Heat has historically resulted in more mortality than any other severe weather-related phenomenon in the United States, with the U.S. Centers for Disease Control attributing more than six hundred deaths to extreme heat each year. Agricultural workers are particularly vulnerable to environmental heat exposure: mortality rates due to heat amongst crop workers are twenty times higher than in the general worker population. The vulnerability of this group of workers to heat is exacerbated by factors such as economic vulnerability, immigration status, language barriers, access to health care, and the absence of worker heat standards in all but three of the fifty United States. Climate change threatens to increase the risk of heat-related illness in agricultural workers, but so far there has been no nation-wide evaluation of the expected change in heat exposure in a warmer climate for this group of workers. Here, we estimate baseline and future exposure of agricultural workers in the main growing regions of the continental U.S. to extreme heat. Given the diverse health impacts of different types of heat events, we compare metrics for both single day extremes and multi-day heat waves, and calculate how these statistics will change at the county level with 2 and 4 degrees Celsius of global warming. Our findings serve as a guideline for determining regionally appropriate heat standards, and underscore the need for agencies in all agricultural states to make preparations for a warmer climate.

With plate tectonics operating on Earth, the preservation potential for mantle reservoirs from the Hadean Eon (>4.0 Ga) has been regarded as very small. The quest for such early remnants has been spurred by the observation that many Archean rocks exhibit excesses of 182W, the decay product of short-lived 182Hf. However, it remains speculative, if Archean 182W anomalies and also 182W deficits found in many young ocean island basalts (OIBs) mirror primordial Hadean mantle differentiation or just variable contributions from older meteorite building blocks delivered to the growing Earth. Here, we present a high-precision 182W isotope dataset for 3.22-3.55 Ga old rocks from the Kaapvaal Craton, southern Africa. In expanding previous work, our study reveals widespread 182W deficits in different rock units from the Kaapvaal Craton and also the very first discovery of a negative co-variation between short-lived 182W and long-lived 176Hf-143Nd-138Ce patterns, a trend of global significance. Amongst different models, these distinct patterns can be best explained by the presence of recycled mafic restites from Hadean protocrust in the ancient mantle beneath the Kaapvaal Craton. Further, the data provide unambiguous evidence for the operation of silicate differentiation processes on Earth during the lifetime of 182Hf, i.e., the first 60 million years after solar system formation. The striking isotopic similarity between recycled protocrust and the low 182W endmember of modern OIBs might also constitute the missing link bridging 182W isotope systematics in Archean and young mantle-derived rocks.

A document by Matthew Kenneth Brown. Click on the document to view its contents.

A common deviation from typical subduction models occurs when thrust sheets of oceanic-crust and upper-mantle rocks are emplaced over more buoyant continental lithosphere. The archetypal example of ophiolite obduction is the Semail ophiolite in the United Arab Emirates (UAE)-Oman orogenic belt, formed and obducted onto the Arabian continental margin during the Late Cretaceous. The Strait of Hormuz syntaxis, the northern extent of the UAE-Oman mountains, marks the transition from ocean-continent convergence in the Gulf of Oman to continental collision along the Zagros Mountains. Based on new seismic data from a focused recording network, we infer crustal and mantle deformation in the northeastern corner of the Arabian plate (including the southern Zagros and the UAE-Oman mountains), using observations from anisotropic tomography and shear-wave splitting measurements. We recover a change of ~90˚ in the axis of fast-anisotropic orientations in the crust from the Zagros to the UAE-Oman mountain belt, consistent with the dominant strike of the orogenic belts. We also find evidence for localized fossil deformation in the lithospheric mantle underlying the UAE-Oman mountain range, possibly related to stress-induced tectonism triggered by underthrusting of the proto-Arabian continental margin beneath the overriding Semail ophiolite. These orientations, averaging 15˚ anticlockwise, provide the first geophysical verification of geological

Feedback control algorithms, an important tool in climate intervention strategy design, are widely used in stratospheric aerosol injection (SAI) simulations but have never been implemented for marine cloud brightening (MCB). Using the Community Earth System Model (CESM2), we present the first simulations of feedback control-regulated MCB. Our controller, which regulates global mean temperature (T0) by varying the area of MCB coverage over time, successfully maintains the desired T0 of 1.5°C above the preindustrial in the SSP2-4.5 global warming scenario comparably to a contemporary SAI controller. After 35 years of intervention, the surface temperature response when MCB has been gradually ramped up over time in this way is similar to a constant intervention with similar global mean temperature (including strong regional heterogeneity), but system memory may cause differences in Arctic sea ice and the Atlantic Meridional Overturning Circulation (AMOC).

