For publications earlier than 2019, view our publications archive.
| Alexander, Sarah; Yang, Guang; Addisu, Girmachew; Block, Paul: Forecast-informed reservoir operations to guide hydropower and agriculture allocations in the Blue Nile basin, Ethiopia. In: International Journal of Water Resources Development, 37 (2), pp. 208-233, 2021. (Type: Journal Article | )|
| Peters, Shanan E; Rowley, David B: Long-Term Evolution of Earth's Continental Surface Elevation. In: EarthArXiv, 2021. (Type: Journal Article | | )|
Determining the timescale over which continental surface elevation (hypsometry) evolves is difficult because it reflects a combination of isostasy and dynamic topography operating in concert with erosion and deposition. Here, we use 252 million year old and younger shallow marine sediments exposed at the surface as tracers of net change in continental surface elevation over time. In aggregate, we find that the elevations of Triassic and younger surface-exposed shallow marine sediments closely mirror global continental hypsometry. However, dispersion in the elevations of marine sediments increases with increasing depositional age away from a constant modal elevation of ~0 m. This empirical age-elevation relationship is consistent with the expectations of a diffusion model, wherein shallow marine sediments are continually deposited near 0 m in the submerged and initially subsiding regions of the continents and then undergo vertical displacements down and up with a constant stochastic distribution of rates. When such a model is tuned to empirical age-elevation data, an asymptotically-stable distribution of surface elevations congruent with observed continental hypsometry emerges on a timescale of 10^7-10^8 years.
| Lipp, A. G.; et al,: The composition and weathering of the continents over geologic time. In: Geochemical Perspectives Letters, 17 , pp. 21-26, 2021. (Type: Journal Article | | )|
The composition of continental crust records the balance between construction by tectonics and destruction by physical and chemical erosion. Quantitative constraints on how igneous addition and chemical weathering have modified the continents’ bulk composition are essential for understanding the evolution of geodynamics and climate. Using novel data analytic techniques we have extracted temporal trends in sediments’ protolith composition and weathering intensity from the largest available compilation of sedimentary major element compositions: ∼15,000 samples from 4.0 Ga to the present. We find that the average Archean upper continental crust was silica-rich and had a similar compositional diversity to modern continents. This is consistent with an early Archean, or earlier, onset of plate tectonics. In the Archean, chemical weathering sequestered ∼25 % more CO2 per mass eroded for the same weathering intensity than in subsequent time periods, consistent with carbon mass balance despite higher Archean outgassing rates and more limited continental exposure. Since 2.0 Ga, over long (>0.5 Gyr) timescales, crustal weathering intensity has remained relatively constant. On shorter timescales over the Phanerozoic, weathering intensity is correlated to global climate state, consistent with a weathering feedback acting in response to changes in CO2 sources or sinks.
| Williams, John W.; Ordonez, Alejandro; Svenning, Jens-Christian: A unifying framework for studying and managing climate-driven rates of ecological change. In: Nature Ecology & Evolution, 5 (1), pp. 17-26, 2021, ISSN: 2397-334X. (Type: Journal Article | | )|
During the Anthropocene and other eras of rapidly changing climates, rates of change of ecological systems can be described as fast, slow or abrupt. Fast ecological responses closely track climate change, slow responses substantively lag climate forcing, causing disequilibria and reduced fitness, and abrupt responses are characterized by nonlinear, threshold-type responses at rates that are large relative to background variability and forcing. All three kinds of climate-driven ecological dynamics are well documented in contemporary studies, palaeoecology and invasion biology. This fast–slow–abrupt conceptual framework helps unify a bifurcated climate-change literature, which tends to separately consider the ecological risks posed by slow or abrupt ecological dynamics. Given the prospect of ongoing climate change for the next several decades to centuries of the Anthropocene and wide variations in ecological rates of change, the theory and practice of managing ecological systems should shift attention from target states to target rates. A rates-focused framework broadens the strategic menu for managers to include options to both slow and accelerate ecological rates of change, seeks to reduce mismatch among climate and ecological rates of change, and provides a unified conceptual framework for tackling the distinct risks associated with fast, slow and abrupt ecological rates of change.
