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Over the past three decades, assessments of the contemporary global carbon budget consistently report a strong net land carbon sink. Here, we review evidence supporting this paradigm and quantify the differences in global and Northern Hemisphere estimates of the net land sink derived from atmospheric inversion and satellite-derived vegetation biomass time series. Our analysis, combined with additional synthesis, supports a hypothesis that the net land sink is substantially weaker than commonly reported. At a global scale, our estimate of the net land carbon sink is 0.8 ± 0.7 petagrams of carbon per year from 2000 through 2019, nearly a factor of two lower than the Global Carbon Project estimate. With concurrent adjustments to ocean (+8%) and fossil fuel (−6%) fluxes, we develop a budget that partially reconciles key constraints provided by vegetation carbon, the north-south CO₂gradient, and O₂trends. We further outline potential modifications to models to improve agreement with a weaker land sink and describe several approaches for testing the hypothesis. 

Satellite-based evapotranspiration (ET) products inform decision-making regarding water availability and plant water use from sub-field to watershed scales. These products are validated using eddy covariance flux towers, where observations are subject to the influence of landscape heterogeneity due to a constantly shifting contributing area, or flux footprint, governed by surface and atmospheric drivers. In agricultural regions with multiple crop types, local heterogeneity may amplify the importance of appropriate grid cell selection for satellite ET comparisons. We evaluate the extent to which different satellite ET products capture both ET magnitudes and spatial variability due to landscape heterogeneity. We compare ECOSTRESS 70m instantaneous and daily ET products to flux tower observations in central Illinois with measurements at two heights, representing different but overlapping flux footprint areas. We estimate satellite ET based on a flux footprint weighting, gridded averages around the tower, and for crop-specific corn or soybean grid cells. In this region, the disALEXI daily ET product has better overall performance relative to the PT-JPL daily product, which is more sensitive to overpass times and tends to overestimate instantaneous ET. However, the PT-JPL model reflects more variability at high spatial resolution. Specifically, a footprint-derived ET improves the data-model comparison relative to disALEXI, and PT-JPL more closely replicates crop-specific and field-specific differences as inferred from the 2-height experimental setup. This study highlights differences in how models integrate spatial inputs, which lead to different representations of spatial variability for the same nominal resolution. This can also have important implications for understanding and predicting field-level differences in land-atmosphere fluxes. 

Environmental observation networks, such as AmeriFlux, are foundational for monitoring ecosystem response to climate change, management practices, and natural disturbances; however, their effectiveness depends on their representativeness for the regions or continents. We proposed an empirical, time series approach to quantify the similarity of ecosystem fluxes across AmeriFlux sites. We extracted the diel and seasonal characteristics (i.e., amplitudes, phases) from carbon dioxide, water vapor, energy, and momentum fluxes, which reflect the effects of climate, plant phenology, and ecophysiology on the observations, and explored the potential aggregations of AmeriFlux sites through hierarchical clustering. While net radiation and temperature showed latitudinal clustering as expected, flux variables revealed a more uneven clustering with many small (number of sites < 5), unique groups and a few large (> 100) to intermediate (15–70) groups, highlighting the significant ecological regulations of ecosystem fluxes. Many identified unique groups were from under-sampled ecoregions and biome types of the International Geosphere-Biosphere Programme (IGBP), with distinct flux dynamics compared to the rest of the network. At the finer spatial scale, local topography, disturbance, management, edaphic, and hydrological regimes further enlarge the difference in flux dynamics within the groups. Nonetheless, our clustering approach is a data-driven method to interpret the AmeriFlux network, informing future cross-site syntheses, upscaling, and model-data benchmarking research. Finally, we highlighted the unique and underrepresented sites in the AmeriFlux network, which were found mainly in Hawaii and Latin America, mountains, and at under- sampled IGBP types (e.g., urban, open water), motivating the incorporation of new/unregistered sites from these groups. 