Excessive dissolved inorganic nitrogen (DIN) added to the urban river systems by point-source inputs, such as untreated wastewater and wastewater treatment plant (WWTP) effluent, constitutes a water-quality problem of growing concern in China. However, very little is known about their impacts on DIN retention capacity and pathways in receiving waters. In this study, a spatially-intensive water quality monitoring campaign was conducted to support the application of the river water quality model WASP7.5 to the PS-impacted Nanfei River, China. The DIN retention capacities and pathway of a reference upstream Reach A, a wastewater-impacted Reach B and an effluent-dominated Reach C were quantified using the model results after a Bayesian approach for parameter estimation and uncertainty analysis. The results showed that the untreated wastewater discharge elevated the assimilatory uptake rate but lowered its efficiency in Reach B; while the WWTP effluent discharge elevated both denitrification rate and efficiency and made Reach C a denitrification hotspot with increased nitrate concentration and hypoxic environment. The effects of the point-source inputs on the DIN retention pathways (assimilatory uptake vs. denitrification) were regulated by their impacts on river metabolism. Despite different pathways, the total DIN retention ratios of Reaches A, B and C under low-flow conditions were 30.3% km-1, 14.3% km-1 and 6.5% km-1, respectively, which indicated the instream DIN retention capacities were significantly impaired by the point-source inputs. This result suggests that the DIN discharged from point-source inputs to urban rivers will be transported downstream with the potential to create long-term ecological implications not only locally but also regionally.

We have taken a key step in evaluating the importance of ionospheric outflows relative to electrodynamic coupling in the thermosphere’s impact on geospace dynamics. We isolated the thermosphere’s material influence and suppressed electrodynamic feedback in whole geospace simulations by imposing a time-constant ionospheric conductance in the ionospheric Ohm’s law in a coupled model that combines the multi-fluid Lyon-Fedder-Mobarry magnetosphere model with the Thermosphere Ionosphere Electrodynamic General Circulation Model and the Ionosphere Polar Wind Model that includes both polar wind and transversely accelerated ion species. Numerical experiments were conducted for different thermospheric states parameterized by F10.7 for interplanetary driving representative of the stream interaction region that swept past Earth on 27 March 2003. We demonstrate that thermosphere through its regulation of ionospheric outflows influences magnetosphere-ionosphere (MI) convection and the ion composition, symmetries, x-line perimeter and magnetic merging of the magnetosphere. Feedback to the ionosphere-thermosphere from evolving MI convection, and Alfvénic Poynting fluxes and soft (~ few 100 eV) electron precipitation originating in the magnetosphere, in turn, modify the evolving O+ outflow properties. The simulation results identify a variety of observed magnetospheric features that are attributable directly to the thermosphere’s material influence: Asymmetries in O+ outflow fluxes and velocities in the pre/postnoon low-altitude magnetosphere, dawn/duskside lobes and pre/postmidnight plasmasheet; O+ distribution of the plasmasheet; magnetic x-line location and reconnection rate along it. O+ outflows during solar maximum conditions (high F10.7) tend to counteract the plasmasheet’s pre/postmidnight asymmetries caused by the night-to-day gradient in ionospheric Hall conductance.

Climatic changes with warmer temperatures in mid-latitudes require the need to improve the simplified vegetation scheme of the regional climate model COSMO-CLM, which is not capable of modelling complex processes depending on temperature, water availability and day length. Thus, we have implemented the physically based Ball-Berry approach coupled with photosynthesis processes based on Farquhar and Collatz models for C3 and C4 plants in COSMO-CLM (v 5.16). The implementation of the new algorithms includes the replacement of the “one-big leaf” by a “two-big leaf” approach. We performed single column simulations with COSMO-CLM over three observational sites with C3 grass plants in Germany for the period from 1999 to 2015 (Parc, Linden and Lindenberg domain, Fig.1). Hereby, we tested three alternative formulations of the new algorithms. The first formulation (COSMO_v3.5) is based on the Community Land Model (CLM v3.5) algorithms for stomatal resistance, which depend on leaf photosynthesis, CO2 partial and vapor pressure and minimum stomatal conductance. The second one is COSMO_v4.5, which is based on the phenology algorithms of CLM v4.5 including the soil water stress function. The third one is similar to COSMO_v4.5 but with additional equations for dry leaf calculations (COSMO_v4.5e). The results revealed major differences in the annual cycle of stomatal resistance compared to the control simulation (COSMO_orig) with the original algorithm (Fig. 1). The biggest changes are from October to April when stomata are closed. The summer values of experiments are closer to measured values, than COSMO_orig. Further, changes in the stomatal resistance algorithms improve the accuracy of calculated transpiration rate and total evapotranspiration. The results indicate that changes in stomatal resistance and photosynthesis algorithms can improve the accuracy of other parameters of the COSMO-CLM model by comparing them with FLUXNET data and meteorological observations at the sites, and GLEAM datasets. Figure 1: The stomatal resistance based on COSMO-CLM experiments (a - annual cycle; b - daily values from 01.06.2011 to 15.09.2011) for: I – Parc domain, II – Linden domain, III – Lindenberg domain. This research was funded by the German Research Foundation (DFG) through grant number 401857120