| Briley, Laura J; Rood, Richard B; Notaro, Michael: Large lakes in climate models: A Great Lakes case study on the usability of CMIP5. In: Journal of Great Lakes Research, 47 (2), pp. 405-418, 2021, ISSN: 0380-1330. (Type: Journal Article | | )|
Large lakes have an impact on regional weather. In addition, they can be both sensitive to and influence regional climate changes. In the climate models that are used to investigate future climate changes, lakes are greatly simplified and sometimes absent. At the regional scale, this can have strong implications for the quality of the model information about the future. Through our work with climate information users in the Laurentian Great Lakes region, we have found that basic credibility of the information requires the underlying climate models simulate lake-atmosphere-land interactions. We are not aware of efforts within the scientific community to make known how individual large lakes are represented in models and how those representations translate to the quality of the data for particular regions. We share our framework for identifying how the Laurentian Great Lakes are represented in the Coupled Model Intercomparison Project (CMIP) version 5 climate models. We found that most CMIP5 models do not simulate the Great Lakes in a way that captures their impact on the regional climate, which is a credibility issue for their projections. We provide a perspective on the usability of CMIP5 for practitioners in the Great Lakes region and offer recommendations for alternative options.
| Yu, X; Millet, D B; Wells, K C; Henze, D K; Cao, H; Griffis, T J; Kort, E A; Plant, G; Deventer, M J; Kolka, R K; Roman, D T; Davis, K J; Desai, A R; Baier, B C; McKain, K; Czarnetzki, A C; Bloom, A A: Aircraft-based inversions quantify the importance of wetlands and livestock for Upper Midwest methane emissions. In: Atmospheric Chemistry and Physics, 21 (2), pp. 951–971, 2021. (Type: Journal Article | )|
| Vermeuel, Michael P; Cleary, Patricia A; Desai, Ankur R; Bertram, Timothy H: Simultaneous Measurements of O3 and HCOOH Vertical Fluxes Indicate Rapid In-Canopy Terpene Chemistry Enhances O3 Removal Over Mixed Temperate Forests. In: Geophysical Research Letters, 48 (3), pp. e2020GL090996, 2021, (e2020GL090996 2020GL090996). (Type: Journal Article | | )|
Abstract Dry deposition, the second largest removal process of ozone (O3) in the troposphere, plays a role in controlling the natural variability of surface O3 concentrations. Terrestrial ecosystems remove O3 either through stomatal uptake or nonstomatal processes. In chemical transport models, nonstomatal pathways are roughly constrained and may not correctly capture total O3 loss. To address this, the first simultaneous eddy covariance measurements of O3 and formic acid (HCOOH), a tracer of in-canopy oxidation of biogenic terpenes, were made in a mixed temperate forest in Northern Wisconsin. Daytime maximum O3 deposition velocities, vd (O3), ranged between 0.5 and 1.2 cm s−1. Comparison of observed vd (O3) with observationally constrained estimates of stomatal uptake and parameterized estimates of cuticular and soil uptake reveal a large (10%–90%) residual nonstomatal contribution to vd (O3). The residual downward flux of O3 was well correlated with measurements of HCOOH upward flux, suggesting unaccounted for in-canopy gas-phase chemistry.
| Chu, Housen; Luo, Xiangzhong; Ouyang, Zutao; Chan, Stephen W; Dengel, Sigrid; Biraud, Sébastien C; Torn, Margaret S; Metzger, Stefan; Kumar, Jitendra; Arain, Altaf M; Arkebauer, Tim J; Baldocchi, Dennis; Bernacchi, Carl; Billesbach, Dave; Black, Andrew T; Blanken, Peter D; Bohrer, Gil; Bracho, Rosvel; Brown, Shannon; Brunsell, Nathaniel A; Chen, Jiquan; Chen, Xingyuan; Clark, Kenneth; Desai, Ankur R; Duman, Tomer; Durden, David; Fares, Silvano; Forbrich, Inke; Gamon, John A; Gough, Christopher M; Griffis, Timothy; Helbig, Manuel; Hollinger, David; Humphreys, Elyn; Ikawa, Hiroki; Iwata, Hiroki; Ju, Yang; Knowles, John F; Knox, Sara H; Kobayashi, Hideki; Kolb, Thomas; Law, Beverly; Lee, Xuhui; Litvak, Marcy; Liu, Heping; Munger, William J; Noormets, Asko; Novick, Kim; Oberbauer, Steven F; Oechel, Walter; Oikawa, Patty; Papuga, Shirley A; Pendall, Elise; Prajapati, Prajaya; Prueger, John; Quinton, William L; Richardson, Andrew D; Russell, Eric S; Scott, Russell L; Starr, Gregory; Staebler, Ralf; Stoy, Paul C; Stuart-Haëntjens, Ellen; Sonnentag, Oliver; Sullivan, Ryan C; Suyker, Andy; Ueyama, Masahito; Vargas, Rodrigo; Wood, Jeffrey D; Zona, Donatella: Representativeness of Eddy-Covariance flux footprints for areas surrounding AmeriFlux sites. In: Agricultural and Forest Meteorology, 301-302 , pp. 108350, 2021, ISSN: 0168-1923. (Type: Journal Article | | )|
