coupled climate uncertainty analyses.
Vegetation is an important component of terrestrial ecosystem as it supports other biological activities through the photosynthetic production. The biophysical and biochemical parameters of vegetation retrieved from satellite observations have been used extensively in studying the physiological states and growing conditions of vegetation that enabling global vegetation monitoring. Most of vegetation remote sensing applications using data from MODIS, Landsat, and Sentinel, though it would be beneficial, from the user perspective, to have an even more diverse data sources that not only secure data sustainability in case satellite retirement or sensor failure, but also enables research opportunities such as multi-sensor data fusion/integration and multi-angle remote sensing that can take advantage of observations acquired from different spaceborne sensors. In this regard, it would be worth to explore the potential of the large number of Chinese Earth Observation Satellites (CEOS) that have been put into orbit over past decade. Here we summarized the recent advances in applying CEOS remote sensing of vegetation and its associated applications. We focused on the uncertainty and limitations for retrieving several commonly-used vegetation parameters by critically examining the case studies conducted over different vegetation types. Suggestions for research opportunities that can benefit from the additional data from CEOS are also provided. The hope is to provide the community an overview of what could be useful to their specific ecological, environmental and global change studies by leveraging the growing data volume from the orbiting CEOS sensors.
Survey evidence has indicated that a significant percentage of the population does not fully embrace the scientific consensus regarding climate change. This paper assesses whether the hourly temperature data support this denial. The analysis examines the relationship between hourly CO2 concentration levels and temperature using hourly data from the NOAA-operated Barrow observatory in Alaska. At this observatory, the average annual temperature over the 2015-2020 period was about 3.37 oC higher than in 1985–1990. A time-series model to explain hourly temperature is formulated using the following explanatory variables: the hourly level of total downward solar irradiance, the CO2 value lagged by one hour, proxies for the diurnal variation in temperature, proxies for the seasonal temperature variation, and proxies for possible non-anthropomorphic drivers of temperature. The purpose of the time-series approach is to capture the data’s heteroskedastic and autoregressive nature, which would otherwise “mask” CO2’s “signal” in the data. The model is estimated using hourly data from 1985 through 2015. The results are consistent with the hypothesis that increases in CO2 concentration levels have nontrivial consequences for hourly temperature. The estimated annual contributions of factors exclusive of CO2 and downward total solar irradiance are very small. The model was evaluated using out-of-sample hourly data from 1 Jan 2016 through 31 Aug 2017. The model’s out-of-sample hourly temperature predictions are highly accurate, but this accuracy is significantly degraded if the estimated CO2 effects are ignored. In short, the results are consistent with the scientific consensus on climate change.
Simulation models of multi-sector systems are increasingly used to understand societal resilience to climate and economic shocks and change. However, multi-sector systems are also subject to numerous uncertainties that prevent the direct application of simulation models for prediction and planning, particularly when extrapolating past behavior to a nonstationary future. Recent studies have developed a combination of methods to characterize, attribute, and quantify these uncertainties for both single- and multi-sector systems. Here we review challenges and complications to the idealized goal of fully quantifying all uncertainties in a multi-sector model and their interactions with policy design as they emerge at different stages of analysis: (1) inference and model calibration; (2) projecting future outcomes; and (3) scenario discovery and identification of risk regimes. We also identify potential methods and research opportunities to help navigate the tradeoffs inherent in uncertainty analyses for complex systems. During this discussion, we provide a classification of uncertainty types and discuss model coupling frameworks to support interdisciplinary collaboration on multi-sector dynamics (MSD) research. Finally, we conclude with recommendations for best practices to ensure that MSD research can be properly contextualized with respect to the underlying uncertainties.