The uplift of the southern African Plateau is often attributed to mantle processes, but there are conflicting theories for the specific timing and drivers of topographic development. Evidence for most proposed plateau development histories is derived from continental erosion histories, marine stratigraphic architecture, or landscape morphology. Here we use a landscape evolution model to integrate these three types of data for southern Africa, including a large dataset of low temperature thermochronology, sediment flux rates to surrounding marine basins. We explore three main hypotheses for surface uplift: 1) southern Africa was already elevated at the time of Gondwana breakup, 2) uplift and continental tilting occurred in the mid-Cretaceous, or 3) uplift occurred in the mid to late Cenozoic. We test which of these three intervals of plateau development are plausible by using an inversion method to constrain the range in erosional and uplift model parameters that can best reproduce the observed data. Results indicate two families of uplift histories are most compatible with the data. Both have limited initial topography with some topographic uplift and continental tilting starting in the east at ~95 Ma. In one acceptable scenario, nearly all of the topography, ~1400 m, is created at this time with little Cenozoic uplift. In the other acceptable scenario, only ~500 m of uplift occurs in the mid-Cretaceous with another ~850 m of uplift in the mid-Cenozoic. The two model scenarios have different geodynamic implications, which in the future could be evaluated by direct comparison between geodynamic and landscape model predictions.

We examine the average evolution of precipitation-induced height-integrated conductances, along with field-aligned currents, in the nightside sector of the polar cap over the course of a substorm. Conductances are estimated from the average energy flux and mean energies derived from auroral emission data. Data are binned using a superposed epoch analysis on a normalised time grid based on the time between onset and recovery phase ($\delta$t) of each contributing substorm. We also examine conductances using a fixed time binning of width 0.25 hr. We split the data set by magnetic latitude of onset. We find that the highest conductances are observed for substorms with onsets that occur between 63 and 65 degrees magnetic latitude, peaking at around 11 mho (Hall) and 4.8 mho (Pedersen). Substorms with onsets at higher magnetic latitudes show lower conductances and less variability. Changes in conductance over the course of a substorm appear primarily driven by changes (about 40% at onset) in the average energy flux, rather than the average energy of the precipitation. Average energies increase after onset slower than energy flux, later these energies decrease slowly for the lowest latitude onsets. No clear expansion of the main region 1 and region 2 field-aligned currents is observed. However, we do see an ordering of the current magnitudes with magnetic latitude of onset, particularly for region 1 downwards FAC in the morning sector. Peak current magnitudes occur slightly after or before the start of the recovery phase for the normalised and fixed-time grids.

Policymakers are trying to cut carbon-dioxide emissions and have promoted generating electricity using solar, wind, wave converters and tidal turbines. But a larger need is to supplement petroleum, the polluting but superb transportation fuel. Ocean Thermal Energy Conversion plants operated during the past 40 years show that OTEC plants have the (1) reliability and (2) massive scale to synthesize a sustainable new global fuel to replace dwindling petroleum supplies. For reliability, we will review the experience of the two OTEC plants currently operating in Japan and Hawai’i. Both plants have demonstrated robust performance for heat exchangers and power components. This record is possible because OTEC uses components similar to typical power plant or air-conditioning machinery. Mini-OTEC generated the first net power in 1978, and it was designed and built in only a year. Today’s onshore plants easily synchronize with the grid frequency, and generate dispatchable electric power instead of the intermittent power from most renewable energy sources. Recent OTEC floating designs benefit from the offshore industry’s hull and power cable research & development. For scale, large OTEC plants operating on the tropical high seas are a feasible supply chain to make transportation fuel in globally-significant volumes. Two recent computer studies suggest that industrial OTEC will have benign biological and climate impact. In comparison, it would require 100% of the US corn harvest to furnish only 30% of US gasoline needs – with no jet fuel or diesel. The expensive drama of obtaining permits for renewable energy projects show that the land and shoreline are already crowded, yet the solar energy equivalent to seven offshore Sahara Deserts is being ignored. Finally, policies and costs supporting or hindering OTEC will be compared for eight nations and the United States, including findings by the International Energy Agency’s Ocean Energy Systems committee. These results explain the current state of this attractive ocean energy resource.