Large datasets of greenhouse gas and energy surface-atmosphere fluxes measured with the eddy-covariance technique (e.g., FLUXNET2015, AmeriFlux BASE) are widely used to benchmark models and remote-sensing products. This study addresses one of the major challenges facing model-data integration: To what spatial extent do flux measurements taken at individual eddy-covariance sites reflect model- or satellite-based grid cells? We evaluate flux footprints—the temporally dynamic source areas that contribute to measured fluxes—and the representativeness of these footprints for target areas (e.g., within 250–3000 m radii around flux towers) that are often used in flux-data synthesis and modeling studies. We examine the land-cover composition and vegetation characteristics, represented here by the Enhanced Vegetation Index (EVI), in the flux footprints and target areas across 214 AmeriFlux sites, and evaluate potential biases as a consequence of the footprint-to-target-area mismatch. Monthly 80% footprint climatologies vary across sites and through time ranging four orders of magnitude from 103 to 107 m2 due to the measurement heights, underlying vegetation- and ground-surface characteristics, wind directions, and turbulent state of the atmosphere. Few eddy-covariance sites are located in a truly homogeneous landscape. Thus, the common model-data integration approaches that use a fixed-extent target area across sites introduce biases on the order of 4%–20% for EVI and 6%–20% for the dominant land cover percentage. These biases are site-specific functions of measurement heights, target area extents, and land-surface characteristics. We advocate that flux datasets need to be used with footprint awareness, especially in research and applications that benchmark against models and data products with explicit spatial information. We propose a simple representativeness index based on our evaluations that can be used as a guide to identify site-periods suitable for specific applications and to provide general guidance for data use.
| Cavender-Bares, Jeannine; B Reich, Peter; A Townsend, Philip; Banerjee, Arindam; Butler, Ethan; Desai, Ankur; Gevens, Amanda; E Hobbie, Sarah; Isbell, Forest; Laliberté, Etienne; Meireles, José Eduardo; Menninger, Holly; P Pavlick, Ryan; Pinto-Ledezma, Jesús; Potter, Caitlin; C Schuman, Meredith; Springer, Nathan; Stefanski, Artur; Trivedi, Pankaj; Trowbridge, Amy; Williams, Laura; G Willis, Charles; Yang, Ya: BII-Implementation: The causes and consequences of plant biodiversity across scales in a rapidly changing world. In: Research Ideas and Outcomes, 7 , pp. e63850, 2021. (Type: Journal Article | | )|
The proposed Biology Integration Institute will bring together two major research institutions in the Upper Midwest—the University of Minnesota (UMN) and University of Wisconsin-Madison (UW)—to investigate the causes and consequences of plant biodiversity across scales in a rapidly changing world—from genes and molecules within cells and tissues to communities, ecosystems, landscapes and the biosphere. The Institute focuses on plant biodiversity, defined broadly to encompass the heterogeneity within life that occurs from the smallest to the largest biological scales. A premise of the Institute is that life is envisioned as occurring at different scales nested within several contrasting conceptions of biological hierarchies, defined by the separate but related fields of physiology, evolutionary biology and ecology. The Institute will emphasize the use of ‘spectral biology’—detection of biological properties based on the interaction of light energy with matter—and process-oriented predictive models to investigate the processes by which biological components at one scale give rise to emergent properties at higher scales. Through an iterative process that harnesses cutting edge technologies to observe a suite of carefully designed empirical systems—including the National Ecological Observatory Network (NEON) and some of the world’s longest running and state-of-the-art global change experiments—the Institute will advance biological understanding and theory of the causes and consequences of changes in biodiversity and at the interface of plant physiology, ecology and evolution.INTELLECTUAL MERITThe Institute brings together a diverse, gender-balanced and highly productive team with significant leadership experience that spans biological disciplines and career stages and is poised to integrate biology in new ways. Together, the team will harness the potential of spectral biology, experiments, observations and synthetic modeling in a manner never before possible to transform understanding of how variation within and among biological scales drives plant and ecosystem responses to global change over diurnal, seasonal and millennial time scales. In doing so, it will use and advance state-of-the-art theory. The institute team posits that the designed projects will unearth transformative understanding and biological rules at each of the various scales that will enable an unprecedented capacity to discern the linkages between physiological, ecological and evolutionary processes in relation to the multi-dimensional nature of biodiversity in this time of massive planetary change. A strength of the proposed Institute is that