Given the complexity of global poverty and climate change, it reasons that engineering education has focused on “Engineers as Changemakers,” seeking to inspire engineers to tackle the world’s wicked problems. However, in practice, the desire for engineers to see themselves as changemakers eclipses the autonomy of local communities, especially in international interventions. By focusing on empowerment, engineers unintentionally reinforce themselves as the power and knowledge holders. Inspired from works by Robert Chambers and Paulo Freire, we propose a new mindset for engineering education that shifts the focus from engineers as changemakers to engineers as facilitators and consultants. In this framework, the local community is viewed as the changemaker, affirming them as the primary acting agent of their lives. We illustrate the impact of this mindset shift in practice through the analysis of two technological case studies, both of which follow non-governmental organizations (NGOs) seeking to make long-lasting change with community members. Although the explicitly stated intentions of both groups are very similar, the NGO in one of the cases seeks to affirm the agency of community partners, referring to them as experts and drivers of the project. Meanwhile, the NGO in the other case utilizes language of empowerment, referring to themselves as the educators and providers of sustainable practices and technology. The impact of these mindsets is illustrated through qualitative data regarding stakeholder relationships and the community’s response to each project. Through these case studies, we see that liberative and collaborative technical interventions require a reimagining of the relationship between the engineer and community. As engineering educators, we are responsible for challenging the 

The energy extraction from urban wind at small-to-medium scale is limited due to lower performance and high capital cost of wind energy systems. This study aims to optimize the passive yaw control mechanism of a motionless wind energy system utilizing opposing S1210 airfoils, focusing on enhancing alignment with variable wind directions. A computational fluid dynamics (CFD) framework evaluates five tail vane designs NACA0012, triangular, trapezoidal, arrow, and rounded to assess their aerodynamic performance in generating lift, minimizing drag, and producing turning moments for self-alignment. Results demonstrate that the NACA0012 airfoilshaped vane achieves superior efficiency, balancing high lift (15 % greater than alternatives) and low drag, enabling robust turbine orientation even at wind speeds of 8 m/s. However, off-axis wind angles exceeding 15◦ degrade performance drastically, reducing the coefficient of performance (COP) by 26 % and 81 % at 20◦ and 25◦, respectively, highlighting the importance of passive yaw control. The findings contribute to optimizing the paired airfoil wind energy system for improved performance in urban wind conditions. The study concludes that integrating streamlined tail vanes, such as the NACA0012, significantly enhances the viability of motionless wind turbines for urban deployment, offering a cost-effective solution to harness low-to-medium wind speeds with minimal maintenance. 

How close relatives maintain species boundaries in sympatry remains a critical question in biodiversity research. Here we introduce Lobelia sect. Lobelia (Campanulaceae) as a useful clade for investigating such questions. Polyphyly within this clade was strongly suspected because many of the 26 species are cross-compatible and show remarkable overlap in distribution, morphology, ecology, and life history. Indeed, the species Lobelia × rogersii has a purported hybrid origin from Lobelia puberula and Lobelia brevifolia, and the well-known cultivar Lobelia × speciosa results from mating between Lobelia siphilitica and Lobelia cardinalis. We carried out a comprehensive evolutionary investigation of Lobelia sect. Lobelia, including phylogenetic inference, divergence time estimates, and population structure analyses using 729 accessions from 193 natural population sites representing 1–13 individuals per population per species. In contrast to expectations, nearly all species were recovered as reciprocally monophyletic with strong topological support and low levels of interspecific gene flow. An exception to this general pattern is observed in the Florida panhandle, where Lobelia glandulosa and Lobelia apalachicolensis co-occur and appear to be actively hybridizing. We conclude that North American Lobelia species are genetically cohesive, despite significant geographic overlap, frequent co-occurrence, morphological similarity, and broad interfertility in artificial crosses. 

This paper investigates quenching solutions of an one-dimensional, two-sided Riemann–Liouville fractional order convection–diffusion problem. Fractional order spatial derivatives are discretized using weighted averaging approximations in conjunction with standard and shifted Grünwald formulas. The advective term is handled utilizing a straightforward Euler formula, resulting in a semi-discretized system of nonlinear ordinary differential equations. The conservativeness of the proposed scheme is rigorously proved and validated through simulation experiments. The study is further advanced to a fully discretized, semi-adaptive finite difference method. Detailed analysis is implemented for the monotonicity, positivity and stability of the scheme. Investigations are carried out to assess the potential impacts of the fractional order on quenching location, quenching time, and critical length. The computational results are thoroughly discussed and analyzed, providing a more comprehensive understanding of the quenching phenomena modeled through two-sided fractional order convection-diffusion problems. 

Introduction to the project.