Quantification of river flow is a significant component of water resource management needed to develop infrastructure, prepare for drought or flood, and ensure equitable resource use. Yet, these data have often been deficient in rural regions generally dependent on smaller river systems, especially in low- and middle- income countries, and in places where no remote gaging capabilities currently exist. A relationship between river flow and width has been previously demonstrated in attempts to record and monitor flow with only satellite-based measurements; however, those methods have focused on rivers with a width of > 30m and have shown extreme errors when compared to historical gaging records. A new technique for monitoring river flow remotely is presented here, which uses Manning’s equation for open channel flow coupled with width measurements from satellites. This technique allows for the creation of a remotely-sensed historical river flow record and uses the minimum number of ground-based measurements for the calibration of Manning’s equation. Cross-river depth profile, discharge, and slope are necessary for initial calibration. This method used four-band satellite images with 3m-resolution for width measurements, with images being adjusted for the Normalized Difference Water Index (NDWI) for better delineation of the water’s edge. Buffalo Creek, in Freeport, Pennsylvania and the Mutale River, in the Limpopo Province of South Africa, were used as study locations. An estimation of flow at each site was obtained using every available satellite image of those transects. Preliminary results indicated successful calibration of Manning’s equation for the individual river transects, and verification of this method yielded flow estimation with an average of 74% error at Buffalo Creek and 48% error at the Mutale River, when compared to historical data from gages present near the study sites. The primary challenge of using this method on smaller rivers is the determination of width from the satellite images. Automated techniques to delineate the water’s edge are presented as recommendations to increase accuracy. This method may be used as an additional tool in river flow monitoring for water resource management.

A document by Michael Lockwood. Click on the document to view its contents.

The location of the Subtropical Front (STF), the boundary between Subtropical and Subantarctic Water in the Southern Ocean is proposed to be controlled by the strength and location of the Southern Hemisphere westerly winds. We use a hydrodynamic hindcast model and recent observations to test if changes in the westerly winds can cause meridional shifts in the STF over interannual to decadal time scales by modulating local Ekman transport. We find that increased, or northward, shifted westerly winds lead to an enhanced northward Ekman transport over large parts of the Southern Ocean, resulting in a northward shift in the STF. Conversely for weaker or southward shifted westerly winds. Regions with strong eddy variability, such as western boundary current systems of the Agulhas and East Australian Current behave differently, as the Sverdrup balance causes an opposite shift. In these regions an increase in westerly winds lead to a southward shift in the STF. A southward shift of STF has been observed between 2004-2019. However, the shift is smaller than the latitudinal shifts in the location of the zero wind stress curl and maximum westerly winds (-0.4° latitude/decade). This discrepancy is due to positive Ekman trends resulting from the intensification of the westerly winds, which oppose the southward migration. Changes in the Ekman transport and the overall southward shift of the STF have also resulted in an observed positive trend in chlorophyll-a concentrations south of the STF, which could have ramifications for the biological pump and carbon uptake in the Southern Ocean.

Optical and acoustic sensors have been widely used in laboratory experiments and field studies to investigate suspended particulate matter concentration and particle size over the last four decades. Both methods face a serious challenge as laboratory and in-situ calibrations are usually required. Furthermore, in coastal and estuarine environments, the coexistence of mud and sand often results in multimodal particle size distributions, amplifying erroneous measurements. This paper proposes a new approach of combining a pair of optical-acoustic signals to estimate the total concentration and sediment composition of a mud/sand mixture in an efficient way without an extensive calibration. More specifically, we first carried out a set of 54 bimodal size regime experiments to derive empirical functions of optical-acoustic signals, concentrations, and mud/sand fractions. The functionalities of these relationships were then tested and validated using more complex multimodal size regime experiments over 30 optical-acoustic pairs of 5 wavelengths (420, 532, 620, 700, 852 nm) and 6 frequencies (0.5, 1, 2, 4, 6, 8 MHz). In the range of our data, without prior knowledge of particle size distribution, combinations between optical wavelengths 620-700 nm and acoustic frequencies 4-6 MHz predict mud/sand fraction and total concentration with the variation < 10% for the former and < 15% for the later. This approach therefore enables the robust estimation of suspended sediment concentration and composition, which is particularly useful in cases where calibration data is insufficient.