it leverages prior federal investments in research and formalizes partnerships with foreign institutions heavily invested in related biodiversity research. Most of the planned projects leverage existing research initiatives, infrastructure, working groups, experiments, training programs, and public outreach infrastructure, all of which are already highly synergistic and collaborative, and will bring together members of the overall research and training team.BROADER IMPACTSA central goal of the proposed Institute is to train the next generation of diverse integrative biologists. Post-doctoral, graduate student and undergraduate trainees, recruited from non-traditional and underrepresented groups, including through formal engagement with Native American communities, will receive a range of mentoring and training opportunities. Annual summer training workshops will be offered at UMN and UW as well as training experiences with the Global Change and Biodiversity Research Priority Program (URPP-GCB) at the University of Zurich (UZH) and through the Canadian Airborne Biodiversity Observatory (CABO). The Institute will engage diverse K-12 audiences, the general public and Native American communities through Market Science modules, Minute Earth videos, a museum exhibit and public engagement and educational activities through the Bell Museum of Natural History, the Cedar Creek Ecosystem Science Reserve (CCESR) and the Wisconsin Tribal Conservation Association.
| Yang, Guang; Zaitchik, Benjamin; Badr, Hamada; Block, Paul: A Bayesian adaptive reservoir operation framework incorporating streamflow non-stationarity. In: Journal of Hydrology, 594 , pp. 125959, 2021, ISSN: 0022-1694. (Type: Journal Article | | )|
Water reservoir operating rules are typically derived based on the assumption of streamflow stationarity, however, this assumption could be undermined by climate change. Adaptive reservoir operation is one of the most effective strategies to support water resources management under non-stationarity, yet until now, adaptive strategies considering non-stationarity across multiple time scales are rarely investigated. We propose an adaptive reservoir operation framework that incorporates streamflow non-stationarity across time scales simultaneously. Specifically, we first decompose the streamflow into four frequency categories to detect non-stationarity features through reservoir operation simulations. Next, we incorporate the non-stationarity information from each frequency category into adaptive reservoir operation by using Bayesian Model Averaging. We apply this framework to reservoir operation of the Grand Ethiopian Renaissance Dam on the Blue Nile River and evaluate its effectiveness with streamflow simulated from 21 general circulation models (GCMs) for two greenhouse gases emission scenarios. We find that streamflow non-stationarity from all GCMs varies by future period and frequency category. The proposed Bayesian adaptive reservoir operation framework can detect streamflow non-stationarity across all frequency categories and predominantly outperforms conventional adaptive strategies, especially in terms of firm power output. In general, firm output increases under the Bayesian framework as the power generation reliability increases. The proposed framework offers a robust approach to identify adaptive strategies for reservoir operation to address streamflow non-stationarity.
| Rollinson, Christine R; Dawson, Andria; Raiho, Ann M; Williams, John W; Dietze, Michael C; Hickler, Thomas; Jackson, Stephen T; McLachlan, Jason; Moore, David JP; Poulter, Benjamin; Quaife, Tristan; Steinkamp, Jörg; Trachsel, Mathias: Forest responses to last-millennium hydroclimate variability are governed by spatial variations in ecosystem sensitivity. In: Ecology Letters, 24 (3), pp. 498-508, 2020. (Type: Journal Article | | )|
Abstract Forecasts of future forest change are governed by ecosystem sensitivity to climate change, but ecosystem model projections are under-constrained by data at multidecadal and longer timescales. Here, we quantify ecosystem sensitivity to centennial-scale hydroclimate variability, by comparing dendroclimatic and pollen-inferred reconstructions of drought, forest composition and biomass for the last millennium with five ecosystem model simulations. In both observations and models, spatial patterns in ecosystem responses to hydroclimate variability are strongly governed by ecosystem sensitivity rather than climate exposure. Ecosystem sensitivity was higher in models than observations and highest in simpler models. Model-data comparisons suggest that interactions among biodiversity, demography and ecophysiology processes dampen the sensitivity of forest composition and biomass to climate variability and change. Integrating ecosystem models with observations from timescales extending beyond the instrumental record can better understand and forecast the mechanisms regulating forest sensitivity to climate variability in a complex and changing world.