The natural flow regime within a watershed can be considered as the expected temporal patterns of streamflow variation in the absence of human impacts. While ecosystems have evolved to function under these conditions, the natural flow regime of most rivers has been significantly altered by human activities. Land use change, including the development of agriculture and urbanization, is a primary cause of the loss of natural flow regimes. These changes have altered discharge volume, timing, and variability, and consequently affected the structure and functioning of river ecosystems. The Meramec River watershed is located in east central Missouri and changes in land use have been the primary factor impacting flow regimes across the watershed. In this study, a watershed model, the Soil and Water Assessment Tool (SWAT), was developed to simulate a long-term time series of streamflow (1978-2014) within the watershed. Model performance was evaluated using statistical metrics and graphical technique including R-squared, Nash-Sutcliffe efficiency, cumulative error, and 1:1-ratio comparison between observed and simulated variables. The calibrated and validated SWAT model was then used to quantify the responses of the watershed when it was a forested natural landscape. An Indicator of Hydrologic Alteration (IHA) approach was applied to characterize the flow regime under the current landcover conditions as well as the simulated natural flow regime under the no land use change scenario. Differences in intra- and inter-annual ecologically relevant flow metrics were then compared using SWAT model outputs in conjunction with the IHA approach based on model outputs from current and no land use change conditions. This study provides a watershed-scale understanding of effects of land use change on a river’s flow variability and provides a framework for the development of restoration plans for heavily altered watersheds.

Stochastic methods have been typically used for the design and operations of hydraulic infrastructure. They allow decision makers to evaluate existing or new infrastructure under different possible scenarios, giving them the flexibility and tools needed in decision making. In this paper, we present a novel stochastic streamflow simulation approach able to replicate both temporal and spatial dependencies from the original data in a multi-site basin context. The proposed model is a multi-site extension of the modified Fractional Gaussian Noise (mFGN) model which is well-known to be efficient to maintain periodic correlation for several time lags, but presents shortcomings in preserving the spatial correlation. Our method, called Weighted-mFGN (WmFGN), incorporates spatial dependency into streamflows simulated with mFGN by relying on the Cholesky decomposition of the spatial correlation matrix of the historical streamflow records. As the order in which the decomposition steps are performed (temporal then spatial, or vice-versa) affects the performance in terms of preserving the temporal and spatial correlation, our method searches for an optimal convex combination of the resulting correlation matrices. The result is a Pareto-curve that indicates the optimal weights of the convex combination depending on the importance given by the user to spatial and temporal correlations. The model is applied to Bio-bio River basin (Chile), where the results show that the WmFGN maintains the qualities of the single-site mFGN, while significantly improving spatial correlation.

Isolating significant signals from temporal variations in autotrophic and heterotrophic components of ecosystem respiration (Reco) is required to better quantify the temperature sensitivity of the land carbon cycle processes. Here we present diurnal and seasonal patterns in field and model-based components of respiration and investigate their responses to environmental conditions at a dry eucalypt forest, the Cumberland Plain SuperSite of the Australian Terrestrial Ecosystem Research Network. We conducted measurement campaigns of total CO2 flux from the soil surface (Rsoil), soil microbial respiration (Rmicrobe), root respiration (Rroot), litter respiration (Rlitter), and stem respiration (Rstem) in 2018. In total, six infrared gas analyzers with closed, dynamic auto-chambers and six forced diffusion auto-chambers were used for periodic campaigns. Further, Reco and its components were simulated using the Community Atmosphere-Biosphere Land Exchange model (CABLE), constrained by eddy covariance measurements and chamber measurements of Rsoil. A new version of CABLE was implemented with the Dual Arrhenius Michaelis Menten (DAMM) formulation to assess the importance of substrate availability for simulating Rmicrobe. We found that respiration rates showed similar diurnal patterns among the components, showing diurnal hysteresis between respiration components and temperature. In this dry ecosystem, the respiratory components were more responsive to seasonally increasing temperature in wet than in dry periods, and the responses were dependent on atmospheric relative humidity affecting the litter layer moisture content. The temperature sensitivity was significantly higher in Rstem than in other components. Based on observed fluxes of Rmicrobe in trenched plots and Rsoil in intact soil plots, the mean contribution of Rroot to Rsoil was less than 20 % for the dry seasons, while mean Rstem was two times greater than mean Rsoil suggesting that Rstem should be not overlooked in ecosystem flux estimations. This study highlights that partitioning the respiratory components and accounting for their different temperature-responses will be necessary to reduce uncertainty in modelling carbon-climate feedbacks.