| Cohen, J; Zhang, X; Francis, J; Jung, T; Kwok, R; Overland, J; Ballinger, T J; Bhatt, U S; Chen, H W; Coumou, D; Feldstein, S; Gu, H; Handorf, D; Henderson, G; Ionita, M; Kretschmer, M; Laliberte, F; Lee, S; Linderholm, H W; Maslowski, W; Peings, Y; Pfeiffer, K; Rigor, I; Semmler, T; Stroeve, J; Taylor, P C; Vavrus, S; Vihma, T; Wang, S; Wendisch, M; Wu, Y; Yoon, J: Divergent consensuses on Arctic amplification influence on midlatitude severe winter weather. In: Nature Climate Change, 10 (1), pp. 20-29, 2020, ISSN: 1758-6798. (Type: Journal Article | | )|
The Arctic has warmed more than twice as fast as the global average since the late twentieth century, a phenomenon known as Arctic amplification (AA). Recently, there have been considerable advances in understanding the physical contributions to AA, and progress has been made in understanding the mechanisms that link it to midlatitude weather variability. Observational studies overwhelmingly support that AA is contributing to winter continental cooling. Although some model experiments support the observational evidence, most modelling results show little connection between AA and severe midlatitude weather or suggest the export of excess heating from the Arctic to lower latitudes. Divergent conclusions between model and observational studies, and even intramodel studies, continue to obfuscate a clear understanding of how AA is influencing midlatitude weather.
| Wang, Yue; Widga, Chris; Graham, Russell W; McGuire, Jenny L; Porter, Warren; Wårlind, David; Williams, John W: Caught in a bottleneck: Habitat loss for woolly mammoths in central North America and the ice-free corridor during the last deglaciation. In: Global Ecology and Biogeography, 30 (2), pp. 527-542, 2020. (Type: Journal Article | | )|
Abstract Aim Identifying how climate change, habitat loss, and corridors interact to influence species survival or extinction is critical to understanding macro-scale biodiversity dynamics under changing environments. In North America, the ice-free corridor was the only major pathway for northward migration by megafaunal species during the last deglaciation. However, the timing and interplay among the late Quaternary megafaunal extinctions, climate change, habitat structure, and the opening and reforestation of the ice-free corridor have been unclear. Location North America. Time period 15–10 ka. Major taxa studied Woolly mammoth (Mammuthus primigenius). Methods For central North America and the ice-free corridor between 15 and 10 ka, we used a series of models and continental-scale datasets to reconstruct habitat characteristics and assess habitat suitability. The models and datasets include biophysical and statistical niche models Niche Mapper and Maxent, downscaled climate simulations from CCSM3 SynTraCE, LPJ-GUESS simulations of net primary productivity (NPP) and woody cover, and woody cover based upon fossil pollen from Neotoma. Results The ice-free corridor may have been of limited suitability for traversal by mammoths and other grazers due to persistently low productivity by herbaceous plants and quick reforestation after opening 14 ka. Simultaneously, rapid reforestation and decreased forage productivity may have led to declining habitat suitability in central North America. This was possibly amplified by a positive feedback loop driven by reduced herbivory pressures, as mammoth population decline led to the further loss of open habitat. Main conclusions Declining habitat availability south of the Laurentide Ice Sheet and limited habitat availability in the ice-free corridor were contributing factors in North American extinctions of woolly mammoths and other large grazers that likely operated synergistically with anthropogenic pressures. The role of habitat loss and attenuated corridor suitability for the woolly mammoth extinction reinforce the critical importance of protected habitat connectivity during changing climates, particularly for large vertebrates.
| Baldocchi, Angela K; Reed, David E; Loken, Luke C; Stanley, Emily H; Huerd, Hayley; Desai, Ankur R: Comparing Spatial and Temporal Variation of Lake-Atmosphere Carbon Dioxide Fluxes Using Multiple Methods. In: Journal of Geophysical Research: Biogeosciences, 125 (12), pp. e2019JG005623, 2020, (e2019JG005623 2019JG005623). (Type: Journal Article | | )|
Abstract Lakes emit globally significant amounts of carbon dioxide (CO2) to the atmosphere, but quantifying these rates for individual lakes is extremely challenging. The exchange of CO2 across the air-water interface is driven by physical, chemical, and biological processes in both the lake and the atmosphere that vary at multiple spatial and temporal scales. None of the methods we use to estimate CO2 flux fully capture this heterogeneous gas exchange. Here, we compared concurrent CO2 flux estimates from a single lake based on commonly used methods. These include floating chambers (FCs), eddy covariance (EC), and two concentration gradient-based methods labeled fixed (F-pCO₂) and spatial (S-pCO₂). At the end of summer, cumulative carbon fluxes were similar between EC, F-pCO₂, and S-pCO₂ methods (−4, −4, and −9.5 gC m−2), while methods diverged in directionality of fluxes during the fall turnover period (−50, 43, and 38 gC m−2). Collectively, these results highlight the discrepancies among methods and the need to acknowledge the uncertainty when using any of them to approximate this heterogeneous flux.
| Zhang, Ying; You, Liangzhi; Lee, Donghoon; Block, Paul: Integrating climate prediction and regionalization into an agro-economic model to guide agricultural planning. In: Climatic Change, 158 (3), pp. 435-451, 2020, ISSN: 1573-1480. (Type: Journal Article | | )|
Advanced skill in seasonal climate prediction coupled with sectoral decision models can provide decision makers with opportunities to benefit or reduce unnecessary losses. Such approaches are particularly beneficial to rainfed agriculture, the livelihood choice for the majority of the world's poor population, for which yields are highly sensitive to climate conditions. However, a notable gap still exists between scientific communities producing predictions and the end users who may actually realize the benefits. In this study, an interdisciplinary approach connecting climate prediction to agricultural planning is adopted to address this gap. An ex ante evaluation of seasonal precipitation prediction is assessed using an agro-economic equilibrium model to simulate Ethiopia's national economy, accounting for interannual climate variability and prediction-guided agricultural responses. Given the high spatial variability in Ethiopian precipitation, delineation of homogeneous climatic regions (i.e., regionalization) is also considered in addition to growing season precipitation prediction. The model provides perspectives across various economic indices (e.g., gross domestic product, calorie consumption, and poverty rate) at aggregated (national) and disaggregated (zonal) scales. Model results illustrate the key influence of climate on the Ethiopian economy, and prospects for positive net benefits under a prediction-guided agricultural planning (e.g., reallocation of crop types) strategy, as compared with static business-as-usual agricultural practices.
| Alkama, Ramdane; Koffi, Ernest N; Vavrus, Stephen J; Diehl, Thomas; Francis, Jennifer Ann; Stroeve, Julienne; Forzieri, Giovanni; Vihma, Timo; Cescatti, Alessandro: Wind amplifies the polar sea ice retreat. In: Environmental Research Letters, 15 (12), pp. 124022, 2020. (Type: Journal Article | | )|
The rapid polar sea ice retreat and its drivers are challenging and still unresolved questions in climate change research. In particular, the relationship between near-surface wind speed and sea ice extent remains unclear for two main reasons: (1) observed wind speeds over Polar Regions are very sparse, and (2) simulated winds by climate models are dependent on subjective parameterizations of boundary layer stratification, ultimately leading to large uncertainty. Here, we use observation-based data (passive microwave sea ice concentration and six different reanalysis datasets) together with output from 26 climate models (from the CMIP5 archive) to quantify the relationships between near-surface wind speed and sea ice concentration over the past 40 years. We find strong inverse relationships between near-surface wind speed and sea ice concentration that are consistent among the six reanalysis datasets. The poleward wind component is particularly increasing in years of reduced sea ice concentration, which contributes to the enhancement of the atmospheric (surface oceanic) poleward heat flux by up to 24 ± 1% (29 ± 2%) in the Arctic and 37 ± 3% (51 ± 3%) in the Antarctic seas, therefore boosting the impact of polar sea ice loss and contributing to polar amplification of climate warming. In addition, our results show a marginal contribution of the dynamical (pushing/opening/compacting) effects of wind on sea ice compared to the thermodynamic effects which in turn play a lower role than the associated change in local surface Autumn–Winter turbulent and Spring–Summer radiative fluxes. Climate models generally produce similar results but with lower magnitude, and one model even simulates the opposite relationship wind/sea-ice. Given the rapid changes in polar climate and the potential impacts on the mid-latitudes, it is urgent that model developments make use of evidence from satellite observations and reanalysis datasets to reduce uncertainties in the representation of relationships between polar winds and sea ice.
| Poe, Jeralyn; Reed, David E; Abraha, Michael; Chen, Jiquan; Dahlin, Kyla M; Desai, Ankur R: Geospatial coherence of surface-atmosphere fluxes in the upper Great Lakes region. In: Agricultural and Forest Meteorology, 295 , pp. 108188, 2020, ISSN: 0168-1923. (Type: Journal Article | | )|
Surface-atmosphere fluxes are known to vary at multiple time scales, but uncertainty is high as to how fluxes change spatially within regions. With an increase in the number of eddy covariance towers, we are now able to examine the geospatial coherence of ecosystem fluxes, using time-series correlation. Eighteen sites from Michigan and Wisconsin were used in this study, ranging from 100 m to 600 km apart. Surface-atmosphere fluxes from a six-month period were used to quantify spatial coherence on a pair-wise basis. Using geospatial statistics, carbon and sensible heat (H) fluxes were found to be 95% correlated directly outside of their flux footprint and 56% correlated up to a distance of ~35 km. Latent (LE) and momentum (τ) fluxes were less correlated, 83% directly outside of their flux footprint and 40% at a distance of ~130 km albeit, at a much larger spatial distance than for the carbon and sensible heat fluxes. All fluxes showed strong spectral resonance at diel and seasonal timescales, with 1-, 2- and 3-month periods being common modes of variability among H, LE, and τ fluxes. Results based on Empirical Orthogonal Function show distinct transitions of net ecosystem exchange from fall to winter before photosynthesis or respiration while H and τ do not exhibit coherent trends. This work demonstrates the potential of quantifying geospatial coherence of surface-atmosphere fluxes in the Midwestern United States, with the ability to predict fluxes beyond the spatial limit of a single flux tower footprint. Ultimately, expanding the flux measurements to larger scales would allow better spatial scaling of terrestrial surface-atmosphere fluxes between tower footprint and modeling or remote sensing scales.
| Tadesse, Tsegaye; Hollinger, David; Bayissa, Yared; Svoboda, Mark; Fuchs, Brian; Zhang, Beichen; Demissie, Getachew; Wardlow, Brian; Bohrer, Gil; and, Kenneth Clark: Forest Drought Response Index (ForDRI): A New Combined Model to Monitor Forest Drought in the Eastern United States. In: Remote Sensing, 12 (21), pp. 3605, 2020, ISSN: 2072-4292. (Type: Journal Article | )|
| Mehta, Nirav; Sanchez, Sergio; Marpu, Prashanth; Desai, Ankur; Krishayya, NSR: Tree cover and diversity modulate the response of carbon storage to precipitation variability in an Indian semi-arid forest. In: Current Science, 119 , pp. 1517-1525, 2020. (Type: Journal Article | | )|
Water availability is the central limiting factor for vegetation carbon allocation in semi-arid forests. However, the sensitivity of this relationship likely varies as a function of total tree cover and tree diversity. In the present study, a set of re-measured semi-arid forest plots in India were analysed to test how sensitive biomass, productivity and soil organic carbon (SOC) accumulation were to variability in precipitation from plot-level and remote sensing solar-induced fluorescence (SIF) measurements. Variability in mean precipitation at zones I and II impacted tree density, recorded as 150 and 400 trees ha-1 respectively. Results show that low tree cover plots had lower woody biomass NPP (NPPwood) and lower SIF sensitivity to inter-annual variation of precipitation. Increment in NPPwood over a five-year period was significantly smaller (P < 0.05) in zone I (0.21 Mg ha-1 year-1 , CI95, 0.14-0.28) than at zone II (2.44 Mg ha-1 year-1 , CI95, 1.43-3.45). Mean annual SOC increment at 0-5 cm depth varied between 0.13 and 0.75 Mg ha-1 year-1 across the study area. Results highlight the importance of tree cover diversity in modulating the response of semi-arid forests to carbon storage across a precipitation gradient.
| Breeden, Melissa L; Clare, Ryan; Martin, Jonathan E; Desai, Ankur R: Diagnosing the Influence of a Receding Snow Boundary on Simulated Midlatitude Cyclones Using Piecewise Potential Vorticity Inversion. In: Monthly Weather Review, 148 (11), pp. 4479-4495, 2020. (Type: Journal Article | )|